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Analysis of the weak interactions within the crystal structures of 33 complexes of various 4′-aromatic derivatives of 2,2′:6′,2″-terpyridine (tpy) shows that interactions that exceed dispersion are dominated, as expected, by cation...anion contacts but are associated with both ligand–ligand and ligand–solvent contacts, sometimes multicentred, in generally complicated arrays, probably largely determined by dispersion interactions between stacked aromatic units. With V(V) as the coordinating cation, there is evidence that the polarisation of the ligand results in an interaction exceeding dispersion at a carbon bound to nitrogen with oxygen or fluorine, an interaction unseen in the structures of M(II) (M = Fe, Co, Ni, Cu, Zn, Ru and Cd) complexes, except when 1,2,3-trimethoxyphenyl substituents are present in the 4′-tpy.

Diverse isomers of cyclohexanedicarboxylic acid (chdcH$_2$) have been used to synthesize uranyl ion complexes in the presence of various possible counterions and, but for one case, under (solvo-)hydrothermal conditions. The cis isomer of 1,2-chdcH$_2$ gives the complex [UOV$_2$(c-1,2-chdc)(H$_2$O)2]·H$_2$O (1), which crystallizes as an enantiomerically pure helical monoperiodic structure, while partial isomerization of the cis into the trans form yields [PPh$_4$]$_2$[(UO$_2$)$_3$(c-1,2-chdc)$_2$(rac-t-1,2-chdc)(H$_2$O)]·$_2$H$_2$O (2), a ladderlike monoperiodic assembly. The pure (1R,2R) enantiomer of t-1,2-chdcH$_2$ gives [UO$_2$(R-t-1,2-chdc)(H$_2$O)] (3) containing a diperiodic assembly of hcb topological type. When reacted at room temperature, its racemic counterpart produces [UO$_2$(rac-t-1,2-chdc)(EtOH)]·H$_2$O (4), a diperiodic species with the fes topological type isomorphous to other similar solvates. Using a mixture of the cis and trans isomers of 1,3-chdcH$_2$ gives [NH$_4$][NBu$_4$][(UO$_2$)$_2$(c-1,3-chdc)$_2$(t-1,3-chdc)] (5), the first instance of a triperiodic uranyl-containing framework obtained with this ligand. Finally, the complex [H$_2$NMe$_2$]$_2$[(UO$_2$)$_2$(t-1,4-chdc)$_3$] (6), containing the trans isomer of 1,4-chdc 2-, crystallizes as a triperiodic framework with ths topology, and displays sixfold-interpenetration, the highest degree found up to now in a uranyl ion complex. These results are discussed together with previous ones obtained with this highly versatile family of cyclohexanedicarboxylate ligands.

Data deposited in the Cambridge Structural Database (CSD) for compounds of scandium, yttrium, lanthanum and lutetium(III) have been analysed to assess the structural similarities of complexes of the different metal ions. 29 sets of compounds of Sc, Y, La and Lu where at least three of the elements form compounds with the same ligands have been identified and their crystal structures analysed. In 14 of them, scandium and lutetium have the same coordination number; in the remaining 15 they do not. Similarly, there are 10 examples where there is a difference in coordination number between Lu and Y for compounds with the same ligands. For the other 19 either the coordination numbers are the same or that compounds for both the elements under consideration have not been reported. Overall structural differences correlate well with the size of the metal ions and provide no true chemical basis for arranging Lu rather than La in one triad with Sc and Y.

This article belongs to the Special Issue Supramolecular Chemistry in the 3rd Millennium; International audience; Consideration of the extensive family of known uranyl ion complexes of polycarboxylate ligands shows that there are quite numerous examples of crystalline solids containing capsular, closed oligomeric species with the potential for use as selective heterogeneous photo-oxidation catalysts. None of them have yet been assessed for this purpose, and some have obvious deficiencies, although related framework species have been shown to have the necessary luminescence, porosity and, to some degree, selectivity. Aspects of ligand design and complex composition necessary for the synthesis of uranyl ion cages with appropriate luminescence and chemical properties for use in selective photo-oxidation catalysis have been analysed in relation to the characteristics of known capsules.

