The structure and bonding in cis-HMn(CO)4PPh3 have been studied by low-temperature neutron and high-resolution X-ray diffraction, the latter study using a charge-coupled device (CCD) area detector. A charge density analysis, including the deformation density, a full topological analysis of ρ, and selected topological analysis of -▽2ρ, has been conducted, cis-HMn(CO)4PPh3 adopts an approximately octahedral geometry, the largest deviation being the C(1)-Mn-C(3) angle of 160.0(1)°. The hydride ligand (Mn-H(1), 1.573(2) Å) is nucleophilic in nature (i.e., hydridic, with an effective atomic charge of -0.4e) and makes a short contact (2.101(3) Å) with an electrophilic (+0.3e) ortho phenyl hydrogen. The electrostatic component of the Hδ+⋯Hδ- interaction energy is calculated to be 5.7 kcal/mol from the experimental data. This electrostatic evidence coupled with the geometry (C-H⋯H 129.0(2)° and H⋯H-Mn 126.5(1)°) and the identification of an H⋯H bond path in the charge density distribution strongly supports the characterization of this interaction as an intramolecular C-H⋯H-Mn hydrogen bond. Both the deformation density and the topological study clearly illustrate the σ-donor nature of both the H-Mn and Ph3P-Mn interactions and the σ-donor/π-acceptor nature of the manganese-carbonyl bonds. The topological study further confirms the decrease in C-O bond order upon coordination to the metal and demonstrates for the first time by this method that the metal-ligand bonds, although showing characteristics of a closed-shell interaction, do have a significant dative covalent component to the bond. The latter is reinforced by a study of the derived Mn d-orbital populations, in which populations of the dz2 and dx2-y2 orbitals are significantly higher than would be predicted by a simple crystal field theory model of metal-ligand bonding.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry