OXIDATIVE ADDITION OF HALOGENS TO THE QUADRUPLE BOND OF MO2X4(DPPM)2 (X = CL, I, BR) - SYNTHESIS, STRUCTURAL CHARACTERIZATION, AND MAGNETIC-PROPERTIES OF MO2CL4I2(DPPM)2, MO2BR6(DPPM)2, AND MO2I6(DPPM)2

Oxidative-addition reactions of Y2 (Y = Cl, Br, I) to the quadruply bonded complexes Mo2X4(dppm)2 (X = Cl, Br, I) produce the corresponding edge-sharing bioctahedral molecules Mo2X4Y2(dppm)2 in high yield. All nine of these compounds are now available and have been investigated by infrared and UV-visible spectroscopy as well as by electrochemical methods. Structural determinations of three of them, Mo2Cl4I2(dppm)2 (2), Mo2Br6(dppm)2 (4), and Mo2I6(dppm)2 (8), have been carried out, although in the case of 4 refinement is incomplete. Pertinent crystal data are as follows: for 2, P1BAR, a = 9.922 (3) angstrom, b = 13.013 (5) angstrom, c = 12.152 (5) angstrom, alpha = 93.31 (3)-degrees, beta = 107.06 (2)-degrees, gamma = 108.63 (2)-degrees, V = 1402 (1) angstrom3, Z = 1; for 4, P1BAR, a = 16.069 (6) angstrom, b = 20.994 (6) angstrom, c = 10.756 (6) angstrom, alpha = 102.43 (3)-degrees, beta = 106.99 (4)-degrees, gamma = 77.52 (3)-degrees, V = 3343 (3) angstrom3, Z = 2; for 8, P2(1)/n, a = 16.194 (8) angstrom, b = 11.090 (2) angstrom, c = 20.574 (7) angstrom, beta = 108.72 (4)-degrees, V = 3499 (6) angstrom3, Z =2. Compound 2 has bridging Cl atoms, and each terminal position is occupied by a 1:1 mixture of Cl and I. The Mo-Mo distances in 2, 4, 8, and Mo2Cl6(dppm)2 are respectively 2.827 (1), 2.879 (2), 3.061 (1), and 2.789 (1) angstrom. Magnetic susceptibility data over a temperature range 5-300 K have been fitted to an expression that allows evaluation of the gap between a ground singlet state and a low triplet state. For 2 the gap is > 1750 cm-1, while for the other three compounds whose structures are known, Mo2X6(dppm)2, X = Cl, Br, and I, the S-T gap is 1100-1400 cm-1, indicating that both direct M-M coupling and indirect coupling across the mu-X atoms play a part.