Structural characterisation of a further series of crystalline solids in which [Ln(dipic)3]3− anions (dipic = pyridine-2,6-dicarboxylate; Ln = La, Gd) are accompanied by chiral Co(III)-containing cations provides new examples of layered lattices where sheets of anions and (cations + water) alternate. Δ,Λ-[Co(en)3]3+ (en = ethane-1,2-diamine) forms crystals where, depending on the degree of hydration, the cation sheets are either homo- or heterochiral but the anion sheets are always heterochiral. Δ-[Co(en)3]3+ provides lattices where the anion sheets remain heterochiral, resulting in unusual solids containing a single enantiomer of the cation along with both enantiomers of the chiral anion, rather than two diastereomeric crystals containing the separate anions. Classical resolution of the anions only appears to occur in the presence of a functionalised cage amine complex cation, Δ-[Co((NO2)2sar)]3+ (sar = sarcophagine = 3,6,10,13,16,19-hexa-azabicyclo[6.6.6]icosane) which gives crystals in which direct H-bonding interactions between the cations and anions are surprisingly limited and the success of the resolution requires consideration of a variety of other factors.

The unsymmetrical hydrazonobis(acylhydrazone) ligand L exists in solution as a mixture of isomers but complexes to Hg(II) with a major conformational change, affording a mixture of parallel and antiparallel binuclear double helicates. On crystallisation of the triflate salt, however, the antiparallel strand isomer is selected presumably due to the optimisation of several weak interactions. (c) 2012 Elsevier Ltd. All rights reserved.

Structural characterisation of a number of hydrated solids containing chiral, kinetically inert [Co(A–A)3]3+ cations (A–A = 2,2′-bipyridine, 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine) and chiral, kinetically labile [Ln(dipic)3]3– anions (Ln = La, Eu, Tb, Ho, Er, Lu, Y, though not for all cobalt cations; dipic = dipicolinate = pyridine-2,6-dicarboxylate) show a remarkable range of associations between the lattice components, though all are racemic arrays. Analysis of the structures in terms of short interatomic contacts between the components shows that, whereas numerous contacts of the heteroaromatic ligands do occur, very few define an arrangement which could be truly termed “π-stacking” where the rings are closely parallel and atom overlaps in projection are substantial. Water is important in the highly hydrated lattice structures, not only because of hydrogen-bonding interactions with itself and carboxylate-O atoms but also because of its interactions with the aromatic units. The family [Co(bipy)3][Ln(dipic)3]·~13H2O are essentially isomorphous for the full range of Ln plus Y (triclinic, P\bar{1}, a = 12.3, b = 14.3, c = 16.5 A, α = 94, β = 94, γ = 108 ˚, Z = 2). Among the heavier lanthanides, the potential symmetry of the anion/cation combination is realised in the trigonal space group P\bar{3}, both species lying together as an ion-pair, disposed on the trigonal axis for [Co(phen)3][Ln(dipic)3]·22H2O (Ln = Eu, Er; a = 15.2, c = 16.8 A, Z = 2).

Reactions of the tridentate Schiff-base ligands HL1, HL2 and HL3 formed from pyridine-2-aldehyde and 2-aminophenol plus two of its methoxycarbonyl derivatives, with AgNO3, [Cu(CH3CN)4]PF6, Cu(NO3)2, Co(NO3)2 and Zn(NO3)2 give complexes of the following types: [Ag(HL)2]NO3; (1a, 2a, 3a); [CuII(HL)L]PF6 (1b, 2b, 3b); [CuII(HL)L]NO3 (1c, 2c, 3c); and [M(HL)L]2[M(NO3)4] where M Co(II) (1d, 2d, 3d); or Zn(II) (1e, 2e, 3e), which in principle define the basic characteristics of the metal sites in certain metallogrids. The complexes have been characterized by spectroscopic techniques and elemental analysis. The solid state structures of complexes 2b and 2e have been established by X-ray crystallography.

