[Cr(bipy)(C2O4)2]−—a versatile building block for the design of heteropolymetallic systems 2. Syntheses and crystal structures of CuCr2(bipy)2(μ-C2O4)4(C2O4)4(H2O)2·112H2O and (AgCr(bipy)(μ-C2O4)2(H2O)2)2 and magnetic properties of the copper(II) derivative

The compounds CuCr2(bipy)2(μ-C2O4)2(H2O)2·112H2O (1) and (AgCr(bipy)(μ-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) Å, β = 124.83(3)°, 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) Å, the CrO bonds vary from 1.945(3) to 1.982(3) Å, and the CrN bonds are 2.031(4) and 2.054(3) Å. The Cr…Cu distances are 5.288 Å. Crystal 2 is monoclinic, P21/c, a = 14.639(16), b = 15.553(10), c = 16.899(12) Å, β = 114.70(4)°, Z = 4 and R = 0.0629, and contains discrete tetranuclear cycles formed by two chromium and two silver 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) Å, while the CrO bonds are in the range 1.942(7) to 1.982(6) Å. 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.