Structural studies on organoarsenic(V) compounds by means of chlorine-35 nuclear quadrupole resonance spectroscopy

Abstract

A ³⁵Cl n.q.r. study of AsPhCl₄, AsPh₂Cl₃, and AsPh₃Cl₂ indicates that they have trigonal-bipyramidal structures in the solid state, with the phenyl groups occupying equatorial positions. The mono- and di-phenyl compounds are thought to be isostructural with the corresponding phosphorus compounds. Trichlorodimethylarsenic(V) and AsMe₃Cl₂ also have the trigonal-bipyramidal form in the solid, with the methyl groups occupying equatorial sites, unlike their phosphorus analogues which are ionic. Attempts to synthesise AsMeCl₄ by chlorination of AsMeCl₂ have led to explosions at low temperatures, and this compound appears to be extremely unstable if it exists at all. 1 : 1 Adducts of the arsenic(v) compounds with Lewis acids, X, such as BCl₃, SbCl₅ or ICl, have been prepared; these showed the expected ionic structure [AsR_nCl_4–n][XCl]. Substituent effects in the cations, where R = Me or Ph, are similar to those in the analogous phosphonium, silane, and germane series, and support the involvement of As(d_π)–Cl(p_π) bonding. Chlorine-35 n.q.r. frequencies are also reported for the compounds Ph₃CCl, SiPh₃Cl, GePh₂Cl₂, and GePh₃Cl.