After vacuum dehydration, a number of hydrated trivalent lanthanoid trifluoromethanesulfonates (“triflate”, “OTf” = F3CSO3), when recrystallized from various alcohol (ROH) solutions, yield solvates Ln(OTf)3·xROH, x = 3, 5 or 6. The following have been defined crystallographically (R/Ln/x): Me/La/3;Me/Gd/6; Et/Sm/3; Et/Gd/5 iPr/Nd,Sm/3. The Me/Gd/6complex, Gd(OTf)3·6MeOH is a mononuclear/ionic form [(MeOH)6Gd(O–OTf)2](OTf), the gadolinium environment being octacoordinate, square-antiprismatic with the O–OTf donors quasi-trans on different faces of the coordination polyhedron; the Et/Gd/5 complex is neutral, molecular, mononuclear [(EtOH)5Gd(O–OTf)3], also with an octacoordinate, square-antiprismatic coordination sphere, derivative of that of the methanol solvate. The remainder form one-dimensional polymeric arrays, successive lanthanoid atoms linked by (μ-O–OTf–O′)3 triads, at either end of a tricapped trigonal prismatic array, the ROH molecules contributing the capping atoms. A (“baseline”) (re-)determination of the “parent” Sm(OTf)3·9H2O is also recorded.

Readily synthesised, water-stable pyridylazetidine-based Pd(II) complexes have been studied as catalysts for the Sonogashira coupling reaction. Under low catalyst loadings, various aryl bromides and chlorides were efficiently coupled with phenylacetylene at only moderately elevated temperatures (50–70 °C) and, in some cases, even at room temperature. Not only was the catalysis efficient under mild conditions but it was also operative in aerated, partly aqueous and phosphine-free media.

A relatively simple azetidine derivative with 2-aminoethyl and 2-pyridyl substituents functions as a tridentate ligand towards Cu(II), giving species in which the CuN3 unit is essentially planar and that, in the solid state, show a subtle balance between mononuclear and binuclear forms, allowing both to be simultaneously present in some lattices. Displacement of the ligand from Cu(II) by the use of cyanide results in the formation of cyanogen, which appears to slowly react with the free amine to give an oxamidine characterised in its doubly-deprotonated form as its binuclear Ni(II) complex.

The metalloamphiphile [Zn(1-decylammonio-8-methylsarcophagine)](ClO4)3·2H2O crystallises in the non-centrosymmetric space group P1 to give a polar crystal, which can be converted to one with a centrosymmetric lattice (space groupI2/a) through deprotonation.

Selective functionalisation of the tridentate ligand 1-(2-aminoethyl)-3-methyl-3-(2-pyridyl)azetidine at its terminal amino-nitrogen atom can be readily achieved by both reductive alkylation and simple alkylation reactions to give tri-, quadri-, quinque- and sexi-dentate derivatives. Simple alkylation by 2-picolinyl chloride provides the only example of a second reaction pathway where the azetidine ring of the reactant has undergone activation towards ring opening. Structural characterisation of the Cu(II) complexes of these ligands has revealed several remarkable aspects of their solid-state coordination chemistry, including the formation of infinite helical aggregates through pi-stacking and tetramerisation through carboxylate bridging, as well as further examples of the crystallisation of mixed species found to be rather common with complexes of the parent ligand.

International audience; Reactions in CH3CN:CH2Cl2 (2:1) under Ar of the dimethyl-quaterpyridine ligand C22H18N4 (L) with Mn(ClO4)2, Fe(BF4)2, CoCl2, Co(NO3)2, Zn(NO3)2, Cd(CH3COO)2 and HgCl2 give complexes of the type [ML(H2O)mXn]2[MXp], where X denotes the initial counterions, with m=1, n=1, p=4 or m=2, n=0, p=6. The complexes have been characterized by spectroscopic techniques and elemental analysis. The solid state structures of two forms of the CoCl2 complex have been established by X-ray crystallography, enabling an analysis of the interactions occurring in crystals of this type.

Readily-synthesised, water-stable Pd(II) complexes of azetidine-based tridentate ligands have been studied as catalysts for the Suzuki–Miyaura coupling reaction. They are highly active for the coupling of aryl bromides with aryl boronates and also effective for the coupling of aryl chlorides.

