Magnetic and luminescence properties of Cu(II), Cu(II)_4O_4 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

摘要

The hydrothermal reaction of Cu(NO_3)_2 _ 3H_2O, Cu(ClO_4)_2 _ 6H_2O, or CdSO_4 8/3H_2O with benzene_1,3,5-tricarboxylic acid (H_3btc) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers and networks (MOFs)~1__{[Cu(H_2btc)_2(μ-btre)]) (1), 3,‘{[Cu_4(__5-btc)_2(μ_3_OH)_2(μ_4-btre)] _ 2H_2O) (2), and~ 3__{[Cd_3(__6-btc)_2(μ_4-btre)] . H_2O) (3). The centrosymmetric tetranuclear, chair-shaped or stepped-cubane Cu_4O_4 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 Cu_4 unit with three different magnetic exchange pathways with 2J_1 = 258, 2J_2 = _416, and 2J_3 = 484 cm~(-1) from the magnetic susceptibility measurement between 1.9 and 300 K. For this Cu_4O_4 unit the Eigenvalues associated with the zero field spin Hamiltonian were cal_culated by solving the 16 x 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 fluores_cence at 421 nm upon excitation at 317 nm (not seen in the free btre ligand).