Oxidative addition of halogens to the quadruple bond of bis[bis(diphenylphosphino)methane]tetrahalodimolybdenum (halo = chloro, iodo, bromo): synthesis, structural characterization, and magnetic properties of Mo2Cl4I2(dppm)2, Mo2Br6(dppm)2, and Mo2I6(dppm)2 Academic Article uri icon

abstract

  • 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, [formula omitted], a = 9.922 (3) Å, b = 13.013 (5) Å, c = 12.152 (5) Å, α = 93.31 (3)°, β = 107.06 (2)°, γ = 108.63 (2)°, V = 1402 (1) Å3, Z = 1; for 4, [formula omitted], a = 16.069 (6) Å, b = 20.994 (6) Å, c = 10.756 (6) Å, α = 102.43 (3)°, β = 106.99 (4)°, γ = 77.52 (3)°, V= 3343 (3) Å3, Z = 2; for 8, P21/n, a = 16.194 (8) Å, b = 11.090 (2) Å, c = 20.574 (7) Å, β = 108.72 (4)°, V = 3499 (6) Å3, 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) Å. 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 μ-X atoms play a part. © 1991, American Chemical Society. All rights reserved.

author list (cited authors)

  • Cotton, F. A., Daniels, L. M., Dunbar, K. R., Falvello, L. R., O'Connor, C. J., & Price, A. C.

citation count

  • 14

publication date

  • May 1991