Ligand-deprotonation induced structural diversity in a ternary CuII-triazole-tetracarboxylate self-assembly system: Synthesis, crystal structures, and magnetic behavior

Abstract

Four ligand-deprotonation induced coordination polymers, {[Cu₄(atr)₄(H₂O)₂(btec)₂]·2.5H₂O}_n (1), {[Cu₃(atr)₄(H₂O)₂(μ₃-OH)(Hbtec)]·2ClO₄·2H₂O}_n (2), [Cu(atr)₂(H₂O)(H₂btec)]_n (3), and [Cu(atr)₂(H₂O)₂(H₂btec)]_n (4) (atr = 4-amino-1,2,4-triazole and H₄btec = 1,2,4,5-benzenetetracarboxylic acid), were obtained by delicate tuning of the pH value of the reactant mixture. All compounds have been structurally and magnetically characterized. The competitive bridging roles of the two different ligands as well as the degree of deprotonation of the aromatic tetracarboxylic ligand resulted in the formation of four different networks: a coplanar Cu^II₄ cluster-based 3D framework for 1, triangular Cu^II₃-core-derived 2D layers for 2, and H₂btec²⁻-bridged 1D zig-zag or linear chains for 3 and 4, respectively. Magnetic measurements reveal antiferromagnetic couplings with variable strength ranging from −188.9 to −0.712 cm⁻¹ within the isolated Cu^II₄, Cu^II₃, and H₂btec²⁻-bridged Cu^II nodes in 1–4. These couplings are essentially determined by the spatial orientation and coordination characteristics of the homo- and heterobridges between the adjacent spin carriers.