Triazolate-based 3D frameworks and a 2D layer with centrosymmetric CuII7, CuII5, CuII4 clusters and tunable interlayer/interchain compactness: hydrothermal syntheses, crystal structures and magnetic properties

Abstract

Four 1,2,3-triazolate-based coordination polymers (CPs) with varied dimensionality, different nuclearity numbers and core topologies, [Cu₄(μ-OH)(μ₃-OH)(ta)₂(btec)]_n (1), {[Cu₆(μ₃-OH)₂(ta)₈(tp)]·2.5H₂O}_n (2), {[Cu₅(μ₃-OH)₂(ta)₄(ip)₂]·2H₂O}_n (3) and {[Cu₅(μ-OH)₂(μ₃-OH)₂(ta)₂(pa)₂]·2H₂O}_n (4) (ta = 1,2,3-triazolate, btec = 1,2,4,5-benzenetetracarboxylate, tp = terephthalate, ip = isophthalate and pa = phthalate), were hydrothermally synthesized by varying the numbers and positions of the carboxylate group appended on the phenyl tether, and structurally and magnetically characterized. The former three entities are three-dimensional (3D) robust frameworks with a (4⁴·6²)(4¹¹·6⁵)₂(4¹³·6¹⁰·8⁵) topological net containing centrosymmetric Cu^II₇ clusters, square-planar Cu^II₁ cores and tetratopic btec⁴⁻ linkers for 1, a pillared-layered structure consisting of Cu^II₅ + Cu^II₁-based coplanar layers and ditopic tp²⁻ pillars for 2 as well as a microporous architecture derived from Cu^II₅ clusters and directional ip²⁻ connectors for 3. In contrast, complex 4 exhibits an undulated two-dimensional (2D) layer with alternating Cu^II₄ + Cu^II₁ chains interconnected by anionic pa²⁻ connectors. Crystallographically, the increment of the local nuclearity from Cu^II₄ up to Cu^II₇ in 1–4 benefits greatly from the synergistic co-coordination of the hydroxyl group and the coplanar ta⁻ ligand towards the metal ion, and the interlayer/interchain compactness is significantly tuned by the position isomerism of the dicarboxylate moieties. Due to the antiferromagnetic coupling in the local clusters and the asymmetric superexchange by μ₃-ta⁻ mediator, these complexes exhibit different spin ground states (paramagnetic S = 1 and 1/2, ferrimagnetic S = 1/2 as well as spin canting) at low temperatures, which are informative for polynuclear-based magnetic materials.