Ligand preferences in ytterbium ions complexation with carboxylate-based metal-organic frameworks

Two coordination polymers of ytterbium were synthesized by employing 4,4′,4″-s-triazine-2,4,6-triyl-tribenzoic acid (H3TATB), 4,4′,4-benzene-1,3,5-triyl-tribenzoic acid (H3BTB), and 3,5-pyridinedicarboxylic acid (3,5-PDC) ligands and were characterized by single-crystal X-ray diffraction analysis. Reaction of ytterbium(III) chloride in the presence of H3BTB and 3,5-PDC ligands gives preferred complexation with the 3,5-PDC ligand, producing [Yb2(3,5-PDC)(ClO4)3][NH(Me)3] (1). However, under exactly the same reaction conditions, reaction of ytterbium(III) chloride in the presence of 3,5-PDC and H3TATB resulted in complexation with H3TATB to form [(CH3)2NH2][Yb4(TATB)4(HCO2)(H2O)2]·3H2O (2). The crystal structure results showed a layered structure for 1 and a metal-organic framework structure for 2. This indicates that the complexation preference of the ytterbium ion is H3TATB ≥ 3,5-PDC ≥ H3BTB. Conversely, the uncomplexed ligand in the metal-organic framework (2) is an auxiliary agent during the synthesis, which shows polytopic linker controls crystal properties, to form suitable crystals for single-crystal structure determination. The prepared coordination compounds were used as heterogeneous catalysts in an oxidation amidation reaction with different aldehydes and benzylamine hydrochloride.