Non-coordinated Water Molecules Research Articles

Synthesis of crystalline NiO nanorodes from a new Ni(II) nano-coordination compound and its application in sonocatalytic dye removal

Nanostructures of a new nickel(II) coordination compound of [Ni(ntaH2)2].2H2O, 1, (where ntaH3 is nitrilotriacetic acid) were synthesized, and characterized by scanning electron microscopy (SEM), x-ray powder diffraction (XRPD), and FT-IR spectroscopy. Moreover, the structure of compound 1 was determined using the single crystal x-ray diffraction technique. The asymmetric unit of 1 consists of one half of the [Ni(ntaH2)2] complex where the Ni ion is located on the center of symmetry, and one non-coordinated water molecule. The ntaH2 ligand coordinated to the metal center in a tridentate fashion provides a slightly distorted octahedral geometry around the nickel(II) ion. Non-covalent interactions i.e. hydrogen bonding extend the molecular structure into a 3D supramolecular array. Compound 1 was found to be a cost-effective precursor for nanoscale nickel oxide which was obtained in good yield. NiO nanorods were fully characterized and examined as a sonocatalyst to remove the methyl orange (MO) from the aqueous solution in the absence of any oxidants. Knowing that increasing metal concentrations endangers the aquatic ecosystems, the above treatment of the Ni(II) ion might be considered as an effective decontamination of nickel-bearing wastewaters and a facile route to converting it to a desirable NiO product.

Solubility of d-Element Salts in Organic and Aqueous-Organic Solvents: VII. Structure of Nickel Chloride Solvatocomplexes

Four complexes [Ni(DMA)2(H2O)4]Cl2·2H2O, [Ni(DMF)2(H2O)4]Cl2·2H2O, and [Ni(DMA)6][NiCl4], [Ni(DMF)2(H2O)2Cl2] were isolated from ternary water-organic saline systems containing nickel chloride and N, N-dimethylacetamide-water and N, N-dimethylformamide-water binary solvents. The obtained complexes were studied by X-ray structural analysis. The formation of hydrogen bonds between water molecules of the nickel ion solvate sphere, chloride ions, and non-coordinated water molecules located in the cavity of the crystal structure was detected.

The Fate of Water at the Electrochemical Interfaces: Electrochemical Behavior of Free Water Versus Coordinating Water.

The water reduction that produces hydrogen is one key reaction for electrochemical energy storage. While it has been widely studied in traditional aqueous electrolytes for water splitting (electrolyzers), it also plays an important role for batteries. Indeed, the reduction of water at relatively high potential prevents the practical realization of high-voltage aqueous batteries, while water contamination is detrimental for organic battery electrolytes. Nevertheless, recent studies pointed toward the positive effect of traces of water for Li-air batteries as well as for the formation of solid-electrolyte interphase. Herein, we provide a detailed understanding of the role of the solvation on water reduction reaction in organic electrolytes. Using electrochemistry, classical molecular dynamics simulations, and nuclear magnetic resonance spectroscopy, we were able to demonstrate that (1) the hydrophilicity/hydrophobicity of the species inside the electrochemical double layer directly controls the reduction of water and (2) water-coordinating strong Lewis acids such as Li+ cation are more reactive than free water (or noncoordinating) water molecules.

Coordination polymers of zinc(II) and manganese(II) made by complexation of calix[4]arene functionalized with carboxylates afford alveolar materials

25,27-bis(methoxycarboxylic acid)-26,28-dihydroxycalix[4]arene (calixH2), so call here calix[4]arene dimethoxycarboxylic acid, was investigated for its ability to build metal–organic frameworks. When reacted with zinc or manganese chloride in DMF and deprotonated with trimethylamine it gives Zn (1) and Mn (2) coordination compounds. These crystallize in the triclinic P-1 space group and are isostructural as shown by X-ray diffraction on single crystals. The crystal structures evidence the coordination of calix[4]arenedimethoxycarboxylic acid through the carboxylate groups. This makes a 1D coordination polymer running along the c axis direction in which [MII2(calix)2(H2O)3(DMF)2] (M = Zn or Mn) neutral units are connected. Last step refinements of the crystal structure reveal a lot of residual electron density which was ascribed to uncoordinated disordered water and DMF molecules. This was treated with the SQUEEZE routine of the program PLATON from which the solvent accessible voids per unit cell volume was calculated to be 24.5% for compound 1 (Zn) and 24.9% for compound 2 (Mn). Complementary differential thermal analyses (DTA) combined with thermogravimety analysis (TGA) and mass spectrometry (MS) are in agreement with large amount of incorporated and non-coordinated water and DMF molecules. Adsorption isotherms of N2 measured for compound 1 do not show any significant porosity. The temperature dependence of the magnetic susceptibility (χ) of compound 2 evidences antiferromagnetic interactions and was best fitted with a weak antiferromagnetic exchange coupling between the manganese(II) ions J = − 1.5 cm−1 and small antiferromagnetic inter-dinuclear interactions zJ = − 1.2 cm−1 (g = 2.02).

