Two unique antiferromagnetic 3D frameworks with unusual CuII4 cluster and alternate CuII4 + CuII1 structural motif tuned by aromatic polycarboxylate coligand

Abstract

Two new 3-amino-1,2,4-triazole (amtrz)-based 3D MOFs, [Cu₄(amtrz)₂(μ₃-OH)₂(btc)₂]_n (1), and [Cu₅(amtrz)₂(H₂O)₂(μ₃-OH)₂(btec)₂]_n (2) (btc³⁻ = 1,3,5-benzenetricarboxylate and btec⁴⁻ = 1,2,4,5-benzenetetracarboxylate), were hydrothermally synthesized and structurally and magnetically characterized. Each cationic [Cu₄(amtrz)₂(μ₃-OH)₂]⁶⁺ cluster in 1 is periodically extended into an infinite 3,6-connected rtl-type topological network via six btc³⁻ ligands. In contrast, analogous Cu^II₄ clusters to 1 and square-planar Cu^II₁ cores in 2 are alternately interlinked through btec⁴⁻ linkers to generate a 3D (4⁴·6²)₂(4⁶·6⁴)₄(4⁸·6⁶·8)₃ framework, which is a scarcely observed higher-dimensional coordination polymer with a Cu^II₄ + Cu^II₁ motif. More interestingly, both the coordination polymers display strong antiferromagnetic couplings up to −154.6 cm⁻¹ due to the favorable multiple heterobridges in the analogous Cu^II₄ component.