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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.

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’.

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.

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.