Five new proton transfer compounds, (Hapy)[Cr(pydc)2]·5H2O·[pydcH2] (1), (Hacr)[Cr(pydc)2]·2H2O (2), (H9a-acr)[Cr(pydc)2]·4.27H2O (3), [Co(pydc)(pydcH2)]·3H2O (4) and [Ni(pydcH)2]·H3O·2H2O (5) (where pydcH2 = pyridine-2,6-dicarboxylic acid; apy = 2-aminopyridine; acr = acridine and 9a-acr = 9-aminoacridine) have been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction techniques. Crystallographic analysis revealed that compounds 1–5 have distorted octahedral geometries with pydc2− and pydcH− ions or pydcH2 coordinated as tridentate ligands to each metal ion through one oxygen atom of each carboxylate group and the nitrogen atom of the pyridine ring. Compounds 1–3 consist of cationic complexes where the dipicolinic acid is coordinated to the metal ion in the dianionic form, whereas 4 and 5 are neutral complexes. In 4, the acid is coordinated to the metal ion in the neutral form, which is quite rare. In the crystal structures of the different complexes, extensive O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds, as well as other noncovalent interactions involving aromatic rings (C–H⋯π, C–O⋯π and π⋯π stacking), were described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks.

Crystal engineering with coordination compounds of NiII, CoII, and CrIII bearing dipicolinic acid driven by the nature of the noncovalent interactions

In continuation of our previous brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes by Aghabozorg et al. [1], we briefly surveyed the current research in the field of proton transfer compounds supramolecular synthons and their self-assembled metallic complexes from the points of view of Crystal Engineering and Density Functional Theory (DFT) since 2008. Our research groups have recently focused on the proton delivery from acids, which are considered to be suitable proton donors, to amines as proton acceptors. The results were the production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metal centers in the preparation of metal-organic compounds. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Our review and investigation of compounds revealed that they mainly focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron, mainly on the various interactions involved, including van der Waals, ion pairing, hydrogen bondings, face to face ν-β stackings and edge to face C-Hπ, C-Oπ, N-H3π and SS. These interactions were the most commonly used strategies in the extension of supramolecular structures.

A brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes (part II)

In this study Ziziphus nummularia (ZPN) as a good, available and inexpensive adsorbent has been introduced and used for the removal of Bromocresol Green (BCG) from several water solutions successfully. The effect of various parameters such as pH, dye concentration, amount of adsorbent, size of adsorbent particles, and contact time on removal processing was investigated. To investigate the mechanism of adsorption, several kinetic models were tested including Lagergren, pseudosecond-order, particle diffusion, film diffusion, and Elovich models. Adsorption isothermal data could be interpreted by the Langmuir, Freundlich, Tempkin, and Dubinin–Rudushkevich (DR) isotherm models. Thermodynamic parameters like free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) of the system were calculated.

Removal of Bromocresol Green from Aqueous Solution via Adsorption on Ziziphus nummularia as a New, Natural, and Low-Cost Adsorbent: Kinetic and Thermodynamic Study of Removal Process

The Cr(III) and Ca(II) complexes (dmpH)[Cr(pydc)2]•H2O (1) and [Ca2(pydc)2(H2O)6].2pydcH2 (2) were synthesized by reaction of 2,9-dimethyl-1,10-phenanthroline (dmp) and pyridine-2,6-dicarboxylic acid (pydcH2) with Cr(NO3)3 and Ca(NO3)2, respectively, and characterized using IR spectroscopy, single crystal X-ray diffraction method and solution studies. The space group and crystal system of these two compounds are P2
 1/c and monoclinic. The crystal dimensions are a = 9.785(3) A, b = 25.671(4) A, c = 9.3402(16) A, β = 90.790(17)° for (1) and a = 9.1319(4) A, b = 14.8430(8) A, c = 12.2449(7) A, β = 98.227(5)° for (2). In complex (1), a water molecule presents in the crystal packing, linking the anionic and cationic fragments together by hydrogen bonding and thus increases the stabilization of crystal lattices. In complex (2), the coordinated water molecules relate each dimer to adjacent dimers forming infinite molecular ribbons by strong hydrogen bondings. Hydrogen bonding and ion pairing play an important role in stabilizing these crystals. The complexation reactions of pydc, dmp and pydc+dmp with Cr3+ and Ca2+ ions in aqueous solution were investigated by potentiometric pH titrations and the equilibrium constants for all major complexes formed were evaluated.

Chromium(III) and Calcium(II) complexes obtained from dipicolinic acid: Synthesis, characterization, X-Ray crystal structure and solution studies

Cobalt (II), zirconium(IV), calcium(II) complexes with dipicolinic acid and imidazole derivatives: X-ray studies, thermal analyses, evaluation as in vitro antibacterial and cytotoxic agents

The homonuclear water-soluble and air stable compounds (dmpH) (H5O2) au][M(pydc)2].0.5H2O (M = Ni(II) (1), Cu(II) (2), Zn(II) (3); pydcH2 = pyridine-2,6-dicarboxylic acid, dipicolinic acid, dmp = 2,9-dimethyl-1,10-phenanthroline) have been prepared by self-assembly synthesis in aqueous solution at room temperature, and characterized by IR, 1H NMR, 13C NMR, elemental analysis and X-ray diffraction single crystal analyses for 1, 2 and 3. The complexes 1–3 represent the isostructural features. Extensive hydrogen bonding interactions involving all aqua ligands, dipicolinate oxygens and lattice water molecules further stabilize the complex units by linking them to form three dimensional polymeric networks. The stoichiometry and stability of the all three complexes in aqueous solution were investigated by potentiometric pH titration.

Synthesis, characterization, crystal structures, and solution studies of Ni(II), Cu(II) and Zn(II) complexes obtained from pyridine-2,6-dicarboxylic acid and 2,9-Dimethyl-1,10-Phenanthroline

E. Sadr-khanlou

Papers

Chromium(III) and Calcium(II) complexes obtained from dipicolinic acid: Synthesis, characterization, X-Ray crystal structure and solution studies

Synthesis, characterization, crystal structures, and solution studies of Ni(II), Cu(II) and Zn(II) complexes obtained from pyridine-2,6-dicarboxylic acid and 2,9-Dimethyl-1,10-Phenanthroline