Takako Kudo

Theoretical study on the dimerization of silanone and the properties of the polymeric products (H2SiO)n (n = 2, 3, and 4). Comparison with dimers (H2SiS)2 and (H2CO)2

Calculs ab initio de la surface de potentiel de dimerisation de H 2 Si=O. Comparaison de structure, frequences de vibration et energie de dimerisation du dimere cyclique avec les proprietes correspondantes de (H 2 SiS) 2 et (H 2 CO) 2

Hexasilabenzene (Si6H6). Is the benzene‐like D6h structure stable?

Ab initio molecular orbital theory has been applied to the structure of hexasilabenzene (Si6H6), the silicon analog of benzene (C6H6). The minimum energy structure is calculated to be planar with D6h symmetry, as in the case of benzene, with flexible basis sets at the Hartree–Fock level of theory. Through the estimation of a significant effect of electron correlation, however, a chair‐like puckered structure of D3d symmetry is proposed for hexasilabenzene. The preference of D3d over D6h is explained in terms of some ‘‘multiradical’’ character of the skeletal bonding (i.e., the antiferromagnetic‐like localization of electrons onto each Si).

Theoretical study of a silylene-oxygen adduct. Is a silanone oxide structure (H2SiOO) kinetically stable in the singlet state?

Abstract In an attempt to reinforce our recent experiments on silylene-oxygen adducts, the structure and kinetic stability of silanone oxide (H 2 SiOO) in the singlet state have been investigated at several levels of theory. It is found that silanone oxide has a non-planar, pyramidal structure and undergoes rapid cyclization to siladioxirane, unlike the corresponding carbon compound (H 2 COO).

Jahn-teller distortions of SiH4+ and Si(CH3)4+

Abstract In view of current interest in silane radical cations, the Jahn-Teller distortions of SiH 4 + and Si(CH 3 ) 4 + to the D 2d , C 3v , C 2v , and C s structures are investigated by means of ab initio calculations with flexible basis sets and electron correlation. The C s structure is found to be the most stable in SiH 4 , as suggested in a recent theoretical study. On the other hand, the C 3v structure is the most stable in Si(CH 3 ) 4 + , unlike the suggestion from the ESR study. This contrasts with the fragile C 3v structure in SiH 4 + . The relative stabilities (kcal/mol) of SiH 4 + and Si(CH 3 ) 4 + decrease in the order C s (0.0) > C 2v (8.5)> C 3v (13.7) > D 2d (27.2) at the MP4 SDTQ/6-31+G(2df, 2p)//MP2/6-31G(d, p)+ZPC level and C 3v (0.0)>C 2v (6.1)>C s (16.3) at MP2/6-31G(d)//HF/6-31G (d)+ZPC level, respectively. In both SiH 4 + and Si(CH 3 ) 4 + , the C 2v structures are not energy minima but transition structures for the rearrangement to the most stable structures. An interesting finding is that Si(CH 3 ) 4 + is much more stable to fragmentation than SiH 4 + .

The GeH4+ radical cation. An ab initio study of its ground-state structure and kinetic stability

Abstract In contrast with previous studies, it is found that the most stable structure of the GeH 4 + radical cation has C s symmetry and the relative stability decreases in the order C s > C 3v > D 2d . In addition no C 2v structure can be a minimum on the potential energy surface of GeH 4 + . The most stable C s structure dissociates relatively easily to GeH 2 + + H 2 rather than to GeH 3 + + H.

MR CI calculations of the low-lying excited states of silanone (H2SiO)

Abstract The low-lying valence and Rydberg excited states of H 2 SiO are calculated with the multiple-reference configuration-interaction (MR CI) method. In order to characterize these excited states, the results are compared with those of H 2 CO.

Features of the H2SiO potential energy surface. Stabilization of a silicon—oxygen double bond

In view of intense current interest in silicon—oxygen double bonds, the singlet potential energy surface of H2SiO has been explored through ab initio calculations, which is found to differ significantly from the H2CO potential energy surface. Also examined are the effects of fluorine substitution on the relative stabilities of H2SiO and its isomers.

THEORETICAL STUDY OF THE AROMATIC AND POLYHEDRAL COMPOUNDS WITH Ge, Sn AND Pb SKELETONS

The properties of the aromatic and polyhedral compounds whose skeletons are made of the heavier group 14 elements such as Ge, Sn, and Pb are investigated by means of ab initio molecular orbital calculations. The aromaticity and structures of the heavier analogues of benzene and its fused benzenoid systems are discussed. Also investigated are the strain energies of the heavier analogues of the polyhedral carbon compounds such as [n]prismane and dodecahedrane. Several interesting properties are predicted. Introduction Carbon compounds have played a central role in organic chemistry. It is currently of considerable interest to replace the skeletal carbons by the heavier homologues in anticipation of new chemical properties, as in recent reviews of the neutral compounds·) and radical cations.) Silicon is the nearest neighbor in group 14. Thus, the properties of silicon skeletons have been extensively investigated from experimental and theoretical points of view.) Much interest is now directed toward the still heavier skeletons. ~) We summarize here our recent theoretical study of aromatic and polyhedral compounds whose skeletons are made of germanium, tin, and lead. Our primary concern is to clarify what is characteristic of these heavier skeletons compared with carbon (or silicon) skeletons. For this purpose, emphasis will be put on the applicability of the important concepts such as aromaticity and stain established well in carbon chemistry. All calculations were carried out with the ab initio effective core potentials (ECPs)) on Ge, Sn, and Pb using the double-zeta (DZ) basis set^) augmented by a set of six d-type polarization functions (d exponents 0.246 for Ge, 0.183 for Sn, and 0.164 for Pb).) The relativistic ECPs were used for Sn and Pb. For carbon and silicon compounds, all-electron calculations were carried out with the split-valence d-polarized 6-31G* basis set.) The effect of electron correlation was incorporated using second-order Moller-Plesset (MP2) perturbation theory.) Aromatic Compounds As well known, benzene (CßHg) is unique with its stability and reactivity. This has been ascribed to the aromatic stabilization due to the cyclic derealization of 6π electrons, as the Hückel

Restricted hartree-fock calculations on CGeH4 and CGeH+5: The properties of a germanium-carbon double bond

Abstract In an attempt to examine the properties of a germanium-carbon double bond, the title species were investigated by ab initio SCF methods. The geometry, proton affinity, and thermodynamic stability of H 2 GeCH 2 are discussed in comparison with previous data on H 2 CCH 2 and H 2 SiCH 2 .

Jahn-Teller distortions in SnH4+ and PbH4+

Abstract As a continuation of our recent studies of the Jahn-Teller distortions in SiH 4 + and GeH 4 + , ab initio calculations including electron correlation have been performed for the heavier analogues, SnH 4 + and PbH 4 + , to clarify the general features from a unified point of view. In contrast with previous studies, it is found that both SnH 4 + and PbH 4 + have C s symmetry in the ground states, as do SiH 4 + and GeH 4 + , and the relative stabilities decrease in the order C s a C 3v D 2d ; no significant minimum is found in C 2v symmetry. Among the radical cations, PbH 4 + shows the strongest tendency to take C s symmetry but readily decomposes to PbH 2 + and H 2 .