Solution and solid state studies of the complexation of Hg2+ and Pb2+ by the homologous bis-tridentate ligands 1 and 2H2 obtained by condensation of bis(methylhydrazino)phenylpyrimidine and bis(hydrazino)phenylpyrimidine, respectively, with pyridine-2-carboxaldehyde, have provided evidence for the formation of both grid and rack species. With Hg2+, there is little indication for other than grid species, the grid complex [Hg4(2H2)4](CF3SO3)8 being characterised crystallographically. With Pb2+, the only crystalline species readily isolated are rack complexes of the ligands 1 and 2H2.

Ditopic bis(acylhydrazone) ligands, derived from the reactions of carbohydrazides with 2-phenylpyrimidine-4,6-dicarbaldehyde and designed for grid formation with octahedrally coordinating transition-metal ions, exhibit a varied coordination chemistry depending upon the degree of their deprotonation. The neutral acylhydrazones are relatively poor ligands and are seemingly involved in multiple, labile complexation equilibria varying with the solvent and the particular metal salt in solution; nevertheless, grid complexes of different forms can be isolated in the solid state. Although only limited study has been made of the singly deprotonated ligands, grid species appear to be much more readily isolated. With the doubly deprotonated ligands, grid formation is strongly favoured in both the solution and solid states. As a consequence, the grid structures form spontaneously in the presence of a base by self-assembly from their components without need to preform the ditopic ligands. Extensive structural studies have been carried out both to establish the grid structures and to analyse the nature of the supramolecular interactions possible for neutral and charged grid species. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Both the consequences of 1,3-cyclization of calix[4]arenes by diamide formation, and the effect of 2- and 2,4-alkoxycarbonylmethylation of two 1,3-bridged calix[4]azacrowns on their metal ion-binding capacities have been studied by synthesis of the derivatives in their cone conformation and measurement of the stability constants for their complexation in a range of alkaline earth and transition metal cations. In these two cases, the conformation of the ligand in the solid state has been defined in detail by a crystal structure determination. In the first case, a tubular architecture performing methanol channels is displayed, however, in the second case a zigzag architecture generated by a chloroform network connecting calixarene molecules is present. Speciation in solution appears to be limited to the formation of 1:2 and/or 1:1 and/or 2:1 (M–L) complexes, depending on the system, with values of the stability constants determined by absorption spectroscopy in acetonitrile, lying in the ranges log β12 ca. 10, log β11 ca. 2–5, and log β21 ca. 7–9. There is evidence for selectivity toward Cu(II) and for some unexpected anion effects. None of these ligands appear to be an efficient extractant for the metals as their picrate.

A number of new (sarcophagine)cobalt compounds containing oligopeptide substituents terminated by a mercaptoethylamide unit, [Co(R)(R')sar] 2 6+ (R = NH 2 , CH 3 ; R' = NHpeptide-CONHCH 2 CH 2 S-), have been prepared utilising the carboxymethyl complexes [Co(R){N(CH 2 C0 2 H)}sar] 3+ (R = NH 2 , CH 3 ), and subsequently characterised. The amino acid residues, terminating with cystamine groups, were introduced into the carboxymethyl complexes using standard peptide coupling chemistry. The solid-state structures of [Co(CH 3 )-{N(CH 2 CO 2 H)}sar]Cl 4 ·H 2 O, [Co(CH 3 ){N(CH 2 CO 2 H) 2 }sar]Cl 3 · 2H 2 O and [Co(CH 3 ){N(CH 2 CO 2 ) 2 )sar]Cl·6.5H 2 O were determined by single-crystal X-ray diffraction experiments, the first two forming lattices containing homochiral sheets of cations in planes parallel to [0,0,1]. In the structure of [Co(CH 3 ))-{N(CH 2 CO 2 H)}sar]Cl 4 ·H 2 O, the cations are of the same absolute configuration, but this alternates from one sheet to the next. In the dihydrate, [Co(CH 3 ){N(CH 2 CO 2 H) 2 }sar]-Cl 3 ·2H 2 O, the structure appears to be very similar. The sheet alternation is different from the structure of the monohydrate, [Co(CH 3 ){N(CH 3 CO 2 H))sar]Cl 4 ·H 2 O. The deprotonated imidodiacetate complex, [Co(CH 3 ){N(CH 2 CO 2 ) 2 }sar]Cl·6.5H 2 O, was prepared in an unrelated reaction; the structure displays hydogen-bonding interactions involving the carboxylate groups and coordinated NH units. The solution electrochemistry of these compounds has been investigated using both cyclic voltammetry and differential pulse voltammetry. The compounds exhibited pH-dependent, quasi-reversible redox behaviour. A monolayer was prepared by the interaction of [Co(R)sar(GlyNHCH 2 CH 2 S-)] 2 6+ and a gold microelectrode using both conventional "self assembly" (SAM) and electrodeposition (EDM) techniques. Surface cyclic voltammograms were measured, which, after a period of induction associated with surface reorganisation, were typical of an ordered monolayer. The monolayer was characterised by XPS, showing peaks assigned to the presence of S, Co, N, O and C. Ellipsometry gave a film thickness of 7 ± 1 A, consistent with the formation of a mono- rather than a multi-layer.

