Cr(bipy)(C2O4)2]-: A Versatile Building Block for the Design of Heteropolymetallic Systems. Crystal Structures of [BaCr2(bipy)2(C2O4)4(H2O)]n·nH2O, [MnCr2(bipy)2(μ-C2O4)4]n, and [CoCr2(bipy)2(μ-C2O4)2(C2O4)2(H2O)2]·H2O

Abstract

The self-assembly of the building blocks [Cr(bipy)(C2O4)2]- with bivalent metal ions (Ba(II), Mn(II), and Co(II)) led to three completely different structures: [BaCr2(bipy)2(C2O4)4(H2O)]n·nH2O (1), [MnCr2(bipy)2(μ-C2O4)4]n (2), and CoCr2(bipy)2(μ-C2O4)2(C2O4)2(H2O)2·H2O (3). The molecular and crystal structures of the three compounds were determined. Crystal 1 is monoclinic, P21/n, with a = 15.949(11) Å, b = 13.206(9) Å, c = 16.957(12) Å, β = 113.39(4)°, and Z = 4. The compound is a scaffolding-like material with a unique three-dimensional structure. Crystal 2 is monoclinic, P21/c, with a = 8.674(4) Å, b = 13.416(8) Å, c = 27.82(2) Å, β = 107.30(4)°, and Z = 4. Its structure reveals a novel heterobimetallic chain with octacoordinated manganese(II) atoms. The geometry of the manganese atoms is described as a flattened square antiprism. The Co compound (3) is monoclinic, C2/c, with a = 20.505(5) Å, b = 11.093(3) Å, c = 17.346(4) Å, β = 125.02(2)°, and Z = 4. Its structure consists of discrete linear {CrCoCr} trinuclear species with the cobalt atom lying on an inversion center. The [Cr(bipy)(C2O4)2]- units retain their original environment and accomplish different coordination functions, acting as terminal and/or bridging ligands. The synthetic approach, namely the reaction of an aqueous suspension of the barium derivative, 1, with a transition metal sulfate, seems to have a wide applicability in designing new heterobimetallic systems.