Lanthanide contraction and chelating effect on a new family of lanthanide complexes with tetrakis(O-isopropyl)methyle-nediphosphonate: synthesis, structures and terahertz time-domain spectroscopy

Sixteen lanthanide–diphosphate complexes [LnL2(H2O)4Cl]Cl2 (Ln = La3+ for 1, Ln = Ce3+ for 2), [LnL2(H2O)4]Cl3·6H2O (Ln = Nd3+ for 3, Ln = Sm3+ for 4, Ln = Eu3+ for 5, Ln = Gd3+ for 6, Ln = Tb3+ for 7, Ln = Dy3+ for 8, Ln = Er3+ for 9), {[LaL2(H2O)4Cl]Cl2}2 (10), [PrL2(OH)2(H2O)Cl] [PrL2(H2O)4Cl]Cl2 (11), [LaL2(H2O)5Cl]Cl2·2H2O (12), [YbL2(H2O)3Cl]Cl2·H2O (13), [NdL2(H2O)3Cl]Cl2·3H2O (14), [HoL2(H2O)Cl2]Cl·H2O (15), [Sc2L2(H2O)4(OH)2]Cl4·4H2O·2CH3OH (16) (L = tetrakis(O-isopropyl)methylenediphosphonate) have been synthesized by the reaction of lanthanide chlorides and L ligand in the solvent of acetonitrile (with ethanol or DMF) at room temperature. The title complexes were characterized by IR, elemental analysis, single-crystal X-ray diffraction analysis, thermal analysis, 1HNMR and 31PNMR spectroscopy. Complexes 1–15 are mononuclear complexes and complex 16 is a binuclear cluster complex. Complex 12 is the intermediate of complex 1. Complexes 11–13 display a one-dimensional chain formed by hydrogen bonds and the structures of complexes 14, 16 can be simplified as two-dimensional mesh 63 topology formed by hydrogen bonds. In those lanthanide complexes, the lanthanide ion with an atomic number smaller than Pr element tends to form a nine-coordinated structure and that with the atomic number larger than Pr element tends to form an eight or lower number-coordinated structure. Pr element has two kinds of coordination situations, with coordination numbers of nine or eight. The terahertz (THz) time-domain spectra of these complexes were also studied.