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

Abstract

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.