ANTIMONY(III) COMPLEXES WITH CARBOXYLIC-ACIDS .2. PREPARATION AND CRYSTAL-STRUCTURES OF [SB2AG2(C6H6O7)4] AND [SBNA(C6H6O7)2(H2O)2].H2O [C6H6O7 = CITRATE (2-)]

The antimony(III)-silver(I) and -sodium(I) complexes with citric acid (C6H8O7), [Sb2Ag2(C6H6O7)4] 1 and [SbNa(C6H6O7)2(H2O)2].H2O 2, have been prepared and their crystal structures determined by X-ray diffraction and refined to residuals of R = 0.023 and 0.017 for 2403 and 2969 observed reflections respectively. Crystals are monoclinic, space group P2(1)/n, and P2(1)/a. Complex 1 has two dimers in a cell of dimensions a = 6.557(4), b = 12.149(2), c = 20.50(1) angstrom and beta = 98.12(3)-degrees, while there are four monomers of 2 in a cell with a = 14.470(5), b = 7.193(3), c = 18.747(6) angstrom and beta = 92.22(2)-degrees. In each structure antimony is bonded to two oxygens of two crystallographically independent citrate(2-) residues in classic pseudo-trigonal-bipyramidal antimony(III) four-co-ordination [Sb-O 2.007(2)-2.218(2), 1; 1.988(1)-2.164(1) angstrom, 2]. These oxygens are from the alpha-hydroxycarboxylate groups giving five-membered chelate rings. In 1 each antimony centre is in turn linked through one of these carboxylate groups to two silver(I) ions in an asymmetric bis(carboxylato-O,O') bridge [Ag-O 2.314(2) and 2.661(2) angstrom]. Hydroxyl groups complete the angular three-co-ordination about each silver [Ag-O 2.323(2) angstrom], giving a centrosymmetric cyclic dimer structure. In contrast, complex 2 is monomeric with the sodium and two co-ordinated waters [Na-Ow 2.404(2) and 2.512(2) angstrom] forming a tris(oxo)-bridged complex unit (two oxygens from the alpha-hydroxycarboxy groups), with a Na-O range of 2.413(2)-2.562(2) angstrom [Na...Sb 3.665(1) angstrom].