Magneto-Structural Relationship of Tetragonally-Compressed Octahedral Iron(II) Complex Surrounded by a pseudo-S6 Symmetric Hexakis-Dimethylsulfoxide Environment

Abstract

Since the octahedral high-spin iron(II) complex has the 5T2g ground term, the spin-orbit coupling should be considered in magnetic analysis; however, such treatment is rarely seen in recent papers, although the symmetry-sensitive property is of interest to investigate in detail. A method to consider the T-term magnetism was well constructed more than half a century ago. On the other hand, the method has been still improved in recent years. In this study, the octahedral high-spin iron(II) complex [Fe(dmso)6][BPh4]2 (dmso: dimethylsulfoxide) was newly prepared, and the single-crystal X-ray diffraction method revealed the tetragonal compression of the D4-symmetric coordination geometry around the iron(II) ion and the pseudo-S6 hexakis-dmso environment. From the magnetic data, the sign of the axial splitting parameter, Δ, was found to be negative, indicating the 5E ground state in the D4 symmetry. The DFT computation showed the electronic configuration of (dxz)2(dx2−y2)1(dyz)1(dxy)1(dz2)1 due to the tetragonal compression and the pseudo-S6 environment of dmso π orbitals. The electronic configuration corresponded to the 5E ground term, which was in agreement with the negative Δ value. Therefore, the structurally predicted ground state was consistent with the estimation from the magnetic measurements.