Double coned inverse sandwich complexes [M-(η4-C4H4)-M′] of Gr-IA and Gr-IIA Metals: theoretical study of electronic of structure and second hyperpolarizability

Double coned inverse sandwich complexes of Gr-IA and Gr-IIA metals have been considered for the theoretical study of electronic structure and second hyperpolarizability by employing density functional theory methods for different exchange and correlation functionals. For the investigated metal complexes the 6-311++G(d,p) basis set can give reliable values of NLO property. The chosen complexes are found to be thermally stable with respect to the dissociation into neutral fragments. Interesting charge transfer interaction has been noted. The replacement of a lighter metal atom with a heavier one leads to the significant enhancement of the longitudinal component of second hyperpolarizability. The relatively much stronger enhancement of second hyperpolarizability has been noted for the alkaline earth metal complexes compared to that of alkali metals. The emergence of second hyperpolarizability of alkali/alkaline earth metal inverse sandwich complexes can be explained qualitatively in terms of the two-state model. The largest magnitude of second hyperpolarizability (~107 au) has been predicted for the Ca-C4H4-Ca complex which may be ascribed to the smallest transition energy and the highest transition moment associated with the most intense linear transition.