Pentacoordinated manganese(III) bis-o-iminobenzosemiquinonates: Looking for spin-crossover phenomenon

Abstract

A series of pentacoordinated bis-o-iminobenzosemiquinonato manganese(III) complexes with general formula (imSQR)2MnX (where imSQR – is a radical anion of corresponding o-iminobenzoquinone/o-aminophenol, X – halogen, azide, isocyanate) has been synthesized and characterized in detail. 4,6-Di‑tert‑butyl‑N-(2,6-dimethylphenyl)-o-iminobenzoquinone (imQMe), 4,6-di‑tert‑butyl‑N-(2-methoxyphenyl)-o-aminophenol (APOMeH2), and 4,6-di‑tert‑butyl‑N-(2-trifluoromethylphenyl)-o-aminophenol (APCF3H2) were used as initial substances to provide both sterical and electronic variety of paramagnetic ligands in (imSQR)2MnX complexes (R = Me, X = Cl (1), Br (2), I (3), N3 (4), NCO (5); R = OMe, X =Br (7), I (8), N3 (9); R = CF3, X = Cl (10), Br (11), I (12), N3 (13), NCO (14)). Molecular structures of 2, 9–11 have been established by single-crystal X-ray analysis. The increasing of the sterical bulkiness of imSQR ligands leads to the significant distortion of coordination polyhedrons from the almost ideal square pyramid (SP) for 10 and 11 to significantly distorted one towards trigonal bipyramid (TB) for 9 and 2. According to the magnetic susceptibility measurements of polycrystalline samples of 1–14, strong antiferromagnetic metal-ligand spin interactions between unpaired electrons of high-spin MnIII ion (h.s., d4, SMn = 2) and two imSQ ligands (SR = 1/2) lead to observed triplet ground state in all complexes.