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

Using a semi-flexible quadritopic N-donor ligand, 5,5-bipyrimidine (bpym), four new azide-based coordination polymers, {[Co-2(bpym)(N-3)(4)]<bold>MeCN</bold>}(n) (1), [Co(bpym)(N-3)(2)](n) (2), [Mn(bpym)(N-3)(2)](n) (3) and {[Ni-3(bpym)(3)(N-3)(6)]2H(2)O}(n) (4) were synthesized and structurally characterized. With bpym aciting as a planar (4)-bridging ligand, the resulting compound, 1, comprised a net-to-net 3D framework composed of two grid-like 4(4)-subnets, Co(EE-N-3)(2)-based and Co-2(bpym)-based sheets, with a (4,6)-connected (4(2)6(4))(4(8)6(6)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 (4)-bpym ligands, while compound 3 adopted a 3D pillared-layer structure with a bcu topology based on Co(EE-N-3)(2)-based 4(4)-layers and two-connected twisted (2)-bpym pillars. In contrast, compound 4 had a 2D layered structure composed of 1D Ni(ii) chains with alternating double EE-N-3 and double EO-N-3 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-N-3 bridges. In compound 4, the antiferromagnetic and ferromagnetic interactions were transmitted through double EE-N-3 and double EO-N-3 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.