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-aminocyclopent-1-ene-1-dithiocarboxylate with pendent pyrazolyl groups (Me 2 pzCH 2 ) 2 NC 2 H 3 RNHC 5 H 6 CSSCH 3 (R = H, Hmmecd, and R = CH 3, Hmmpcd, both having N 4 S donor atoms set) have been reported. The molecular structures of [Zn(mmpcd)]ClO 4 ( 1b ) and [Cu(mmpcd)]ClO 4 ( 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 P 1̄, a = 9.900(3) Å, b = 15.379(5) Å, c = 8.858(2) Å, α = 99.93(2)°, β = 93.62(2)°, γ = 100.38(2)°, V = 1300.5(7) Å 3, and Z = 2; while 2b crystallizes in the monoclinic space group P 2 1 / n, a = 12.859(6) Å, b = 12.642(3) Å, c = 16.503(2) Å, β = 102.67(2)°, V = 2617(1) Å 3, 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/AgNO 3 ).