MOF-Based Sorbents Used for the Removal of Hg2+ from Aqueous Solutions via a Sorption-Assisted Microfiltration.

Mercury is considered to be one of the most important chemicals of public health concern. Therefore, it is necessary to develop an effective method of removing mercury ions from aqueous solutions to protect people from exposure to this element. This paper presents research on the application of a sorption-assisted microfiltration (SAMF) hybrid process for the removal of Hg2+ from aqueous solutions. As adsorbents used in the process, the metal-organic-framework-UiO-66-type materials have been considered. The methods of synthesis of two types of metal-organic-framework (MOF) sorbents were developed: UiO-66_MAA modified with mercaptoacetic acid (MAA) and a composite of UiO-66 with cellulose. The results of the experiments performed proved that the separation of Hg2+ from water solutions conducted in such a system was effective; however, a relatively long initial contact time of reagents before filtration was required. The experimental results can be used to optimize the parameters of the SAMF process in order to obtain an effective method of Hg2+ removal from aqueous solutions.

Crystal structure of catena-poly[[[aqua-lithium(I)]-µ-pyrimidine-2-carboxyl-ato-κ(4) N (1),O (2):N (3),O (2')] hemihydrate].

The title compound, {[Li(C5H3N2O2)(H2O)]·0.5H2O} n , comprises four symmetry-independent Li(C5H3N2O2)(H2O) units which form mol-ecular ribbons running along the c-axis direction. Within each ribbon, the ligand mol-ecule, acting in a µ2-mode, bridges two adjacent Li(+) cations using both of its N,O-bonding sites. The coordination environment of each of the four Li(+) cations can be described alternatively as either slightly distorted trigonal-bipyramidal or slightly distorted square-pyramidal. The ribbons are inter-connected by a network of O-H⋯O hydrogen bonds.

catena-Poly[[lithium-µ2-(di-hydrogen pyrazine-2,3,5,6-tetra-carboxyl-ato)-κ(6) O (2),N (1),O (6);O (3),N (4),O (5)-lithium-di-µ-aqua-κ(4) O:O] 2.5-hydrate].

The title coordination polymer, {[Li2(C8H2N2O8)(H2O)2]·2.5H2O} n , is built up from mol-ecular ribbons propagating in the c-axis direction of the ortho-rhom-bic unit cell; the ligand bridges two Li(+) ions using both its N,O,O'-bonding sites and adjacent Li(+) ions are bridged by pairs of water mol-ecules. The coordination geometry of the metal ion is distorted trigonal bipyramidal, with the ligand O atoms in the axial sites. Two of the carboxyl-ate groups of the ligand remain protonated and form short symmetric O-H⋯O hydrogen bonds. In the crystal, the ribbons inter-act via a network of O-H⋯O hydrogen bonds in which coordinating water mol-ecules act as donors and carboxyl-ate O atoms within adjacent ribbons act as acceptors, giving rise to a three-dimensional framework. O-H⋯N inter-actions are also observed. The asymmetric unit contains quarter of the ligand and the complete ligand has 2/m symmetry; the Li(+) ion lies on a special position with m.. site symmetry. Both bridging water mol-ecules have m2m site symmetry and both lattice water mol-ecules have m.. site symmetry; one of the latter was modelled with a site occupancy of 0.25.

(µ-Di-hydrogen pyrazine-2,3,5,6-tetra-carboxyl-ato-κ(6) O (2),N (1),O (6);O (3),N (4),O (5))bis-(di-aqua-lithium) monohydrate.

The structure of the title compound, [Li2(C8H2N2O8)(H2O)4]·H2O, is composed of dinuclear mol-ecules in which the ligand bridges two symmetry-related Li(I) ions, each coordinated also by two water O atoms, in an O,N,O'-manner. The Li and N atoms occupy special positions on twofold rotation axes, whereas a crystal water mol-ecule is located at the inter-section of three twofold rotation axes. The Li(I) cation shows a distorted trigonal-bipyramidal coordination. Two carboxyl-ate groups remain protonated and form short inter-ligand hydrogen bonds. The mol-ecules are held together by a network of hydrogen bonds in which the coordinating and solvation water mol-ecules act as donors and carboxyl-ate O atoms as acceptors, forming a three-dimensional architecture.

Tri-aqua-(pyrazole-4-carboxyl-ato-κN (1))lithium.

