Reaching the Maximal Unquenched Orbital Angular Momentum L = 3 in Mononuclear Transition-Metal Complexes: Where, When and How?

The conditions for achieving the maximal unquenched orbital angular momentum L = 3 and highest magnetic anisotropy in mononuclear 3d complexes with axial coordination symmetry are examined terms of ligand field theory. It is shown that, apart from known linear two-coordinate 3d7 complex CoII(C(SiMe2ONaph)3)2 characterized by record single-molecule magnet (SMM) performance (with largest spin-reversal barrier Ueff 450 cm−1), can also be obtained 3d2 (V3+, Cr4+) trigonal-prismatic 3d3 (Cr3+, Mn4+) 3d8 (Co+, Ni2+) complexes. A comparative assessment SMM 3d2, indicates that they unlikely to compete CoII(C(SiMe2ONaph)3)2, whose close physical limit a metal.