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.

The crystal structure of (�)-2-[4-(4-chlorophenoxymethyl)phenoxy]propionic acid has been determined by direct methods using three-dimensional X-ray diffraction data. The crystals are triclinic, P1, Z 2, a 9.345(2), b 12,602(2), c 6.741(1) �, α 101.37(1), β 97.42(1), γ 101.75(1)�. The structure refined to give a final R 0.084 for 2172 observed reflections. The acid molecules form centrosymmetric hydrogen bonded cyclic dimers [O. . .O,2.619(4) �] about a centre of symmetry in the cell. The oxopropionic acid side chain has a synplanar-synplanar (carbonyl) conformation while the planar p-chlorophenoxymethyl substituent in the p-position has a synclinal orientation relative to the primary phenoxy residue.

Infrared and Raman studies132 on room temperature forms of both caesium and rubidium nitrates are almost identical, indicating similar site group symmetries. However, different space groups have been determined from X-ray diffraction measurements. They were reported to be P31m (C32,2), a = 1087, c = 776 pm, for caesium nitrate [phase 111,s and P3112 (D33) or P321.2 (D35), a = 1048, c = 745 pm, for rubidium nitrate [phase IVl.4 Two interesting results emerged from an analysis of full three-dimensional single crystal neutron data of caesium nitrate. The data were collected in one sextant on a spherical crystal (diameter 5 mm, p = 0.21 cm-I), using the single crystal diffractometer of the Australian Institute for Kuclear Science and Engineering installed on the Australian Atomic Energy Commission's reactor HIFAR at Lucas Heights, New South Wales :(1) Because only the I = 3n type reflections are present for (001) values, a threefold screw axis in the c direction is indicated. (2) The structure amplitudes for (hkl) reflections are significantly different from those for the (khl) type (Table l ) , indicating that the Laue group is 3, rather than 3m which was previously reported.3 Therefore, the space group is either P31 (C32) or its enantiomorph P32 (C33). The difference in intensities is considered to be real and not due to misorientation of the crystal [1(200) = I(020) = I(ZO0) = 1(020)].Neutron powder spectra (Table 2) of the room temperature forms of both caesium and rubidium nitrates were similar, indicating that the compounds were isomorphous. The samples were contained in a vanadium can mounted on a neutron powder diffractometer.

The molecular adducts of the heterocyclic base 2-aminopyrimidine with the aromatic and aromatic aliphatic carboxylic acids salicylic acid, 2,6-dihydroxybenzoic acid and 4-aminobenzoic acid, phenoxyacetic acid, (2,4-dichlorophenoxy)acetic acid, and (3,4-dichlorophenoxy)acetic acid have been prepared, and their interactive modes characterized by single-crystal X-ray diffraction methods. In addition, the complexes with (4-chlorophenoxy)acetic acid, (2,3-dichlorophenoxy)acetic acid, (4-chloro-2-methylphenoxy)acetic acid and (2,4,5- trichlorophenoxy)acetic acid have been characterized by analytical methods, including infrared spectroscopy. Except for the phenoxyacetic acid adduct (2:1), all form 1:1 molecular associations in which the carboxylic acid shows a variable tendency to protonate the hetero nitrogen of the base. The 1:1 complex of 2-aminopyridine with 2,6-dihydroxybenzoic acid has also been characterized by single-crystal X-ray diffraction.