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

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 H 2 PBP(Me), H 2 PBP(Ph), H 2 BBP(Ph), and one new ligand H 3 TPBTP (Me), in conjunction with Cu 2 + cations. These coordination polymers were characterized with single crystal Xray 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 Cu 2 + was found to have a negligible influence on the size of the direct or indirect band gap.