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

A paramagnetic octahedral trans-dihydroxychromium(IV) complex, [Cr(OH)(2)(salophen)] (1) (H(2)salophen 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 d(2) (S=1) system with a triplet ground state. Compound 1 exhibits powder EPR spectra at RT and LNT, which show the allowed transition Delta M-s=+/- 1 (g=2.0038) as well as the "forbidden" half-field transition (Delta M-s=+/- 2) at g=4.2080. Two successive reduction waves are observed in the cyclic voltammogram of 1 in CH3CN at -0.84 and -1.63V (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 mu(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) angstrom). Compound 2 and the corresponding Cr(III) compound K[Cr(NCS)(2) (salophen)]center dot H2O (3) show significant difference in their electronic structures as revealed from their electronic spectra.