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Highly selective rare-earth separation has become increasingly important due to the indispensable role of these elements in various cutting-edge technologies including clean energy. However, the similar physicochemical properties of rare-earth elements (REEs) render their separation very challenging, and the development of new selective receptors for these elements is potentially of very considerable economic and environmental importance. Herein, we report the development of a series of 4-phosphoryl pyrazolone receptors for the selective separation of trivalent lanthanum, europium, and ytterbium as the representatives of light, middle, and heavy REEs, respectively. X-ray crystallography studies were employed to obtain solid-state structures across 11 of the resulting complexes, allowing comparative structure–function relationships to be probed, including the effect of lanthanide contraction that occurs along the series from lanthanum to europium to ytterbium and which potentially provides a basis for REE ion separation. In addition, the influence of ligand structure and lipophilicity on lanthanide binding and selectivity was systematically investigated via n-octanol/water distribution and liquid–liquid extraction (LLE) studies. Corresponding stoichiometry relationships between solid and solution states were well established using slope analyses. The results provide new insights into some fundamental lanthanide coordination chemistry from a separation perspective and establish 4-phosphoryl pyrazolone derivatives as potential practical extraction reagents for the selective separation of REEs in the future.

The development of molecule-based switchable materials remains an important challenge in the field of molecular science. Achievement of a structural phase transition induced by adsorption/desorption of guest molecules in spin crossover (SCO) Co(II) compounds is of significant interest because of the possibility that the spin state of the magnetic anisotropic high-spin (HS, S= 3/2) and low-spin (LS, S= 1/2) states can be switched via the induced changes in associated intermolecular interactions. In this study, we demonstrated a reversible magnetic switching associated with spin state conversion, along with a single-crystal to single-crystal (SCSC) phase transition induced by dehydration/rehydration. [Co(terpy)2](BF4)2·H2O (1·H2O; terpy = 2,2′:6′,2′′-terpyridine) assembles in the solid state via π–π and CH−π interactions involving adjacent terpyridine cores along the abdirection to form two-dimensional (2D) layered domains. 1·H2O exhibits gradual and incomplete SCO, from fully HS to ca. 0.5 HS, and the field-induced single-molecule magnet (SMM) behavior attributed to the presence of the anisotropic partial high-spin Co(II) species. 1·H2O undergoes a SCSC transformation accompanied by a change from the tetragonal space group I41/ato P42/nvia a dehydration process. Dehydrated 1exhibits a reverse thermal hysteresis behavior (T1/2↑= 287 K; T1/2↓= 270 K) in the gradual SCO region from fully HS to ca. 0.5 HS, followed by an ordinary thermal hysteresis (T′1/2↑= 195 K; T′1/2↓= 155 K) to fully LS Co(II). A temperature-dependent single-crystal X-ray structural analysis revealed that the reverse hysteresis can be attributed to an order/disorder structural phase transition of the BF4–anions involving a symmetry breaking to yield the monoclinic space group P21/nand orbital (angular momentum) transition (LT). Both the SCSC phase transition and magnetic behavior are switchable by dehydration/rehydration processes; thus 1again adsorbs water at room temperature to give both the original structure and its magnetic behavior.

Preferential formation of cis- or trans-palladium(II) complexes controlled via the exocyclic binding sites embedded in dithiamacrocycles (L1= −S(CH2)2S–; L2= −S(CH2)2O(CH2)2S−) is reported. From the reaction with K2PdCl4, the shorter sulfur-to-sulfur separation in L1preferentially leads to the formation of cis-[Pd(L1)Cl2] (1), while L2, incorporating a larger sulfur-to-sulfur separation, coordinates in a trans fashion to form a cyclic dimer, trans-[Pd2(L2)2Cl4] (2). The observed results illustrate the possibility for the controlled formation of cis/trans square-planar complexes through binding-site design. When palladium(II) acetate was substituted for K2PdCl4in the above reaction, L1gave no product, while L2resulted in the formation of a unique tripalladium(II) complex, [Pd3(L2)(CH3C(═N)OC(═N)CH3)(CH3COO)4] (3), in which three PdIIatoms are linked by acetimidic anhydride, CH3C(═N)OC(═N)CH3, derived from the acetonitrile solvent employed. In the 1H NMR spectrum for 3, specific methylene signals for methylene protons adjacent to S donors exhibit large complexation-induced splitting of the geminal proton signals into axial and equatorial proton peaks, thus indicating magnetically nonequivalent geminal protons that reflect the restricted conformation of the metallabicycle.

A wheel-like heptanuclear Ni(II) cluster, [Ni7L16(μ3-OH)6]Cl2·6MeOH (1) (HL1= N-(3-amino-2,2-dimethylpropyl)-2-hydroxybenzamide), was synthesized, and its crystal structure and magnetic properties were investigated in detail. Magnetic characterization revealed the presence of intra-cluster ferromagnetic coupling and the best fit for the data gave the following parameters: J1= +7.24 cm−1, J2= +0.31 cm−1, g= 2.16. The magnetization versus field measurements revealed that the saturated value is in accordance with an S= 7 ground state (M5T= 14.5 µβ). This appears to be the first reported example of an oxo-bridged Ni7wheel system with all metal centers ferromagnetically coupled and with an S= 7.We report a unique heptanuclear wheel-type Ni(II) cluster that involves all its Ni(II) ions in ferromagnetic interactions. To the best of our knowledge, this is the first example of an alkoxo- or hydroxo-bridged Ni7wheel system for which all metal centers in the cluster are ferromagnetically coupled to result in an S= 7 ground spin state.

Two-dimensional Hofmann-type coordination polymers of type Mn(H2O)2[Pd(CN)4]·xH2O (1·xH2O; x= 0, 1, and 4), Mn(H2O)(MeOH)[Pd(CN)4]·2MeOH (2·2MeOH), and Mn(MeOH)2[Pd(CN)4]·MeOH (3·MeOH) have been synthesized. The homosolvent-bound 1·4H2O, 1·H2O, and 3·MeOHpolymers consist of undulating layer structures, whereas the structure of heterosolvent-bound 2·2MeOHconsists of “Janus-like” flat layers in which water-bound and MeOH-bound-sides are present. 1·4H2Oand 1·H2Oexhibited anisotropic two-dimensional thermal expansions involving structural transformations of the undulating layers; one layer axis expands while the other contracts. 2·2MeOHexhibits anisotropic thermal expansion in which the flat layers shift sideways as the temperature is increased, with colossal interlayer expansion occurring (αc= +200 MK–1over 140–180 K, αc= +165 MK–1over 200–280 K). 3·MeOHalso showed colossal interlayer expansion (αc= +216 MK–1) together with expansion of the undulating layers.

