Crystal structure of [1,2-bis(dimethylarsino)hexafluoropropane]tetracarbonylmolybdenum, Me2AsCF(CF3)CF2AsMe2·Mo(CO)4

Abstract

Crystals of [1,2-bis(dimethylarsino)hexafluoropropane]tetracarbonylmolybdenum, Me₂AsCF(CF₃)CF₂AsMe₂·-Mo(CO)₄, are monoclinic, a= 25·06, b= 13·27, c= 11·56 Å, β= 102·8°, Z= 8, space group C2/c. The structure was determined with Mo-K_α diffractometer data by Patterson, electron-density, and full-matrix least-squares methods, the final R being 0·073 for 1510 observed (of a total of 1750) reflexions. The Mo–As bond distances being 2·572(4)Å. The five-membered chelate ring is non-planar, the As–C–C–As dihedral angle being 47°, so that the ligand has a staggered conformation, with the CF₃ group in an equatorial position. The two axial C–F bonds, 1·51 (3)Å, are significantly longer than the equatorial C–F bond, 1·37(4)Å, than the CF₃ bonds, mean 1·28 Å and than a normal C–F bond, 1·33 Å. The C–C bond length, 1·40(4)Å, is significantly less than the single-bond distance. These unusual features, and the detailed values of the valency angles in the ligand, are explicable in terms of a bonding system which involves donation of molybdenum nonbonding d electrons, via the arsenic 4d orbitals, into orbitals of the fluorocarbon group.