Supramolecular association involving anion–π interactions in Cu(II) coordination solids: Experimental and theoretical studies

Two new coordination solids, [Cu2(µ-tp)(phen)4](NO3)2·2H2O (1) and [Cu(pa)2(NO3)(H2O)]NO3·H2O (2) (phen = 1,10-phenanthroline, tp = terephthalate, pa = picolinamide), were synthesized from purely aqueous media and characterized using elemental analysis, spectroscopic methods (IR, UV–Vis–NIR and ESR) and the single crystal X-ray diffraction technique. In the crystal structures of 1 and 2, supramolecular networks have been built up involving associations with OH⋯O, CH⋯O and π–π stacking interactions. In addition, both compounds show anion–π interactions involving non-coordinated nitrate ions and the aromatic rings of the complexes. The nitrate anions and non-coordinated water molecules in both compounds, with the graph set representation R24(8), act as cross-links between symmetry related cationic chains via hydrogen bonding interactions to form 2D layered supramolecular architectures. Theoretical investigations have been carried out on all the supramolecular contacts, including anion–π interactions, taking into account the particular position of the anion toward the aromatic ring observed in the crystal structures. Calculations reveal that in addition to the electrostatics, induction and dispersion components are also significant towards the stabilization of the supramolecular interactions. The phase purity and thermal stability of the compounds were verified by powder X-ray diffraction (PXRD) and thermogravimetric (TG) analyses, respectively. The microbial activities have been investigated for compound 1.

Lanthanide complexes with zwitterionic amidoximes stabilized by noncoordinating water molecules

We present the first structural report of lanthanides complexed with free amidoxime ligands as part of our ongoing research effort to understand the interactions of amidoximes with metal ions in seawater. Three isomorphous lanthanide complexes with acetamidoxime (AcAO) having the formula Ln2(NO3)6(AcAO)3(OH2)3·3H2O (Ln = Pr3+, Nd3+, Gd3+) have been crystallized and structurally characterised. Notably, the AcAO ligands coordinate in a bridging mode as zwitterions, which creates pre-organised hydrogen bonding cavities into which water molecules are incorporated. Charge-assisted hydrogen bonds to these water molecules appear to stabilize the zwitterionic form and thus the overall complex, underscoring the importance of supramolecular phenomena and overall complex geometry on the relative stability of amidoxime complexes. This has implications for controlling their selectivity towards metal ions.

Crystal structure of poly[[di-μ3-acetato-tetra-aqua-bis-(μ2-cyclo-hexane-1,4-di-carboxyl-ato)dilanth-an-um(III)] dihydrate

The title compound, {[La2(CH3COO)2(C8H10O4)2(H2O)4]·2H2O} n or [La2(ac)2(e,a-cis-1,4-chdc)2(H2O)4]·2H2O, where ac is acetate and 1,4-chdc is cyclo-hexane-1,4-di-carboxyl-ate anion, is a binuclear lanthanum(III) complex. Each metal atom is deca-coordinated by four O atoms from two distinct 1,4-chdc2- ligands, four O atoms from three acetate groups and two O atoms from coordinated water mol-ecules to form a distorted bicapped square-anti-prismatic geometry. Two non-coordinated water mol-ecules are also present in the formula unit. The most remarkable feature of this compound is that it possesses a only cis conformation for cyclo-hexane-1,4-di-carb-oxy-lic acid, although the raw material consists of a mixture of cis and trans isomers. The μ3-η2:η2 coordination mode of the bridging acetate group and the flexible di-carboxyl-ate fragments of 1,4-chdc2- results in the formation of infinite two-dimensional lanthanide-carboxyl-ate layers within the crystal structure. The directionality of strong inter-molecular O-H⋯O and weak C-H⋯O inter-actions provides robustness to the layers, which leads to the construction of a three-dimensional supra-molecular network. The crystal studied was refined as a two-component twin.

