In situ hydrolysis of a carbophosphazene ligand leads to one-dimensional lanthanide coordination polymers. Synthesis, structure and dynamic magnetic studies

Abstract

An in situ hydrolysis of the P–Cl bonds of the carbophosphazene [{NC(NMe₂)}₂{NPCl₂}] (L^PCl₂) in the presence of hydrated lanthanide(III) nitrates in a dichloromethane and methanol (2 : 1) solvent mixture afforded a series of novel 1D coordination polymers: [{Ln(L^HPO₂)₃(NO₃)₂(CH₃OH)(H₂O)} (Cl)]_n {where Ln(III) = Gd (1), Tb (2), Dy (3), or Er (4) and L^HPO₂ is the hydrolyzed carbophosphazene (L^PCl₂) ligand}. X-ray crystallographic analysis revealed that complexes 1–4 are isostructural and crystallized in the monoclinic crystal system having P2₁/c space group. The coordination polymers are formed because of the involvement of the geminal P(O)(OH) moieties of the carbophosphazene ligand. Each lanthanide(III) ion is 9-coordinate (9O) in a distorted muffin geometry. Magnetic measurements revealed that both Dy^III and Er^III analogues exhibit field-induced single-molecule magnet (SMM) behavior at 0.8 kOe and 2.2 k Oe, respectively. At such dc fields, the dynamic magnetic susceptibility displays complex behavior with a triple magnetic relaxation contribution for 3, while two contributions were identified for 4. The observed static and dynamic magnetic behavior for complexes 1–4 were further rationalized with the aid of BS-DFT and CASSCF/SO-RASSI/SINGLE_ANISO calculations.