Three rare Co(II)–organic frameworks were synthesized by tuning the relative reactant ratios of Co^II : 2,4-H₂pydc (2,4-H₂pydc = 2,4-pyridinedicarboxylic acid) and introducing different structure-directing amines under hydrothermal conditions. Compound {[Co₃(2,4-pydc)₃(EtOH)(H₂O)₃]·EtOH}_n (1), which was prepared using a 1 : 1 ratio of Co^II : 2,4-H₂pydc, consisted of a tricobalt(II) cluster that was employed to form a two-side-open box and these boxes were further self-assembled into a rare single-walled metal–organic nanotube (MONT). When the ratio was adjusted to 2 : 1 and accompanied with 4,4′-dipyridyl-piperazine (dpyp), the formation of zigzag chains of {[Co₄(2,4-pydc)₄(H₂O)₁₀]}_n (2) with a tetracobalt(II) cluster unit occurred, finally these chains were linked into a 2D sheet with a 4⁴-sql topology. However, compound {[Co(2,4-pydc)₂(H₂O)₂]·[Co(dpyp)(H₂O)₄]}_n (3) was synthesized under similar reaction conditions as for 2 except that triethylamine was added. 3 contained the polymeric chains of {[Co(dpyp)·(H₂O)₄]²⁺}_n and the monocobalt complex [Co(2,4-pydc)₂(H₂O)₂]²⁻, which were cooperatively connected via hydrogen bonding to form a 2D layer with a 4⁴-sql topology. A pseudo-merohedral twinning law was applied to the twin case during the X-ray structural analysis of 2 that facilitated the R₁ value to drop drastically.

A Co₃ cluster-based three-dimensional (3D) framework, [Co₃(4-ptz)₄(N₃)₂(H₂O)₂]·4DMF (1; 4-Hptz = 4-(1H-tetrazol-5-yl)pyridine), exhibits ferromagnetic interactions and slow-magnetic relaxation behavior.

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.

Three new azide-bridged coordination polymers, [M(N₃)(tzbp)]_n (M = Cu, 1·Cu; Mn, 2·Mn; Co, 3·Co), were successfully prepared by introducing a bifunctional tetrazolate/2,2′-bipyridine ligand, 6-(1H-tetrazol-5-yl)-2,2′-bipyridine (Htzbp).