Constructing novel Cd(ii) metal–organic frameworks based on different highly connected secondary building units via alteration of reaction conditions

Abstract

Upon solvothermal reactions between Cd(II) salt and 5-pyridyl-tetrazolate (4-Ptz) under different reaction conditions, three new Cd(II) metal–organic frameworks (MOFs), namely [Cd₃(4-Ptz)₅(H₂O)₂(μ₃-OH)·3DMA·5H₂O·CH₃OH]_n (1), [Cd₅(4-Ptz)₈(CH₃OH)₂(μ₃-OH)₂·2DMA·4H₂O·3CH₃OH]_n (2) and [{Cd₉(4-Ptz)₁₄(AC)₂(μ₃-OH)₂(H₂O)₄}·8DMA·H₂O·3CH₃OH]_n (3), were synthesized based on different highly connected secondary building units (SBUs). In the presence of triethylamine, 1 was constructed based on an 8-connected triangular trinuclear Cd₃ SBU and exhibits a three-dimensional framework, while 2 was generated upon the addition of HCl, assembled through a close packing of the octahedron cages consisting of unprecedented 12-connected 4-Ptz bridged Cd₅ SBUs and thus showing high thermal and chemical stability. For generating 3, two different kinds of Cd₃ SBUs, including an 8-connected triangular SBU and a 10-connected linear SBU, were constructed and further integrated into a distorted octahedron-based net under the addition of both triethylamine and NaCl. In addition to the structural analysis, we also focused on the investigation of gas adsorption and solid-state fluorescence properties of 2.