Coordination-induced spin-state change in manganese(V) complexes: the electronic structure of manganese(V) nitrides

This work illustrates that manganese(V) nitrido complexes are able to undergo a coordination-induced spin-state change by altering the ligand field from trigonal to tetragonal symmetry. For the reversible coordination of acetonitrile to trigonal [(TIMEN(xyl))Mn(N)](2+) (1; high-spin S = 1; with TIMEN(xyl) = tris[2-(3-xylylimidazol-2-ylidene)ethyl]-amine), a temperature-dependent coordination-induced spin-state switch is established. Starting from the manganese(V) nitrido complex 1, the synthesis and characterization of a series of octahedral, low-spin (S = 0) manganese(V) nitrido complexes of the type [(TIMEN(xyl))Mn(N)(L)](n+) (L = MeCN (2), (t)BuNC (3), CN(-) (4), NCS(-) (5), F(-) (6), μ-{Ag(CN)2}(-) (7), with n = 1, 2) is described. These represent the first examples of d(2) transition metal complexes showing a coordination-induced spin-state change. Spectroscopic, as well as ligand-field theory and density functional theory studies suggest a transition from a 2 + 2 + 1 orbital splitting in the trigonal case to a 1 + 2 + 1 + 1 splitting in tetragonal symmetry as the origin of the coordination-induced spin-state change.