The behavior of single-ion magnets (SIMs) that reflects large distortions of their coordination environments caused by the packing of long alkyl chains for two Co(II) complexes of the type [Co(Cn-terpy)2](BF4)2(Cn-terpy = 4′-alkoxy-2,2’:6′,2″-terpyridine; n= 10 (1), 16 (2)) is reported. 1·2MeOH, which features a highly distorted octahedral high-spin Co(II) center, exhibits field-induced slow magnetic relaxation under an applied dc field of 1000 Oe. Further detailed analysis of the relaxation process indicated the prevalence of the Raman process at low temperature. Surprisingly, 2shows a reverse spin transition (rST) and also exhibits remarkable field-induced SIM behavior, revealing the presence of magnetic anisotropy for this high-spin Co(II) species that is triggered by a structural phase transition. We present here the first examples of the coexistence of field-induced slow magnetic relaxation and rST associated with structural phase transitions involving long-alkyl-chain conformational changes from gauche to anti. These results indicate the prospect of inducing SIM properties in other distorted high-spin Co(II) species bearing long alkyl chains.

In contrast to monofunctional electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) or oxygen reduction reaction (ORR), trifunctional catalysts for simultaneously generating H2, O2and H2O provide a crucial means for improving the overall efficiency of water electrolysis. Herein we present a series of nonnoble metal [M = Fe(III), Co(II), Ni(II)]-nitrogen co-doped oxidized graphite rods (M-N/OGRs) that function as in situ working electrodes for tri-functional OER, HER and ORR electrocatalysis. The enhanced performance of the hybrid catalysts appear mostly associated with dual active site mechanisms originating from the synergic effects of M-N/Co-doped on the surface of the OGR. Our findings suggest that, the development of multifunctional electrocatalysts with optimal catalytic activity using transition metals and nitrogen doped OGR opens new doors for in situ synthesized electrocatalysts for use in clean electrochemical energy storage and conversion technologies.Nonprecious metal [M = Fe(III), Co(II), Ni(II)]-nitrogen co-doped oxidized graphite rods (M-N/OGRs) functioning as in situ working electrodes for tri-functional OER, HER and ORR electrocatalysts are described herein.

Water dispersible metal complex nanoparticles were synthesized using the polyethylene glycol (PEG) coating method. The ?mT values at room temperature for the NPs 1–3were calculated using the Evans method, and the proton relaxation times, T1 and T2, were measured employing MRI. Both relaxation times were observed to decrease with increasing ?mT value.Water dispersible metal complex nanoparticles were synthesized by using the polyethylene glycol (PEG) coating method. The ?mT values at room temperature for the NPs for 1–3were determined by the Evans method, and the Proton relaxation times, T1 and T2 were measured by MRI. The proton relaxation times decreased as the ?mT value increased.

Viel Platz: Ein großer dreieckförmiger Dreikernkomplex mit zugänglichen Bindungszentren wurde synthetisiert, strukturell charakterisiert und in ein chirales Metall‐organisches Gerüst eingebaut (siehe Bild). Im resultierenden 3D‐Gerüst mit einem Triamin als verbrückender Gruppe beträgt der Anteil der Hohlräume 56 % des Volumens. In diesen Hohlräumen können Lösungsmittel und verschiedene Gase adsorbiert werden.

A rare ruthenium(II) triple helicateof the type [Ru2L3]4+(L=5,5′′′‐dimethyl‐2,2′:5′,5′′:2′′,2′′′‐quaterpyridine) was synthesized in an unusually high yield by using microwave heating in ethylene glycol (see scheme). Efficient separation of the [Ru2L3]4+helicate into its Pand Misomers by DNA affinity chromatography indicated selective binding of P‐[Ru2L3]4+with various DNA sequences.

Amide‐functionalised salen ligands capable of extracting metal salts have been synthesised and characterised. Single‐crystal X‐ray structure determinations of complexes of NiSO4, [Ni(L)(SO4)], confirm that the ionophores are in a zwitterionic form with NiIIbound in the deprotonated salen moiety and the SO42−ion associated with protonated pendant N′‐amidopiperazine groups. Treatment of [Ni(L)(SO4)] with base removes the protons from the pendant amido–amine group resulting in loss of the SO42−ion and formation of metal‐only complexes of type [Ni(L−2H)], which have been characterized by single‐crystal X‐ray diffraction. Three of the ligands with solubilities suitable for solvent extraction studies show loading and stripping pH‐profiles that are suitable for the recovery of CuSO4or CuCl2from industrial leach solutions. The copper‐only complexes, [Cu(L−2H)], are selective for Cl−over SO42−in both solvent extraction and bulk liquid membrane transport experiments and were found to bind Cl−in two steps via the formation of a 1:1:1 [Cu(L−H)Cl] assembly, followed by a 1:1:2 [Cu(L)Cl2] assembly as the pH of the aqueous phase is lowered. The anion transport selectivity was evaluated for a number of other mono‐charged anions and interestingly the ligands were found to display a preference for the Br−ion. To probe the influence of the Hofmeister bias on the selectivity of anion complexation, single‐phase potentiometric titration experiments were employed to investigate the binding of SO42−and Cl−by one of the copper only complexes, [Cu(L−2H)] in 95 %/5 % MeOH/water. Under these conditions selectivity was reversed (SO42−>Cl−) confirming that the Hofmeister bias, which reflects the relative hydration energies of the anions, dominates the selectivity of anion extraction from aqueous media into CHCl3.

A series of pendant arm aza-thioether macrocycles containing hydrogen-bonding amide functionalities have been synthesised and the single crystal X-ray structures of [12]aneS3N–CONHCOPh, [12]aneS3N–CSNHCOPh, [12]aneS2ON–CONHCOPh, [12]aneS2ON–CH2CONHCONH–tBu, [15]aneS2ON2–(CH2CONHCONH–tBu)2 and [15]aneS3N2–(CH2CONHPh)2 are presented. The structural results confirm that the majority of the macrocyclic C–S linkages adopt gauche conformations with all sulfur atoms being exo-orientated with respect to the macrocyclic ring, while the oxygen atoms, when present, are endo-orientated. The pendant arms, formed by reaction of the parent macrocycle with acyl isocyanates, are twisted from co-planarity and typically form a distorted U-shape with angles between planes formed around the carbonyl units varying from 50.81° to 68.05°. The dominant motif in these structures involves dimeric units linked through hydrogen-bonds: however, such a network is disrupted in [12]aneS3N–CSNHCOPh by the substitution of a carbonyl unit for a thiocarbonyl unit. When more than one amide unit is present in the pendant arm, intramolecular hydrogen-bond networks are observed resulting in coplanar pendant arms and highly directional hydrogen-bonding. Inclusion of a methylene linker between the macrocycle and carbonyl function in the pendant arm inhibits intermolecular hydrogen-bond formation resulting in interaction of the amide proton with the macrocyclic nitrogen centres. A single crystal X-ray structure of [Ag([12]aneS3N–CH2CONH–tBu)(NO3)] confirms binding of Ag(i) to the macrocyclic moiety with additional hydrogen-bonding [N–H⋯O 2.901(3) Å] between the macrocyclic pendant arm amide unit and the nitrate anion demonstrating that in the solid-state these ligands can act as heteroditopic receptors for metal salts. Overall, the solid-state structure of this complex is a one-dimensional polymer in which the Ag(i) cation is in a distorted square-pyramidal geometry with the apical sulfur donor emanating from an adjacent macrocyclic molecule. The efficacy of these ligands in competitive membrane transport and liquid–liquid metal ion extraction of Co(ii), Ni(ii), Cu(ii), Zn(ii), Cd(ii), Ag(i) and Pb(ii) has been assessed using selected ligands. In preliminary experiments, clear extraction and transport selectivity for Ag(i) was observed in all systems investigated, while only modest extraction of TcO4− was identified.

