An Unusual Stable Mononuclear MnIII Bis‐terpyridine Complex Exhibiting 
Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation 
and Theoretical Study

Romain, Sophie; Duboc, Carole; Neese, Frank; Rivière,  Eric; Hanton, Lyall R.; Blackman, Allan G.; Philouze, Christian; Leprêtre,  Jean‐Claude; Deronzier, Alain; Collomb, Marie-Noelle

doi:10.1002/chem.200801442

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An Unusual Stable Mononuclear Mn^III Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study

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Romain, S., Duboc, C., Neese, F., Rivière, E., Hanton, L. R., Blackman, A. G., et al. (2009). An Unusual Stable Mononuclear Mn^III Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis, Physical Characterisation and Theoretical Study. Chemistry – A European Journal, 15(4), 980-988. doi:10.1002/chem.200801442.

Cite as: https://hdl.handle.net/21.11116/0000-0008-334C-A

Abstract

The mononuclear manganese 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), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1³⁺ ion is a rare example of a mononuclear Mn^III complex stabilised solely by neutral N ligands. Complex 1³⁺ is obtained by electrochemical oxidation of the corresponding Mn^II compound 1²⁺ in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1²⁺ 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(PF₆)₃⋅2 CH₃CN were obtained by an electrocrystallisation procedure. X‐ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high‐spin character. The electronic properties of 1³⁺ 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(PF₆)₃⋅2 CH₃CN. 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.