Molecular and Electronic Structure of Nitridocyanometalates of Chromium(V) and Manganese(V):  A Combined Experimental and DFT Study

The six-coordinate complexes [M(N)(CN)5]3- (M = Cr, Mn) have been isolated as salts of robust rhodium amine complexes. [Rh(en)3][Mn(N)(CN)5]·H2O (1) and [Rh(tn)3] [Cr(N)(CN)5]·2H2O (2) have been characterized by single-crystal X-ray crystallography: 1 crystallizes in the hexagonal space group P63 with a = b = 15.810(2) Å, c = 13.844(3) Å, V = 2996.8(8) Å3, and Z = 6; 2 crystallizes in the orthorhombic space group Pbcn with a = 9.723(1) Å, b = 14.564(2) Å, c = 31.498(4) Å, V = 4460.3(8) Å3, and Z = 8. In 1, all the anions are oriented with their Mn⋮N directions almost coparallel to the crystallographic 3-fold axis. Polarized single-crystal UV−vis spectroscopy of 1 confirms the validity of the Jørgensen−Ballhausen−Gray d-orbital splitting scheme with the lowest energy transition being d xy → {d yz ,d zx }. Single-crystal EPR spectroscopy of [Cr(N)(CN)5]3- diluted into 1 shows the hyperfine (53Cr) and super-hyperfine (14N) tensors to be quite anisotropic with different major axes. For the hyperfine interaction we observe A ∥ > A ⊥, whereas, for the super-hyperfine interaction to the terminal nitrido ligand, the reverse ordering is found: A⊥ > A ∥. The complexes [M(N)(CN)5]3-, trans-[M(N)(CN)4(py)]2-, and [M(N)(CN)4]2- (M = Cr, Mn) were investigated by DFT methods. Good reproduction of the molecular structures, vibrational, and UV−vis spectra was obtained. However, pronounced differences between local density and gradient corrected functionals were observed in the description of the weak bonding to the ligands trans to the nitrido ligand. For the five-coordinate [M(N)(CN)4]2- complexes the LUMO is predicted to be a strongly admixed d z 2 (M)−p z (M) hybrid.