Intermolecular interactions, photocatalysis and THz-TDS interrelationships for lanthanide phosphine oxide complexes based on {PW₁₂}

A series of rare earth complexes containing (α-PW₁₂O₄₀)^3- and PO ligand are synthesized by water bath in 70 °C, [Ln(OPPh₃)₄(H₂O)₃](PW₁₂O₄₀)·4CH₃CN (Ln = La, Pr, Nd, Sm, Gd, Tb, Ho 1-7) (OPPh₃ = Triphenylphosphine oxide, {PW₁₂} = phosphotungstic acid). The precise structures are confirmed by X-ray single crystal diffraction and the result shows all complexes are isostructural. Complexes 1-7 are fully characterized by PXRD, FT-IR, TGA, UV diffuse reflectance spectra and terahertz time-domain spectroscopy (THz-TDS). Complex 3 exhibits the highest photocatalytic degradation efficiency for methylene blue (MB) in this series of complexes. The experimental results showed that the photodegradation efficiency can remain constant at the level of 95% after five consecutive cycles. The photocatalytic reaction kinetics and mechanism of complexes were investigated. Additionally, complexes also exhibit photocatalytic hydrogen evolution activity. THz-TDS was used to characterize the complexes and its raw materials, the characteristic peaks of OPPh₃ (broad peak at 1.20 THz) and phosphotungstic acid (sharp peaks at 0.23, 0.32 THz) were obtained.