Antimony(III) complexes with carboxylic acids. Part 2. Preparation and crystal structures of [Sb2Ag2(C6H6O7)4] and [SbNa(C6H6O7)2(H2O)2]·H2O [C6H6O7= citrate(2–)]

Abstract

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 P2₁/n, and P2₁/a Complex 1 has two dimers in a cell of dimensions a= 6.557(4), b= 12.149(2), c= 20.50(1)Å and β= 98.12(3)°, while there are four monomers of 2 in a cell with a= 14.470(5), b= 7.193(3), c= 18.747(6)Å and β= 92.22(2)°. 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)Å, 2]. These oxygens are from the α-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)Å]. Hydroxyl groups complete the angular three-co-ordination about each silver [Ag–O 2.323(2)Å], 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)Å] forming a tris(oxo)-bridged complex unit (two oxygens from the α-hydroxycarboxy groups), with a Na–O range of 2.413(2)–2.562(2)Å[Na ⋯ Sb 3.665(1)Å].