Cyano-bridged heterodinuclear complexes of nickel(II) and palladium(II). A disordered structure for the linkage isomer [LPd-CN-NiL](ClO₄)

Abstract

The homodinuclear [M₂L₂μ(CN)](ClO₄) complexes and the heterodinuclear [LPd-CN-NiL](ClO₄) and [LNi-CN-PdL](ClO₄) complexes of nickel(II) and palladium(II) have been synthesized with a tridentate ligand HL (methyl 2-[(2'-aminoethyl)amino]cyclopent-1-enedithiocarboxylate). In solution both the isomers dissociate, [LNi-CN-PdL]⁺ much more rapidly than [LPd-CN-NiL]⁺, and a steady state equilibrium between the [LPd-CN-NiL]⁺, [Pd₂L₂μ-(CN)]⁺, and [Ni₂L₂μ-(CN)]⁺ species is established. The isomer [LPd-CN-NiL]⁺ exhibits a band at 555 nm that is absent in the other isomer and homodinuclear complexes. The X-ray structure of [LPd-CN-NiL](ClO₄) has been studied. Crystals of the compound are monoclinic, a = 8.964(2), b = 23.852(2), c = 14.096(2) Å, β = 105.92(1)°, Z = 4, space group P2₁/a. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R_w = 0.054 and Rw = 0.034 for 4426 reflections with I ≥ 2.5σ(I). The two metal centres are in a square-planar environment provided by the N₂S donor set of the ligand and cyanide bridge, but the metal atoms as well as C and N atoms of µ-CN could not be distinguished due to disorder. An alternate stacking of Pd-CN-Ni and Ni-NC-Pd units has been proposed to explain the 1:1 occupancy of the atoms concerned.