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) center dot 3H(2)O, Cu(ClO4)(2) center dot 6H(2)O, or CdSO4 center dot 8/3H(2)O with benzene-1,3,5- tricarboxylic acid (H(3)btc) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers and networks (MOFs) 1(infinity){[Cu(H(2)btc)(2)(mu-btre)]} (1), 3(infinity){[Cu-4(mu(5)-btc)(2)(mu(3)-OH)(2)(mu(4)-btre)] center dot 2H(2)O} (2), and 3(infinity){[Cd-3(mu(6)-btc)(2)(mu(4)-btre)] center dot 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 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 Cu4O4 unit the Eigenvalues associated with the zero field spin Hamiltonian were calculated 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 fluorescence at 421 nm upon excitation at 317 nm (not seen in the free btre ligand). (C) 2008 Elsevier B. V. All rights reserved.