[Cr(bipy)(C2O4)(2)](-) - A versatile building block for the design of heteropolymetallic systems .2. Syntheses and crystal structures of CuCr2(bipy)(2)(mu-C2O4)(2)(C2O4)(2)(H2O)(2)center dot 1(1)/2H2O and (AgCr(bipy)(mu-C2O4)(2)(H2O)(2))(2) and magnetic properties of the copper(II) derivative

The compounds CuCr2(bipy)(2)(mu-C2O4)(2)(C2O4)(2)(H2O)(2) . 11/2H(2)O (1) and (AgCr(bipy)(mu-C2O4)(2)(H2O)(2))(2) (2) have been obtained by self-assembling [Cr(bipy)(C2O4)(2)](-) building blocks with Cu(II) and Ag(I) ions, respectively. The molecular and crystal structures of the two compounds were determined. Crystal 1 is monoclinic, C2/c, a = 20.379(14), b = 11.037(4), c = 17.480(7) Angstrom, beta = 124.83(3)degrees, Z = 4 and R = 0.0369. Its structure consists of discrete linear {CrCuCr} trinuclear species with the copper atom lying on an inversion center. The copper atom exhibits [4 + 2] axially elongated octahedral geometry, the apical positions being occupied by two oxalato oxygen atoms. The Cu-O bond distances are 1.953(4) (H2O), 1.998(3) and 2.357(3) Angstrom, the Cr-O bonds vary from 1.945(3) to 1.982(3) Angstrom, and the Cr-N bonds are 2.031(4) and 2.054(3) Angstrom. The Cr ... Cu distances are 5.288 Angstrom. Crystal 2 is monoclinic, P2(1)/c, a = 14.639(16), b = 15.553(10), c = 16.899(12) Angstrom, beta = 114.70(4)degrees, Z = 4 and R = 0.0629, and contains discrete tetranuclear cycles formed by two chromium and two sliver atoms bridged by the oxalato groups. The silver atoms are penta-coordinated, exhibiting distorted trigonal bipyramidal geometries. The Ag-O bond distances vary from 2.350(8) to 2.548(7) Angstrom, while the Cr-O bonds are in the range 1.942(7) to 1.982(6) Angstrom. The magnetic susceptibility data of 1 reveal an irregular spin state structure with S = 5/2 ground state and an antiferromagnetic interaction between the central copper(II) and the chromium(III) atoms (J = - 18.8 cm(-1)).