Four tetrazolate-based 3D frameworks with diverse subunits directed by inorganic anions and azido coligand: hydro/solvothermal syntheses, crystal structures, and magnetic properties

Abstract

Four tetrazolate (tz⁻)-based magnetic metal–organic frameworks, [Cu₅(μ₃-OH)₂(SO₄)₂(tz)₄]_n (1), {[Cu₃(tz)₄Cl₂]·1.4CH₃OH}_n (2), [Cu(N₃)(tz)]_n (3) and {[Cu₅(tz)₉]Cl·4H₂O}_n (4), were hydro/solvothermally synthesized, and structurally and magnetically characterized. Structural analyses reveal that the former two samples exhibit the same eight-connected topological framework assembled from different subunits. Hourglass-shaped {Cu₅(μ₃-OH)₂}⁸⁺ cores in 1 are periodically extended by mixed μ₃-/μ₄-tz⁻ and μ₄-SO₄²⁻ heterolinkers, while the linear {Cu₃(μ-Cl)₂}⁴⁺ blocks in 2 are repeatedly intersected by ditopic μ₃-tz⁻ connectors. In contrast, the square grid-shaped network of 3 is constructed from linear {Cu(μ_1,1-N₃)}⁺ chains and μ₃-tz⁻ linkers. Complex 4 consists of trigonal-prismatic {Cu₈(μ₃-tz)₆}¹⁰⁺ subunits, which are interlinked into hexagonal microporous architecture by mirror-symmetry μ₄-tz⁻ ligands. Thus, the various subunits of 1–4 are significantly tuned by the co-coordination of the inorganic anions and/or the azido co-ligand, and the backbone extensions are directed by the polytopic tetrazolate ligand. Magnetically, different ordering arrangements of the non-zero magnetizations produced in the local Cu^II₅ and Cu^II₃ subunits eventually lead to unusual ferrimagnetic and canted antiferromagnetic properties in 1 and 2. Strong antiferromagnetic couplings mediated by the mixed tz⁻ and/or azido bridges result in overall S = 0 spin ground-states of 3 and 4.