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A Quantum Chemical Study of the Structure, Bonding Characteristics and Nonlinear Optical Properties of Aryloxido and Salicylaldehydo Derivatives of [XW5O18]3― (X = Zr or Ti)

The bonding characteristics, first hyperpolarizabilities, and origin of the nonlinear optical (NLO) properties of aryloxido and salicylaldehydo derivatives of [XW5O18]3– (X = Zr or Ti) have been investigated using density functional theory (DFT). The flexible bonding behavior of the linkage oxygen (OL) atom attracted our attention initially, and NBO analysis revealed that there aret two different kinds of π-interactions involving the OL atom in these systems. In two aryloxido derivatives (systems 1 and 2), OL–metal π-interactions are largely OL–M p-d in character, whereas in the salicylaldehydo derivatives (system 3) we observed another kind of π-interaction, namely OL–C p-p π-bonding. The differences in molecular composition in our studied systems are very slight. However, the β0 values differ significantly. Thus, system 3 has the largest β0 value(559.27 × 10–30 esu), which is 170 times larger than that of system 1. This variation can be traced to the different electronic transitions and charge-transfer characteristics. The heteropolyanion cluster and organic ligand are both electron-rich groups. A small change in molecular composition or architecture can therefore significantly modify the configuration and overlapping of molecular orbitals, thus causing a “butterfly effect” upon the electronic transitions and charge-transfer characteristics.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)