Abstract
General crystallographic investigations have been carried out on the complexes of dihalogeno-(N,N,N',N'-tetramethylethylenediamine) M(II) ((TMED)MX2), where M = Zn, Cd or Hg and X = C1, Br or I. All except TMEDZnI2 crystallize in the space group P21/c. TMEDZnI2 crystallizes in space group C2/c. Three complexes viz. TMEDZnC12, TMEDCdBr2 and TMEDZnI2 were chosen for detailed crystallographic investigations. The crystal and molecular structure of all three have been determined. The crystals of TMEDZnC12 belong to the monoclinic system: P21/c, a = 7.716(3), b = 13.335(9), c = 11.545(5)A, beta = 105.59(6)° and Z = 4. The structure was solved by Fourier methods and refined by full-matrix least squares to a final R (conventional) of 6.7%. Anisotropic thermal parameters were evaluated for the non-hydrogen atoms but the hydrogen atoms were assigned the isotropic thermal parameters of the carbon atom to which they were bonded. The geometry around the zinc atom is distorted tetrahedral, with the Zn - C1 and Zn - N average bond lengths of 2.207(4) and 2.08(1)A respectively. TMEDCdBr2 crystallizes in the monoclinic system: P21/c, a = 7.532(2), b = 10.689(6), c = 14.674(7)A, beta = 91.91(7)° and Z = 4. The structure was solved by Fourier methods and refined by full-matrix least squares to a final R 6.1%. Each cadmium atom is octahedrally co-ordinated by two pairs of bromine atoms, giving average Cd - Br bond lengths of 2.753(2) and 2.844(2)A and a pair of nitrogen atoms in the cis configuration with an average Cd - N bond length of 2.46(1)A. The average Br - Cd - Br and N - Cd - Br angles are 88.1 and 90.6° respectively. The bromine atoms provide bridges to the metal atoms and form a structure consisting of infinite chains with the chain direction approximately parallel to the x-axis The crystals of TMEDZnI2 are monoclinic: C2/c, a = 13.118(8), b = 7.811(5), c = 13.566(8)A, beta = 111.39(4)° and Z - 4. The zinc and the nitrogen atoms have tetrahedral configurations. The molecule possesses crystallographic two-fold symmetry, the diad axis passing through the C - C bond of the TMED-ring. The mercury and zinc complexes have tetrahedral geometry in general and the cadmium complexes have octahedral geometry.