Application of photoelectron spectroscopy to molecular properties. Part 61. First gas-phase generation of a cis chloroiminoarsane ClAs=NSiMe3 and a cis chloroiminophosphane ClP=(NSiMe2Bu)-Bu-t. Characterization by photoelectron spectroscopy

Photoelectron spectroscopy-flash vacuum thermolysis in the gas phase allowe d us to synthesize, for the first time, the cis forms of two weakly hindere d, low-coordinate arsenic and phosphorus compounds (ClPn=NSiR3; Pn=P, As), as well as to characterize them by their ionization energies. In order to a ssign the different bands in the PE spectra and to estimate the effect of t he substituents SiMe3 and Cl on the electronic and structural properties of these compounds, we performed calculations using density functional theory (hybrid functional B3LYP) with the basis set 6-311G(d,p). The thermodynami c stabilization of these halogenated systems appears in the important antip eriplanar interactions between the nitrogen lone pair n(N) and the sigma (A sCl)* (or sigma (PCl)*) orbital. For these two compounds, in spite of a poo r 2p pi (N)-3p pi (P)/4p pi (As) overlap, it was observed that the substitu tion of a chlorine atom on the pnictogen (As, P) and a silyl group on nitro gen (negative hyperconjugation) leads to a relatively high ionization energ y for the pi (PnJN) orbital [IE(pi (PnJN))approximate to 10 eV].