Several pathways to macromonocylic polyamine ligands with pendent hydroxymethyl substituents have been explored. The new ligands have all been characterised by single-crystal, X-ray structure determinations on their complexes with Co(III) (one case) and Cu(II). As in some related systems, four-membered ring species, here oxetanes rather than azetidines, appear to be involved as reaction intermediates and can be quite readily isolated, providing reactants of potential for the construction of even more complicated multidentate ligands.

Consideration of crystallographic data concerning metal complexes of hexa-azabicyclo[6.6.6]icosane, “sarcophagine”, and various derivatives provides evidence for the importance of hydrogen-bonding, labile metal ion coordination, aliphatic- and aromatic-group interactions in determining the lattice structures. These “cage amine” complexes not only involve different metal ions, almost all rendered kinetically inert towards substitution by their complexation, but they can be obtained in conformationally locked forms and with a wide variety of substituents, so that they have considerable potential as supramolecular tectons.

A macrobicylic ligand 1 formed by the A,D-bridging of a calix[6]arene with a 2,9-disubstituted 1,10-phenanthroline unit reacts with Yb(III) under basic conditions in dimethylformamide (dmf) to give a neutral, mononuclear complex characterised by X-ray crystallography as [Yb(1-3H)(dmf)] · 3dmf. The structure shows that although the metal can be considered to lie within a cavity formed by the “concave reagent” ligand, this does not entirely prevent its coordination to a dmf molecule between arms of the macrobicycle. Stability constant measurements indicate that 1 forms complexes of similar strength across the lanthanide(III) series.

Crystal structure determinations on the hydrated forms of the complexes M2UO2(dipic)2, M = H, Rb, Cs, dipic = dipicolinate = pyridine-2,6-dicarboxylate, all of which show strong solid-state luminescence from the uranyl centre, have as a common feature extended π-stacking arrays of the dipicolinate ligands. Comparisons with related but non-luminescent complexes indicate that these stacking arrays may be associated with efficient energy transfer from the dipicolinate “antennae” to the uranyl unit. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Structure determinations for the dimethylsulfoxide (dmso) solvate of lead(II) picrate (picrate = pic = 2,4,6-trinitrophenoxide), formally a centrosymmetric dimer, [Pb2(dmso)4(pic)4], and for unsolvated mercury(I) picrate, a polymer of conventional mercurous dimers, [Hg2(pic)2] n , show that, despite considerable differences in the form of the metal unit, there are remarkable similarities in the mode of coordination of the bridging picrate ligands. In both lattices, parallel arrays of picrate rings can be discerned but appear to be associated with short N…O, O…O or O…C contacts rather than C…C. In the Pb compound, there is also evidence of intramolecular contacts to dmso-S.

