COORDINATION CHEMISTRY OF MIXED PYRIDINE-PHENOL LIGANDS - POLYNUCLEAR COMPLEXES OF 6-(2-HYDROXYPHENYL)-2,2'-BIPYRIDINE WITH NI-II, CD-II MN-II AND MN-II MN-III

A series of complexes with the N,N,O-terdentate ligand 6-(2-hydroxyphenyl)-2,2'-bipyridine (HL(1)) has been prepared and structurally characterised. The complexes are [Ni(2)L(2)(1)(dmf)(2)(H2O)(2)][BPh(4)](2) 1 (dmf = dimethylformamide), [Cd(2)L(2)(1)(HL(1))(dmf)(2)][BPh(4)](2) 2, [Mn(4)L(6)(1)][BPh(4)](2) 3 and [Mn(2)L(3)(1)(MeCN)]-[PF6](2) 4. In the centrosymmetric complex 1 one ligand L(1) is associated with each metal but the phenolates are bridging, giving a Ni-2(II)(mu-O)(2) core; the remaining two co-ordination sites are occupied by H2O and dmf (O-co-ordinated) ligands. In complex 2 one Cd-II ion is octahedrally co-ordinated by two ligands L(1); the two phenolates bridge to the second Cd-II, whose co-ordination sphere is completed by two dmf ligands and the two pyridyl donors of another equivalent of HL(1), whose pendant phenol remains protonated and forms hydrogen-bonding interactions to lattice solvent molecules. Complex 3 in contrast is an unusual example of a linear chain, with a Mn-II(mu-O)(2)Mn-II(mu-O)(2)Mn-II(mu-O)(2)Mn-II core (where O denotes a bridging phenolate) and highly distorted six co-ordinate Mn-II centres: the chain formation is apparently facilitated by the absence of any stereoelectronic preference for the Mn-II ions which can readily tolerate the distorted geometries. Complex 4 contains a Mn-II centre, co-ordinated by two ligands L(1), and a Mn-III centre which shares two phenolates with the Mn-II and also has a terdentate L(1) and a MeCN ligand to complete the co ordination sphere. The Mn-III centre shows Jahn-Teller elongation along one of the axes. The contributions of factors such as the metal oxidation state, the co-ordination modes available to the ligand, and non-covalent interactions (hydrogen bonding, aromatic pi-stacking) to the structures of the complexes are discussed.