Spectroscopic studies for the changes of a Cr(II) compound in solution triggered by the deprotonation of an aqua ligand

Recently, we reported dioxygen binding and its activation by the Cr(II) compound [Cr(H2O)(LISQ)2] (1) [(LISQ)1- is o-iminothionebenzosemiquinonate(1-) π-radical]. In this work, we report the existence of ferromagnetism in its solid form. The plot of (χm)-1 versus T from 250 to 20 K reveals a Curie-Weiss constant of θ ~26 K suggesting a ferromagnetic coupling. A theoretical simulation on the susceptibility curve and the fitting of the χm versus T yielded g = 1.83 ± 0.002, J = 33.4 ± 0.001 cm-1, and θ = 25.2 ± 0.02 K with J D. Increase in EPR line width on cooling helped us calculate the Cr(II)-Cr(II) distance in the proposed dimer. Also we find that deprotonation of the aqua ligand in 1 is essential for dioxygen binding and its activation. Reaction with dioxygen is completely inhibited when there is no deprotonation. Reaction of 1 with dioxygen in pyridine (py) resulted in isolation of the O=Cr(IV) compound [O=Cr(LAP)2(py)] (2) [(LAP)1- is o-aminothiophenolate anion] and no monomeric O=Cr(V) has been detected by EPR. 1H NMR study of 1 in d6-DMSO with time shows increase in intensity of the -NH2 peak at 5.46 ppm, suggesting gradual reduction of the -NH groups in (LISQ)1- ligands.