Bonding in a binuclear metal carbonyl: experimental charge density in Mn₂(CO)₁₀

Abstract

X-ray diffraction data (Ag Ka and Mo Net radiation) have been collected at 74 K on dimanganese decacarbonyl Mn2(CO)I 0, and the crystal structure was refined. The atomic positional and thermal parameters were determined from high-angle AgKa data to avoid systematic errors due to bonding effects. The molecular geometry is discussed. The distortions are larger than at room temperature: for example, the torsion angle of the two Mn(CO) 5 fragments is 50.2 °, compared to 47.4 ° at room temperature, and 45 ° for an ideal D4a symmetry. 'X-X' deformation-density maps were computed and averaged over chemically equivalent sites. No significant charge-density accumulation is observed on the Mn-Mn bond. The configuration around the Mn atoms is essentially octahedral, with about 75% of the 3d electrons in the diagonal orbitals (dxy,d~z,dy ~) and the remaining 25% in d: and dx2_/. Atomic charges were determined both by direct integration and by least-squares refinement. Directly integrated charges are very small. Mn seems slightly negative. Both methods of charge integration show a clear difference between axial and equatorial carbonyls, which is confirmed by comparing their electron density with that of free carbon monoxide: the differences are characteristic of a a-bonding n-backbonding mechanism, and are larger for the axial carbonyls than for the equatorial carbonyls. This confirms the stronger bonding of the axial carbonyls, also responsible for the longer C-O bond and the shorter Mn-C bond.

An Interacting Quantum Atoms Analysis of the Metal–Metal Bond in [M2(CO)8]n Systems

“…We will not further discuss these interactions here, given that the subject is actually the interaction between two metal moieties. The symmetrical bridge: Co 2 (CO) 8 The more relevant IQA results for this molecule are collected in Table 2. As anticipated in the introduction, bridged metal dimers do not show any direct MM bond path.…”

“…15 For example, although the 18-electron rule predicts a direct bond in the bridged isomer of Co 2 (CO) 8 , no BCP was found between the two cobalt atoms. 16 This automatically rules out a direct MM bond 12 and raises the question how to quantify the electron localization or delocalization in a bond.…”

Excitation Energies for Transition Metal Compounds from Time-Dependent Density Functional Theory. Applications to MnO4-, Ni(CO)4, and Mn2(CO)10

“…In geometry A, 71 the most important orbital transition is 8e 1 f 2a 2 which has a weight of 61% in r 1 E 1 and 28% in s 1 E 1 . This is consistent with Levenson and Gray's analysis.…”

“…Three different geometries were used as the results appeared to be strongly geometry dependent. Two of these geometries are experimental, 71,72 while the third was a BP-optimized geometry of ref 70 (Table 6, row 9), which was also used in unpublished ∆SCF test calculations. 73 Further technical details concern the convergence of the SCF procedure, the numerical integration accuracy, the criterion for neglecting tails of functions in regions of space where they are close to zero, the convergence of the iterative procedure for solving the excitation energy eigenvalue equation (eq 2), and the criterion for the orthonormality of the trial vectors in this procedure.…”

Charge-density distribution in crystals of CuAlO2 with d–s hybridization

“…For some of the transition-metal compounds, however, it is necessary to consider the s-and p-orbital contributions or the d-s and d-p hybridizations. Martin, Rees & Mitschler (1982) studied the chargedensity distribution in Mn2(CO)~ 0 from the X-ray diffraction data and refined the electron populations in the 4s orbital of Mn by the least-squares method for the first time. They obtained the electron configuration 3dS"254s TM, but the value of the 4s population is incorrect, because it exceeds the maximum population.…”