The methyl, silyl and germyl esters of the pseudo-halogen acids. A comparison of structural data from experimental and ab initio studies

Abstract

Equilibrium structures have been sought for the methyl, silyl and germyl esters of HN 3, HNCO, HNCS and HNCSe, at the SCF and SCF+MP2 levels, with a triple zeta valence + polarisation basis set. For some of the molecules, SCF calculations yield linear heavy-atom skeleta, which are corrected to non-linear structures at the MP2 correlated level; the germyl series require higher-order correlation. In all of these studies the threefold axis of the H 3M group (M = C, Si, Ge) was allowed to deviate from the MN bond axis; the direction was towards a more linear system. The barrier heights between equilibrium and the linear form are: MeN 3 83.57, MeNCO 10.68, MeNCS 4.27 and MeNCSe 4.76 kJ mol −1.