A new Cu(II) metal–organic architecture driven by ether-bridged dicarboxylate: Photocatalytic properties and Hirshfeld surface analysis
Graphical abstract
A new Cu(II) coordination polymer synthesized and used as photocatalyst against aromatic dyes 
Introduction
Organic dyes have been widely used in solar cells, biological imaging, textiles, medicines, and several other industries [1], [2], [3], [4]. However, its uncontrolled discharge in the water is harmful to living beings due to their inherent toxicity and carcinogenicity [5]. Over the past years, various technologies and methods have been used to eradicate organic dyes from wastewater [6], [7], [8], [9], [10]. Among these methods, photodegradation is deemed to be one of the effective means of eradication of dyes [11], [12], [13]. Amongst plethora of photocatalysts deployed for the removal and decomposition of dyes, the semiconducting material TiO2 is still considered as the most attractive photocatalysts due to its environmental friendliness, non-toxicity, affordability and chemical stability [14]. Apart from TiO2, many traditional semiconductors have been extensively used as photocatalysts to degrade organic dyes [15], [16], [17]. Despite their utility as photocatalysts, these materials have some experimental impediments such as loss of reactivity, separation, recyclability and so on. Therefore, materials and inorganic chemists are in continuous pursuit to develop new catalytic materials having high catalytic efficiency for photodegradation of dyes [18], [19], [20].
The multifarious structures of coordination polymers (CPs) have confirmed their applicability in the fields of electrochemistry, heterogeneous catalysis, gas separation and storage, luminescence, ion exchange, magnetism, as well as drug delivery [21], [22], [23], [24], [25], [26]. The metal clusters and organic connectors that engender secondary building units (SBUs) play important role in producing CPs with various desirable dimensions. Also, the final/eventual structure of CPs are affected by varied experimental parameters such as, temperature, metal center coordination geometry, organic connector, type, solvent ratio, and pH value [27], [28], [29], [30]. Amongst these factors, organic connectors play crucial role in the design, as well as the assembly of CPs. In view of this feature associated with the ligand, aromatic dicarboxylates and imidazole ligands have been frequently selected to build CPs because of their distinctive properties: (1) varied coordination modes; (2) variable connector lengths; and (3) ability to display distinct bite angles.
With these aspects and invigorated by the previous investigations, in the work presented herewith, the 1,3-bis(3ˊ-carboxylatophenoxy)benzene (H2L) and 1,1′-(1,4-butanediyl)bis(imidazole) (bbi) were selected as ligands and co-ligands, respectively (Scheme S1) to coordinate with Cu(II) ion. The selection of H2L is because of the fact that it possess two potential coordination sites, and can act as an example to display the role of the pH in controlling the molecular structure of the coordination polymers. While the bis(imidazole) linkers with –CH2- spacers can rotate to meet various conformations when it was bonded to metal ions and induce the properties of the mixed CPs. Moreover, It was found that the Cu(II)-based transition metal–oxygen subunits not only has photocatalytic activity but also possess superior chemical catalytic activity to activate oxidants [4b]. Using H2L ligand and bbi co-ligand, herein, a highly stable coordination polymers {[Cu(L)(bbi)(H2O)]•H2O}n (1) was obtained which was used as photocatalysts for the photodegradation of aromatic dyes. The pertinent results of the investigation is presented herewith.
Section snippets
Experimental
The materials and methods, X-ray crystallography and photocatalytic method are presented in the supporting information.
Structure description of {[Cu(L)(bbi)(H2O)]•H2O}n (1)
The single crystal X-ray diffraction indicated that in coordination polymer 1, primarily, two L linkers bind to two Cu(II) to form a coordination macrocycle in which Cu(II) with square-pyramidal geometry are existing. Each Cu(II) coordinates with two O from two L2− and two N from two bbi in equatorial plane, and the axial site is occupied by O of aqua ligand (Fig. 1a and 1b). Furthermore, each coordinate macrocycle is bonded to four bbi co-ligands to extend into another two macrocycle to form a
Conclusion
In the study presented herewith, a new Cu(II) based coordination polymer had been synthesized which exhibited 1D double chain architecture extending into 2D layer through packing and hydrogen bond interactions. This newly designed polymer was used as photocatalyst for the decomposition of model dyes MV, Rh B and MB. The polymer was found to display best photocatalytic decomposition for MB dye. Furthermore, the trapping studies confirmed that •OH was the main reactive oxygen species in the
Author statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors acknowledge financial assistance from Natural Science Research Project of Anhui Province (1708085QB47 and 2108085MB51), Key Research and Development Program Project of Anhui Province (1804a09020087), Supported by Foundation of State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering (2017-K32), Postdoctoral Research Project of Anhui Province (2020B452), Postdoctoral Research Project of West Anhui University (WXBSH2019002), College Students'
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H···O hydrogen-bonding interactions. 2 exhibits (4,4)-connected 2D networks showing point symbol (42·64)(4·64·8). 1 and 2 both displayed high photocatalytic activities for the decomposition of methylene blue (MB) and methyl violet (MV). 1 and 2 can degrade 87.2% and 91.7% MB, respectively, in 75 min under visible light irradiation. 1 and 2 could degrade 82.2% and 91.8% MV, respectively, in 105 min under visible light irradiation. Therefore, 2 possessed better photocatalytic performance. The trapping experiments and ESR test indicated that 
O2– was the primary species in the process of MB degradation of 1 and 2. In addition, Hirshfeld surface analysis was also adopted to further address the probable mechanistic pathway.