Département de chimie moléculaire

The mononuclear Mn bis-terpyridine complex [Mn(tolyl-terpy)2](X)3 (1(X)3; X = BF4, ClO4, PF6; tolyl-terpy = 4'-(4-methylphenyl)-2,2':6',2''-terpyridine), contg. Mn in the unusual +III oxidn. state, was isolated and characterized. The 13+ ion is a rare example of a mononuclear MnIII complex stabilized solely by neutral N ligands. Complex 13+ is obtained by electrochem. oxidn. of the corresponding MnII compd. 12+ in anhyd. MeCN. Under these conditions the cyclic voltammogram of 12+ exhibits not only the known MnII/MnIII oxidn. at E1/2 = +0.91 V vs. Ag/Ag+ (+1.21 V vs. SCE) but also a 2nd metal-based oxidn. process corresponding to MnIII/MnIV at E1/2 = +1.63 V (+1.93 V vs. SCE). Single crystals of 1(PF6)3·2MeCN were obtained by an electrocrystn. procedure. X-ray anal. unambiguously revealed its tetragonally compressed octahedral geometry and high-spin character. The electronic properties of 13+ were studied in detail by magnetic measurements and theor. calcns., from which a D value of +4.82 cm-1 was precisely detd. D. functional and complete active space SCF ab initio calcns. both correctly predict a pos. sign of D, in agreement with the compressed tetragonal distortion obsd. in the x-ray structure of 1(PF6)3·2MeCN. The different contributions to D were calcd., and (1) the spin-orbit coupling part (+2.593 cm-1) is predominant compared to the spin-spin interaction (+1.075 cm-1) and (2) the excited triplet states make the dominant contribution to the total D value. [on SciFinder(R)]