CADMIUM BIPYRIDINE NET-WORKS: Cd(4,4'-BPY)2Xn;yH2O for X=NO3-, ClO4- and SiF62-
T. K. Christensen and J.-E. Jorgensen
Dep. Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark. tede@kemi.aau.dk
Keywords: Net-work compounds.
The crystal structures of Cd(4,4'-bpy)2Xn;yH2O for X=NO3-, ClO4- and SiF62- have been determined by single X-ray diffraction methods. The aim of the study was to determine the influence the anions on the formation and geometry of the net-work.
{[Cd(4,4'-bpy)2(H2O)2](H2O)2(NO3)2}Y contains 2D square nets with Cd(II) ions at the corners and 4,4'-bpy's on the sides. Cd is octahedrally coordinated to four 4,4'-bpy's and two water molecules which are located in trans positions. Despite the fact that each layer has holes with dimensions of 11.8x11.8 A the largest channels has only dimensions of 9.5x7.6 A, due to the relative displacements ofthe layers. It was found that the structure is monoclinic (C 2/c) and the distance between the 2D square nets is 4.84 A. The {[Cd(4,4'-bpy)2(NO3)2(C6H4Br2)2}Y net-work has ortho-dibromobenzene intercalated between the planes which increases the inter-plane separation to 6.30 A [1].
{[Cd(4,4'-bpy)2(H2O)2]SiF6}Y is also a net-work compound, but the framework structure consist of interpenetrating square nets perpendicular to each other. The crystal structure is tetragonal (P 4/n c c). Every layer is a 2D square net as in the corresponding nitrate containing compound. The net-work is made up with cadmium in the centre of each square. The two water molecules are coordinated to Cd in the trans positions, and they are forming hydrogen-bonds to the hexafluorosilicate anions. It is this hydrogen-bonding which stabilises the interpenetrated net-work.
{[Cd(4,4'-bpy)3(H2O)2](4,4'-bpy)2(H2O)4(ClO4)2}Y does not form a 2D net-work but only a 1D coordination polymer. In spite of many attempts it have not been possible to synthesis a net-work with perchlorate as anion. The crystal structure is monoclinic (C c). Cd(II) is coordinated to two in-chain bpy's as well as to two "free" bpy's. The distorted octrahedral coordination is completed by two water molecules in trans positions.