Electronic structure and magnetic properties of rhenium complexes with an iminoxolene ligand: experimental and...

Two rhenium complexes with reduced forms of iminoquinone as ligands (L^Dipp = N-(2,6-diisopropylphenyl)-3,5-di-tert-butyl-o-benzoquinoneimine), [ReCl₃(L^Dipp)(PPh₃)] (1) and [ReCl₃(L^Dipp)(OPPh₃)] (2), have been synthesized. The metrical oxidation states (MOS) of the iminoxolene ligand L^Dipp in both complexes, equal to -1.29(9), -1.36(11) and -1.44(8) for structures 1, 2 and 2·4C₆H₆, respectively, lie between the values for iminosemiquinolate ((ISQ^Dipp)^-·) and amidophenolate ((AP^Dipp)^2-). The ¹H and ¹³C NMR spectra of both complexes exhibit paramagnetically shifted but narrow signals, allowing the use of conventional 2D NMR techniques for the complete assignment of H and C atoms. High-level ab initio calculations revealed a pronounced multi-configurational nature of the ground triplet state of both complexes, with the spin population localized predominantly on Re, with some delocalization of the negative spin density to iminoxolene. Magnetic measurements showed that, for both complexes in the range of 2-300 K, the χT product increases almost linearly with temperature, in quantitative agreement with the results of high-level ab initio calculations, which predicted very high positive values of the ZFS parameter D for the ground triplet states of both complexes.