Structure and Photoelectron Spectrum of Tetramethyldiarsane

Abstract

A systematic theoretical investigation of tetramethyldiarsane is presented to help understand its structure and photoelectron spectrum. Full potential energy curve along the C-As-As-C torsion was calculated at the Hartree-Fock (HF) level, and complete geometry optimizations were performed at HF, second-order Many-Body Perturbation Theory (MBPT(2)), and Coupled-Cluster Singles and Doubles (CCSD) levels of theory. Two conformers, anti and gauche, have been found in accordance with the experimental observations. The calculated geometries are in good agreement with the electron diffraction results. Ionization energies were computed by the Equation-of-Motion Coupled-Cluster (EOM-CC) method. The calculations predict a substantial lone-pair splitting for both conformers which contradicts the original assignment of the photoelectron spectrum by Cowley et al. According to the new assignment, the first and third bands belong to the lone pairs of the anti rotamer, the second band is attributed to the n + lone-pair combination in the gauche conformer, while the peak of the n combination is merged with the intense first band previously ascribed exclusively to the anti rotamer. The conformer ratios calculated from the present assignment of the photoelectron spectrum are in good agreement with the quantum-chemical results. Since our assignment contradicts the theoretical reasoning, which the original assignment was based on, a new explanation is presented. We find that the s-character of the lone-pair orbitals increases in the order of nitrogen, phosphorus, arsenic, and antimony which explains not only the increasing pyramidalization of the Me 2 E moiety but also the increasing splitting of the energy of the lone-pair MOs.

Photoelectron Spectra of Phosphine Analogue Complexes of Co(CO)3NO and CpMn(CO)3

“…However, unlike group 16 lone pairs, the lone-pair ionization energy does not decrease significantly from P to Sb; therefore, there is no better energy match between the metal orbitals and the lone pair. The explanation of this comes from the finding that the s character of the lone pair orbitals increases significantly from P to Sb, , stabilizing the lone pair orbitals on the ligands and leading to reduced overlap with the metal d orbitals.…”

Element−Element Bonds. IX.1 Structures of Tetrakis(trifluoromethyl)diphosphane and -diarsane: Experimental and Theoretical Investigations

“…Calculations on the tetramethyl derivatives give similar results with respect to their conformational preferences (Table 7): the hydrazine 1b with its almost pure p-type lone pairs adopts the gauche conformation, whereas the corresponding diphosphane 2b and diarsane 3b prefer the trans conformation as described already by Szta ´ray and Szalay. 55 NBO analyses on the gauche conformers of 1b, 2b, and 3b result in s characters of the lone The energies of the gauche conformers are set to zero. c The C2 symmetrical conformer is characterized as an extremely flat transition state with an imaginary frequency.…”

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

“…The relative instability of cis-1 is mainly due to a steric repulsion between the two phenyl groups disposed at the same side with respect to the naphthalene plane. In addition, a repulsive interaction is also expected between two lone pairs on the phosphorus atoms of cis-1, although it is reported to be faint owing to a significant s character of the lone pair on the phosphorus [13,14]. Such steric and lone pair repulsions are absent in trans-1, as is evident in Fig.…”

“…Calcd for C 32 H 16 (m,2H,3,8.17 (d,J HH = 8.2 Hz, 2H, 4,5-naph). 13 3.4. Synthesis of (OC) 5 Cr(l-trans-1)Cr(CO) 5 (2c) 2c was prepared as described above for 2a, using Cr(CO) 6 .…”

“…1 H NMR (d, in CDCl 3 ): 6.57 (m, 4H, m-Ph), 6.93 (t, J HH = 7.8, J PH = 7.8, 4H, o-Ph), 7.14 (2H p-Ph), 7.84 (m,2H,2,7.98 (m,2H,3,8.13 (d,J HH = 8.2 Hz,2H,4,. 13 3.10. Synthesis of (OC) 5 Mo(l-cis-1)Mo(CO) 5 (cis-2b) and (OC) 5 Cr(l-cis-1)Cr(CO) 5 (cis-2c) cis-2b and cis-2c were prepared as described above for cis-2a.…”