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.

Zero-field splitting in nickel(II) complexes: A comparison of DFT and multi-configurational wavefunction calculations

“…Similar conclusions for other Mn(III) systems were reached in other papers from Neese's group. 26,79,80 Moreover, some model Mn(III) complexes were the topic of an ab initio study by Maurice et al 81,82 The conclusion of this discussion might be that the difficult systems, with spatially nearly degenerate states, require the use of the most advanced theoretical tools, such as the NEVPT2/QDPT combination. What is surprising, to a certain extent, is the fact that our calculations for the apparently "easy" case of nickel(II), with the triplet ground state quite far below the excited states, show the same trend as the "difficult" ions.…”

Theoretical Insights into the Magnetostructural Correlations in Mn3-Based Single-Molecule Magnets

“…[17][18][19][20][21] In addition, a somewhat rough but qualitatively to semiquantitatively correct ligand-field modeling of the same properties has been demonstrated. 22,23 It is the aim of the present work to study the magnetostructural correlations in Mn 3 O SMMs by combining the numerical results as provided by DFT and the semiempirical valence bond configuration interaction (VBCI) model, which will be used to analyze and understand the DFT results.…”

Homoleptic and heteroleptic complexes of chromium(III) containing 4′-diphenylamino-2,2′:6′,2″-terpyridine ligands

“…[33]. Each of these metal(III) complexes assembles with the same π-stacked motif shown in Figure 2a [30,34], KAYHIC [35], KEMWEG [36], KUWKOD [37] and QOLYUM [38] …”