Terminal vs bridge bonding of methylene to metal systems: Al/sub 2/CH/sub 2/ as a model system

Journal Article · Sat Jan 01 04:00:00 EST 1983 · J. Chem. Phys.; (United States)

OSTI ID:6876982

Fox, D J; Schaefer, III, H F

The metal dimer-methylene system M/sub 2/CH/sub 2/ is the simplest which can in principle display both terminal M--M--CH/sub 2/ and bridging M 2 M geometrical structures. Having previously studied the terminal Al--CH, Al--CH/sub 2/, and Al--CH/sub 3/ metal-organic fragment species, the Al/sub 2/CH/sub 2/ system was chosen to allow a competition between the terminal and bridged structures. Nonempirical molecular electronic structure theory was used, with double zeta (DZ) and DZ + polarization basis sets in conjunction with both self-consistent field (SCF) and configuration interaction (CI) methods. Among structures considered, the bridging arrangement, with the Al /sup C/ Al and CH/sub 2/ planes perpendicular to each other, lies lowest energetically. For this structure the Al--Al distance is 3.61 A, the Al--C distance 2.00 A, and the methylene bond angle 105.5/sup 0/. The completely planar structure, found by twisting the methylene group by 90/sup 0/, is predicted to lie 31 kcal higher, but has a much shorter Al--Al distance 3.03 A. The terminal structure lies 46 kcal above the absolute minimum on the energy surface and has r/sub e/(Al--Al) = 2.87 A, r/sub e/(Al--C) = 1.81 A, and a methylene bond angle of 112.2/sup 0/. All of the above structures are closed-shell singlets in their lowest electronic states, but the energies of several triplet species are also discussed. The Al--C bond energy for the terminal structure is 81 kcal, in good agreement with that predicted (77 kcal) earlier by comparable methods for AlCH/sub 2/. However, for the bridging Al/sub 2/CH/sub 2/, the Al/sub 2/ xxx CH/sub 2/ dissociation energy is much larger, 127 kcal. Vibrational frequencies for the bridging and terminal Al/sub 2/CH/sub 2/ species are presented and discussed.

• Research Organization: Department of Chemistry and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
• OSTI ID: 6876982
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 78:1; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALUMINIUM
CHEMICAL BONDS
CONFIGURATION INTERACTION
DIMERS
ELEMENTS
METALS
METHYLENE RADICALS
RADICALS
SELF-CONSISTENT FIELD