Group 15 Complexes With Carboxylic Acids. V. The Preparation and Crystal Structures of {Ag₅As₄(C₄H₂O₆)₄(H₂O)₅(X)}_n[(C₄H₂O₆) = (+)-Tartrate(4-); X = NO₃^-, ClO₄^-]

Abstract

The structures of two isomorphous silver(I) complexes with arsenic(III) (+)- tartrate [Ag₅As₄(C₄H₂O₆)₄(H₂O)₅(X)]_n [X = NO₃- (1), ClO₄^- (2)] have been determined by X-ray methods and refined to residuals R of 0.045 (1) and 0.028 (2) for 3822 and 3849 observed reflections respectively. Crystals are monoclinic, space group P2₁ with Z 2 in cells of dimensions a 12.057(3), b 10.651(1), c 12.496(3)Ǻ, β 93.37(2)° for (1), and a 12.170(5), b 10.570(1), c 12.634(4)Ǻ, β 92.74(2)° for (2). The two complexes are isostructural , with polymer framework structures based upon two configurationally identical [As₂(C₄H₂O₆)₂]^2- dimer ions, analogous to these in the tartar emetic structure [As-O (hydroxyl): 1.790(7)-1.804(8)Ǻ(1); 1.768(4)-1.818(4)Ǻ(2). As-O (carboxyl): 1.966(9)-2.118(8)Ǻ(1); 1.940(5)-2.127(5)Ǻ(2)]. However, an arsenic of one of the dimers forms a short bond to a silver atom [As-Ag, 2.729(2)Ǻ(1), and 2.723(1)Ǻ(2)], completing a trigonal-bipyramidal coordination about arsenic. The arsenic dimers are in turn linked by a chain of five silver cation centres through both carboxyl and hydroxyl oxygens which also form intrachain links. All five water molecules are bonded to silver ions, with three of them bridging silver centres. The main difference between the two structures arises from the replacement of the nitrate group in (1) by a perchlorate in (2).