A Quantum Chemical Study of the Structure, Bonding Characteristics and Nonlinear Optical Properties of Aryloxido and Salicylaldehydo Derivatives of [XW 5 O 18 ] 3– (X = Zr or Ti)

The bonding characteristics, first hyperpolarizabilities, and origin of the nonlinear optical (NLO) properties of aryloxido and salicylaldehydo derivatives of [XW 5 O 18 ] 3– (X = Zr or Ti) have been investigated using density functional theory (DFT). The flexible bonding behavior of the linkage oxygen (O L ) atom attracted our attention initially, and NBO analysis revealed that there aret two different kinds of π‐interactions involving the O L atom in these systems. In two aryloxido derivatives (systems 1 and 2 ), O L –metal π‐interactions are largely O L –M p‐d in character, whereas in the salicylaldehydo derivatives (system 3 ) we observed another kind of π‐interaction, namely O L –C p‐p π‐bonding. The differences in molecular composition in our studied systems are very slight. However, the β 0 values differ significantly. Thus, system 3 has the largest β 0 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)