Crystal structure of aqua-(1H-pyrazole-κN2)(pyridine-2,6-di-carboxyl-ato-κ3O2,N,O6)copper(II) dihydrate.

In the title compound, [Cu(C7H3NO4)(C3H4N2)(H2O)]·2H2O, the CuII atom is coordinated by three O atoms and two N atoms, provided by a tridentate pyridine-2,6-di-carboxyl-ate (pdc), one pyrazole and one water ligand, forming a slightly distorted square-pyramidal geometry [range of O-Cu-O and O-Cu-N bond angles = 79.55 (8)-166.22 (10)°]. The water mol-ecule is positioned at the apical position. In the crystal, the complex mol-ecule and the two crystallographically independent non-coordinating water mol-ecules are linked into a supra-molecular layer structure parallel to the ab plane via O-H⋯O and N-H⋯O hydrogen bonds.

Hydrothermal Synthesis, Crystal Structure, and Properties of 1D Zigzag Chain Zinc(II) Coordination Polymer Constructed from Nicotinic Acid and 1,4-Bis(imidazol-1-ylmethyl)benzene

A zinc–nicotinate complex, {[Zn(na) 2 ( µ- pbix)]∙H 2 O} n (1) , was obtained from the reaction of zinc(II) acetate with nicotinic acid (Hna) and 1,4-bis(imidazol-1-ylmethyl)benzene (pbix) in water at 120 °C under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, single crystal and powder X-ray diffraction. The thermal stability and luminescent property for 1 were also reported. The asymmetric unit of 1 consists of one zinc(II) center, one pbix ligand, two na anions and one non-coordinated water molecule, giving a formula of {[Zn(na) 2 ( µ- pbix)] ∙ H 2 O} n . The Zn(II) ion is coordinated by two nitrogen atoms from two different 1,4-bis(imidazol-1-ylmethyl)benzene ligands and two oxygen atoms from two different nicotinate (na) anions, thus showing a distorted tetrahedral geometry. The adjacent Zn(II) ions are linked into an infinite 1D zigzag chain by 1,4-bis(imidazol-1-ylmethyl)benzene ligands. Grand canonical Monte Carlo (GCMC) simulations were also performed to compute single-component H 2 adsorption isotherms at a pressure range of 0.01–100 bar and at 298 K and 77 K. The maximum H 2 uptake in 1 was found as 68 cm 3 / g STP at 100 bar and 77 K. This study will be useful to accelerate the hydrothermal synthesis of new coordination polymers for gas storage applications.

Crystal structure of bis-(acetato-κ2O,O')di-aqua-[1-(pyridin-2-yl-methyl-idene-κN)-2-(pyridin-2-yl-κN)hydrazine-κN1]terbium(III) nitrate monohydrate.

In the title compound, [Tb(C2H3O2)2(C11H10N4)(H2O)2]NO3·H2O, the Tb3+ ion is nine-coordinated in a distorted tricapped trigonal-prismatic geometry by the three N atoms of the tridentate 1-(pyridin-2-yl-methyl-idene)-2-(pyridin-2-yl)hydrazine ligand, four carboxyl-ate O atoms of two chelating acetate groups and two O atoms of the coordinating water mol-ecules. The organic hydrazine ligand is disordered over two orientations with a refined occupancy ratio of 0.52 (3):0.48 (3). All bond lengths in the coordination environment of the Tb3+ ion are slightly larger than those observed in the isostructural Y3+ and Er3+ complexes. In the crystal, the complex cations are linked by pairs of O-H⋯O hydrogen bonds into dimers. These dimers, nitrate anions and non-coordinating water mol-ecules are joined by O-H⋯O and N-H⋯O hydrogen bonds into a three-dimensional structure.

