The use of a semi-flexible bipyrimidyl ligand for the construction of azide-based coordination polymers: structural diversities and magnetic properties

Abstract

Using a semi-flexible quadritopic N-donor ligand, 5,5′-bipyrimidine (bpym), four new azide-based coordination polymers, {[Co₂(bpym)(N₃)₄]·MeCN}_n (1), [Co(bpym)(N₃)₂]_n (2), [Mn(bpym)(N₃)₂]_n (3) and {[Ni₃(bpym)₃(N₃)₆]·2H₂O}_n (4) were synthesized and structurally characterized. With bpym aciting as a planar μ₄-bridging ligand, the resulting compound, 1, comprised a net-to-net 3D framework composed of two grid-like 4⁴-subnets, Co(EE-N₃)₂-based and Co₂(bpym)-based sheets, with a (4,6)-connected (4²·6⁴)(4⁸·6⁶·8)₂ topology. Compound 2 adopted a 3D pillared-layer framework with a pts topology based on six-connected Co(II) centers and four-connected twisted μ₄-bpym ligands, while compound 3 adopted a 3D pillared-layer structure with a bcu topology based on Co(EE-N₃)₂-based 4⁴-layers and two-connected twisted μ₂-bpym pillars. In contrast, compound 4 had a 2D layered structure composed of 1D Ni(II) chains with alternating double EE–N₃ and double EO–N₃ bridges in an EE–EE–EO sequence and two-connected bpym linkers. The magnetic properties of 1–4 were investigated. The findings indicate that 1 showed weak ferromagnetism due to spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, T_C = 12.6 K. In contrast, compound 2 exhibited weak ferromagnetism due to spin-canted antiferromagnetism and antiferromagnetic ordering. In compound 3, antiferromagnetic interactions dominated between the Mn(II) centers through the EE–N₃ bridges. In compound 4, the antiferromagnetic and ferromagnetic interactions were transmitted through double EE–N₃ and double EO–N₃ bridges, respectively, resulting in an AF–AF–F topological ferrimagnetic Ni(II) chain. Furthermore, field-induced magnetic phase transitions of metamagnetism for 2 and 4 were also observed below T_N = 3.6 K and 8.2 K, respectively.