title: An unusual stable mononuclear Mn(III) bis-terpyridine complex exhibiting Jahn-Teller compression: electrochemical synthesis, physical characterisation and theoretical study.
abstract: The mononuclear manganese bis-terpyridine complex [Mn(tolyl-terpy)(2)](X)(3) (1(X)(3); X=BF(4), ClO(4), PF(6); tolyl-terpy=4'-(4-methylphenyl)-2,2':6',2"-terpyridine), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1(3+) ion is a rare example of a mononuclear Mn(III) complex stabilised solely by neutral N ligands. Complex 1(3+) is obtained by electrochemical oxidation of the corresponding Mn(II) compound 1(2+) in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1(2+) exhibits not only the well-known Mn(II)/Mn(III) oxidation at E(1/2)=+0.91 V versus Ag/Ag(+) (+1.21 V vs. SCE) but also a second metal-based oxidation process corresponding to Mn(III)/Mn(IV) at E(1/2)=+1.63 V (+1.93 V vs. SCE). Single crystals of 1(PF(6))(3)2 CH(3)CN were obtained by an electrocrystallisation procedure. X-ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high-spin character. The electronic properties of 1(3+) were investigated in detail by magnetic measurements and theoretical calculations, from which a D value of +4.82 cm(-1) was precisely determined. Density functional and complete active space self consistent field ab initio calculations both correctly predict a positive sign of D, in agreement with the compressed tetragonal distortion observed in the X-ray structure of 1(PF(6))(3)2 CH(3)CN. The different contributions to D were calculated, and the results show that 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.
authors.affiliation: Université Joseph Fourier Grenoble 1/CNRS, Département de Chimie Moléculaire, UMR-5250, Institut de Chimie Moléculaire de Grenoble FR-CNRS-2607, BP-53, 38041 Grenoble Cedex 9, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Romain
authors.forename: Carole
authors.initials: C
authors.lastname: Duboc
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Eric
authors.initials: E
authors.lastname: Rivière
authors.forename: Lyall R
authors.initials: LR
authors.lastname: Hanton
authors.forename: Allan G
authors.initials: AG
authors.lastname: Blackman
authors.forename: Christian
authors.initials: C
authors.lastname: Philouze
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Leprêtre
authors.forename: Alain
authors.initials: A
authors.lastname: Deronzier
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Collomb