The crystal and molecular structure of μ-hydrido-μ-diphenylphosphido-bis (tetracarbonylmanganese), (CO)₄Mn(H)(P(C₆H₅)₂)Mn(CO)₄

The crystal and molecular structure of μ-hydrido-μ-diphenylphosphido-bis(tetracarbonylmanganese), (CO)₄Mn(H)(P(C₆H₅)₂)Mn(CO)₄, has been determined from three-dimensional X-ray data collected by counter methods at room temperature. The material crystallizes in space group C_2h⁶-I2/c of the monoclinic system with four molecules in a cell of dimensions a = 16.76, b = 8.15, c = 17.03,β = 110° 46′. The structure has been refined by least-squares techniques to a final R factor on F of 7.2%. The average position of the bridging hydrogen atom was successfully included in this refinement. Twofold molecular symmetry is imposed on the well-separated molecular units. The geometry about the independent manganese atom is distorted octahedral, and the molecular structure results from the sharing of an edge of two manganese octahedra at the twofold axis. Each manganese atom is coordinated to four carbonyl groups, to the bridging phosphorus atom, and to the bridging hydrogen atom. Although the molecule is required to have symmetry 2, it has nearly symmetry mm. It is shown that from diffraction results alone it is not possible here, or in previous similar studies, to distinguish between the symmetric placement of the hydrogen atom between the two metal atoms in a single-minimum potential well and the placement of the hydrogen atom between the two metal atoms in a symmetric double-minimum potential well. The former description is consistent with a bonding scheme involving a symmetric, bent, three-center, two-electron bond between Mn-H-Mn; the latter is consistent with a Mn-H σ bond and a Mn-Mn metal-metal bond. A model involving an asymmetric potential well in which the hydrogen is preferentially associated with one manganese atom can be eliminated.