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

Abstract

A paramagnetic octahedral trans-dihydroxy chromium(IV) complex with dianionic tetradentate Schiff base salophen and crystal structure of its trans-diisothiocyanato analog, Journal of Coordination Chemistry, 65:20, 3623-3640, A paramagnetic octahedral trans-dihydroxychromium(IV) complex, [Cr(OH) 2 (salophen)] (1) (H 2 salophen ¼ N,N 0 -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 d 2 (S ¼ 1) system with a triplet ground state. Compound 1 exhibits powder EPR spectra at RT and LNT, which show the allowed transition DM s ¼ AE1 (g ¼ 2.0038) as well as the ''forbidden'' half-field transition (DM s ¼ AE2) at g ¼ 4.2080. Two successive reduction waves are observed in the cyclic voltammogram of 1 in CH 3 CN at À0.84 and À1.63 V (vs. Ag/ AgCl), respectively. Compound 1 readily reacts with Mn 2þ ion, a Cr(IV)-specific reductant and also undergoes -OH substitution reactions in solution with NCS À and imidazole. The transdiisothiocyanato analog, [Cr(NCS) 2 (salophen)] (2), with eff ¼ 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)] Á H 2 O (3) show significant difference in their electronic structures as revealed from their electronic spectra.