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Diradical Character and Second Hyperpolarizability of Alkaline Earth Metal Inverse Sandwich Complexes Involving Cyclopentadienyl and Cyclooctatetraene Ligands
Author(s) -
Takamuku Shota,
Nakano Masayoshi
Publication year - 2018
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201800267
Subject(s) - chemistry , hyperpolarizability , diradical , metal , alkaline earth metal , antiaromaticity , cyclooctatetraene , computational chemistry , inorganic chemistry , crystallography , molecule , aromaticity , organic chemistry , singlet state , polarizability , physics , atomic physics , excited state
Using strong‐correlated quantum chemical calculations, we have revealed the relationship between diradical character y and second hyperpolarizability γ [third‐order nonlinear optical (NLO) property] in alkaline earth metal inverse sandwich complexes, which have Mg or Ca atoms as an alkaline earth metal and a four‐ or eight‐membered ring as an organic ligand ( 4‐Mg , 4‐Ca , 8‐Mg , and 8‐Ca ). Through detailed analysis of diradical character with the valence configuration interaction (VCI) model, we have found that the higher period metal leads to a larger metal–metal distance with larger y value 0.8–0.9, while a larger ring size of organic ligand leads to smaller diradical character values due to the larger transfer integral (smaller distance) between metals. These features are explained by orbital diagrams and VCI analysis. Indeed, it is found that 8‐Ca has the largest γ value, which is 4.94 times as large as that of the system with the smallest γ value ( 8‐Mg ). From these results, we obtain a design guideline for efficient third‐order NLO systems based on alkaline earth metal inverse sandwich complexes: a combination of alkaline earth metal with a higher period number and larger organic antiaromatic (4 n π) ring tends to enhance the γ value due to the larger metal–metal distance with keeping an intermediate y value.