Group 15 Complexes with α-Hydroxy Carboxylic Acids: 7. The Preparation and Structure Determination of Sodium (+)-Tartrato Arsenate(III), [Na8As10(C4H2O6)8(C4H3O6)2(H2O)19]n; Silver(I) (+)-Tartrato Arsenate(III), [Ag9As10(C4H2O6)9(C4H3O6)(H4As2O5) (H2O)10]n and Rubidium Citrato Antimonate(III), [Rb2Sb4(C6H5O7)2(C6H6O7)2(C6H7O7)4(H2O)2]

Abstract

The structures of sodium (+)-tartrato arsenate(III),[Na₈As₁₀(C₄H₂O₆)₈(C₄H₃O₆)₂(H₂O)₁₉]_n(1), silver (+)-tartrato arsenate(III),[Ag₉As₁₀(C₄H₂O₆)₉(C₄H₃O₆)(H₄As₂O₅)(H₂O)₁₀](2) and rubidium citrato antimonate(III)[Rb₂Sb₄(C₆H₆O₇)₆(C₆H₇O₇)₂(H₂O)₂](3) have been determined by X-ray methods and refined to residuals of 0.085(1), 0.072 (2) and 0.065 (3) for 5018, 4487 and 8207 observed reflections,respectively. The (+)-tartrato complexes (1) and (2) are similar instructure to the two known isomorphous silver(I) (+)-tartratoarsenate(III) complexes in that independent anionic[As₂(tartrate)₂] dimericcages are linked to the sodium or silver counter-cations, respectively,through free carboxyl oxygen atoms. However, the structures are made morecomplex by the presence of labile water molecules in the lattice, resulting insome disorder. Furthermore, charge balance in both (1) and (2) requires thepresence of two and one tri-negative tartrato units, respectively, among theten independent tartrate units in each structure, an unusual feature for Asand Sb complexes with this ligand species. Bond distances within the fivearsenic(III)-(+)-tartrate dimers in each structure are: As–O(hydroxy), 1.75(2)–1.84(2) Å (1); 1.75(3)–1.83(2) Å(2) and As–O (carboxy), 1.94(2)–2.13(3) Å (1);1.95(2)–2.14(2) Å (2). In addition, the structure of (2) has twoshort Ag–As bonds [2.500, 2.524(3) Å] in the terminalsites of two of the f ive independent dimers, as well as an additionalAg–As bond [2.613(4) Å] to an unusual dimeric arseniousacid residue(H₄As₂O₅),part of an As₂AgO₃ hetero-ringforming the polymeric network structure. The antimony(III) citrate complex (3)is isomorphous and isostructural with the previously reported potassiumanalogue which involves mixed-valence citrato ligands in conventionalbis-chelate four-coordination about the antimony centres, linked by bothseven- and eight-coordinate rubidium ions [Rb–O,2.743(10)–3.102(9) Å]. The arsenic and antimony atoms in allcompounds have typical distorted pseudo-trigonal bipyramidal stereochemistry.