Role of Cl• • •Cl halogen bonds in tuning the crystals of Uranyl-Dicholorothiophene carboxylate based hybrid cluster materials through N-donor counter ions

Abstract

• Eight new uranyl complexes containing 2,5-Dichlorothiophene-3-carboxylic acid with differently sized N-donor ligands were utilized to assemble under hydrothermal conditions. • The crystal structures of these uranyl complexes display the propensity of CTDC ligand and its capability of partaking in Cl•••Cl interactions and the Cl•••Cl interactions are confirmed through QTAIM analysis as well. • Photocatalytic behavior under UV light irradiation, shows remarkable advantages in the degradation of organic dyes. Hydrothermal synthesis has afforded eight uranyl bearing hybrid materials with various ancillary ligands such as 2,5-Dichlorothiophene-3-carboxylate (CTDC) as the main ligand and 4,4’-bipyridine (4BPY), 4,4′-Trimethylenedipyridine (4TBY), trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene (TTPY), 1,10-Phenanthroline (PHEN), or 2,2′-Dipyridylamine (2DPY). These uranyl complexes; (UO 2 ) 0.5 (CTDC)(4BPY) 0.5 ( I ), UO 2 (CTDC) 2 (4BPY) 0.5 , ( II ); [(UO 2 ) 4 (μ 3 -O) 2 (μ 2 -OH) 2 (CTDC) 4 (4TBY) 2 ].(H 2 4TBY).2H 2 O ( III ); [(UO 2 ) 2 (μ3-O)(CTDC) 3 ].(HTTPY).H 2 O ( IV ); [(UO 2 )(CTDC) 2 (PHEN)] 2 ( V ); [(UO 2 )(μ 2 -OH)(CTDC)(PHEN)] ( VI ); [UO 2 (CTDC) 3 ] 2 (H2DPY) 2 ( VII ); [UO 2 (CTDC) 3 ] 2 (H4TBY) 2 ( VIII ) were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, FT-IR spectroscopy, thermogravimetric analysis and by their uranyl emission spectra. The complexes ( I ) and ( II ) are the first examples of uranyl complexes with aromatic carboxylates formed in the presence of a coordinated 4,4’-bipyridine ligand. Here, the complexes ( V ) and ( VI ) were concomitant polymorphs while ( II ) and ( VIII ) are polymorphs of ( I ) and ( III ) respectively and were obtained by varying the pH in synthetic procedures. Halogen bonding (Cl···Cl) interactions were found to play a strong role in expanding their dimensionality into 3D and defining their crystal packing patterns. To gain insights into the Cl···Cl interactions, a detailed QTAIM study is taken up. The photocatalytic properties of ( I - VIII ) for degradation of various organic dyes under Hg-lamp irradiation were performed. Interestingly, complexes ( I, II, V ) which are mononuclear uranyl clusters possess the highest efficiency in degradation of organic dyes than the tetranuclear uranyl clusters ( III, IV ). Thus, this work sheds light on the structural features of these uranyl complexes to extend our knowledge and understanding of uranyl chemistry.