Hydrothermal synthesis of dimeric lanthanide compounds: X-ray structure, magnetic study and heterogeneous catalytic epoxidation of olefins

Abstract

A series of dimeric lanthanide carboxylato complexes [La(5-Br-NIC) 3(H 2O) 2] 2·H 2O ( 1); [Gd(5-Br-NIC) 3(H 2O) 2] 2 ( 2), [5-Br-NIC = 5-bromonicotinate] and [Sm(NIC) 3(H 2O) 2] 2 ( 3) [NIC = nicotinate], have been hydrothermally synthesized and structurally characterized by single crystal X-ray analysis. Complexes 1, 2 and 3 are of similar structure and consist of a basic unit [La(carboxylato) 3(H 2O) 2] 2. In compound 1 lanthanide cation is surrounded by one chelating 5-bromo-nicotinato ligand, two bridging oxygen atoms from 5-bromo-nicotinato and two water molecules, in which each La(III) ion is nine coordinated in a tricapped prismatic geometry. However, in compounds 2 and 3 four carboxylate groups link a pair of lanthanide atoms in the O,O′-bridging mode to generate a paddle-wheel-like centrosymmetric dimer. All the compounds exhibit excellent catalytic performance in olefin epoxidation reaction. The variable temperature magnetic susceptibility measurements showed that the magnetic interaction in [Gd(5-Br-NIC) 3(H 2O) 2] 2 ( 2), is antiferromagnetic ( J = −0.048 cm −1), while compound [Sm(NIC) 3(H 2O) 2] 2 ( 3), showed a complicated low-temperature magnetic property.