Solvent induced geometry transformation of trigonal planar Cu(I) complexes of N-((2/4-methyoxy carbonyl) phenyl)-N′-(ethoxy/methoxy carbonyl) thiocarbamides to square-planar Cu(II) complexes: Synthesis, spectral, single crystal, DFT and in vitro cytotoxic study

Abstract

Complexation between copper(II) chloride and three newly synthesized ligands, (N-((2/4-methyoxy carbonyl) phenyl)-N′-(ethoxy carbonyl) thiocarbamides (2/4-MCPET)(1, 2) and (N-(2-methyoxy carbonyl phenyl)-N′-(methoxy carbonyl) thiocarbamide (2-MCPMT)(3) afforded Cu(I) complexes bis(N-((2/4-methoxycarbonyl) phenyl)-N’-(ethoxycarbonyl) thiocarbamide) copper(I) chloride (2/4-MCPET)2CuCl(1a, 2a) and bis(N-((2-methoxycarbonyl) phenyl)-N’-(methoxycarbonyl) thiocarbamide) copper(I) chloride (2-MCPMT)2CuCl(3a). The geometry transformation reaction of above copper(I) complexes in DCM-DMSO (3:1, v/v) mixture of solvents resulted in dark green Cu(II) complexes bis(N-((2/4-methoxycarbonyl) phenyl)-N’-(ethoxycarbonyl) thiocarbamide) copper(II) (2/4-MCPET)2Cu(1a′, 2a′) and bis(N-((2-methoxycarbonyl) phenyl)-N’-(methoxycarbonyl) thiocarbamide) copper(II) (2-MCPMT)2Cu(3a′). Spectroscopic studies together with single crystal analysis of (2-MCPMT)2CuCl revealed trigonal planar structure for Cu(I) complexes in which ligand coordinates to the metal ion in neutral monodentate fashion through sulfur only. The physico-chemical studies of Cu(II) complexes together with single crystal data of (2/4-MCPET)2Cu(1a′) support their distorted square-planar geometry, with formation of 1,3-N,S four-membered chelate ring. The N, S coordination observed for the first time in Cu(II) complexes is stabilized by the intramolecular hydrogen bonding present in them. Complex 1a shows quasi-reversible redox behavior assignable to Cu(I)/Cu(II) one electron transfer. Theoretical study on (2-MCPET)2Cu(1a′) was performed to concrete the spectral study and structure of the complexes. Ligands and their Cu(I) complexes have been screened for their in vitro cytotoxicity against five human cancer cell lines.