Tuning the porosity of lanthanide MOFs with 2,5-pyrazinedicarboxylate and the first in situ hydrothermal carboxyl transfer

Abstract

Reacting lanthanide nitrates with 2,5-pyrazinedicarboxylic acid (2,5-pzdcH₂) and oxalic acid (oxH₂) hydrothermally at 140 °C yielded a series of MOFs with 1D nano-sized channels, [Ln(2,5-pzdc)(ox)_0.5(H₂O)₂]·4.5H₂O (1-Ln; Ln = Nd, Sm, Eu, Gd, Tb, Dy), different from previously reported ultra-microporous [Ln(2,5-pzdc)_1.5(H₂O)₃]·0.5H₂O. While the oxalic acid was replaced by other dicarboxylic acids like terephthalic acid, malonic acid, glutaric acid, or pyrazole-3,5-dicarboxylic acid, obtained was a novel series of 1D polymers, [Ln(2,5-pzdc)_0.5(2,6-pzdc)(H₂O)₃] (2-Ln; Ln = Pr, Sm, Eu, Tb; 2,6-pzdc²⁻ = 2,6-pyrazinedicarboxylate), with 2,6-pzdc²⁻ formed in situ by formal carboxyl transfer. This represents the first example of carboxyl transfer either in coordination compounds or in hydrothermal synthesis. The Eu and Tb complexes in these two series emit strong ligand sensitized f–f luminescence.