Structure determinations for 2,2′-bipyridine and 1,10-phenanthroline adducts of lead(II) hexafluoroacetylacetonate, [Pb(bipy)2(hfacac)2] (1), [Pb(bipy)(hfacac)2] (2), and [Pb(phen)(hfacac)2] (3), show that the balance of intermolecular forces within the lattices is seemingly sensitive to the adduct stoichiometry but not to the nature of the heteroaromatic base. In 3, a structure, in which there is an apparent preference for CF/aromatic interactions over separate CF/CF and aromatic/aromatic interactions, is essentially identical at both 120 and 293 K.

Characterisation of the products of reactions of the Co(III) complex of a quadridentate amine incorporating an azetidine ring by structural crystallography has shown the bound heterocyclic ring to be stable under quite forcing conditions. With bidentate co-ligands, the tetramine appears to prefer one form of “cis-β” coordination to Co(III). On Cu(II), the tetramine is readily and stereoselectively converted to a macrocycle which may be a useful precursor to pendent-arm derivatives.

Reactions between a tripodal trithiaether-triamine and the monomethoxycarbonylmethyl ether of p-tert-butylcalix[4]arene led to the ready isolation of both di- and triamides, namely di- and tricalixaryl derivatives of the tripod. These molecules, designed as dendrimer precursors, retain a core capable of acting as a multidentate ligand for metal ions. Studies of complex formation with Zn(II) and Co(III) by these new ligands show that indeed there is preferential binding to the core (rather than to the phenolic sites of the calixarene units), suggesting new mechanisms for the control of the structure and stereochemistry of dendrimer species.

Synthetic and structural studies based on the reaction of the Cu(II) complex of sen (3,7-diaza-5-(4′-amino-2-azabutyl)-5-methylnonane-1,9-diamine) with formaldehyde and nitroethane under base catalysis have shown that both syn and anti isomers of pendent-arm macrocycles of the “ryongamine” type can be readily obtained. The Cu(II) complexes of sen and one of its homologues also appear to undergo reactions with methanol which result in the formation of aminal derivatives where orientation of uncoordinated ligand arms is restricted by the aminal ring.

Structural characterisation of hexamine cage complexes, two containing diamagnetic CoIII and one containing paramagnetic CuII, to which both rather short (C4) and relatively long (C13) alkyl substituents have been attached, shows that while the longer “tail” introduces an anticipated bilayer form to the crystalline solid, even the shorter tail can be associated with a form of aggregation of lipophilic entities in the crystal. The short tail at least may also be involved in interactions with anions of a complex type. As surfactants, functionalised cage complexes contain a head group, which is a multi-site hydrogen-bonding entity, and which can thus provide a mechanism for further aggregation concomitant with that of any apolar functionality. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

A crystal structure determination for bis(4-hydroxycarbonylpyridinium) chloride tetrachloroferrate(III) monohydrate shows some striking differences in the lattice compared to that of the related tetrachloroplatinate(II) compound. A variety of intermolecular contacts indicate that, while common forces may be operative in these and other related lattices, their diverse features may reflect a close balance between polar hydrogen-bonding interactions and those involving the aromatic rings.

Thermal decomposition in air of the series of complexes [Co(NH3)6][Ln(dipic)3]·x H2O, [Cr(en)3][Ln(dipic)3]·y H2O and [Cr(urea)6][Ln(dipic)3]·z H2O (Ln = La – Lu, excluding Pm but plus Y; dipic = 2,6-pyridinedicarboxylate) to give oxide phases has been examined. The products were characterised by powder X-ray diffraction, magnetic and surface area measurements. From the Co-containing species, either Co3O4 + Ln2O3 or perovskite (CoLnO3) products result, while the Cr-containing species provide CrLnO4 phases in addition, the monazite form of CrNdO4 being detected for the first time in this way. Underpinning consideration of the solid state decomposition mechanisms, single-crystal X-ray structure de-terminations have been performed on [Co(NH3)6][Ln(dipic)3]·n H2O across the Ln series, defining differing phases (alltriclinic P) for n = 5 (encompassing Ln = La–Pr), n = 8(.5) (Ln = Tm – Eu) and n = 10 (Ln = Pr – Er, including Y), and also on one of the low-temperature decomposition products, [Co(NH3)6]Cl·dipic·2 H2O (1). The structure of 1 provides evidence that conventional π-stacking of the dipicolinate anions may be of some importance in determining the solid state array, whereas consideration of all structures involving [Ln(dipic)3]3– anions indicates that “edge-to-face” interactions between dipicolinate ligands of adjacent complex anions may also be determinants of the formation of sheet-like arrays of the trianions commonly observed in these compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The influence of the development of bioinorganic chemistry upon the fundamental concepts of coordination chemistry is considered in terms of several of the more remarkable structural studies now known of metalloproteins containing multiple metal complex centres. To cite this article: J. Harrowfield, C. R. Chimie 8 (2005).