Neutral trinuclear (triangular) copper(ii) complexes of type [Cu3L3] incorporating the 1,4-aryl linked bis-β-diketonato bridging ligands, 1,1-(1,4-phenylene)-bis(butane-1,3-dione) (H2L2), 1,1-(1,4-phenylene)-bis(pentane-1,3-dione) (H2L3) and 1,1-(1,4-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L4) have been demonstrated to react with selected heterocyclic nitrogen donor bases to generate extended supramolecular architectures whose structures have been confirmed by X-ray diffraction. Thus on reaction with 4,4′-bipyridine (bipy), [Cu3(L2)3] yields polymeric structures of type {[Cu3(L2)3(bipy)(THF)]·2.75THF}nand {[Cu3(L2)3(bipy)(THF)]·bipy·0.75THF}nwhile with pyrazine (pyz), {[Cu3(L2)3(pyz)]·0.5THF}nwas obtained. Each of these extended structures contain alternating triangle/linker units in a one-dimensional polymeric chain arrangement in which two of the three copper sites in each triangular ‘platform’ are formally five-coordinate through binding to a heterocyclic nitrogen atom. Interaction of the multifunctional linker unit hexamethylenetetramine (hmt) with [Cu3(L3)3] afforded an unusual, chiral, three-dimensional molecular framework of stoichiometry [Cu3(L3)3(hmt)]n. The latter incorporates the trinuclear units coordinated to three triply bridging hmt units. In marked contrast to the formation of the above structures incorporating bifunctional linker units and five-coordinate metal centres, the trinuclear platform [Cu3(L2)3] reacts with the stronger difunctional base 1,4-diazabicyclo[2.2.2]-octane (dabco) to yield a highly symmetric trigonal columnar species of type {[Cu3(L4)3(dabco)3]·3H2O}nin which each copper centre is octahedrally coordinated.

The interaction of the extended, fully-conjugated macrocycle, dipyridyldibenzotetraaza[14]annulene (1), with the square planar palladium(ii) and platinum(ii) complexes [M(dppp)(triflate)2]·2H2O (M = Pd, Pt) has been investigated in both solution and the solid state. In each case solid products showing a 1 : 1 ratio of metal complex : 1were obtained. A 1 : 1 mixture of 1and [Pd(dppp)2(triflate)2]·2H2O in dichloromethane yielded two major products as evidenced by the presence of two singlets in the 31P {1H}-NMR spectrum of the reaction solution. Similarly, two singlets were evident in the corresponding spectrum obtained on dissolving the 1 : 1 product in nitrobenzene. The temperature and concentration dependence of the spectra clearly showed that the two species present in each case were in equilibrium. From the temperature dependence, the low field signal was assigned to the smaller of the two species. Broadly parallel behaviour was observed for the corresponding platinum-containing system. The MS-ESI spectrum of the platinum derivative showed the presence of a dinuclear species corresponding to [Pt(dppp)(1)]22+and an X-ray structure of this product confirmed that a corresponding dinuclear complex exists in the solid state. This product has a geometry in which two curved macrocyclic side units bridge two metal centres to yield an ellipse-shaped structure. Attempts to employ pulsed-field gradient spin-echo (PGSE) 31P NMR confirmed that the lower-field resonance corresponded to the smaller of the two species in solution. STM (HOPG) imaging of the palladium- and platinum-containing products revealed arrays that appear to be composed of “zipper-like” rows of dimer units, with the dimensions of the latter comparing well with those found in the X-ray structure of [Pt(dppp)(1)]22+.

New examples of adducts between di- (and, in one instance, tetra-) functional nitrogen ligands and planar ‘platform-like’ dinuclear copper(ii) complexes, [Cu2L2], incorporating the 1,3-aryl linked bis-β-diketonato bridging ligand 1,1′-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione) (H2L) have been synthesised. The X-ray structures of six adduct species are reported. The interaction of [Cu2(L)2] with the ditopic ligand aminopyrazine (apyz) yielded the sandwich-like tetranuclear species [(Cu2L2(apyz))2]. A variable-temperature magnetochemical investigation of this product indicated weak antiferromagnetic coupling between the (five-coordinate) copper centres, mediated by the 2-aminopyrazine linkers. An analogous structure, [(Cu2L2(dabco))2] (dabco = 1,4-diazabicyclo[2.2.2]octane), was generated when dabco was substituted for aminopyrazine while use of 4,4′-dipyridyl sulfide (dps) and 4,4′-(1,3-xylylene)-bis(3,5-dimethylpyrazole) (xbp) as the ditopic ‘spacer’ ligands resulted in polymeric species of type [Cu2L2(dps)]nand [Cu2L2(xbp)]n, respectively. These latter species exist as one-dimensional chain structures in which copper(ii) centres on different dinuclear platforms are linked in a ‘zigzag’ fashion. In contrast, with 2,2′-dipyridylamine (dpa) a discrete complex of type [Cu2L2(dpa)2] formed in which one potential pyridyl donor from each 2,2′-dipyridylamine ligand remains uncoordinated. The use of the potentially quadruply-bridging hexamethylenetetramine (hmt) ligand as the linker unit was found to give rise to an unusual two-dimensional polymeric motif of type [(Cu2(L2)2)3(hmt)2]n. The product takes the form of a (6,3) network, incorporating triply bridging hexamethylenetetramine units.

Synthesis of the 2,2′-dipyridylamine derivatives di-2-pyridylaminomethylbenzene 1, 1,2-bis(di-2-pyridylaminomethyl)benzene 2, 1,3-bis(di-2-pyridylaminomethyl)benzene 3, 2,6-bis(di-2-pyridylaminomethyl)pyridine 4, 1,4-bis(di-2-pyridylaminomethyl)benzene 5, and 1,3,5-tris(di-2-pyridylaminomethyl)benzene 6are reported together with the single-crystal X-ray structures of 2, 3, and 5. Reaction of individual salts of the type AgX (where X = NO3−, PF6−, ClO4−, or BF4−) with the above ligands has led to the isolation of thirteen Ag(i) complexes, nine of which have also been characterised by X-ray diffraction. In part, the inherent flexibility of the respective ligands has resulted in the adoption of a range of coordination arrangements. A series of liquid–liquid (H2O/CHCl3) extraction experiments of Ag(i) with varying concentrations of 1–6in the organic phase have been undertaken, with the counter ion in the aqueous phase being respectively picrate, perchlorate and nitrate. In general, extraction efficiencies for a given ionophore followed the Hofmeister order of picrate > perchlorate > nitrate; in each case the tris-dpa derivative 6acting as the most efficient extractant of the six systems investigated. Competitive seven-metal bulk membrane transport experiments (H2O/CHCl3/H2O) employing the above ligands as the ionophore in the organic phase and equimolar concentrations of Co(ii), Ni(ii), Zn(ii), Cu(ii), Cd(ii), Pb(ii) and Ag(i) in the aqueous source phase were also undertaken, with transport occurring against a pH gradient. Under the conditions employed 1and 5yielded negligible transport of any of the metals present in the source phase while sole transport selectivity for Ag(i) was observed for 2–4and 6.

