Two new POM-based compounds modified by lanthanide–Schiff base complexes with interesting NLO properties

Two POM-based lanthanide derivatives, namely {triaqua[2,6-diacetylpyridine bis(semicarbazone)-κ5 O,N,N′,N′′,O′]terbium(III)}-μ-oxido-[tricosa-μ2-oxido-dodecaoxido-μ12-phosphato-dodecamolybdenum(VI)] pentahydrate (1), [Tb(C11H15N7O2)(H2O)3][PMo12O40]·5H2O, and the dysprosium(III) analogue (2), have been isolated successfully by the reaction of Keggin–POM [PMo12O40]3− (abbreviated as PMo12 ), the Ln3+ ion and the Schiff base 2,6-diacetylpyridine bis(semicarbazone) (DAPSC) ligand under hydrothermal conditions. [Ln(DAPSC)(H2O)3][PMo12O40]·5H2O is a PMo12 -supported cluster featuring a lanthanide–Schiff base complex [denoted Ln– L (Schiff base)]. Single-crystal X-ray diffraction analysis reveals that the LnIII ion is in a distorted tricapped trigonal prismatic arrangement, coordinated by six O atoms and three N atoms. Two O atoms and three N atoms are provided by one DAPSC ligand, while the additional O atoms originate from a PMo12 cluster and three water molecules. Hydrogen-bonding interactions between adjacent clusters form an interesting three-dimensional supramolecular structure. The identities of 1 and 2 were characterized by IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction. Interestingly, both compounds possess excellent two-photon absorption (TPA) responses to the third-order nonlinear optics (NLO) (2264 GM for 1 and 941 GM for 2), suggesting that they have potential applications in the field of nonlinear optics (NLO). To our knowledge, 1 and 2 are the first POM-based Ln– L (Schiff base) complexes showing excellent two-photon responses. Meanwhile, the electrochemical properties of both compounds were studied in detail.