Ab initio calculation of the inversion barrier in the germyl radical

Abstract

Equilibrium geometry, vibrational frequencies and inversion barrier of the GeH3 radical have been calculated using ab initio molecular orbital methods at both the SCF and correlated levels. At the SCF level, the effect of several small and medium size basis sets of Ge on these properties are studied systematically. Electron correlation corrections as incorporated via fourth-order unrestricted Moller-Ptesset perturbation theory in conjunction with large Gaussian basis sets were found to reduce the GeH3 inversion barrier appreciably relative to the UHF values. The final barrier height of 4.5 kcal/mol can be compared with a recent estimate of 4.4 kcal/mol inferred from the REMPI study.

CH3• Is Planar Due to H−H Steric Repulsion. Theoretical Study of MH3• and MH3Cl (M = C, Si, Ge, Sn)

“…Our results agree well with most of the available literature data (Tables and ). − At the Hartree−Fock level, 8b,10d the H−M−H angle β (=120, 110.9, 110.7, and 109.3°; Table ) decreases again along CH 3 • , SiH 3 • , GeH 3 • , and SnH 3 • , but it is slightly more pyramidal than ours at NL-SCF/TZ2P. Similar results were also obtained at the LSD level,8a but here SiH 3 • (β = 111.6°) is slightly more pyramidal than GeH 3 • (β = 113°). The most accurate ab initio studies available (CISD and CASSCF) yield again an SiH 3 • (β = 111.1 or 112.6°) 9f,10e which is less pyramidal than GeH 3 • (β = 110.7°) 9d.…”

“…The MH 3 • radical appears naturally, namely as a building block, in the investigation of the MH 3 −X bond. Furthermore, the MH 3 • series displays a trend which is interesting by itself: the degree of pyramidalization as well as the height of the inversion barrier increases when M is running down in group 14, starting with the flat D 3 h symmetric methyl radical (Chart ). − Similar trends are known for the closed-shell group 15 (AH 3 ) and group 16 hydrides (AH 2 ) − as well as for the allylic CH 2 CHMH 2 - anions where M is a group 14 atom . This is generally explained in MO theoretical terms through the operation of a second-order Jahn−Teller effect (Scheme ): 11,13 (1) the mixing between the nonbonding n p z SOMO and the M−H antibonding LUMO stabilizes and pyramidalizes MH 3 • ; (2) this effect becomes stronger for the heavier (more electropositive and diffuse) central atoms M, because the SOMO−LUMO gap becomes smaller due to the higher energy of the n p z SOMO and the less M−H antibonding nature of the LUMO; (3) the Jahn−Teller effect is opposed by the rising energy of the 1e 1 orbitals which is ascribed to the loss of M−H bonding overlap; (4) thus, only CH 3 • remains planar because the Jahn−Teller effect is not strong enough in this case to outweigh the 1e 1 destabilization.…”

“…i IR (inferred using two assumed forms of potential function): ref b. j UHF/6-31G*: ref b. k CASSCF/MRSDCI: ref d.…”

Theoretical design of the biradical character in 1,3-diphosphacyclobutanediyl and homologous structures

“…40 This might change for the higher homologues in the series where the unpaired electrons are located at the silicon or germanium centers and pyramidalization at these atomic centers is to be expected. 41,42 Whether parent 1 possesses a closed shell system, with c 1 c c 2 , or is biradical in nature, with c 1 E c 2 , depends on the ability of the neighbouring phosphorus atoms to p-overlap with the p-orbitals at the carbon centers. Two extreme cases can be recognized: (a) the phosphorus atoms are strongly pyramidalized, the destabilizing interaction of the phosphorus lone pairs will be small, the HOMO is energetically close to the LUMO and a biradical nature prevails.…”