In the monomeric title complex, [Li(C4H3N2O2)(H2O)3], the Li(+) cation is coordinated by a pyrazole N atom and three water mol-ecules in a distorted tetra-hedral geometry. The carboxyl-ate group is deprotonated. The complex mol-ecules are involved in O-H⋯O and N-H⋯O hydrogen bonding, forming layers stacked along the b axis.

Solid-state DFT-assisted Raman study of titaniate nanostructures.

The first principle solid-state computations in frame of Density Functional Theory have been employed to analyze the Raman spectra of typical titaniate nanostructures. The Raman scattering studies of the nanotitaniates synthesised hydrothermally at different temperature conditions are reported. Local Density Approximation in combination with linear-response computations have delivered detailed analysis of Raman spectra based on the reference Na2Ti3O7 and NaHTi3O7 structures. The interpretation of the most prominent spectral features commonly reported in the literature have been postulated.

Pyrimidine-4-carb-oxy-lic acid.

The crystal structure of the title compound, C5H4N2O2, is built of acid mol-ecules located on a mirror plane. They form sheets stacked along the b-axis direction. The mol-ecules inter-act via O-H⋯N hydrogen bonds, forming [001] chains, and weak van der Waals inter-actions.

Tetra-aqua-(pyrimidine-4,6-dicarboxyl-ato-κ(2) N (1),O (6))magnesium monohydrate.

In the title compound, [Mg(C6H2N2O4)(H2O)4]·H2O, the Mg(II) ion is coordinated by a fully deprotonated pyrimidine-4,6-dicarboxyl-ate mol-ecule, via a ring N and a carboxyl-ate O atom, and by four water O atoms at the apices of a slightly distorted octa-hedron. In the crystal, mol-ecules are linked by O-H⋯O and O-H⋯N hydrogen bonds, forming a three-dimensional network.

Poly[(µ4-3-carb-oxy-pyrazine-2-carboxyl-ato)(µ4-nitrato)dilithium].

In the title compound, [Li2(C6H3N2O4)2(NO3)] n , the two symmetry-independent Li(I) ions are each in a trigonal-bipyramidal coordination and are bridged by N,O-bonding ligands, forming mol-ecular ribbons propagating in [010]. Each Li(I) ion is also coordinated by two O atoms from nitrate ions, connecting the ribbons into a three-dimensional network. Very strong intra-molecular O-H⋯O hydrogen bonds occur between the carboxyl and the carboxylate group.

catena-Poly[[di-aqua-bis-(µ3-5-carboxyl-ato-1H-pyrazole-3-carb-oxy-lic acid-κ(3) O (3):O (3);O (5))dilithium(I)] monohydrate].

The basic structural unit of the title polymeric ribbon, {[Li2(C5H3N2O2)2(H2O)2]·H2O} n , is a centrosymmetric dinuclear complex in which the two Li(I) ions are bridged by two carboxyl-ato O atoms, to generate a centrosymmetric Li2O2 core. These are connected into a chain along [01-1] by carboxylic acid-carbonyl-O bonds. The tetra-hedral coordination of the Li(I) cation is completed by an aqua ligand. The carboxylic acid is involved in an intra-ribbon hydrogen bond. A solvate water molecule showing positional (50:50) disorder is observed. Polymeric ribbons along [01-1] are connected by O-H⋯O, N-H⋯O and O-H⋯N hydrogen bonds into a three-dimensional architecture.

Di-µ-aqua-bis-[aqua-(5-carboxyl-ato-1H-1,2,3-triazole-4-carb-oxy-lic acid-κ(2) N (3),O (4))lithium].

The crystal structure of the title compound, [Li2(C4H2N3O4)2(H2O)4], contains centrosymmetric dinuclear mol-ecules in which two Li(I) ions are bridged by two water O atoms. The metal ion is coordinated by one N,O-bidentate ligand and three water O atoms (one of them is symmetry generated), with one of the bridging water O atoms in the apical position of a distorted square pyramid. The carboxyl-ate group that participates in coordination to the metal ion remains protonated; the other is deprotonated and coordination inactive. An intra-molecular O-H⋯O hydrogen bond between carboxyl-ate groups is observed. In the crystal, dimers are linked by O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, generating a three-dimensional network.

catena-Poly[[aqua-lithium(I)]-µ-3-carb-oxy-5,6-di-methyl-pyrazine-2-carboxyl-ato-κ(4) O (2),N (1):O (3),N (4)].

