Crystal-to-crystal transformations and photoluminescence changes in the Cu( i ) coordination networks based on a formamidinate ligand

• Published in: CrystEngComm Vol. 16; no. 46; pp. 10640 - 10648
• Main Authors: Hsu, Wayne, Chen, Kuan-Ting, Li, Yu-Sian, Cheng, Po-Wen, Chen, Tsun-Ren, Chen, Jhy-Der
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• Subjects: Cadmium; Emission; EMISSIONS; Ethanol; ETHYL ALCOHOL; LIGANDS; LUMINESCENCE; Networks; PHASE TRANSFORMATIONS; Three dimensional; Transformations; Two dimensional
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/C4CE01791A

One-pot solvothermal reactions of 4-aminopyridine and triethylorthoformate with Cu(O 2 CCH 3 ) 2 in acetone (ACT), dimethylformamide (DMF), tetrahydrofuran (THF), methanol (MeOH) and ethanol (EtOH) afforded 2D coordination networks, anti -{[Cu(4-pyf)]·ACT} n , 1a , (4-Hpyf = N , N′ -bis(pyridine-4-yl)formamidine), anti -{[Cu(4-pyf)]·DMF} n , 1b , anti -{[Cu(4-pyf)]·THF]} n , 1c , syn -{[Cu 4 (4-pyf) 4 ]·2MeOH} n , 2a , and syn -{[Cu 4 (4-pyf) 4 ]·2EtOH} n , 2b , whereas the reaction of Cu(O 2 CCH 3 ) 2 , 4-aminopyridine, triethylorthoformate and CuX 2 (X = BF 4 − and ClO 4 − ) in ethanol gave the 3D coordination networks syn -{[Cu 3 (4-pyf) 2 ](BF 4 )·2H 2 O·EtOH} n , 3a , and syn -{[Cu 3 (4-pyf) 2 ](ClO 4 )·EtOH} n , 3b , which were characterized by X-ray crystallography. Complexes 1a–3b are the first 2D and 3D coordination networks showing closed-shell Cu( i )–Cu( i ) interactions that are supported by the formamidinate ligands. Reversible crystal-to-crystal transformations were observed for the 2D anti - and syn -coordination networks upon solvent exchange. Irreversible anti to syn crystal-to-crystal transformations can be shown upon solvent removal and the important intermediate, syn -{[Cu 4 (4-pyf) 4 ]·2THF} n , 2c , which verifies the temperature-dependent transformation, was structurally characterized. The configurations of the structures have significant influence on the emission properties. While the syn -complexes show broad emission bands, those of the anti -complexes are not detectable, indicating that cuprophilicity is unlikely to play significant roles in determining the emission of 1a–3b . The 2D anti - and syn -complexes that show outwardly dangling pyridyl rings may adsorb Cd salts through Cd–N interactions.