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN–R–NHSO2R1= L) have been shown to be easily deprotonated to give neutral 2 : 1 complexes, [M(L− H)2], with Co(ii), Ni(ii), Cu(ii) or Zn(ii). The Ni(ii) and Cu(ii) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N42−donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail SOH–N(amine)bonding between the two bidentate ligands. In the related tetrahedral Zn(ii) complex the ends of the mutually perpendicular bidentate N2−units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N′-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2 : 1 complexes, these ligands are relatively weak extractants, showing >50% loading of Cu(ii) in “pH-swing” equilibria, 2 L(org) M2= [M(L− H)2](org) 2 H, only when the pH of the aqueous phase is raised above 4.

The metal-directed assembly of molecular frameworks incorporating the ditopic heterocyclic ligand 1-(4-pyridyl)imino-2-(4-pyridyl)isoindoline (L) associated with nonlinear coordination vectors, is presented. Two infinite metallo-arrays of empirical formula [CdL(NO3)2(EtOH)]n·(1.4 H2O)n and [FeL2(NCS)2]n·{(2 CHClCCl2)·(1.4 MeOH)·(2.9 H2O)}nhave been characterised. The X-ray structures of both arrays are reported. The cadmium(II) framework consists of co-aligned 1D coordinate polymer chains while the iron(II) framework consists of rhombic grids with 2D polymeric connectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

A selection of 1 : 1 (palladium/ligand) complexes of cyclam derivatives incorporating from one to three N-benzyl groups has been synthesized. Related 3 : 1 species of two symmetrically branched, tri-cyclam species incorporating 1,3,5-?tribenzyl' or phloroglucinol cores are also reported. The X-ray crystal structures of the palladium complexes of two isomeric forms of the N,N?-dibenzylated (single-ring) macrocycle have been determined. In each complex the palladium ion occupies the N4-plane of the respective macrocycles in a square planar arrangement, with each complex cation adopting a stable trans-III configuration.

The NO2S2-donor macrocycle L1 was synthesised from the ring closure reaction between Boc-N-protected 2,2′-iminobisethanethiol 3 and 2,2′-ethylenedioxybisbenzyl chloride 4 followed by deprotection of the Boc-group. α,α′-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L1to yield the corresponding N-linked product L2. The X-ray structure of L2as its HBr salt is described. A range of Cdii and Hgii complexes of L16–9 and L210–12 were prepared and characterised. Reaction of HgX2X Br or I with L1afforded HgL1Br2Hg2Br6·2CH2Cl26and HgL1I27, respectively. For 6, the Hgii ion in the complex cation has a distorted tetrahedral coordination environment composed of S2N donor atoms from L1and a bromo ligand. In 7the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentatemanner viaone S and one N atom. The remaining two coordination sites are occupied by iodide ions. HgL1ClO4ClO48was isolated from the reaction of HgClO42and L1. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O2S2-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of CdNO32·4H2O with L1afforded CdL1NO32·0.5CH2Cl29in which L1acts as a tridentate ligand, binding exo-fashion viaits S2N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX2X Br or I with L2yielded the isostructural 2 : 1 metal : ligand complexes, Hg2L2Br410and Hg2L2I411. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L2and two coordinated halides. Contrasting with this, the reaction of L2with CdNO32·4H2O yielded a 1-D coordination network, Cd2L2NO34·2CH2Cl2n12in which each ring of L2is exo-coordinated viatwo S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium viaa nitroso µ2-O bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The CdL20.5NO32 units are linked by an inversion to yield the polymeric arrangement.

The synthesis of new linked bis and trisring tetraazamacrocyclic bifunctional reagents for use in an alternative strategy for radiolabelling antibodies is described. For comparison with the above systems, a new single ring bifunctional system incorporating a dioxocyclam ring is also reported.

Pseudo-macrocyclic complexes of copperii, and in one instance nickelii, incorporating the bidentate ligands methyl N-4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-ylimidocarbamate and N,N-dimethyl-N′-4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-ylguanidine are reported and their X-ray structures compared with those previously reported for related complexes of two N-4-oxo- 5,5-diphenyl-4,5-dihydro-1H-imidazol-2-ylalkanimidamides. A feature of these complexes is that they are capable of forming hydrogen bonded chains or chains in which adjacent complexes are linked by phenyl ‘embraces’. Changes in supramolecular structure arising from small changes in ligand structure or on crystallisation from different solvents are also discussed.

The metal-directed assembly of new molecular frameworks incorporating 4-4-pyridylpyrazole L, containing non-linear coordination vectors, is presented. Three metallo-arrays of types CoLH2NO34, CoLH2H2O4NO34·H2O and Zn2L–H2Cl2·2EtOH are reported. The cobaltii in CoLH2NO34 displays distorted octahedral geometry, with the two protonated pyridyl–pyrazole ligands coordinated through their pyrazole nitrogen atoms in a trans-orientation; the remaining four coordination sites are occupied by nitrate anions. Two internal hydrogen bonds occur between each pyrazole NH and the oxygens of adjacent coordinated nitrato ligands. Short intermolecular hydrogen bonds also occur between the two pyridinium hydrogens and bound nitrate ligands on different molecules to yield a two-dimensional hydrogen-bonded array. Two of these arrays interpenetrate to form an extended two dimensional layer; such layers stack throughout the crystal structure. A second product of type CoLH2H2O4NO34·H2O exists as two crystallographically independent, but chemically similar, forms. In each form, the two protonated pyridyl–pyrazole ligands occupy transpositions about the cobalt, with the remaining four coordination sites being filled by water molecules to yield a distorted octahedral coordination geometry. Intramolecular hydrogen-bonding is observed between the two non-coordinated pyrazoyl nitrogen atoms and bound water oxygen atoms. The third complex, Zn2L–H2Cl2·2EtOH, contains dimer units consisting of two zincii ions bridged by two pyrazoylate groups in which the coordination geometry of each zinc approximates a tetrahedron. Each zinc is bound to two deprotonated pyridine–pyrazole ligands L–H, one pyridyl group from a different dimeric unit and one chloro ligand. Each pyridyl nitrogen thus connects each of these zinc dimers to an adjacent dimer unit, forming a three-dimensional network containing small voids. The latter are occupied by ethanol molecules which form hydrogen bonds to the chloro ligands.

