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).