The asymmetric unit of the title compound, [Li(C8H6N2O4)(H2O)] n , comprises three Li cations, two of which are located on a twofold rotation axis, two carboxylate anions and three water mol-ecules, of which two are situated on the twofold rotation axis being aqua ligands. Both carboxylate anions are in µ2-bridging mode. All Li ions show a trigonal-bipyramidal coordination mode; the two located in special positions are bridged through N,O-bonding sites generating a polymeric ribbon along the c-axis direction. The Li cation in a general position creates an independent polymeric ribbon through N,O-bonding sites of the two symmetry-related ligands; the trigonal-bipyramidal coordination is completed by an aqua ligand. In both carboxylate anions, a carboxyl-ate and a carb-oxy-lic acid group form an intra-molecular hydrogen bond. The polymeric ribbons running along [001] are inter-connected by hydrogen bonds in which the water mol-ecules act as donors and carboxyl-ate O atoms act as acceptors, giving rise to a three-dimensional architecture.

Poly[hexa-aqua-bis-(µ(4)-pyrimidine-4,6-dicarboxyl-ato)tetra-lithium].

The asymmetric unit of the title compound, [Li(4)(C(6)H(2)N(2)O(4))(2)(H(2)O)(6)](n), comprises two Li(+) ions bridged by a completely deprotonated pyrimidine-3,6-dicarboxyl-ate ligand and coordinated by two water mol-ecules; the asymmetric units related by an inversion operation create a structural unit which forms part of a two-dimensional polymeric structure parallel to (10-1). One of the Li(+) ions shows a distorted tetra-hedral arrangement involving two symmetry-related coordinating water mol-ecules and two carboxyl-ate O atoms. The other Li(+) ion is in distorted trigonal-bipyramidal geometry defined by N and O atoms of the ligands and a water mol-ecule. Water O atoms are proton donors to carboxyl-ate O atoms forming hydrogen bonds.

Bis(µ(3)-pyrimidine-4-carboxyl-ato)bis-(µ(2)-pyrimidine-4-carboxyl-ato)tetra-kis-(aqua-lithium).

The asymmetric unit of the title compound, [Li(4)(C(5)H(3)N(2)O(2))(4)(H(2)O)(4)], contains two symmetry-independent Li(I) ions, two symmetry-independent ligands and two symmetry-independent coordinated water mol-ecules. They form a dinuclear unit in which the two Li(I) ions are bridged by two carboxyl-ate O atoms from the two ligands. Two dinuclear units related by an inversion centre form the tetra-meric mol-ecule. One of the Li(I) ions shows a distorted tetra-hedral coordination geometry, the other a distorted trigonal-bipyramidal environment. The tetra-mers are held together by hydrogen bonds in which coordinated water mol-ecules act as donors, and the carboxyl-ate O atoms act as acceptors. A hydrogen bond between coordinated water molecule as donor and a ring N atom as acceptor is also observed.

Poly[µ(2)-aqua-µ(2)-(pyrazine-2-carboxyl-ato)-lithium].

The structure of the title compound, [Li(C(5)H(3)N(2)O(2))(H(2)O)](n), contains an Li(I) ion with a distorted trigonal-bipyramidal coordination environment involving the N and O atoms of pyrazine-2-carboxyl-ate ligands with a bridging carboxyl-ate group, and two aqua O atoms also in a bridging mode. The symmetry-related Li(I) ions bridged by a carboxyl-ate O atom and a coordinating water O atom form an Li(2)O(2) unit with an Li⋯Li distance of 3.052 (4) Å, which generates mol-ecular ribbons propagating in the c-axis direction. The ribbons are held together by a network of O-H⋯O hydrogen bonds in which the coordinating water mol-ecules act as donors and the carboxyl-ate O atoms as acceptors.

Poly[bis-(µ(6)-benzene-1,3,5-tricarboxyl-ato-κ(7)O(1),O(1'):O(1'):O(3):O(3'):O(5):O(5'))tetra-kis-(dimethyl-formamide-κO)trimagnesium(II)].

The asymmetric unit of the polymeric title compound, [Mg(3)(C(9)H(3)O(6))(2)(C(3)H(7)NO)(4)](n), contains three Mg(II) ions bridged by carboxyl-ate O atoms from two fully deprotonated benzene-1,3,5-tricarboxyl-ate (BTC) trianions and four metal-coordinated dimethyl-formamide (DMF) mol-ecules. One Mg(II) ion is octa-hedrally coordinated by six carboxyl-ate O atoms. The other two cations are each octa-hedrally coordinated by four carboxyl-ate O atoms and two O atoms donated by two DMF mol-ecules: in one, the DMF mol-ecules are cis and in the other they are trans. The three Mg(II) octa-hedra form clusters, which are bridged by the BTC trianions, generating a three-dimensional structure.