A range of 1,3-aryl linked, bis-β-diketone derivatives LH2 has been employed to synthesise neutral bisligand, dinuclear complexes incorporating square-planar copperii and trisligand dinuclear helical derivatives containing octahedral ironiii. The 1H NMR spectra of the free ligands contain singlet peaks at ca. 16.2 ppm, indicative of enolic protons, confirming that the bis enol tautomer is present in solution. An X-ray structure of a ligand from the series incorporating tert-butyl terminal substituents confirms that the same tautomer persists in the solid and that the relative orientation of the bis-β-diketone fragments is such that the coordination vectors lie at approximately 120° to each other. The planar, dinuclear copper complexes form 1 : 2 adducts with pyridine and 4-dimethylaminopyridine, confirmed by X-ray structures, that incorporate five-coordinate metal centres. Based on this behaviour, the prospect of linking copper centres in the dinuclear complexes using the difunctional heterocyclic bases, 4,4′-bipyridine, 4,4′-trans-azopyridine and pyrazine as co-ligands has been probed. However, 4,4′-bipyridine was observed to coordinate through only one of its heterocyclic nitrogen atoms in the solid state to form a 1 : 2 Cu2L2: 4,4′-bipyridine adduct, analogous to the structures obtained with the above mono-functional nitrogen bases. Nevertheless, an X-ray structure determination shows that the related difunctional base, 4,4′-trans-azopyridine, coordinates in a bridging fashion viaboth its heterocyclic nitrogen atoms on alternate sides of each planar Cu2L2 unit to produce an infinite one dimensional metallo chain. In contrast, with pyrazine, a new neutral, discrete assembly of type Cu4L4pyrazine2 is formed. The X-ray structure shows that two planar dinuclear complexes are linked by two pyrazine molecules in a sandwich arrangement such that the coordination environment of each copper ion is approximately square pyramidal with the overall tetranuclear structure thus taking the form of a ‘dimer of dimers’.

The novel supramolecular assembly of composition [{(bz3tren)H4}4+· (ReO4)—· 3(Cl)—] resulted from the self‐organization of a mixture of tris[2‐(benzylamino)ethyl]amine (bz3tren), HCl and NH4ReO4at a molar ratio of 1:4.7:1 in methanol. The crystal architecture is characterized by stacks of repeating sandwich‐type building blocks that contain charge‐assisted N—H···O(Re) hydrogen bonds [N···O 2.81‐2.86Å] and weaker C—H···O(Re) interactions [C···O 3.11Å]. The stacks are further linked by N—H···Cl [N···Cl 3.03Å] and weaker C—H···Cl [C···Cl 3.47‐3.74Å] interactions into two‐dimensional layers bordered by the benzyl groups of the [(bz3tren)H4]4+cations. Edge‐to‐face C—H···π interactions involving the aromatic rings occur within and between the layers. The protonation constants of bz3tren in methanol were determined by potentiometric titration. The corresponding structures of the ligand in its different protonation states were calculated at the DFT‐level.

Comparative solvent extraction waterchloroform studies of Niii and Cuii employing a dinonyl-substituted N3O2-donor macrocycle L2 as extractant have been undertaken from sulfate, chloride, nitrate and acetate-containing aqueous media. Contrary to expectations, efficient extraction of both metal sulfates was observed, the degree of extraction being comparable or slightly enhanced relative to that observed for each of the other anionic systems. X-Ray diffraction studies of NiL1H2O3SO4·4H2O and CuL1H2OSO4·6.67H2O where L1is the unsubstituted derivative of L2 show that each complex occurs as a hydrogen-bonded ‘cluster’, with the sulfate anions involved in hydrogen bonded networks that incorporate ligand amine protons and water molecules; in the copper complex, which adopts a dimeric arrangement, simultaneous sulfate binding to a copper site is also present. In each complex the macrocyclic ligand fails to coordinate viaits ether oxygen donors but instead is arranged so that the metal ion and sulfate anions are somewhat shielded hydrophobically from the exterior of the complex cluster assembly.

The interaction of six aryl-linked bis-β-diketones, including a new naphthylene linked species, with copperii, ironiii and, in one instance galliumiii, has been investigated with the aim of obtaining metallo-supramolecular assemblies exhibiting different geometries. New examples of two assembly types incorporating the above bis-β-diketones L were generated. The first type is represented by a range of molecular triangles of formula Cu3L–H23solventnwhile the second is given by a corresponding selection of less-common neutral molecular tetrahedra of formula Fe4L–H26solventnas well as Ga4L–H26·8.5THF·0.5H2O; an example of each type has been characterised by X-ray crystallography. A magnetochemical investigation of Fe43–H26·6THF is reported. The susceptibility is Curie like and consistent with very weak coupling occurring between the ironiii d5high spin centres. The X-ray structures of two trinuclear copperii as well as a tetranuclear ironiii and a tetranuclear galliumiii assembly confirm their discrete triangular and tetrahedral geometries, respectively. The structure of the galliumiii species is closely related to that of the corresponding ironiii species. The tetrahedral structures provide rare examples of such assemblies encapsulating guest solvent molecules – in each case tetrahydrofuran is incorporated in the central cavity.

Host–guest formation between 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane 1 and lipophilic organic carboxylic acids in chloroform has been investigated and the effect of such ligand assembly on the solvent extraction of copperii and silveri has been probed. NMR titration experiments in the absence of a metal ion confirm the formation of weak 1 1 and 1 2 macrocycle carboxylic acid assemblies in CDCl3between 1and palmitic hexadecanoic acid or 4-tert-butylbenzoic acid while difunctional salicylic acid showed a 1 2 interaction that is somewhat stronger. The interaction between the former two acids and the tetra-N-benzylated macrocycle is significantly less than that reported previously for its non-substituted parent, cyclam; a result that likely reflects the presence of the less-basic, more sterically hindered tertiary nitrogens in 1relative to the secondary nitrogens present in cyclam. Carboxylic acid-containing assemblies of this type have been used as extractants in a series of solvent extraction waterchloroform experiments. From both previous observations as well as from entropy considerations, it was anticipated that the use of a host–guest assembly of the above type for metal-ion complexation might contribute to enhanced metal ion binding and concomitant enhanced metal ion extraction. Such behaviour is postulated to arise from the components of the coordination sphere being, at least in part, assembled for complex formation. In accord with this, the use of the ligand assembly involving palmitic acidmacrocycle 1was found to lead to enhanced synergistic extraction of copperii at a metal ion concentration of 10−3mol dm−3while, for silveri, synergism was somewhat marginal at this concentration but was clearly apparent under related conditions when the silver concentration was reduced to 10−4mol dm−3. Similar behaviour towards silver was also observed when 4-tert-butylbenzoic acid was substituted for palmitic acid, while the use of salicylic acid resulted in enhanced synergistic extraction at both metal ion concentrations.

