The Rare Examples of Thiosemicarbazonato Chromium(III) Complexes: Crystal Structures of [Cr(Hsal 4-Metsc)2]Cl CH3OH and [Cr(Hsal 4-Phtsc)2]Cl

Marina Cindrić,Mirta Rubčić

doi:10.5562/cca2153

Abstract

Reactions of salicylaldehyde 4- methylthiosemicarbazone (H2L1) and salicylaldehyde 4- phenylthiosemicarbazone (H2L2) with assorted chromium(III) precusors, [Cr(H2O)6]Cl3, [Cr(H2O)6](NO3)33H2O and [Cr(H2O)6](CH3COO)3, afforded new mononuclear chromium(III) complexes of the general formula [Cr(HL)2]X (X = Cl−, NO3 − and CH3COO−). In all isolated compounds, Cr(III) ion is coordinated by the O, N, S atoms of the two singly deprotonated thiosemicarbazonato ligands, which are present in the thione form. All complexes have been characterized in the solid-state by means of chemical analyses, TG analysis and IR spectroscopy. The crystal and molecular structures of [Cr(Hsal 4- Metsc)2]ClCH3OH and [Cr(Hsal 4-Phtsc)2]Cl have been determined on the basis of single-crystal X- ray diffraction data. In accordance with kinetic inertness of neutral chromium(III) complexes all our attempts to prepare thiosemicarbazonato complexes via ligand-exchange reaction with [Cr(acac)3] have been unsuccessful.

Highlights

Investigation of transition metal complexes and understanding their function in biological systems is a challenging research area
In the course of this research, which was aimed at inspecting the chemistry of chromium(III) with potentially tridentate thiosemicarbazone ligands (H2L), we have successfully isolated six new mononuclear complexes of the type [Cr(HL)2]X (Scheme 1)
Appearance of signals in both regions suggests that the ligand is present in the thione form, whereas the emergence of signals only in the higher energy region is indicative of the N2−H group deprotonation.7b) IR spectra of all complexes [1,2,3,4,5,6] display two broad bands between 2500 cm−1 and 3300 cm−1 suggesting the presence of ligands in the thione form

Summary

Introduction

Investigation of transition metal complexes and understanding their function in biological systems is a challenging research area. One of the most controversial transition metal in term of biological activities is chromium. The first data about one chromium(III) complex as a biological molecule was published in 1950. The results of their experiments on nutrient-deficient rats suggested that [Cr(pic)3] (pic = 2-pyridinecarboxylate) could act as „glucose tolerance factor“.2. Toxicological studies showed that the nature of the ligand is one of the crucial factors that determine the toxicity of Cr(III) biological molecules, and these effects were studied in relation to ligand-exchange and redox reactions. Cr(III) complexes are kinetically inert and this is one of their main chemical properties that could be responsible for toxicity through altering structures and functions of membranes, proteins and nucleic acids.

Methods

Results

Conclusion