Electron localization function (ELF) study on intramolecular delocalization of the electron density in the H2X, H2CX and XO2 (X = O, S, Se, Te) molecules: Role of the atomic core and lone pair

A nature of the chemical bond and delocalization of the electron density in the H2X, H2CX and XO2 (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[ΩI, Ωj], which reveals a correlation between the electron density distributions in basins ΩI and Ωj is analyzed. Going from the oxygen to tellurium atom one observes gradual decrease of the electron delocalization between the lone pairs of chalcogen: V1(X) ↔ V2(X) and increase of delocalization between the lone pairs and core basin V1(X) ↔ C(X) ↔ V2(X). In H2O, H2S and H2CO, H2CS dominates an exchange between lone electron pairs: cov[V1(X), V2(X)] > cov[Vi = 1,2(X), C(X)], meanwhile for Se and Te containing molecules prevails a delocalization with core region: cov[Vi = 1,2(X), C(X)] > cov[V1(X), V2(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 O3 molecule reveals dominating delocalization between the lone pair V(O) and electron density of the O–Oi = 1,2 bonds: V(O,Oi = 1) ↔ V(O) ↔ V(O, Oi = 2), meanwhile an exchange between the chalcogen core C(X) and lone pair V(X): C(X) ↔ V(X) prevails in SO2, SeO2 and TeO2.