Structural diversity and non-covalent interactions in Cd(II) and Zn(II) complexes derived from 3,5-dinitrobenzoic acid and pyridine: Experimental and theoretical aspects

One dinuclear Cd(II) complex, [Cd-2(mu-L)(2)(L)(2)(py)(4)] (1), and a mononuclear Zn(II) complex, [Zn(L)(2)(py)(2)] (2), have been prepared in aqueous methanol-DMF medium at ambient conditions by self-assembly from the metal(II) nitrates, 3,5-dinitrobenzoic acid (HL) and an ancillary pyridine (py) ligand. The complexes have been substantiated by elemental analyses, IR spectroscopy, UV-Vis spectra, fluorescence, PXRD and single-crystal X-ray diffraction studies. Complex 1 is a new triclinic (P (1) over bar) polymorph. The monoclinic (P2(1)/n) form (CSD reference code VESWOG) has previously been reported by Guo et al. (2006). The binuclear core in 1 comprises of two bridging 3,5-dinitrobenzoates, each of the Cd(II) centers is further coordinated to one bidentate 3,5-dinitrobenzoate and two pyridine ligands thereby completing a six-coordinate octahedral geometry. The structural aspects associated with the two polymorphs have been discussed in detail. In 2, the coordination environment around the Zn(II) ion is distorted tetrahedral with two monodentate 3,5-dinitrobenzoate moieties and two pyridine ligands. Density functional theory (DFT) calculations have been employed to calculate the energy difference between the polymorphic pair (1 and VESWOG). Finally, in the crystal packing of 1 and 2, the importance of various non-covalent interactions, such as p-p, lone pair(lp)-pi and pi-hole, has been highlighted and analyzed computationally. (C) 2015 Elsevier B.V. All rights reserved.