A 3D Adenine-based Cd-MOF: Synthesis,Structure and Photoluminescent Sensing for an Aromatic Azo Compound

A new Cd-MOF containing the nucleobase adenine and multicarboxylates, Cd₂(tdc)₂(1H-ade)₂(H₂O) (H₂tdc = 2,5-thiophene carboxylic acid, 1H-ade = adenine), was synthesized successfully under hydrothermal condition and characterized by single-crystal X-ray diffraction, infrared spectrum, thermogravimetric analysis and photoluminescence. The two crystallographically unsymmetrical Cd atoms are bridged by 2,5-tdc ligands with (κ¹-κ¹)-(κ¹)-μ₃ and (κ¹–κ¹)–μ₂ modes into two dimensional extended layers, which are further pillared with the neutral ade molecules to form a 3D frameworks stabilized by extensive π ··· π interactions between imidazole-, pyrimidine- and thiophene-rings. Inspection of the structure reveals that the architecture can be simplified as a 3,4,5- connected networks with a Schläfli symbol of (6² · 8)(4² · 6³ · 8)(4² · 6⁵ · 8³). The photochemical property shows that the luminescent emission can be significantly quenched by aromatic azo compounds. The quenching effect coefficient (K_sv) for bis(4-imidazol-1-yl-phenyl)diazene is determined to be 4.1 × 10⁴ m ^–1, indicating the title compound as a potential fluorescent sensing materials.