The bonding and photoelectron spectra of Mn(CO)5H and Mn(CO)5CH3

✍ Scribed by M.B. Hall; M.F. Guest; I.H. Hillier

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 134 KB
• Volume: 15
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(72)80380-4

✦ Synopsis

Ab initio SCF MO calculations of the electronic structure of Mn(CO)sH and Mn(CO)sCH 3 predict small (< 0.4 eV) splitting between the metal e and b2 orbitals and lead to a new interpretation of their photoelectron spectra which does not necessitate invoking 7r back-bonding to the -CH 3 group in the case of Mn(CO)sCH 3.

The low energy (He(I)) photoelectron (PE) spectra of a series of simple manganese pentacarbonyl derivatives (Mn(CO)sX) show three main regions [1]. A number of bands corresponding to IP's of less than 11 eV have been interpreted in terms of ionisation from metal e and b 2, and from non-bonding orbitals of the group X (e.g., halogen). A broad band in the region 13-16 eV is attributed to orbitals derived from the 5o and In orbitals of CO, and a weak band at higher energy (~ 18 eV) to arise from orbitals correlating with the 4o orbital of CO. Although the two high energy bands are insensitive to the nature of the group X, the position and intensity of the basis in the low energy region are dependent upon X, and have been used to provide information on the nature of the Mn-X bond in these molecules. In the hydride two bands in this region at 9.0 and 10.6 eV, with intensity ratio approximately 2:1 have been assigned to the e and b 2 metal orbitals respectively, whilst Mn(CO)5CH 3 shows two bands at 8.5 and 9.1 eV with intensity ratio approximately 1:2. Assignment of these bands to the metal b 2 and e orbitals has led to the suggestion that the preferential stabilization of the metal e orbitals arises from back-bonding into n* methyl orbitals, a result at variance with the generally accepted nature of the metal-carbon (methyl) bond in such molecules [2].

We here describe the results of all-electron ab initio SCF MO calculations of the electronic structure of these two molecules which lead to a different inter-