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Reaction of nickel(II) or copper(II) acetate with 2-(aminomethyl)pyridine 1 and pyridine-2,6-dicarboxylate ion 2 in aqueous methanol in a 1 : 1 : 1 molar ratio leads to the crystallization in high yield of exclusively one product in each case. For nickel(II), a neutral mixed-ligand complex [Ni · 1 · 2 · (OH2)] is obtained, whereas with copper(II) an ionic complex [Cu · 12 · (OHCH3)][Cu · 22] forms wherein each complex ion contains exclusively one type of ligand. The outcome appears to be directed by the metal ion employed, the two forms being effectively coordination isomers, albeit differing in central metal ion. The neutral complex [Ni · 1 · 2 · (OH2)] · 4¼H2O crystallizes in the triclinic space group P¯1, with two independent nickel centres and ten (some with partial occupancy) water molecules in the asymmetric unit. Each nickel lies in a distorted octahedral environment, with the three N-donor and O-donor sets occupying meridional positions. A complex system of hydrogen bonding and Π-stacking operates in the crystal, with arrays of complex units arranged in ‘dimer tapes’ surrounded by water molecules. The ionic [Cu · 12 · (OHCH3)][Cu · 22] · 2CH3OH complex crystallizes in the monoclinic P21/c space group. The cation adopts a distorted square-based pyramidal geometry with a coordinated methanol in the axial position, although another is weakly interacting in the other axial site. The anion exists in the previously described octahedral geometry with two meridionally-disposed tridentate ligands with the pyridines disposed in trans positions. Three-dimensional ordering in the structure is directed by ‘ribbons’ of hydrogen bonding.

The cyano-bridged CuIItetrenH22WIVCN82·5H2O tetren tetraethylenepentaamine 1, CuIItetrenH2CuIItetrenHWVCN8WIVCN8·2.5H2O 2, CuIIdien2WIVCN8·4H2O dien diethylenetriamine 3 and its isomorphous molybdenumiv analogue 4 have been prepared and structurally characterised. 1and 2are built from the W2Cu2μ-CN4squares extended into 1-D structure by cyano-bridges. 2-D 3and 4form a square grid pattern with tungsten atoms in the corners and –CN–Cudien–NC– linkages on the edges of the squares. The magnetic behaviour of 1and 3indicates the presence of two isolated CuIIspins S 12 with a very weak antiferromagnetic coupling through the diamagnetic NC–WIV–CN bridges in the low temperatures. Assembly 2exhibits a weak ferromagnetic interaction between CuIIand WVisolated by diamagnetic WIVCN84−spacer from another CuIIcentre within WV–CN–CuII–NC–WIV–CN–CuIIunit and the antiferromagnetic interaction between the CuII2WVWIVunits.

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A ligand in which two pyridylimine binding units are linked by a 1,5‐naphthalene spacer is prepared and its silver(I) coordination chemistry investigated. In the solid state, a pair of CH⋅⋅⋅N interactions between pyridylimine units link the free ligands into chain structures, with further CH⋅⋅⋅N and some π‐stacking interactions linking these chains into a three‐dimensional structure. The spacer constrains the ligand to dinucleate, and with silver(I) the metal coordinates to two pyridylimine units from two separate ligands and this leads to the formation of coordination polymers with a range of different anions. Different twisting motifs within the ligand control the tacticity of these coordination polymers and both isotactic, helical polymers and syndiotactic (achiral) polymers result. The core of the isotactic polymer strands contains two metallo‐vectors and results in long‐range ordering of the metal centres into a 2×ngrid arrangement. The solution behaviour indicates that exchange between the diastereomeric forms occurs. Since this must involve inversion at the metal centres, atactic species may also form a component of the solution library.

Multiple competing molecular interactions (metal–ligand, π‐stacking and hydrogen‐bonding) in the silver(I) complexes of 4′‐thiomethyl‐2,2′:6′,2″‐terpyridine give rise to a range of different molecular architectures, in which the metal–ligand coordination requirements are satisfied in quite different ways. Polynuclear supramolecular spirals, aggregated mononuclear and aggregated dinuclear units are all structurally characterised. The metallo‐supramolecular architecture obtained displays a remarkable dependence both on the choice of non‐coordinated anion and the type of solvent used (coordinating or non‐coordinating). The anion dependence is particularly surprising, since the anions are not integrated into the centre of the supramolecular structure. The solution behaviour is also solvent and anion dependent, with aggregation of planar mononuclear cations observed in acetonitrile, but oligonuclear spiral species implicated in nitromethane. The extraordinarily variable geometries of these systems suggest that they provide a novel example of the “frustration” principle, in which opposing tendencies cannot simultaneously be satisfied and identify an alternative approach to the design of metallo‐supramolecular systems whose structure is responsive to external agents.

