New triplet silylenes M–Si–M′–X along with some unusual cyclic forms (M = Li, Na, and K; M′ = Be, Mg, and Ca; X = F, Cl, and Br)

Abstract

Comparison of 54 M–Si–M′ –X species is carried out using quantum mechanical ab initio and DFT computations at B3LYP/6-311++G**, QCISD(T)/6-311++G**, and CCSD(T)/6-311++G** levels of theory (M = Li, Na, K; M′ = Be, Mg, Ca, and X = F, Cl, Br). All triplet species with M = K appear more linear than their corresponding ones with Li and Na. The electronegativity reactivity descriptor for each halogen (X = F, Cl, Br) is used as a tool to evaluate the interrelated properties of these silylenes. Stability, assumed as singlet–triplet energy difference (∆ES−T ) for each series depends on the substituent’s electropositivity, analyzed by applying appropriate isodesmic reactions. Stability of triplet M–Si–M′ –X silylenes increases as functions of electropositivity of α-substituents and of β -substituents. The purpose of the present work was therefore to assess the influence of different di-alkaline metals with different β -substituents on the singlet–triplet energy gaps.