Structural diversity in four Zn(II)/Cd(II) coordination polymers tuned by flexible pentacarboxylate and N-donor coligands: Photocatalysts for enhanced degradation of dyes

Abstract

Coordination polymers (CPs) are peculiar class of multidimensional materials which can be employed as photocatalytic materials to decompose lethal aromatic dyes present in waste-water discharge. Herein, four new Zn(II)/Cd(II) coordination polymers (CPs) namely [Cd2(H2O)(H3L)2(2,2′-bipy)2]·H2O (1), [Zn2(HL)(H2O)2(2,2′-bipy)2]·H2O (2), [Cd2(HL)(bmb)0.5(H2O)]·2H2O (3) and [Zn4(L)2(bpz)4·H2bpz]·4H2O (4) (H5L = 3,5-bis(3,4-dicarboxylphenoxy)benzoic acid, 2,2′-bipy = 2,2′-bipyridine, bmb = 1,4-bis(2-methylimidazol-1-yl)butane, bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), have been synthesized solvothermally and characterized. The single crystal X-ray diffraction reveals that CPs 1 and 2 exhibit 2D supramolecular framework built by the hydrogen bond interactions between adjacent chains. The CP 3 features a 2D double layer while 4 display 3D 3,3,4,4-connected topology with point symbol {4.6.84}{4.6.8}{62.84}{62.8}. All these newly synthesized materials exhibit photocatalytic properties and the results demonstrated that they exhibit efficient photocatalytic performances to selectively degrade methylene blue (MB) among the dyes viz. methylene orange (MO), acid orange (AO), congo red (CR) and acid chrome blue (ACB) under UV irradiation. A mechanistic investigation toward better understanding of the photocatalytic degradation of MB has been carried out using LC-MS studies. Also computational investigation by performing band gap calculations have been accomplished to address the probable mechanistic pathway which further have been assisted with Hirshfeld surface analysis.