Syntheses, crystal structures and properties of three cyano-bridged one-dimensional coordination polymers based on macrocyclic metallic tectons

Abstract

Three cyano-bridged nickel(II) complexes, namely, [NiL₁][Ni(CN)₄]·3H₂O (1), [NiL₂][Ni(CN)₄]·H₂O·CH₃CN (2) and [NiL₃][Ni(CN)₄]·3H₂O (3) (L₁ = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.1^8,11]octadecane, L₂ = 1,3,6.8.12,15-hexaazatricyclo[13.3.1.1^8,12]eicosane and L₃ = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane), have been synthesized and characterized based on different macrocyclic metallic tectons and diamagnetic [Ni(CN)₄]²⁻. Single crystal X-ray analyses reveal that complexes 1–3 exhibit a similar cyano-bridged one-dimensional chain structure, in which one nickel(II) ion is coordinated by four nitrogen atoms from the macrocyclic ligand and two nitrogen atoms from the bridging cyanide ligands, while the residual nickel(II) ion is coordinated by four cyanide ligands. Interestingly, regulated by the peripheral macrocyclic ligand, complex 1 features an unexpected large porous structure with a pore size of 1 nm, which shows pronounced two-step adsorption of CO₂ gas at 195 K. In additional, the magnetic properties of complexes 1–3 show the presence of weak intrachain ferromagnetic interactions between the paramagnetic nickel(II) ions through the diamagnetic [Ni(CN)₄]²⁻ anions.