Silver(i) coordination is investigated for three ligands of the pyridine-azine class, in which two pyridylimine binding units are linked directly through the imine nitrogen atoms. 1H NMR, X-ray analysis and ESI mass spectrometry indicate the presence of a range of metallo-supramolecular architectures in solution for all three ligands. X-Ray analysis confirms the solid state structures for a dinuclear triple helicate containing five-coordinate silver centres and a dinuclear dimer in which the silver ions are three-coordinate with long range stabilising interactions to trifluoromethanesulfonate counter-ions. A tetranuclear grid-like array is also implied as a component of the solution library. The five-coordinate silver(i) ions in the triple helicate result in a hetero-ligand system with two ligands oriented in a head-to-tail fashion. This is distinct from the triple helicates formed with octahedral metals such as an iron(ii) triple helicate also crystallographically characterised herein.

Reduction of [U(NN'₃)I] [NN'₃ = N(CH₂CH₂NSiMe₂But)₃] with potassium in pentane gives the purple trivalent monomer [U(NN'₃)] in good yield, this compound having previously been synthesised via fractional vacuum sublimation of mixed-valent [{U(NN'₃)}₂(μ-Cl)]. The magnetic susceptibility of this compound is consistent with the presence of U(iii) centres, and this is confirmed by a characteristic near IR spectrum. Its reactions with Lewis bases to give e.g. [U(NN'₃)(Py)] and [U(NN'₃)(HMPA)] are reported, along with the molecular structure of the latter. The complex [U(NN'₃)] is readily oxidised, imido and hydrazido complexes being formed readily by reaction with trimethylsilyl-azide and -diazomethane, respectively. The reaction with methylene trimethylphosproane however led to the formation of an addition compound [U(NN'₃)(CH₂PMe₃)]. Reaction of this latter complex with air gave a few crystals of the unusual hydroxo complex [U(NN'₃)(OH)(CH₂PMe₃)] which was structurally characterised. Reaction of [U(NN'₃)(CH₂PMe₃)] with trimethylamine N-oxide gave pentavalent [U(NN'₃)(O)], or perhaps a dimer thereof. The latter complex reacted with [U(NN'₃)] to give the bridging oxo complex [{U(NN'₃)}₂(μ-O)] which could also be prepared directly by reaction of trimethylamine N-oxide with [U(NN'₃)].

Enantiopure dinuclear silver(i) double helicates were prepared in simple one-pot reactions from commercially available starting materials and the pure complexes isolated as the hexafluorophosphate salts. The (R),(+) and (S),(−) enantiomers of 1,1'-binaphthalene-2,2'-diamine were used as spacer groups and reacted with pyridine-2-carbaldehyde to form chiral didentate imine ligands. These chiral ligands predetermine the chirality of the helicates: the R spacer gives a P helicate and the S spacer an M helicate. The dinuclear double helical structures are confirmed by single crystal X-ray analysis and their persistence in solution is supported by inter-strand NOE data. Enantiopure copper(i) dinuclear species were also prepared by similar one-pot procedures and analysed by 1H NMR, mass spectrometry and circular dichroism.

The reaction of a diphenylpyridine with one equivalent of potassium tetrachloroplatinate in ethanoic acid yields a cyclometallated species which can be induced to undergo a second cyclometallation to give a C∧N∧C tridentate species. Carbonyl derivatives of two such compounds have been structurally characterised. The X-ray structure of the complex [2,6-(4′-C6H13OC6H3)2C5H3NPt(CO)], (1), obtained using 2,6-bis(4′-hexyloxyphenyl)pyridine, has no unusual features. In contrast, the structure of the complex [2,6-(C6H4)2-4-(4′-C8H17OC6H5)C5H2NPt(CO)], (2), which results when using 4-(4′-octyloxy-phenyl)-2,6-diphenylpyridine, has close intermolecular contacts, with a Pt–Pt “bond” of 3.243(1) 4;Å holding the molecules together as dimers. Compound 2 also exists in another form in the solid state, a form that does not appear to contain Pt–Pt bonds.

The crystal structures are reported of trans‐dioxocyclam dihydrate, C10H20N4O2·2H2O, a structural isomer of the well known cis‐dioxocyclam, and of its novel Ni complex, (1,4,8,11‐tetra­aza­cyclo­tetra­decane‐2,9‐dionato‐κ4N)­nickel(II) dihydrate, [Ni(C10H18N4O2)]·2H2O, the first example of a trans­ition metal complex of this ligand. Both mol­ecules lie on crystallographic centres of inversion. The free ligand has two of its N atoms turned outwards from the ring and hydrogen bonded to water mol­ecules. A major conformational change takes place in the complex in which the ligand binds in a transtetradentate fashion, as suggested by the electronic spectrum. The nickel(II) ion is low spin, although the electronic spectrum of the complex in water indicates an equilibrium mixture of low‐spin and high‐spin species. The irreversible electrochemical oxidation of [NiL1] (L1is deprotonated trans‐dioxocyclam, C10H18N4O2) in water occurs at a potential of 0.964 V [versusSHE (standard hydrogen electrode)], which is very similar to that for the Ni–cis‐dioxocyclam complex.

