ns2 lone pair (E) and structural evolution of trichlorides MCl3E (M = N, P, As, Sb and Bi) series. Stereochemistry and ab initio topology of Cl electron pair triplets

The stereochemistry of ns2 lone pair (E) and structural evolution of trichlorides M*Cl3E family (M* = N, P, As, Sb and Bi) is rationalized with help of electronic structure calculations within the density functional theory (DFT). Using the outcome of electron localization function (ELF) particularly, the analyses of ELF plane projections led to precise the topology of lone pair E of M* title elements together with Cl electron pair triplets. All trichlorides (including bromine and iodine analogues for P) exhibit the same tetrahedral geometry with M* set in Cl3E tetrahedron. Such configuration constitutes a convenient system to follow E evolution versus atomic number Z. The first important feature occurs in the cell volume evolution versus Z which shows a dramatic diminution of 10%, upon going from Sb to Bi. This phenomenon is attributed to relativistic effects. From successive sections of ELF data four essential lone pair characteristics were followed: volume VE and radius rE of so-called volume of influence which tend to their limits after Sb, a fact clearly accelerated according to Bi-E and E-Cl evolutions. The small electronic volume of E centroïd accompanied by its electronic cloud, is firmly attracted by Bi in spite of electron speed acceleration (speed multiplied by Z) therefore influencing the condensation of molecular and cell volumes. A particular attention has been paid to electronic cloud in form of torus generated by Cl 3p6 triplet around central Cl anion. Substitution by Br or I for Cl in phosphorus based compound has allowed to show expected bonding increase with Br. Subsequently with I, relativity plays a role and in PI3E, P and E [P.E] sit in a large Iodine octahedron with E situated in its center. [Display omitted]