A paramagnetic octahedral trans-dihydroxy chromium(IV) complex with dianionic tetradentate Schiff base salophen and crystal structure of its trans-diisothiocyanato analog

Abstract

A paramagnetic octahedral trans-dihydroxychromium(IV) complex, [Cr(OH)2(salophen)] (1) (H2salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine), has been synthesized and characterized by elemental analysis, magnetic moment measurement, IR, UV-Vis, and EPR spectroscopic studies. Measured room temperature (RT) magnetic moment value is 2.79 BM for 1, indicating a d2 (S = 1) system with a triplet ground state. Compound 1 exhibits powder EPR spectra at RT and LNT, which show the allowed transition ΔM s = ±1 (g = 2.0038) as well as the “forbidden” half-field transition (ΔM s = ±2) at g = 4.2080. Two successive reduction waves are observed in the cyclic voltammogram of 1 in CH3CN at −0.84 and −1.63 V (vs. Ag/AgCl), respectively. Compound 1 readily reacts with Mn2+ ion, a Cr(IV)–specific reductant and also undergoes –OH substitution reactions in solution with NCS− and imidazole. The trans-diisothiocyanato analog, [Cr(NCS)2(salophen)] (2), with μ eff = 2.80 BM has been structurally characterized by X-ray crystallography and found to contain two N-bonded axial thiocyanato ligands with slightly different axial Cr–N bond lengths (N(3)–Cr(1), 2.032(2); N(4)–Cr(1), 2.015(2) Å). Compound 2 and the corresponding Cr(III) compound K[Cr(NCS)2(salophen)] · H2O (3) show significant difference in their electronic structures as revealed from their electronic spectra.