The C₂-symmetric Schiff-base proligand (H₂L) synthesized by condensation of 2,2'-diamino-6,6'-dimethylbiphenyl and 3,5-di-tert-butylsalicylaldehyde reacted in its deprotonated form with TiX₄ (X = Cl or Br) to give the isomeric mixtures α-cis- and β-cis-[MLX₂]. The molecular structure of α-cis-[TiLBr₂] was determined. The two bromide ligands occupy mutually cis co-ordination sites in a C₂-symmetric structure. Reaction of the isomeric mixture X = Cl with LiNMe₂ leads to the single isomer α-cis-[TiL(NMe₂)₂] as determined by NMR spectroscopy. Reaction of the latter complex with BCl₃ reconverts it into the chloride complex in a similar isomeric mixture as above. While attempts to alkylate the halides were unsuccessful, the reaction of H₂L with [Ti(CH₂Ph)₄] leads to α-cis-[TiL(CH₂Ph)₂] which rapidly converts into a complex [TiL^Bn(CH₂Ph)] in which one of the Ti bound benzyl groups has undergone a highly diastereoselective 1,2-migratory insertion process with one imine group. The molecular structure of this compound shows that the co-ordination sphere of the Ti atom is approximately trigonal bipyramidal. The configuration of the new chiral centre at the former imine group indicates the expected mode of cis migration in the formation of the complex. The migrated benzyl group forms an edge–face interaction with the remaining metal bound benzyl. Controlled hydrolysis of [TiL^Bn(CH₂Ph)] leads to a dimeric species [{Ti(HL^Bn)}₂-(μ-O)₂] in which the amide bond in the starting complex has been protonated to form an amine ligand.

The use of π-stacking interactions to control the aggregation of photo-active metal centres is explored through the design of bis(2,2';6',2"-terpyridyl) metal complexes functionalised with biphenyl ‘tails’. Aryl–aryl interactions control the aggregation of the metal complexes into polymetallic arrays in the solid state. Cobalt(II), ruthenium(II), nickel(II), copper(II), zinc(II) and cadmium(II) bis-ligand complexes and a mixed ligand ruthenium(II) complex have been structurally characterised. The solid-state structures are dependent on which units dominate the π-stacking. For cobalt, ruthenium, nickel and copper, biphenylene–biphenylene interactions lead to linear rod-like arrays, while for the group 12 d¹⁰ ions zinc and cadmium, biphenylene–pyridyl interactions lead to two-dimensional sheets. The addition of the biphenylene tail has favourable effects on the photophysical-properties of the complexes which exhibit room temperature red (ruthenium) or blue (zinc and cadmium) luminescence, both in solution and the solid state.

Two new covalently linked bis(2,2'∶6',2"-terpyridine)-chelating hexadentate ligands, 1,3-bis(2,2'∶6',2"-terpyridyl-5-ylmethylsulfanyl)propane (L¹), and 1,4-bis(2,2'∶6',2"-terpyridyl-5-ylmethylsulfanyl)butane (L²), and their six-coordinate mononuclear metal complexes [ML][PF₆]₂ (M = Fe and Ni; L = L¹ and L²) have been prepared and characterised. The X-ray structures of [NiL](PF₆)₂ (L = L¹ and L²) have been compared to establish that L² has the optimum length of linker to give the least strained mononuclear complex. The marked stability of [ML]²⁺ is demonstrated by kinetic studies that show that one equivalent of L¹ is capable of substituting both 2,2'∶6',2"-terpyridine (terpy) ligands of [Fe(terpy)₂]²⁺ to give [FeL¹]²⁺ in a two stage kinetic process.

The reactions of titanium(III) and (IV) chlorides with the crown thioether [9]aneS3were investigated. [TiCl3-(MeCN)3] gives a purple 1:1 adduct with a proposed octahedral structure involving tridentate fac-attachment of the ligand. With [TiCl4(MeCN)2] the identity of the yellow 1∶1 adduct obtained is discussed in terms of a six-coordinate species with bidentate ligand chelation. The title compound was isolated from the reactions of [9]aneS3with [TiCl3(MeCN)3] [SbCl6] (by accident) and iron filings/SbCl5in MeCN solution and characterised crystallographically. The cation has two macrocyclic ligands coordinated facially to a six-coordinate Fe2+ion; the anion comprises dimeric [(SbCl4)2] units linked together into a polymeric chain by weak halogen bridging.