DFT Analysis of Spin Crossover in Mn(III) Complexes: Is a Two-Electron S=2 to S=0 Spin Transition Feasible?

被引:36
作者
Amabilino, Silvia [1 ]
Deeth, Robert J. [1 ,2 ]
机构
[1] Univ Warwick, Dept Chem, Coventry CV4 7AL, W Midlands, England
[2] Univ Bath, Dept Chem, Bath BA2 7AY, Avon, England
基金
英国工程与自然科学研究理事会;
关键词
MONONUCLEAR MANGANESE(III) COMPLEXES; RAY CRYSTAL-STRUCTURE; STATE ENERGETICS; 1ST EXAMPLE; MAGNETIC-SUSCEPTIBILITY; ENERGY DIFFERENCES; LIGAND; COORDINATION; FUNCTIONALS; REACTIVITY;
D O I
10.1021/acs.inorgchem.6b02793
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Six-coordinate, rigorously octahedral d(4) Mn-(III) spin crossover (SCO) complexes are limited by symmetry to an S = 1 (intermediate spin, IS) to S = 2 (high spin, HS) transition. In order to realize the potential S = 0 to S = 2 transition, a lower symmetry and/or change in coordination number is needed, which we explore here computationally. First, a number of complexes are analyzed to develop a reliable and relatively fast DFT protocol for reproducing known Mn(III) spin state energetics. The hybrid meta-GGA functional TPSSh with a modest split valence plus polarization basis set and an empirical dispersion correction is found to predict correctly the ground spin state of Mn(III) complexes, including true low-spin (LS) S = 0 systems, with a range of donor sets including the hexadentate [N4O2] Schiff base ligands. The electronic structure design criteria necessary for realizing a Delta S = 2 SCO transition are described, and a number of model complexes are screened for potential SCO behavior. Five coordinate trigonal-bipyramidal symmetry fails to yield any suitable systems. Seven-coordinate, approximately pentagonal bipyramidal symmetry is more favorable, and when a known pentadentate macrocyclic donor is combined with pi-acceptor axial ligands, a novel Mn(III) complex, [Mn(P.ABODP)(PF3)(2)](3+) (PABODP = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaene), is predicted to have the right spin state energetics for an S = 0 to S = 2 transition. Successful synthesis of such a complex could provide the first example of a Delta S = 2 SCO transition for d(4) Mn(III). However, the combination of a rigid macrocycle and a high coordination number dilutes the stereochemical activity of the d electrons, leading to relatively small structural changes between HS and LS systems. It may therefore remain a challenge to realize strong cooperative effects in Mn(III) systems.
引用
收藏
页码:2602 / 2613
页数:12
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