Nanoporous lanthanide metal–organic frameworks as efficient heterogeneous catalysts for the Henry reaction

Abstract

A series of self-assembled lanthanide coordination polymers formulated as [La(L1)₂]_n·1n(DMF)H·3n(DMF) (1), [Ce(L1)₂]_n·1n(DMF)H·2n(DMF) (2), [Sm(L1)₂]_n·1n(HCONH₂)H·2n(HCONH₂) (3), [La(L2)(HL2)(H₂O)(DMF)₂]_n (4) and [Ce(L2)(HL2)(H₂O)(DMF)₂]_n (5) [H₂L1: 2-acetamidoterephthalic acid and H₂L2: 2-benzamidoterephthalic acid] has been synthesized from the reactions of H₂L1 or H₂L2 with different lanthanide salts under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, X-ray single-crystal diffraction, powder X-ray diffraction, thermogravimetry and photoluminescence spectroscopy. X-ray diffraction analyses reveal that frameworks 1–3 have similar types of three-dimensional structures, composed of L1²⁻ ligands and trinuclear lanthanide nodes, in which two crystallographically independent lanthanide atoms are present. Frameworks 4 and 5 are isostructural, featuring a double chain-type one-dimensional coordination polymer which expands to 3D by means of H-bond interactions. These frameworks act as heterogeneous polymeric solid catalysts for the nitroaldol (Henry) reaction of different aldehydes with nitroalkanes, in water, and can be recycled without losing appreciable activity.