Direct Observation of Very Large Zero-Field Splitting in a Tetrahedral NiIISe4 Coordination Complex

The high-spin (S = 1) tetrahedral Ni-II complex [Ni{(Pr2P)-Pr-i(Se)NP-(Se)Pr-i(2)}(2)] was investigated by magnetometry, spectroscopic, and quantum chemical methods. Angle-resolved magnetometry studies revealed the orientation of the magnetization principal axes. The very large zero-field splitting (zfs), D = 45.40(2) cm(-1) E = 1.91(2) cm(-1), of the complex was accurately determined by far-infrared magnetic spectroscopy, directly observing transitions between the spin sublevels of the triplet ground state. These are the largest zfs values ever determined directly for a high-spin Ni-II complex. Ab initio calculations further probed the electronic structure of the system, elucidating the factors controlling the sign and magnitude of D. The latter is dominated by spin orbit coupling contributions of the Ni ions, whereas the corresponding effects of the Se atoms are remarkably smaller.