Structure determinations for the dimethylsulphoxide (DMSO) solvates of uranyl triflate, nitrate, picrate and a tetranuclear basic acetate show DMSO to be bound in all cases as an O-donor ligand but with the sulphur atoms involved in a variety of close approaches which may be significant in determining details of the complex ion structures. These close approaches, which generally mean that S may be considered to have ‘3 + 2’ coordination, usually involve O of an adjacent DMSO or oxyanion ligand, but can also involve uranyl-O and can be both intra- and inter-molecular. To cite this article: J.M. Harrowfield et al., C. R. Chimie 8 (2005).

The synthesis of perhaps the best-known Wernerian complex, [Co(en) 3 ] 3+ , is very efficient, but nonetheless results in the formation of various side-products. Today, the use of X-ray crystallography to characterise such materials provides new insights into the reaction pathways of the synthesis and the exact forms possible for the products. The structures of cis -[Co(en) 2 (H 2 NCH 2 CH 2 NH 3 )Cl]Cl[ZnCl 4 ], cis -[Co(en) 2 (NH 3 )Cl]S 2 O 6 , [Co(en)(NH 2 CH 2 CH 2 N=CHCH 2 NH 2 ))Cl][ZnCl 4 ], [Co(en) 2 (N-CH 3 en)][Co(CN) 6 ]·2 H 2 O and [Co(en) 2 (N-CH 3 en)][Co(CN) 6 ], are presently discussed in this regard. To cite this article: J.M. Harrowfield et al., C. R. Chimie 8 (2005) .

Low-temperature, single crystal X-ray structural characterisations of trans-[NiCl2(HOMe)4], trans-O-[Ni(MeOH)2(μ-Cl)(2/2)2](∞∣∞) · 0.5dioxan and trans-trans-[Ni(H2O)2Cl2(O-dioxan-O)(2/2)](∞∣∞) · dioxan are recorded, offering intriguing insights into O-donor/Ni(II) relativities. All nickel atoms in all structures are located on crystallographic inversion centres, the last two compounds being one-dimensional polymers.

Metallocavitands are coordination compounds based on rigidified molecular cavities which possess at least one entry. Those in which the metal centre is rigidly held above the entrance are particularly promising for the study of host-guest interactions between metal-bonded substrates and the internal part of a cavity. Such systems also open the way to highly selective intra-cavity reactions. The present review focusses on conical cavities derived from calixarenes and cyclodextrins and examines their possible use as second coordination sphere ligands.

Problems arising from the extensive disorder characteristic of the crystalline lattice of dmso solvates of metal perchlorates at room temperature can in many cases be ameliorated or removed at `low' temperature. Present studies of several M(ClO 4 ) n · 6dmso ( n =2,3) species and Dy(ClO 4 ) 3 · 8dmso have allowed detailed definition of several homoleptic dmso-solvated metal cations, all of which contain dmso as an O -bound unidentate ligand and which appear to closely confirm the forms of solvated cations deduced from independent solution studies.

Structure determinations for the lanthanide (Ln) complexes [(CH3)2NH2][Gd(dmf)8](ClO4)4, [Tb(dmf)8](ClO4)3 and [Ho(dmf)7(OH2)](ClO4)3 (dmf=N,N-dimethylformamide) show all three to contain an LnO8 coordination unit of essentially square-antiprismatic geometry. The geometry of the inner coordination sphere appears to be little perturbed by quite major differences in the lattice environment of the cations. Attractive interactions between coordinated dmf molecules may be one contributor to the stability of the primary coordination sphere.

