CRYSTAL-STRUCTURES OF LINEAR-CHAIN HALOGEN-BRIDGED BINUCLEAR PLATINUM COMPLEXES, DIHYDRATE FORMS OF K4[PT2CL(POP)4].NH2O, K4[PT2BR(POP)4].NH2O

Crystal structures of the potassium catena-mu-halogenotetrakis(mu-diphosphonato-P,P)-diplatinum(4-) dihydrate, K4[Pt2X(pop)4].2H2O (X = Cl (1) and Br (2); pop = P2O5H2(2-)), have been determined by the single crystal X-ray diffraction method. The complexes are isomorphous to each other and crystallize in orthorhombic, space group Pbnm, Z = 4: for 1, a = 9.553(2), b = 15.440(3), c = 17.123(3) angstrom, V = 2525.6(8) angstrom-3 at room temperature; for 2, a = 9.510(1), b = 15.338(2), c = 17.125(2) angstrom, V = 2497.9(6) angstrom-3 at 125 K. The structures consist of linear chains with a repeating unit of ... Pt(II)-Pt(II) ... X-Pt(III)-Pt(III)-X ... along the c axes. The linear chains are not straight but a little bent to form zigzag chain structures, the bent angles defined by the Pt-Pt bonds and the c axes being 3.34(1)-degrees for 1 and 3.11(1)-degrees for 2, respectively. The Pt-Pt separations, which are bridged by four pyrophosphato ligands (P2O5H2(2-)), are 2.835(1) angstrom for 1 and 2.834(1) angstrom for 2. The bridging halogen atoms are disordered over two sites in the chains, giving short Pt-X and long Pt ... X separations: 2.406(4) and 3.362(4) angstrom for 1 and 2.539(1) and 3.217(1) angstrom for 2, respectively. The deviations of the bridging halogen atoms from the midpoints between two Pt dimers are significantly larger than those of the trihydrate modifications.