Crystal structures and solid-state CPMAS 13C NMR correlations in luminescent zinc(II) and cadmium(II) mixed-ligand coordination polymers constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate

Abstract

The hydrothermal reaction of M(NO₃)₂·4H₂O (M = Zn and Cd) with benzene-1,4-dicarboxylic acid (H₂bdc) or benzene-1,3-dicarboxylic acid (H₂ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) ³_∞{[Zn₂(μ₂-bdc)₂(μ₄-btre)]} (1), ³_∞{[Cd₂(μ₄-bdc)(μ₄-btre)₂](NO₃)₂·H₂O} (2) and ²_∞{[Zn₂(μ₃-ip)₂(μ₂-btre)(H₂O)₂]·2H₂O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-state cross-polarization (CP) magic-angle-spinning (MAS) ¹³C NMR and thermoanalysis, feature 3D metal–organic frameworks for 1 and 2 and 2D double layers which are connected through hydrogen bonds from the aqua ligands for 3. The CPMAS ¹³C NMR spectra picture the symmetry-independent (unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zinc and cadmium coordination polymers 1–3 show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).