A series of 3D lanthanide frameworks constructed from aromatic multi-carboxylate ligand: Structural diversity, luminescence and magnetic properties

Abstract

Reactions of lanthanide(III) nitrates with multi-donor carboxylate ligand in the presence of oxalate anion afforded four new lanthanide coordination polymers with three dimensional (3D) frameworks, namely, {[Ln₂(DPPA)₂(μ₂-C₂O₄)(H₂O)₂]·2H₂O}_n (Ln = Nd (1), Sm (2)) and [Ln₂(HDPPA)₂(DPPA)₂]_n (Ln = Tb (3), Yb (4)), (H₃DPPA = 3-(4-hydroxyl pyridinium-1-yl) phthalic acid and H₂C₂O₄ = oxalic acid). Compounds 1 and 2 are isostructural and isomorphous, featuring oxalate pillared binodal (4,5)-connected porous 3D framework with intersected 1D channels, in which the coordinated and lattice waters are accommodated. The complexes 3 and 4 are also isostructural, but featuring a (4,6)-connected 3D network based on a rectangular window composed of {Ln(HDPPA)}⁺ extended anion chains, further interlinked by DPPA. The Tb(III) analogue exhibits intense characteristic green photoluminescence employing DPPA as an antenna. While Sm(III) compound 2 mainly involves ligand-to-ligand charge transfer. Variable-temperature susceptibility analyses of complexes 1 (Nd), 2 (Sm) and 3 (Tb) revealed that depopulation of the Stark levels together with weak antiferromagnetic interactions between the lanthanide ions lead to a continuous decrease in χ_MT when the samples are cooled from 300 to 2 K.