Tuning the bandgap of Cu(II) phosphinate coordination polymers by ligand selection and coordination geometry

Abstract

Five coordination polymers, denoted as ICR-15, ICR-16, ICR-17, ICR-18, and ICR-19, were prepared using three previously reported phosphinic acids, namely H2PBP(Me), H2PBP(Ph), H2BBP(Ph), and one new ligand H3TPBTP(Me), in conjunction with Cu2+ cations. These coordination polymers were characterized with single crystal X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, thermal analysis, and UV–vis spectroscopy. The crystal structures of the coordination polymers were analysed, revealing a variety of coordination environments and distinct structural motifs. Optical band gaps determined from the UV–vis spectra of the coordination polymers range from 2.8 eV to 3.5 eV, corresponding to wide bandgap semiconductors. Interestingly, the coordination geometry of Cu2+ was found to have a negligible influence on the size of the direct or indirect band gap.