The crystal structures of bis (glycollato) copper (I I), aquobis-(DL-lactato) copper( I I) hemi hydrate, diaquobis-(2hydroxy-2-methylpropionato) copper( I!), diaquobis(methoxyacetato)copper( I I),and diaquobis( phenoxyacetato) copper(l1) have been determined by three-dimensional X-ray structure analysis. All the complexes contain trans-chelate rings, which, apart from the bow-shaped lactate, are coplanar. The copper ions are in elongated tetragonally distorted octahedral environments with two exceptions : in the lactate, copper ions are in a nearly square-pyramidal five-co-ordinate environment; in the methoxyacetate, the octahedron is compressed. Details of the structures may be rationalised in terms of Jahn-Teller distortions and hydrogen-bonding.
MOST bis(monocarboxylato)copper(II) complexes inwhich the ligand is unequivocally unidentate have low magnetic moments (-1.45 B.M. at room temperature) in the solid state and in some non-aqueous solvents,l and may be assumed to have dimeric or polymeric structures. However, in aqueous solution the complexes are mononuclear,2 up to a total copper ion concentration of at least 0 . 1~. The known crystal structures of aminocarboxylatocopper( 11) complexes indicate that 2-and 3-aminocarboxylates are invariably bidentate ligands in the solid state. The high thermodynamic stability and hydration of these copper complexes give little reason to doubt that they are also chelates in aqueous solution. However, for 2-and 3-hydroxy, -alkoxy-, and -aryloxy-carboxylates the situation is less clear. No crystallographic information was available when the present programme was initiated. Copper complexes of the 2-substituted carboxylates R1R2C(OR3)C0,-have magnetic moments of about 1.9 B.M. and are therefore monomeric, though not necessarily chelates. However, complexes of the analogous 3-substituted ligands have low magnetic m~r n e n t s ,~ indicative of the dimeric copper acetate structure.6 Systematic studies of differential proton relaxation in bound ligands indicate that 2-and 3-hydroxycarboxylates and 2-alkoxycarboxylates form chelates with copper(I1) in aqueous solution, but that the 3-alkoxycarboxylates are unidentate ligands. Infrared data in heavy-water solution,s and thermodynamic data are consistent with these deductions. There is a fine balance between the different structures of the complex and between the different functions of the ligand, and we have set out to investigate the structures of hydroxy-and alkoxy-carboxylates in the solid state. In aqueous solution, there is a good linear free-energy relationship of the form
The crystal structure of cimetidine (C10HI6N6 S) has been solved and refined from high-resolution synchrotron X-ray powder data collected on station 8.3 at Daresbury Laboratory. The structure is monoclinic, P21/n, Z = 4, a = 10.7029 (3), b = 18.8262 (1), c = 6.8266 (2) A,, fl = 111.306 (2) °. The data were auto-indexed and the integrated intensities were obtained by pattern decomposition. The structure was solved by direct methods followed by iterative cycles of least-squares refinement and Fourier syntheses. All 17 non-H atoms were located. The structure was then refined using the method of Rietveld [J. Appl. Cryst. (1969), 2, 65-71]. A difference Fourier synthesis after the convergence of the non-Hatom model showed positive electron density at the expected positions of all 16 H atoms, ten of which were significantly above the background. The H atoms were allowed to refine unconstrained and the final agreement factors were R1 = 1-9, Rwp = 8"5 and Rex = 6"9%; the equivalent R factors without the H atoms were RI = 10.3 and R,w= 16.2%, demonstrating the significant contribution of the H atoms to the profile.
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