Poly[hydrazin-1-ium [diaqua-bis-(µ(4)-pyridazine-3,6-dicarboxyl-ato)trilithate] monohydrate].

The structure of the title compound, {(N(2)H(5))[Li(3)(C(6)H(2)N(2)O(4))(2)(H(2)O)(2)]·H(2)O}(n), is composed of mol-ecular dimers, each built up of two symmetry-related Li(I) ions with distorted trigonal-bipyramidal coordinations bridged by two deprotonated ligand mol-ecules via their N,O-bonding sites. Doubly solvated Li(I) ions with a distorted tetra-hedral geometry link adjacent dimers, forming a polymer generated by bridging bidentate carboxyl-ato O atoms to Li(I) ions in adjacent dimers, forming anionic layers parallel to the ac plane with monoprotonated hydrazinium cations and crystal water mol-ecules positioned between them. The layers are held together by an extended system of hydrogen bonds in which the hydrazinium cations and coordinated and crystal water mol-ecules act as donors and carboxyl-ate O atoms act as acceptors.

trans-Diaqua-bis-(1H imidazolium-4,5-di-carboxyl-ato-κ(2)O(4),O(5))magnesium.

The title compound, [Mg(C(5)H(3)N(2)O(4))(2)(H(2)O)(2)], consists of centrosymmetric neutral monomers in which two O,O'-bidentate imidazolinium-4,5-dicarboxyl-ate ligands are bonded to the Mg(II) ion. One of the carboxyl protons is transferred to the N atom of the imidazole ring. The octa-hedral metal-ion coordination is completed by two trans water O atoms. In the crystal, mol-ecules are linked by N-H⋯(O,O) and O-H⋯O hydrogen bonds.

Bis(hydrazin-1-ium) bis-(µ(2)-pyridazine-3,6-dicarboxyl-ato)bis-(aqua-lithiate) octa-aqua-bis-(µ(3)-pyridazine-3,6-dicarboxyl-ato)tetra-lithium.

The unit cell of the title compound, (N(2)H(5))(2)[Li(2)(C(6)H(2)N(2)O(4))(2)(H(2)O)(2)]·[Li(4)(C(6)H(2)N(2)O(4))(2)(H(2)O)(8)], comprises two centrosymmetric complexes, one double negatively charged and one neutral, and two mono-protonated hydrazine cations. The anionic complex molecule is a dimer, built of a pair of symmetry-related pyridazine-3,6-dicarboxyl-ate ligands and a pair of Li(I) ions, each coordinated by two N,O-chelating sites donated by a ligand mol-ecule and an aqua O atom at the apical position. The penta-coordination around the Li(I) ions is partway between a trigonal-bipyramidal and a square-pyramidal arrangement. The two carb-oxy-lic acid groups of the ligand are deprotonated and one carboxyl-ate O atom of each group is not involved in the coordination, and this applies to both the anionic and the neutral complex. The neutral complex molecule is also composed of a pair of Li(I) ions and a pair of ligand mol-ecules related by a centre of symmetry. They form a dimeric core in which the penta-coordination of the Li(I) ions includes two N,O-bonding groups donated by two ligands and an aqua O atom. The penta-coordination is described as partway between a trigonal-bipyramidal and a square-pyramidal arrangement. The coordinated carboxyl-ate group is bidentate-bridging, forming with an Li(H(2)O)(3) unit a neutral tetra-meric mol-ecule. The coordination of the tetra-coordinated Li(I) ion shows a slightly distorted tetra-hedral geometry. An extended system of O-H⋯O and N-H⋯O hydrogen bonds contributes to the stability of the crystal structure.

catena-Poly[[(diaqua-zinc)-µ-3-carb-oxy-pyrazine-2-carboxyl-ato-κN,O;N,O] nitrate].

The crystal structure of the title compound, {[Zn(C(6)H(3)N(2)O(4))(H(2)O)(2)]NO(3)}(n), is built of zigzag cationic chains propagating in [010] with nitrate anions located in the space between the chains. The Zn(II) ion is coordinated by N and O atoms of two symmetry-related ligands in equatorial sites, and by two water O atoms at the axial sites of a distorted octa-hedron. One carboxyl-ate group of the ligand remains protonated, serving as a donor in a short intra-molecular O-H⋯O hydrogen bond. The coordinated water mol-ecules are donors and the nitrate O atoms act as acceptors in a network of O-H⋯O hydrogen bonds.