[Cr(bipy)(C2O4)(2)](-): A versatile building block for the design of heteropolymetallic systems. Crystal structures of [BaCr2(bipy)(2)(C2O4)(4)(H2O)](n)center dot nH(2)O, [MnCr2(bipy)(2)(mu-C2O4)(4)](n), and [CoCr2(bipy)(2)(mu-C2O4)(2)(C2O4)(2)(H2O)(2)]center dot H2O

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) . nH(2)O (1), [MnCr2(bipy)(2)(mu-C2O4)(4)](n) (2), and CoCr2(bipy)(2)(mu-C2O4)(2)(C2O4)(2)(H2O)(2) . H2O (3). The molecular and crystal structures of the three compounds were determined. Crystal 1 is monoclinic, P2(1)/n, with a = 15.949(11) Angstrom, b = 13.206(9) Angstrom, c = 16.957(12) Angstrom, beta = 113.39(4)degrees, and Z = 4. The compound is a scaffolding-like material with a unique three-dimensional structure. Crystal 2 is monoclinic, P2(1)/c, with a = 8.674(4) Angstrom, b = 13.416(8) Angstrom, c = 27.82(2) Angstrom, beta = 107.30(4)degrees, 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) Angstrom, b = 11.093(3) Angstrom, c = 17.346(4) Angstrom, beta = 125.02(2)degrees, 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.