Electron localization function (ELF) study on intramolecular delocalization of the electron density in the H 2X, H 2C [dbnd]X and XO 2 (X = O, S, Se, Te) molecules: Role of the atomic core and lone pair

Abstract

A nature of the chemical bond and delocalization of the electron density in the H 2X, H 2C X and XO 2 (X = O, S, Se and Te) molecules is systematically studied by means of the topological analysis of the electron localization function (ELF). The covariance parameter cov[ Ω I , Ω j ], which reveals a correlation between the electron density distributions in basins Ω I and Ω j is analyzed. Going from the oxygen to tellurium atom one observes gradual decrease of the electron delocalization between the lone pairs of chalcogen: V 1(X) ↔ V 2(X) and increase of delocalization between the lone pairs and core basin V 1(X) ↔ C(X) ↔ V 2(X). In H 2O, H 2S and H 2C O, H 2C S dominates an exchange between lone electron pairs: cov[V 1(X), V 2(X)] > cov[V i = 1,2 (X), C(X)], meanwhile for Se and Te containing molecules prevails a delocalization with core region: cov[V i = 1,2 (X), C(X)] > cov[V 1(X), V 2(X)]. It is proposed that this effect is associated with not negligible penetration of d electrons from the outermost shell of the atomic core into valence shell. A study on the O 3 molecule reveals dominating delocalization between the lone pair V(O) and electron density of the O–O i = 1,2 bonds: V(O,O i = 1 ) ↔ V(O) ↔ V(O, O i = 2 ), meanwhile an exchange between the chalcogen core C(X) and lone pair V(X): C(X) ↔ V(X) prevails in SO 2, SeO 2 and TeO 2.