Structures and photocatalytic properties of two new Zn(II) coordination polymers based on semi-rigid V-shaped multicarboxylate ligands

Two new metal-organic coordination polymers (CPs), aqua-2,2 '-bipyridine-5-(4 '-carboxylphenoxy)isophthalatezinc(ii) polymer [Zn(HL)(2,2 '-bipy)(H2O)](n) (1) and tris-4,4 '-bipyridine-bis-5-(4 '-carboxylphenoxy)isophthalatetrizinc(ii) polymer [Zn-3(L)2(4,4 '-bipy)(3)](n) (2) (H3L = 5-(4 '-carboxylphenoxy)isophthalic acid, 4,4 '-bipy = 4,4 '-bipyridine and 2,2 '-bipy = 2,2 '-bipyridine), were obtained under hydrothermal conditions and characterized by microanalysis, FTIR spectroscopy and single crystal X-ray diffraction. The single crystal X-ray diffraction indicated that in both the CPs the coordination networks exhibited varied topologies and coordination modes around the Zn(ii) centers. CP 1 exhibits a one-dimensional (1D) chain structure, which further forms a 3D supramolecular architecture via intermolecular pi MIDLINE HORIZONTAL ELLIPSIS pi and hydrogen bonding interactions, while 2 possesses a 3D framework generated from a 2D layered motif comprising zinc and tripodal carboxylate subunits pillared by 4,4 '-bpy ligands. Apart from the structural investigation, the photocatalytic performances of both the coordination polymers to photodecompose an aqueous solution of methyl violet (MV) were examined. The results indicated that both the CPs displayed the potential to photodecompose aromatic dyes and in particular 2 showed good photocatalytic activity for dye degradation under light irradiation. The photocatalytic mechanism through which these CPs executed degradation of dyes has been explained with the assistance of band gap calculations using density of states (DOS) and its decomposed partial DOS calculations.