Enforcement of chirality upon a macrocyclic tetramine ligand structure by the introduction of an asymmetric pendent arm which does not significantly modify the macrocycle conformation has no significant effect upon the geometry of the coordination sphere of a bound metal. Where substitution engendering chirality does cause a change in the ligand conformation, in particular for a ligand of restricted stereochemistry, these effects can be much greater. Thus, conversion of 3,7-diazacycloheptane to a macrocycle via attachment of chiral sidearms and ring closure through a template reaction leads to cyclam derivatives with unusual coordination properties.

Reaction between ethane-1,2-diamine and 3,3'-dichloropivalic acid results in different, isomeric tetra-amine derivatives, one a tetraamino carboxylic acid and the other a carboxamidotriamino alcohol, depending upon reaction conditions. Intended conversion of the Cu(II) complex of the former to a cyclam-like macrocycle through reaction with nitroethane and formaldehyde results in isolation of derivatives of both the former and the latter. This can be rationalized by assuming the intermediacy of an azetidinone, a species similar to that seen in simpler reactions of dichloropivalates. A single reaction thereby provides pendent-arm macrocycles where one has an electrophilic and the other a nucleophilic substituent. Parallel chemistry is not seen in the reaction between propane-1,3-diamine and 3,3'-dichloropivalate.

Use of a hydroxyl-functionalized open chain tetramine in a template reaction based on its Cu(II) complex leads, after reduction, to a new tetraaza macrocycle with both amino and hydroxyl substituents. The macrocycle is formed predominantly as its trans (anti) isomer, though the cis form is detectable and both have been structurally characterized in the form of their metal complexes. Although both the Cu(II) and the Co(III) complexes of the tetramine precursor ligand have the hydroxyl group in an axial position of a chair six-membered chelate ring, the trans macrocycle forms Co(III) complexes with this substituent in both equatorial and axial positions.

Structural studies of the dimethyl sulfoxide solvates of the perchlorates of Mg, Sr and Ba show the presence of a variety of complex ion species indicative of the forms possible in solution. While Mg(ClO4)2·6dmso contains the expected [Mg(dmso)6]2+ cation, the crystallised strontium species contains a mononuclear [Sr(dmso)6]2+ cation and two dinuclear species, the complex [(dmso-O)5Sr(μ-dmso-O)3Sr(OH2)(dmso-O)3]4+ containing both seven- and eight-coordinate Sr metal centres, and [{(dmso-O)5Sr(μ-dmso-O)}2]4+ containing seven-coordinate Sr metal centres. The barium complex, of empirical formula Ba(ClO4)2·5dmso, contains a centrosymmetric dimer, [Ba2(dmso-O)6(μ-dmso-O)4(O2ClO2)2]2+, involving an unsymmetrically chelating perchlorate and a nine-coordinate Ba metal centre. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Reaction of the CuII complex of the podand hexamine “sen”, CH3C(CH2NHCH2CH2NH2)3, with formaldehyde and nitroethane under basic conditions provides, as one of the principal products, a complex containing a new ligand which is not only macrocyclic but which has resulted also from reactions to extend one podand arm, to introduce an aminal bridge and to oxidise one of the donor-N atom units to an imine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Crystal structure determinations of, in most cases, hydrated, alkali metal derivatives of the dicarboxylic acids, 2,2′-bipyridine-3,3′-dicarboxylic acid (H2BDC) and chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid, H2CHEL) show numerous similarities, such as in the predominance of O-coordination in generating solid state polymers in which parallel arrays of the essentially planar ligand ring units are apparent, though not necessarily indicative of conventional π-stacking interactions, and some unanticipated differences. In particular, all species derived from chelidamic acid, including its diammonium compound, appear to be complexes of the partially deprotonated pyridone form of this ligand. In both systems, close contacts between atoms constituting the aromatic entities take a variety of forms depending upon the associated metal.