The silver(1) complex with glycolic acid, [Ag2(HOCH2C02)2],.nH20, has been prepared and its structure determined by X-ray diffraction. The structure is based on a bis(carboxy1ato-0 , O ') dimer [Ag-0, 2.234(2), 2.253(2) A; Ag-Ag 2.88lO(9) A], extended in both the axial positions into a network polymer through two oxygens of a bidentate a-hydroxy carboxy residue [Ag-O(hydroxy), 2.607(2) A; Ag-O(carboxy), 2.456(2) A; 0-Ag-0, 63.45(5)']. In this respect, the complex is unique among silver(1) carboxylate dimers.

The crystal structure of N3,N4-dimethylpyrrole-3,4-dicarboxamide monohydrate has been determined and refined to a residual of 0.034 for 1015 observed reflections. Crystals are monoclinic, space group P21/n with Z 4 in a cell of dimensions a 7.367(2), b 19.984(4), c 7.621(2) �, β 117.84(1)�. The pyrrole ring and the substituent amide side chains are essentially coplanar. The side chains are syn-syn related with an intramolecular hydrogen bond between a carbonyl oxygen of one group and the amide hydrogen of the other [O…N, 2.718(2) � ]. Intermolecular hydrogen bonding is also found between the pyrrole NH group and a carbonyl oxygen [N…O, 2.770(2) � ] and between the lattice water and three separate amide residues [N…O, 2.878(2); OH…O, 2.747, 2.865(2) � ].

Valiev's suggestion of excitation of the vibrational modes of the octahedron is considered as a spin relaxation mechanism for 59Co spins in some symmetric, bidentate CoIII complexes. His theory is extended to the spin 7/2 system; the efficiency of the mechanism is very sensitive to the molecular size with larger complexes having much shorter T1 values. Experimental evidence in support of the mechanism is provided by the contradictory values of quadrupole coupling constants calculated experimentally by assuming rotational reorientation to be the dominant time process and by measurements on a variety of CoIII complexes. Rotational correlation times were measured from 13C T1 values of protonated carbons in the complex. An X-ray structure determination of tris(tropolonato)-cobalt(III) is reported in support of the suggested relaxation mechanism. The differences between T1 and T2 in some CoN6 complexes are shown to arise from unresolved 59Co-14N scalar coupling.

The crystal structure of the bismuth(111) complex with (+)-tartaric acid, ammonium aquabis[(+)tartrato(2-)]bismuthate(111) hydrate, has been determined by X-ray methods and refined to a residual R 0.020 for 1288 observed reflections. Crystals are orthorhombic, space group P 212121 with Z 4 in a cell of dimensions a 7.4712 (4), b 10.856(1), c 17.609(3) A. Each nine-coordinate MOQ bismuth centre comprises three bidentate a-hydroxy carboxy residues from two tartrato(2-) ligands (with one bridging), an asymmetric bidentate carboxylato(0,O ') group, and a water. The Bi-0 range is 2.372(7)-2.738(6) .k [mean 2.509(6) A]. The resultant structure is a linear polymer which is stabilized by extensive hydrogen-bonding interactions. Mlcks, R. H., (Ed.) 'Essentials of Materia Medica Pharmacology and Therapeutics' 4th Edn (

(NH4)2[Bi2(C6H4O2)4].(C6H6O2)2.2H2O, a bismuth(III)-catechol complex adduct, has been prepared and its structure determined by X-ray diffraction methods. The complex anion is a centrosymmetric dimer comprising two five-coordinate [ bis ( catecholato (2-)) bismuthate (III)] centres [Bi-O, 2.177(4), 2.222(4) Ǻ and 2.150(3), 2.322(4)Ǻ], bridged by one of the catechol oxygens [Bi-O, 2.653(3)Ǻ]. In addition, the structure is stabilized by hydrogen bonding involving the ammonium ions, the lattice waters and the two adduct catechol molecules.