Hydridic atom arrangement and bonding in the molecular structure of (C(2)H(5))(4)N(+)[Re(2)(mu-H)(3)H(6){CH(3) C(CH(2)P(C(6)H (5))(2))(3)}](-.) CH(3)CN: A complex containing ten-coordinated rhenium.

A complex obtained from the reaction of ReH(2-)(9) with triphos (triphos = CH(3)C(CH(2)P(C(6)H(5))(2))(3)) is found to be a nonahydride dimer in which ReH(2-)(9) is coordinated to RE (triphos)(+) via three H atoms and a Re-Re bond. The ten- coordinated Re atom in this compound is the first example of a transition metal atom with coordination number greater than nine. The structure of the compound was determined at 295K by X-ray diffraction and at 80K by neutron diffraction. The Re-Re bond of 2.594(1)angstroms passes obliquely through a face of the systematically distorted equatorially-girded ReH(9) trigonal prism. The other Re atom is octahedrally coordinated by the three bridging H and the three P atoms. The average bridging Re-H distance at 80K is 1.86(4)angstroms, average terminal Re-H is 1.66(6)angstroms, and average Re-P at 295K is 2.289(4)angstroms. An SCF-Xalpha-SW calculation on [Re(2)(mu-H)(3)H(6)(PH(3))(3)](-) shows the Re-Re bond to be a siguna(2)pi(4) triple bond. The Re-Re bonding orbitals also function as Re-H(br) bonding orbitals; their dual bonding character permits the Re atom to achieve a coordination number greater than nine. In the visible region, (Re(2)H(9)(triphos)] (-) has absorption maxima at ~360(epsilon7.4x10(3) and ~335 (epsilon7.4x10(3))nm. Xalpha-transition state calculations assign this absorption to charge transfer from the phosphine- coordinated to the H(9)-coordinated Re atom. Final wR-agreement indicators are 0.0262 for 2565 independent observed X-ray reflections and 0.0516 for 2562 neutron reflections. This Technical Memorandum replaces TM 11535-840531-13.