Electronic Structure and Magnetic properties of Rhenium Complexes with Iminoxolene Ligand: Experimental and Computational Studies

Two rhenium complexes with reduced forms of iminoquinone as ligands (LDipp = N-(2,6-diisopropylphenyl)-3,5-di-tert-butyl-o-benzoquinoneimine), [ReCl3(LDipp)(PPh3)] (1) and [ReCl3(LDipp)(OPPh3)] (2), have been synthesized. X-ray diffraction data show that the oxidation state of the iminoxolene ligand LDipp in both complexes is intermediate between iminosemiquinolate ((ISQDipp)–∙) and amidophenolate ((APDipp)2–) with non-integer metrical oxidation state (MOS) of –1.29(9), –1.36(11) and –1.44(8) for the structures 1, 2 and 2∙4C6H6, respectively. The 1H and 13C NMR spectra of both complexes exhibit paramagnetically shifted but narrow signals, allowing the use of conventional 2D NMR techniques for full assignment of H and C atoms. High-level ab initio calculations revealed a pronounced multi-configuration nature of the ground triplet state of both complexes, with the MOS value and spin population of iminoxolene being determined by different configurations. Magnetic measurements showed that for both complexes in the range 2−300 K the χT product increases almost linearly with temperature in quantitative agreement with high-level calculations, which predicted a high positive value of the ZFS parameter D for the ground triplet states of both complexes.