Substituent effects at nitrogen/phosphorus atoms of dialkaline earth metal complexes: Excess electron and large second‐hyperpolarizability

Abstract

AbstractA number of imido‐, amido‐, and phosphido‐bridged dialkaline earth metal (M = Be, Mg, and Ca) complexes and their alkali metal (Li and Na) derivatives have been considered to study the ground state structure and the second‐hyperpolarizability. The calculated ground state geometries contain four‐membered MN(P)MN(P) ring having either planar or butterfly‐like bent structure. The second‐hyperpolarizability has been calculated at the HF and CCSD(T) levels using Sadlej's pol and aug‐pc‐2 basis sets, respectively. The addition of second hydrogen/alkali metal atom on nitrogen/phosphorus (N/P) atom substantially reduces the charge transfer from the alkaline earth metal atoms as the high negative charge on N/P exerts stronger push effect on the outermost electron pair in the “ns” sub‐shell of M. The excess electron density on the alkaline earth metal atoms plays a crucial role in the enhancement of second‐hyperpolarizability. The sum‐over‐state method calculated two‐photon contribution of second‐hyperpolarizability has been found to be significant. The variation of second‐hyperpolarizability has been explained satisfactorily in terms of the TD‐CAMB3LYP calculated spectroscopic properties in the light of two‐state model. The calculated mean second‐hyperpolarizabilities of alkali substituted amido‐ and phosphido‐bridged complexes are in the order of 107 au.