Magnetic and luminescence properties of Cu(II), Cu(II)4O4 core, and Cd(II) mixed-ligand metal–organic frameworks constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate

The hydrothermal reaction of Cu(NO3)2 · 3H2O, Cu(ClO4)2 · 6H2O, or CdSO4 · 8/3H2O with benzene-1,3,5-tricarboxylic acid (H3btc) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers and networks (MOFs) 1∞1∞{[Cu(H2btc)2(μ-btre)]} (1), 3∞3∞{[Cu4(μ5-btc)2(μ3-OH)2(μ4-btre)] · 2H2O} (2), and 3∞3∞{[Cd3(μ6-btc)2(μ4-btre)] · H2O} (3). The centrosymmetric tetranuclear, chair-shaped or stepped-cubane Cu4O4 metal building unit in 2 has three different Cu contacts, each involving more than one bridging group. A quasi-butterfly magnetostructural model shows dominant antiferromagnetic interactions in this Cu4 unit with three different magnetic exchange pathways with 2J1 = 258, 2J2 = −416, and 2J3 = 484 cm−1 from the magnetic susceptibility measurement between 1.9 and 300 K. For this Cu4O4 unit the Eigenvalues associated with the zero field spin Hamiltonian were calculated by solving the 16 × 16 matrix in order to obtain here the numerical expression for the magnetic susceptibility. The cadmium-btre framework 3, with bridged Cd strands, shows a strong bluish fluorescence at 421 nm upon excitation at 317 nm (not seen in the free btre ligand).

The tetranuclear Cu4 core has three different Cu contacts, each involving more than one bridging group, and three different magnetic exchange pathways with 2J1 = 258, 2J2 = −416, and 2J3 = 484 cm−1. For this Cu4 unit the Eigenvalues associated with the zero field spin Hamiltonian were calculated by solving the 16 × 16 matrix in order to obtain here the numerical expression for the magnetic susceptibility.Figure optionsDownload as PowerPoint slide