The interaction of two symmetrically branched tris-cyclam derivatives based on 1,3,5-trimethylenebenzene and phloroglucinol cores with nickelii, copperii, zincii and cadmiumii is reported. All four metal ions yield solid complexes in which the metal ligand ratio is 3 1. For both ligand types, spectrophotometric titrations confirm the formation of nickelii and copperii complexes of similar 3 1 stoichiometry in dimethyl sulfoxide. Visible spectral, electrochemical, magnetic moment, ESR and NMR studies have been performed to probe the nature of the respective complexes. Where appropriate, the results from the above metal-ion studies are compared with those from parallel investigations in which the corresponding substituted mono-cyclam analogues were employed as the ligands. A structural determination employing a poorly diffracting crystal of the trinuclear nickelii complex of the tris-cyclam ligand incorporating a 1,3,5-trimethylenebenzene core was successfully carried out with the aid of a synchrotron radiation source. A nickel ion occupies each cyclam ring in a square-planar coordination arrangement, with each cyclam ring adopting the stable trans-III configuration.

Structure–function relationships underlying the interaction of progressively N-benzylated N4O2-donor macrocycles with cobaltii, nickelii, copperii, zincii, cadmiumii, silveri and leadii have been probed using a range of techniques that include X-ray diffraction, DFT computations, solvent extraction, potentiometric stability constant determinations and competitive membrane transport experiments. Collectively, the results indicate that N-benzylation of the secondary amine donor groups of the parent macrocyclic ring results in an enhanced tendency towards selectivity for silveri relative to the other six metals investigated. The observed behaviour serves as additional exemplification of the previously proposed concept of selective ‘detuning’ as a mechanism for metal ion discrimination.

Structure–function relationships underlying the interaction of progressively N-benzylated N₄O₂-donor macrocycles with cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) have been probed using a range of techniques that include X-ray diffraction, DFT computations, solvent extraction, potentiometric stability constant determinations and competitive membrane transport experiments. Collectively, the results indicate that N-benzylation of the secondary amine donor groups of the parent macrocyclic ring results in an enhanced tendency towards selectivity for silver(i) relative to the other six metals investigated. The observed behaviour serves as additional exemplification of the previously proposed concept of selective ‘detuning’ as a mechanism for metal ion discrimination.

The interaction of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O₂N₃-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log K values for the respective 1 ∶ 1 complexes in 95% methanol (I = 0.1; Et₄NClO₄, 25 °C) of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 ∶ 1 silver(i) complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 ∶ 1 copper(ii) complex. The log K results are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor (positive or negative) influence on the affinity towards silver(i) while the corresponding binding strengths towards the remaining six metal ions are significantly reduced—behaviour we term ‘selective detuning’. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log K results, transport selectivity for copper(ii) was exhibited by both systems, with similar transport efficiencies being evident when compared on a ‘per macrocyclic cavity’ basis.

Ditopic ligands have been designed and synthesized for the solvent extraction and membrane transport of transition metal salts for application in metal separation and purification processes. Tetradentate salicylaldimine ligands of the H₂salen type bearing pendant tertiary amine groups undergo a zwitterionic transformation when binding metal salts, forming overall neutral assemblies which can be transferred into non-polar, water-immiscible solvents. A comparison of the solid state structures of copper(II) sulfate and neutral copper-only complexes demonstrates how incorporation of the metal ion into the salen2− unit preorganises the anion binding site to accommodate the sulfate group. The extraction/recovery characteristics of copper and sulfate are reported for a ligand which has been modified to lower the strength of copper-binding and thus facilitate copper-recovery and ligand-recycling. An X-ray structure determination of this 2,2'-biphenylene-bridged ligand indicates a predisposition towards the provision of a non-planar N₂O₂2− donor-set. This is exemplified by its cis-octahedral nickel(II) sulfate complex in which the sulfate acts as a bidentate ligand. Competitive metal ion transport experiments show the selectivity of this ligand for copper(II) transport over a range of other metals including nickel(II) and zinc(II). The pH profiles for loading of Cu2+ (pH_1/2 2.0, i.e. pH at 50 percent extraction) and of SO₄2− (pH_1/2 9.7) into the ligand zwitterion in chloroform have been determined and this has allowed the demonstration of a protocol for loading of CuSO₄, stripping of copper and sulfate separately and recycling of the extractant. Such a protocol provides proof-of-concept for application of these ditopic ligands in metal recovery from sulfide leaching or from acid mine drainage streams.

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four N-benzyl groups with cobalt(ii), zinc(ii), cadmium(ii), lead(ii) and silver(i) nitrates is reported; the results are compared with those obtained in a prior study involving the formation of the corresponding complexes of nickel(ii) and copper(ii) with this ligand series. The isolation of a selection of 1 ∶ 1 (metal ∶ ligand) complexes has been carried out and X-ray diffraction structures of five such products have been determined. In each complex the metal ion is coordinated to the N₄-donor set of the cyclam ring with the latter adopting either a trans-I or a trans-V configuration; monodentate or bidentate nitrato ligands complete the respective coordination spheres. Coordination numbers range from five in a zinc(ii) complex, through six in two cadmium(ii) complexes, to eight in two lead(ii) complexes. Competitive bulk membrane transport experiments (water/chloroform/water) have been carried out in which each of the five benzylated ligands were in turn employed as the ionophore in the chloroform phase. The respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) nitrates. The aqueous receiving phase was buffered at pH 3.0. Under these conditions, high selectivity for copper(ii) was observed for each of the ionophores incorporating one or two N-benzyl groups whereas no transport for any of the seven metals present in the source phase was observed for the tribenzylated derivative. In marked contrast to the above behaviour, the tetra-N-benzyl derivative yielded sole transport selectivity for silver(i) under similar conditions. 1H NMR and 13C NMR titration experiments in CD₃CN–CDCl₃ confirmed the 1 ∶ 1 stoichiometry of the silver(i) tetra-N-benzylcyclam complex in this solvent mixture.

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four benzyl groups with nickel(ii) and copper(ii) is reported. The isolation of a selection of 1 : 1 (metal : ligand) complexes of both metals has been carried out and visible spectral, EPR, electrochemical and X-ray determinations have been employed to probe the nature of the respective complexes in both the solid state and in solution. Emphasis has been given to investigating the effect of the successive N-benzylation along this ligand series on the properties of the above complexes. The UV–VIS spectra obtained for each series of metal complexes indicate that the sequential introduction of N-benzyl substituents produces a change to lower ligand fields of the corresponding macrocyclic tetramines. Cyclic voltammograms of both the nickel(ii) (low-spin) and copper(ii) complexes both yield evidence for M(iii)/M(ii) as well as M(ii)/M(i) couples in acetonitrile.