Crystal structure of the tetraaquabis(thiocyanato-κN)cobalt(II)–caffeine–water (1/2/4) co-crystal

In the structure of the title compound [systematic name: tetra-aqua-bis-(thio-cyanato-κN)cobalt(II)-1,3,7-trimethyl-1,2,3,6-tetra-hydro-7H-purine-2,6-dione-water (1/2/4)], [Co(NCS)2(H2O)4]·2C8H10N4O2·4H2O, the cobalt(II) cation lies on an inversion centre and is coordinated in a slightly distorted octa-hedral geometry by the oxygen atoms of four water mol-ecules and two N atoms of two trans-arranged thio-cyanate anions. In the crystal, the complex mol-ecules inter-act with the caffeine mol-ecules through O-H⋯N, O-H⋯O and C-H⋯S hydrogen bonds and π-π inter-actions [centroid-to-centroid distance = 3.4715 (5) Å], forming layers parallel to the ab plane, which are further connected into a three-dimensional network by O-H⋯O and O-H⋯S hydrogen bonds involving the non-coordinating water mol-ecules.

Facile synthesis of 2D Zn(II) coordination polymer and its crystal structure, selective removal of methylene blue and molecular simulations

A new coordination polymer {[Zn(μ3-ppda)(H2O)(μ-bpa)Zn(μ-ppda)(μ-bpa)]·4H2O}n (1) (ppda = 1,4-phenylenediacetate, bpa = 1,2-bis(4-pyridyl)ethane) has been synthesized by microwave-assisted reaction and characterized by elemental analysis, IR spectroscopy, single-crystal and powder X-ray diffractions. The asymmetric unit of 1 consists of two Zn(II) ions, two bpa ligands, two ppda ligands, one coordinated and four non-coordinated water molecules. In 1, ppda2− anions are linked the adjacent Zn(II) centers to generate 1D double-stranded chains. These chains are connected into 2D sheets by the bridging bpa ligands. Atomically detailed modeling was performed to compute single and binary component adsorption isotherms of H2, CO2, CH4 and N2 in complex 1. Results showed that 1 exhibits a high adsorption selectivity towards CO2 due to its high affinity for CO2. Results of this study will be helpful to guide the microwave-assisted reaction of coordination polymers to design promising adsorbents for gas storage and gas separation applications. The luminescent property of 1 and the selective removal of dyes in 1 have been also discussed. Results showed that 1 can be a potential candidate for luminescence applications and can selectively adsorb methylene blue (MB) dye molecules.

Crystal structure of catena-poly[[[di-aqua-bis-(2,4,6-tri-methyl-benzoato-κO)cobalt(II)]-μ-aqua-κ2O:O] dihydrate

The asymmetric unit of the title one-dimensional polymeric compound, {[Co(C10H11O2)2(H2O)3]·2H2O} n , contains one CoII cation situated on a centre of inversion, one-half of a coordinating water mol-ecule, one 2,4,6-tri-methyl-benzoate (TMB) anion together with one coordinating and one non-coordinating water mol-ecule; the TMB anion acts as a monodentate ligand. In the anion, the carboxyl-ate group is twisted away from the attached benzene ring by 84.9 (2)°. The CoII atom is coordinated by two TMB anions and two water mol-ecules in the basal plane, while another water mol-ecule bridges the CoII atoms in the axial directions, forming polymeric chains running along [001]. The coordination environment for the CoII cation is a slightly distorted octa-hedron. The coordinating and bridging water mol-ecules link to the carboxyl-ate groups via intra- and inter-molecular O-H⋯O hydrogen bonds, enclosing S(6) ring motifs, while the coordinating, bridging and non-coordinating water mol-ecules link to the carboxyl-ate groups and the coordinating water mol-ecules link to the non-coordinating water mol-ecules via O-H⋯O hydrogen bonds, enclosing R22(8) and R33(8) ring motifs. Weak C-H⋯O and C-H⋯π inter-actions may further stabilize the crystal structure.

