SYNTHESIS AND CHARACTERIZATION OF SQUARE-PLANAR AND PSEUDO-TETRAHEDRAL M(II)N2S2

Copper(II), nickel(II) and zinc(II) complexes of methyl-2-amino-1-cyclopentenedithiocarboxylate and N,N'-pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) have been prepared and characterized in order to provide a basis for comparison of neutral neutral molecules involved in planar and pseudo-tetrahedral coordination geometries with similar N2S2 ligand donor sets. Methyl-2-amino-1-cyclopentenedithiocarboxylate chelates as a bidentate ligand through a thioketonate sulfur and an imine nitrogen, forming planar complexes with the divalent ions of copper(II), nickel(II) and zinc(II). The Cu(II) complex exhibits EPR spin Hamiltonian parameters typical of an axial system with g parallel-to = 2.139 and A parallel-to = 175 x 10(-4). N,N'-pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) coordinates as a tetradentate ligand, where the pentamethylene bridge between the nitrogens introduces steric strain forcing distortion of the inner coordination sphere. Spectral data support pseudo-tetrahedral coordination geometries for both Cu(II) and Ni(II). The EPR spectrum of this Cu(II) complex is characteristic of a large tetrahedral distortion with g parallel-to = 2.146 and A parallel-to = 133 x 10(-4) cm-1, while H-1 NMR studies on the Ni(II) analogue indicate paramagnetic contact shifts of resonances, also indicative of tetrahedral distortion. The complexes are examined as possible spectral models of N2S2 coordination environments at the active sites of metalloproteins such as in the type I blue copper(II) and nickel hydrogenase proteins.