Molecular geometry of M(NO)₂ complexes: single crystal X-ray structure of Co(NO)₂(C₅H₅N)₂⁺BF₄⁻, lability of the pyridine ligands of Co(NO)₂(C₅H₅N)₂⁺, and its relevance to the formation of the Co₂(NO)₃⁺ bimetallic core

The BPh4- and BF4- derivatives of Co(NO)2(Py)2+ 3 (Py = pyridine) have been prepared. In solution, whereas Co(NO)2(L)2+BPh4- (L = phosphane) and 3-BF4 are inert, 3-BPh4- decomposes rapidly in the absence of an excess of Py. Complex 3-BF4- crystallizes in the monoclinic system with two independent molecules, A and B, in the asymmetric unit, space group P2(1)/a, a = 14.7633(6) angstrom, b = 13.9739(5) angstrom, c = 15.1667(6) angstrom, beta = 109.334(4)-degrees, 2225 reflections, R = 0.054, Rw = 0.023. The cobalt coordination polyhedron is a distorted tetrahedron. The comparison of the (O)N-Co-N(O) angles of 115.6(3)-degrees (molecule A) and 115.9(3)-degrees (molecule B) with those of other D(NO(M))8+2 pseudotetrahedral dinitrosyl complexes suggests that the lability of the Py ligands of cation 3 reflects the compression experienced by the Co(NO)2+ molecular portion.