Structure of the catena-bis(trimethylamine) cadmium(II)-tetra-mu-cyanonickelate(II) complex and contact self-stabilization of molecules

The [Cd(N(CH3)(3))(2)Ni(CN)(4)] complex crystallites in a tetragonal system , space group 14/mmm with two formula units PET unit cell (XRD, Rigaku AFC- 6A diffractometer, lambda MoKalpha, omega/2 theta scan mode, theta(max) = 3 8 degrees, 635 observed unique reflections, 53 parameters, R = 0027). The s tructure consists of parallel polymer layers made up of coordinated metal a toms and bridging cyanides. The octahedral environment of Cd(11) involves s ix nitrogen atoms of the four cyanide groups in the layer plane (2.323(4) A ngstrom) and the two trimethylamine ligands in the trans-position (2.42(1) Angstrom). The square-planar environment of Ni(11) consists of four carbon atoms of the cyanide ligands (1.857(3) Angstrom). The layers are packed acc ording to van der Waals type; the "hollows" near the nickel atoms are fille d by the "hills" of the trimethylamino groups from the neighboring layer (t he interlayer distance is 7 Angstrom). The spatial complementarity of the l ayers leads to close packing of the complex and explains the lack of a clat hrate-forming ability in the latter. The trimethylamine ligands here play t he same role as guest molecules in Hofmann clathrates, stabilizing the plan ar polymer structure of the complex. This phenomenon is called contact self -stabilization.