Rebuttal of the Existence of Solid Rare Earth Bicarbonates and the Crystal Structure of Holmium Nitrate Pentahydrate

The synthesis routes of Gd(HCO3)3·5H2O and Ho(HCO3)3·6H2O, which are the only known bicarbonates of rare earth metals, were refuted and the published crystal structures were discussed. Because of the structural relationship of Ho(HCO3)3·6H2O to rare earth nitrate hexahydrates,[1] the synthesis of holmium nitrate hydrate was considered and the crystal structure of Ho(NO3)3·5H2O was solved by single crystal X-ray diffraction measurements. Ho(NO3)3·5H2O was determined to crystallize in the triclinic space group P1 (no. 2) with a = 6.5680(14) A, b = 9.503(2) A, c = 10.462(2) A, α = 63.739(14)°, β = 94.042(2)° and γ = 76.000(16)°. The crystal structure consists of isolated [Ho(H2O)4(NO3)3] polyhedra and non-coordinating water molecules. It is isotypic to other rare earth nitrate pentahydrates.

Crystal structure of catena-poly[[copper(II)-μ2-salicylato-[diaqua-copper(II)]-μ2-salicylato] dihydrate

The title compound, {[Cu2(C7H4O3)2(H2O)2]·2H2O} n , contains two copper(II) cations in special positions (one on a twofold rotation axis and one on an inversion centre) and the the salicylate ligand in its dianionic form. By four- and six-coordinate metal coordination, chains are formed parallel to [001], which are extended by O-H⋯O hydrogen bonding into sheets extending parallel to (100). These sheets are weakly connected by O-H⋯O hydrogen bonding via the non-coordinating lattice water mol-ecules into a three-dimensional network.

Isotypic MnII and FeII binuclear complexes of the ligand 5,6-bis-(pyridin-2-yl)-pyrazine-2,3-di-carb-oxy-lic acid.

The title isotypic complexes, bis-[μ-5,6-bis-(pyridin-2-yl)pyrazine-2,3-di-carboxylato]-κ4N1,O2,N6:O3;κ4O3:N1,O2,N6-bis-[di-aqua-manganese(II)] tetra-hydrate, [Mn2(C16H8N4O4)2(H2O)4]·4H2O, (I), and bis-[μ-5,6-bis-(pyridin-2-yl)pyrazine-2,3-di-carboxyl-ato]-κ4N1,O2,N6:O3;κ4O3:N1,O2,N6-bis-[di-aqua-iron(II)] tetrahydrate, [Fe2(C16H8N4O4)2(H2O)4]·4H2O, (II), are, respectively, the mangan-ese(II) and iron(II) complexes of the ligand 5,6-bis-(pyridin-2-yl)-pyrazine-2,3-di-carb-oxy-lic acid. The complete mol-ecule of each complex is generated by inversion symmetry. Each metal ion is coordinated by a pyrazine N atom, a pyridine N atom, two carboxyl-ate O atoms, one of which is bridging, and two water O atoms. The metal atoms have MN2O4 coordination geometries and the complexes have a cage-like structure. In the crystals of both compounds, the complexes are linked by O-H⋯O and O-H⋯N hydrogen bonds involving the coordinating water mol-ecules, forming chains along [100]. These chains are linked by O-H⋯O hydrogen bonds involving the non-coordinating water mol-ecules, forming layers parallel to (011). The layers are linked by pairs of C-H⋯O hydrogen bonds and offset π-π inter-actions, so forming a hydrogen-bonded three-dimensional framework.

Crystal structure of μ-4-oxidobenzoato-κ2O1:O4-bis-[bis-(1,10-phenanthroline-κ2N,N')copper(II)] bis-(4-hy-droxy-benzoate) 7.5-hydrate.

The title hydrated complex, [Cu2(C7H4O3)(C12H8N2)4](C7H5O3)2·7.5H2O, is composed of dinuclear CuII complex cations, noncoordinating 4-hy-droxy-benzoate anions and water mol-ecules of crystallization. In the dinuclear complex cation, the CuII ions are bridged by a 4-oxidobenzoate ligand and thus each metal ion is five-coordinated by two chelating 1,10-phenanthroline (phen) mol-ecules and one anionic O atom in a distorted trigonal-bipyramid geometry. In the crystal, aromatic π-π stacking occurs between phen rings of neighbouring dinuclear CuII complex cations, forming two-dimensional supra-molecular systems parallel to (100).

Crystal structure of di-aqua-bis-(4-tert-butyl-benzoato-κO)bis-(nicotinamide-κN (1))cobalt(II) dihydrate.

