GAS-PHASE ELECTRON-DIFFRACTION STUDY OF THE MOLECULAR-STRUCTURE OF A-CYCLOHEPTATRIENYL)(ETA-CYCLOPENTADIENYL)NIOBIUM, NB(ETA-C7H7)(ETA-C5H5)

The molecular structure of [Nb(eta-C7H7)(eta-C5H5)] in the gas phase h as been determined by electron diffraction at 470 K. The niobium atom is sandwiched by parallel, symmetric rings, with Nb-C distances (r(a)) of 231.5(14) and 239.0(9) pm to the C5H5 and C7H7 rings, respectively . The C-H bonds of the C5H5 group are displaced 2.9(23)-degrees out of the ring plane toward the niobium atom, while those of the C7H7 group are displaced 4.7(24)-degrees, also toward niobium. The mean ring C-C bond length is 143.3(1) pm, with the bonds in the smaller ring being longer than those in the larger ring by, 1.6(7) pm. These parameters a re interpreted and related to those of the anion [Nb(C7H7)(C5H5)]- by consideration of the orbitals involved in bonding between the metal at om and the rings.