Three copper(II) 4-amino-1,2,4-triazole complexes containing differently deprotonated forms of 1,3,5-benzenetricarboxylic acid: Synthesis, structures and magnetism

Three new Cu-II cluster-based magnetic complexes with the same components but different structures and magnetic behavior, [Cu-4(atr)(2)(mu(3)-OH)(2)(btc)(2)](n), (1), ([Cu-3(atr)(6)(H2O)(2)(H(2)btc)(2)]center dot 4H(2)btc center dot 11H(2)O-DMF}(n) (2), and [Cu-3(atr)(6)(Hbtc)(2)(H(2)btc)(2)]center dot 2H(2)O (3) (atr = 4-amino-1,2,4-triazole and H(3)btc = 1,3,5-benzenetricarboxylic acid), were synthesized by varying the preparation methods and fully characterized. Significantly due to the deprotonation extent-dependent binding modes of the aromatic tricarboxylic acid coligand, the former two complexes exhibit polymeric structures with a butterfly-shaped Cu% cluster-based rtl-type framework for 1 and a linear Cu-3(II) subunit-derived coplanar layer for 2, and the last one is a discrete linear Cu-3(II) entity blocked by the terminal tricarboxylate groups. The cooperative antiferromagnetic and ferromagnetic nearest-neighbor interactions mediated by the differently four-fold heterobridges in the local Cu-3(II) cluster result in an S = 0 ground state of 1. Instead, the central Cu-II ion in the linear Cu-3(II) subunit is antiferromagnetically coupled with its two external ones through triple mu-kappa(2)N1:N2-atr homobridges to lead to an S = 1/2 ground state of 2 and 3. (C) 2012 Elsevier Ltd. All rights reserved.