Synthesis and characterization of six-coordinate nitrido complexes of vanadium(V), chromium(V), and manganese(V). Isolation of a dinuclear, mixed-valent mu-nitrido chromium(III)/chromium(V) species

Photolysis of a series of octahedral monoazido complexes of the type [LM(III)(didentate ligand)(N-3)](n+)X(n) of vanadium(III), chromium(III), and manganese(III) in the solid state or in solution yields quantitatively the corresponding six-coordinate nitrido complexes [LM(V)(didentate ligand)(N)](n+)X(n) and 1 equiv of dinitrogen. L represents the macrocycle 1,4,7-triazacyclononane or its N-methylated derivative (L'), the didentate ligands are pentane-2,4-dionate (acac), 2,2,6,6-tetramethylheptane-3,5-dionate (tacac), picolinate (pie), phenanthroline (phen), and oxalate (ox), and X(-) represents perchlorate or hexafluorophosphate. The following nitrido complexes were prepared: [LV(V)(N)(acac)](ClO4) (6), [LCr(V)(N)(acac)](ClO4) (13), [LCr(V)(N)(tacac)](ClO4) (14), [LCr(V)(N)(pic)](ClO4) (15), [LCr(V)(N)(phen)](ClO4)(2) (16), [LCr(V)(N)(ox)] (19), [L'Mn-V(N)(acac)]PF6 (21). Photolysis of [LCr(III)(N-3)(ox)] (17) in the solid state produces the mu-nitrido-bridged mixed-valent species [L(2)Cr(2)(ox)(2)(mu-N)](N-3) (18). The structures of the precursor complex [L'Mn(acac)(N-3)]BPh(4) (20), of 13, and of [L'Mn-V(N)(acac)]BPh(4) (21) have been determined by X-ray crystallography. Complex 13 crystallizes in the orthorhombic space group Pnma, with cell constants a = 27.187(5) Angstrom, b = 9.228(2) Angstrom, c = 7.070(1) Angstrom, V = 1773.7(6) Angstrom(3) and Z = 4; complex 20 crystallizes in the triclinic space group P (1) over bar with a = 14.769(5) Angstrom, b = 16.83(1) Angstrom, c = 16.96(1) Angstrom, alpha = 108.19(5)degrees, beta = 105.06(4)degrees, gamma = 99.78(4)degrees, V = 3719(2) Angstrom(3), and Z = 4; and complex 21 crystallizes in the monoclinic space group P2(1)/n with a 10.443(3) Angstrom, b = 16.035(4) Angstrom, c = 21.463(5) Angstrom, beta = 95.76(1)degrees, V = 3575.9(14) Angstrom(3), and Z = 4. The Cr-V=N and Mn-V=N distances are short at 1.575(9) and 1.518(4) Angstrom, respectively, and indicate a metal-to-nitrogen triple bond.