Derivative of cyclen with three methylene(phenyl)phosphinic acid pendant arms. Synthesis and crystal structures of its lanthanide complexes

Abstract

A new macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraylmethyltrimethylenetris(phenylphosphinic acid) H3L1 was synthesised and its complexes with lanthanides were prepared. X-Ray analysis of seven Ln complexes (Ln = La, Ce, Nd, Eu, Tb, Er, Yb) shows a formation of dimers [LnL1]2 with phosphinic acid bridges in the solid state. All complexes are isostructural and the coordination polyhedra are formed by four N atoms and four O atoms of phosphinic acid groups. A water molecule is placed near the O4 base. The LnOw distance is strongly dependent on Ln(III), it varies from 2.815(6) A in the La complex to 4.448(10) A in the Yb complex. The 31P NMR studies show formation of a rather complex mixture of isomers in solution. The dimer stability in solution is verified by reaction with triphenylphosphine oxide (tppo) and with pyridine N-oxide and by cyclic voltammetry.