The asymmetric unit of the mononuclear cobalt complex, [Co(C11H13O2)2(C6H6N2O)2(H2O)2]·2H2O, contains one half of the complex mol-ecule, one coordinating and one non-coordinating water mol-ecule, one 4-tert-butyl-benzoate (TBB) ligand and one nicotinamide (NA) ligand; the Co atom lies on an inversion centre. All ligands coordinating to the Co atom are monodentate. The four nearest O atoms around the Co atom form a slightly distorted square-planar arrangement, with the distorted octa-hedral coordination completed by the two pyridine N atoms of the NA ligands at distances of 2.1638 (11) Å. The coordinating water mol-ecules are hydrogen bonded to the carboxyl O atoms [O ⋯ O = 2.6230 (17) Å], enclosing an S(6) hydrogen-bonding motif, while inter-molecular O-H⋯O hydrogen bonds link two of the non-coordinating water mol-ecules to the coordinating water mol-ecules and NA anions. The dihedral angle between the planar carboxyl-ate group and the adjacent benzene ring is 29.09 (10)°, while the benzene and pyridine rings are oriented at a dihedral angle of 88.53 (4)°. In the crystal, O-H⋯O and N-H⋯O hydrogen bonds link the mol-ecules, enclosing R 2 (2)(8), R 2 (2)(10) and R 4 (4)(12) ring motifs, forming layers parallel to (001). The C and H atoms of the tert-butyl group of the TBB ligand are disordered over two sets of sites with an occupancy ratio of 0.631 (5):0.369 (5).

1D and 3D supramolecular structures exhibiting weak ferromagnetism in three Cu(II) complexes based on malonato and di-alkyl-2,2’-bipyridines

Three new Cu(II) complexes composed of malonato (mal), methylmalonato (memal), 4,4′-di-tert-butyl-2,2′-bipyridine (tbpy) and 5,5′-dimethyl-2,2′-bipyridine (mebpy) ligands, Cu(H2O)(mal)(tbpy) (1), Cu(H2O)(memal)(tbpy) (2) and Cu4(H2O)4(memal)4(mebpy)4·11H2O (3) were synthesized by simple one-pot solution reactions at ambient conditions. Single-crystal X-ray diffraction analyses reveal that the Cu(II) ions exhibit a distorted five-coordinate square pyramidal geometry. These three complexes display supramolecular arrays due to hydrogen-bonding interactions. Complexes 1 and 2 show 1-D supramolecular structures; 1 forms a double-ion chain, unlike 2, which only generates a single-ion chain. In 3, there are two identical monomers in the asymmetric unit with Z″ = 2; its high number of noncoordinated water molecules, along with hydrogen-bonding interactions between aqua ligand and memal ligand, generate a supramolecular tetramer, which mimics to produce a 3-D supramolecular framework. Besides this fascinating and yet uncommon crystallographic phenomenon in 3, the structural differences found in these complexes arise from the substituted groups in the malonato dianion and in the bipyridine ligands. These compounds exhibit weak ferromagnetic-exchange interactions.

Crystal structure and spectroscopic analysis of a new oxalate-bridged Mn(II) compound: catena-poly[guanidinium [[aqua-chlorido-manganese(II)]-μ2-oxalato-κ(4) O (1),O (2):O (1'),O (2')] monohydrate

As part of our studies on the synthesis and the characterization of oxalate-bridged compounds M-ox-M (ox = oxalate dianion and M = transition metal ion), we report the crystal structure of a new oxalate-bridged Mn(II) phase, {(CH6N3)[Mn(C2O4)Cl(H2O)]·H2O} n . In the compound, a succession of Mn(II) ions (situated on inversion centers) adopting a distorted octa-hedral coordination and bridged by oxalate ligands forms parallel zigzag chains running along the c axis. These chains are inter-connected through O-H⋯O hydrogen-bonding inter-actions to form anionic layers parallel to (010). Individual layers are held together via strong hydrogen bonds involving the guanidinium cations (N-H⋯O and N-H⋯Cl) and the disordered non-coordinating water mol-ecule (O-H⋯O and O-H⋯Cl), as well as by guanidinium π-π stacking. The structural data were confirmed by IR and UV-Visible spectroscopic analysis.