Host–guest formation between N3O2-donor macrocyclic hosts and lipophilic organic acid guests that are themselves potential metal-ion ligandsextractants has been investigated and the implications of formation of such ligand assemblies for the binding of metal ions have been probed. The formation of 2 1 organic acid macrocycle assemblies has been demonstrated using NMR titration experiments in deuterochloroform for 4-tert-butylbenzoic, palmitic, phenylphosphinic, diphenylphosphinic and salicylic acids, with evidence for the additional formation of 1 1 intermediates in some cases. Molecular adducts of this type have been used in solvent extraction waterchloroform experiments to define the effect of assembly formation on metal ion binding. From entropy considerations it was anticipated that the formation of particular host–guest species of the above type might result in enhanced metal ion binding and hence enhanced metal ion extraction – a consequence of the fact that the components of the coordination sphere are, at least in part, assembled for complex formation. Using a range of assemblies of the above type, enhanced synergistic extraction of Cuii ions was confirmed in all cases. Adducts of 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane and 1,12,15-triaza-3,4:9,10-bis4′-tert-butylbenzo-5,8-dioxacycloheptadecane with 4-tert-butylbenzoic acid and salicylic acid have been isolated and their solid-state structures and 1 2 stoichiometries confirmed by X-ray diffraction.

The interaction of cobaltii, nickelii, copperii, zincii, cadmiumii, silveri and leadii with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O2N3-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log Kvalues for the respective 1 1 complexes in 95 methanol I 0.1; Et4NClO4, 25 °C of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent non-benzylated ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 1 silveri complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 1 copperii complex. The log Kresults are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor positive or negative influence on the affinity towards silveri while the corresponding binding strengths towards the remaining six metal ions are significantly reduced—behaviour we term ‘selective detuning’. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log Kresults, transport selectivity for copperii was exhibited by both systems, with similar transport efficiencies being evident when compared on a ‘per macrocyclic cavity’ basis.

Host–guest formation between N₃O₂-donor macrocyclic hosts and lipophilic organic acid guests (that are themselves potential metal-ion ligands/extractants) has been investigated and the implications of formation of such ligand assemblies for the binding of metal ions have been probed. The formation of 2 ∶ 1 (organic acid ∶ macrocycle) assemblies has been demonstrated using NMR titration experiments in deuterochloroform for 4-tert-butylbenzoic, palmitic, phenylphosphinic, diphenylphosphinic and salicylic acids, with evidence for the additional formation of 1 ∶ 1 intermediates in some cases. Molecular adducts of this type have been used in solvent extraction (water/chloroform) experiments to define the effect of assembly formation on metal ion binding. From entropy considerations it was anticipated that the formation of particular host–guest species of the above type might result in enhanced metal ion binding (and hence enhanced metal ion extraction) – a consequence of the fact that the components of the coordination sphere are, at least in part, assembled for complex formation. Using a range of assemblies of the above type, enhanced (synergistic) extraction of Cu(ii) ions was confirmed in all cases. Adducts of 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane and 1,12,15-triaza-3,4:9,10-bis(4'-tert-butylbenzo)-5,8-dioxacycloheptadecane with 4-tert-butylbenzoic acid and salicylic acid have been isolated and their solid-state structures (and 1 ∶ 2 stoichiometries) confirmed by X-ray diffraction.

The syntheses of three new copper(ii) complexes based on the bidentate ligand N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)ethanimidamide are reported. In the solid state these products assemble into elaborate supramolecular structures featuring hydrogen bonds within, and between, complexes as well as weak aryl–aryl and alkyl–aryl interactions between complexes; different coordination geometries and tautomeric forms are also observed. Dimethyl sulfoxide molecules show a variety of interactions within the structures, including coordination to the copper, hydrogen bonding, as well as weak alkyl–aryl interactions with the ligands.

The interaction of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) with a series of mixed-donor, N-benzylated macrocyclic ligands incorporating O₂N₂-, O₃N₂- and O₂N₃-donor sets has been investigated. The log K values for the respective 1 ∶ 1 complexes in 95% methanol (I = 0.1 mol dm−3; Et₄NClO₄, 25 °C) have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) macrocyclic systems. Examples of N-benzylation of individual parent macrocycles leading to enhanced discrimination for silver(i) are presented. In the case of a dibenzylated O₃N₂-ring and a tribenzylated O₂N₃-ring, both 17-membered, high selectivity for this ion was observed relative to the other metal ions investigated. Competitive mixed-metal transport experiments across a bulk chloroform membrane have been performed using the benzylated derivatives as ionophores. For each experiment the source contained equimolar concentrations of the above metal ions and transport was performed against a pH gradient; the aqueous source and receiving phases were buffered at pH 4.9 and 3.0, respectively. In parallel to the log K results, transport selectivity for silver(i) was exhibited by the di- and tri-benzylated ligands mentioned above. The remaining ligands proved to be poor ionophores, showing no significant metal ion transport under the conditions employed. In a further study, high silver ion (transport) selectivity was maintained when the above tribenzylated ligand was incorporated as the ionophore in a polymer inclusion membrane system. Single metal and mixed (seven-metal) solvent extraction experiments employing similar aqueous source and chloroform phases to those used in the bulk membrane transport runs have also been performed for the tribenzylated ligand derivative; significant selectivity for silver was again maintained in these solvent extraction experiments. An X-ray study of [AgL]ClO₄ (where L is the above-mentioned dibenzylated derivative) confirms that all donor atoms of the macrocycle coordinate to the silver ion; the latter is five-coordinate with the complex cation exhibiting a highly distorted trigonal bipyramidal geometry.

A comparative investigation of the interaction of three dibenzo-substituted, mixed oxygen–nitrogen donor macrocycles with cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) has been carried out. The thermodynamic stabilities of the respective complexes in 95% methanol (I = 0.1; Et₄NClO₄, 25 °C) have been determined. All ligands form 1 ∶ 1 (metal ∶ ligand) species with the above metal ions. The results are compared with those obtained previously for related mixed-donor (cyclic) systems. Single crystal structures of six metal complexes of these 20-membered ring ligands have been determined by X-ray diffraction. All of the macrocyclic donor sites participate in binding to the metal ion in the copper(ii) and cadmium(ii) complexes. The copper complex is six-coordinate, while the cadmium complex is eight-coordinate with the addition of a bidentate nitrato ion. A tri-nuclear complex is formed on complexation with silver(i) in which two silver-containing macrocycles are linked by a bridging two-coordinate silver ion. The metal atoms in each of the cobalt(ii), nickel(ii) and zinc(ii) complexes are six-coordinate, however, they are bound to the macrocycle only at the three secondary amine nitrogen sites. The coordination sphere is completed by two nitrato counterions in the zinc(ii) complex, and by a nitrato ion and a methanol molecule in each of the cobalt(ii) and nickel(ii) complexes.

