Zinc(II) and Copper(II) Complexes of Pentacoordinating (N4S) Ligands with Flexible Pyrazolyl Arms: Syntheses, Structure, and Redox and Spectroscopic Properties

Zinc(II) and copper(II) complexes of two new potentially pentadentate ligands based on methyl 2-aminocyclopent1-ene-1-dithiocarboxylate with pendent pyrazolyl groups (Me2pzCH2)2NC2H3RNHC5H6CSSCH3 (R ) H,Hmmecd, and R ) CH3, Hmmpcd, both having N4S donor atoms set) have been reported. The molecular structures of [Zn(mmpcd)]ClO4 (1b) and [Cu(mmpcd)]ClO4 (2b) show a distorted trigonal bipyramidal geometry for the Zn(II) ion and a square pyramidal geometry for the Cu(II) ion. 1b crystallizes in the triclinic space group P1h, a ) 9.900(3) Å, b ) 15.379(5) Å, c ) 8.858(2) Å, R ) 99.93(2)°, â ) 93.62(2)°, γ ) 100.38(2)°, V ) 1300.5(7) Å3, and Z ) 2; while 2b crystallizes in the monoclinic space group P21/n, a ) 12.859(6) Å, b ) 12.642(3) Å, c ) 16.503(2) Å, â ) 102.67(2)°, V ) 2617(1) Å3, and Z ) 4. The structures were refined to final R ) 0.042 for 1b and 0.049 for 2b. The EPR and electronic spectroscopic studies showed that the copper(II) species doped into zinc(II) complex adopts the zinc(II) trigonal bipyramidal structure. The cyclic voltammetric measurements indicated one-electron reversible reduction of the copper(II) complex occurring at -0.74 V, while irreversible oxidation to copper (III) takes place at +0.75 V (Vs Ag/AgNO3).