Topological and magnetic regulation in three cobalt(ii) coordination polymers constructed using a mixed bipyrimidine–tetracarboxylate strategy†

Coordination compounds with slow magnetic relaxation are of great interest due to their magnetic bistability. Herein, three cobalt(II) coordination polymers, formulated as {[Co₂(btca)(bpym)]·4H₂O}_n (1) and {[Co₂(btca)(bpym)]·2DMF·2H₂O}_n (2), {[Co₂(H₂btca)₂(bpym)]}_n (3) (H₄btca = 1,2,4,5-benzenetetracarboxylic acid; bpym = 2,2′-bipyrimidine), were solvothermally synthesized and magnetically characterized. Single-crystal structural analyses reveal that compounds 1 and 2 are Co²⁺ dimer-based one-dimensional (1D) and 2D coordination polymers, respectively, while compound 3 is a Co²⁺ chain-based 2D coordination polymer with a new topology. The Co²⁺ dimers and chains in these compounds are well magnetically isolated due to the bulk tetracarboxylic linker. Magnetic studies reveal that antiferromagnetic interactions exist between the Co²⁺ ions bridged by the bpym ligand. For 1, no relaxation behavior can be detected, suggesting the paramagnetic behavior of 1. Interestingly, alternating current (AC) magnetic measurements observed slow magnetic relaxation under a 1000 Oe field for 2 and 3. These results provide not only three cobalt(II) coordination polymers with varying topology and magnetic behaviors but also a pyrimidine–tetracarboxylic ligand platform for designing new slow magnetic relaxing coordination polymers.