MOLECULAR STEREOCHEMISTRY OF 2 BINUCLEAR METALLOPORPHYRINS CONTAINING M2O34+ UNIT - MU-OXO-BIS(OXO-ALPHA,BETA,GAMMA,DELTA-TETRAPHENYLPORPHINATOMOLYBDENUM(V)) AND TRI-MU-OXO-BIS(ALPHA,BETA,GAMMA,DELTA-TETRAPHENYLPORPHINATONIOBIUM(V))

The molecular stereochemistry of two binuclear metalloporphyrins with molecular formula [O3M2(TPP)2], where M = Nb(V) or Mo(V) and TPP is the dianion of α, β,γ, δ-tetraphenylporphyrin, have been determined by x-ray diffraction techniques using counter data. Crystal data: O3Nb2(TPP)2, monoclinic, space group Ce, Z = 4, a = 10.765 (5) Å, b = 24.913 (6) Å, c = 29.332 (8) Å, cos O = -0.3794 (4); O3Mo2(TPP)2, monoclinic, space group C2/c, Z = 4, a = 18.211 (2) Å,b = 19.309 (3) Å, c = 28.989 (3) Å, cos β = -0.4320 (1). Refinement of the niobium complex was based on 5748 observed data, final discrepancy indices R1 = 0.063 and R2 = 0.073. Refinement of the molybdenum complex was based on 7742 observed data, final discrepancy indices R1 = 0.059 and R2 = 0.089. The niobium complex is seven-coordinate with three bridging oxygen ligands. Unique Nb-O distances are 1.910, 1.990, 1.760, 1.782, 2.278, and 2.440 Å. The average Nb-N bond distance is 2.246 Å. The Nb-Nb separation is 2.872 Å. The molybdenum complex is six-coordinate; the Mo2O34+ unit has the unusual geometry of a linear five-atom grouping with two terminal Mo=O groups and a single Mo—O—Mo bridge. The Mo—O distances are 1.707 and 1.936 Å. This unusual arrangement for a binuclear Mo(V) complex leads to a paramagnetic species. The average Mo—N bond distance is 2.094 Å. © 1978, American Chemical Society. All rights reserved.