Syntheses, structures, luminescence, NMR spectra and terahertz time-domain spectroscopy of nine lanthanide triflate complexes of tetrakis(O-isopropyl)methylenedisphosphonate with a L:Ln ratio of 4:1

Nine lanthanide complexes with a high L:Ln ratio (4:1), [LnL4](OTf)3 (1–8) (L = tetrakis(O-isopropyl)methylenediphosphonate, OTf = SO3CF3, Ln = Ce, Pr, Nd, Sm, Eu, Gd, Dy, Yb) and [DyL4](OTf)3·DMF (9) have been synthesized through easy and effective methods in air. Each complex was synthesized by the reaction of lanthanide triflate with the L ligand in a solvent mixture (acetonitrile and DMF for 1–8, dichloromethane and DMF for 9). The above complexes, except for complex 9, were synthesized in the presence of 1,10-phenanthroline. The title complexes were characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction analysis, luminescence, NMR spectra and terahertz time-domain spectroscopy (THz-TDS). Structure analysis shows that complexes 1–9 consist of one cation [LnL4]3+ and three triflate anions OTf-. Complexes 1–8 crystallized in the orthorhombic system, space group Pbcn, whereas complex 9 belongs to the space group I222. The cationic [LnL4]3+ fragments in complexes 1–8 are self-assembled to construct 2D layers with a (8·2·8·4) net topology by hydrogen bonding interactions. The OTf− cations in 9 are attached directly to the [DyL4]3+ cations to form a 2-fold hydrogen-bonded three-dimensional (3D) cage structure framework. Solid luminescence of complex 5 displays the characteristic bands of Eu3+, due to a long emission lifetime (4.04 ms of 5D0) and high absolute emission quantum yield (53.30%). Terahertz (THz) time-domain spectroscopy of the complexes was also studied.