Competitive transport experiments involving metal ion transport from an aqueous source phase across a chloroform membrane phase into an aqueous receiving phase have been carried out using a series of open-chain mixed-donor ligands as the ionophore in the organic phase. The source phase contained equimolar concentrations of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii), with the source and receiving phases being buffered at pH 4.9 and 3.0, respectively. Clear transport selectivity for silver(i) was observed in all cases. This was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. Stability constant data confirm that all these ligands show significant affinity for silver(i) in methanol. An X-ray diffraction study of the silver(i) complex of a tripodal NS₃-donor ligand from the present series is reported. This complex occurs as two crystallographically independent molecules with both forms having a 1 ∶ 1 silver ∶ ligand ratio. The metal coordination geometry of the first form is distorted tetrahedral, with three coordination sites occupied by the three sulfur atoms of the ligand and the fourth site filled by an oxygen atom of the nitrate anion. The silver ion in the second form is five-coordinate being bound to the ligand's apical nitrogen as well as to its three sulfur donors. The remaining position is again occupied by a nitrate oxygen, with the metal coordination geometry in this case best described as distorted trigonal bipyramidal.

The structures of four supramolecular arrays incorporating concerted triple acceptor–donor–acceptor/donor–acceptor–donor (ADA/DAD) hydrogen bonds are described. The first is comprised of 1 ∶ 1 phthalimide ∶ 2,4-diamino-6-phenyl-1,3,5-triazine units linked into a one-dimensional strand by more loosely connected independent interposed triazine moieties. The second, composed of [bis(dithiobiureto)nickel(ii)∶(3-iminoisoindolinone)₂] units, incorporates similar complementary triplet hydrogen bonding motifs. The third system involves a 1 ∶ 2 assembly between the dianionic complex, bis(biureto)nickelate(ii) and 2,4-diamino-6-phenyl-1,3,5-triazine to yield the bis(tetraethylammonium) salt of the [bis(biureto)nickelate(ii)∶(2,4-diamino-6-phenyl-1,3,5-triazine)₂] dianion unit, the array again extended by secondary interactions. The final assembly investigated is composed of ‘tri-component’ units of type [bis(biguanidino)nickelate(ii)∶(6,7-dimethoxy-2,4(1H, 3H)-quinazolinedione)₂] that feature an excess of hydrogen bond donor groups over acceptor groups. As in the above assemblies, it also incorporates hydrogen bonds between complementary triplet motifs as well as bridging hydrogen bonds between individual units. This last assembly is no longer planar; in the lattice being linked into a two dimensional network by dimethylsulfoxide molecules that act as ‘ancillary’ acceptors for the excess donors present and also as bridging molecules between neighbouring tri-component units. The hydrogen bond geometries in these assemblies are discussed comparatively and also compared with related arrays reported in the literature.

The interaction of four tri-linked N₂S₂-donor macrocyclic ligands and their single ring analogues with silver(i) has been investigated. The 3 ∶ 1 (metal ∶ ligand) stoichiometries of the silver(i) complexes of the tri-linked species in dimethyl sulfoxide-d6/CDCl₃ were confirmed by means of NMR titrations involving the incremental addition of silver(i) nitrate to the respective ligands in the above solvent mixture and following the corresponding induced shifts in the 1H NMR spectrum. Solid 3 ∶ 1 (metal ∶ ligand) complexes were isolated for each of the parent (unsubstituted) tri-linked ligands. Competitive solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-linked ligands as well as their single ring analogues were employed as the extractant/ionophore in the chloroform phase. In both sets of experiments the respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii) nitrates. For membrane transport the aqueous receiving phase was buffered at pH 3. Under the conditions employed, both the solvent extraction and the bulk membrane transport experiments resulted in high extraction/transport selectivity for silver(i) relative to the other six metal ions present.

A supramolecular assembly formed between phthalimide and 2guanidinobenzimidazole, containing a short 2.6924AR NH…N hydrogen bond, is reported. The crystal structure of this species was determined by both Xray and neutron diffraction. The diffraction data reveal that the proton involved in the short hydrogen bond has been transferred from the phthalimide to the guanidinobenzimidazole to form an ion pair. There is also an interesting stacking interaction between the atoms involved in the short hydrogen bond and the π system of a phthalimide molecule that is approximately 3.3 Å away. The structure is compared with the structure of a similar assembly formed between 4nitrophthalimide and 2guanidinobenzimidazole.

Palladium(ii) and platinum(ii) complexes of ligands incorporating three linked, 16-membered, N₂S₂-donor macrocycles, together with their single-ring analogues have been synthesised. The former complexes are of the form [M₃L](PF₆)₆ (where M = Pd or Pt, and L is a linked three-ring macrocyclic species incorporating a 1,3,5-‘tribenzyl’ or a phloroglucinol core). The X-ray structure determination of the single ring species [PdL](PF₆)₂ (where L is a single N-benzylated derivative of the N₂S₂-donor macrocycle) showed that the palladium is coordinated to all four donor atoms of the macrocycle in a ‘square planar’ manner. The electrospray mass spectra of the tri-linked metal-containing species show a series of multiply charged ions resulting from the loss of hexafluorophosphate counter ions and hydrogens, and corresponding to [M −  nPF₆]n+ and [M −  nPF₆ −  mH](n  −  m)+. Expansion of individual charged peaks revealed the expected wide mass range resulting from the presence of three metal ions, each of which possesses a number of isotopes. Spectrophotometric titrations confirm that 3 ∶ 1 (metal ∶ ligand) stoichiometries occur for the complexes of these tri-linked ligands in acetonitrile.

The rigidity of a series of cryptands incorporating an N₂O₆-donor has been shown to have a marked effect on the ability of such species to complex sodium ions. X-Ray and associated computational investigations, including molecular mechanics, semi-empirical (AM1) and ab initio (density functional) studies, coupled with the results of sodium picrate extraction experiments and NMR studies, have been employed to probe the conformational aspects influencing sodium ion complexation along the ligand series. It is concluded that the ease with which a cryptand is able to adopt an endo–endo conformation is an important factor affecting the occurrence of inclusive metal-ion binding in these systems.

A low-temperature single-crystal X-ray structural determination of [CuCl(L¹)]ClO₄·H₂O [where L¹ = meso-2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene] is reported. The coordination geometry of the complex cation approximates square pyramidal, with the chloro ligand occupying an apical position. The latter group is associated with an intermolecular hydrogen bonding network involving the uncoordinated water molecule and the perchlorate counter ion. Density functional theory (DFT) has been applied to modeling the structure of this complex, both in the presence and the absence of the intermolecular hydrogen-bonding network. In the absence of this network a good fit to the X-ray structural parameters was obtained except for the Cu–Cl bond length. For this bond the calculated value (2.346 Å) was significantly shorter than the X-ray value [2.541(2) Å] but, on incorporation of the hydrogen-bonded network, while the major portion of the computed structure remained almost identical to that obtained from the initial calculation, the Cu–Cl bond was now found to be longer at 2.572 Å, approximating the X-ray value quite closely. The study has been extended to similar/related systems for which structural data are available, confirming the wider applicability of this approach in modeling arrays of this type.

The selective use of the tert-butoxycarbonyl protecting group has enabled efficient syntheses of the tri-linked cyclam derivatives (6)–(8). Using a related protecting group strategy, a series of related single-ring, N-benzylated cyclam derivatives (1)–(4) has also been prepared.