When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbents by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L–1. The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS, and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis d...

Zirconium-carbon hybrid sorbent for removal of fluoride from water: oxalic acid mediated Zr(IV) assembly and adsorption mechanism

A series of Mn(II), Cd(II), and Co(II) metal–organic frameworks, namely, {[Mn(L1)(NCS)2(CH3OH)2]·2(CH3OH)}n (1), {[Mn(L2)2(NCS)2(CH3OH)2]}n (2), {[Mn(L3)2(NCS)2]·0.5(CH3OH)·4.5H2O}n (3), {[Cd(L1)(I)2]·3(H2O)}n (4), {[Cd(L2)(I)2]}n (5), {[Cd(L3)(NCS)2]·2.5(H2O)}n (6), {[Co(L1)2(NCS)2]·4(H2O)}n (7), {[Co(L2)2(NCS)2]·(HCCl3) }n (8), and {[Co(L3)2(NCS)2]·3(H2O)}n (9) (where L1 = N,N′-bis(4-pyridylmethyl)-pyromellitic diimide, L2 = N,N′-bis(3-pyridylmethyl)-pyromellitic diimide, L3 = N,N′-bis(4-pyridylmethyl)-naphthalene diimide), were synthesized and structurally characterized by elemental analyses, thermogravimetric (TG) analyses, powder X-ray diffraction, IR spectroscopy, and single-crystal X-ray diffraction. In Mn(II) complexes 1–3, L1 connects the adjacent metal centers to form an infinite one-dimensional (1D) zigzag coordination polymeric chain, L2 acts as a monodentate ligand to give mononuclear coordination motifs, while L3 bridges two metal ions to generate two-dimensional (2D) networks of the (4, 4) ...

Structural Diversity of a Series of Mn(II), Cd(II), and Co(II) Complexes with Pyridine Donor Diimide Ligands

A new semirigid ditopic ligand, N,N′-bis(3-pyridylmethyl)naphthalene diimide (3-pmntd) has been synthesized, and five transition metal complexes, namely, [Cd2(3-pmntd)2I4]·2CHCl3 (1), [Hg(3-pmntd)Cl2]n (2), [Zn(3-pmntd)2(SCN)2]n (3), [Cd (3-pmntd)2(NO3)2]n (4) and {[Co2(3-pmntd)3(NO3)4]·2EtOH}n (5), have been obtained. Complex 1 forms discrete M2L2 metallacycles which are linked by C–H⋯O hydrogen bonds and π⋯π stacking interactions to result in a 2D layer. Complex 2 crystallizes in 1D chains which are further connected by C–H⋯O, C–H⋯Cl hydrogen bonds and π⋯π interactions into a 3D framework. Complexes 3 and 4 show a similar structural feature in the formation of non-interpenetrated 2D networks of (4,4) topology, while complex 5 displays a 2D network of (6,3) topology. The structural differences among these complexes are attributed to the different conformations adopted by the ligands, which are primarily induced by different metal centers with coordination environments restrained by different anions. Photoluminescent properties were also studied for selected complexes.

Synergistic metal and anion effects on the formation of coordination assemblies from a N,N′-bis(3-pyridylmethyl)naphthalene diimide ligand

Four semirigid ditopic ligands, N,N′-bis(3-pyridylmethyl)-pyromellitic diimide (L11), N,N′-bis(4-pyridylmethyl)-pyromellitic diimide (L22), N,N′-bis(3-pyridylmethyl)-naphthalene diimide (L33), and N,N′-bis(4-pyridylmethyl)-naphthalene diimide (L44), reacted with Cd(NO3)2 to result in four cadmium(II) complexes, namely, {[Cd2(L11)2(NO3)4(CH3OH)4]·H2O} (1), [Cd(L22)(NO3)2(CH3OH)2·Cd2(L22)3(NO3)4]·{4(HCCl3)·2H2O}n (2), {[Cd(L33)2(NO3)2]}n (3), and {[Cd(L44)2(NO3)2]·2(CHCl3)}n (4). These complexes have been characterized by elemental analyses, powder X-ray diffraction, thermogravimetric (TG) analyses, IR spectroscopy, and single-crystal X-ray diffraction. Structural analyses show that four types of structures are formed: (1) a discrete M2L2 ring with two Cd ions and two cis-L11 ligands comprising a zero-dimensional molecular rectangle (0D), (2) an unusual zigzag linear chain and a one-dimensional ladder existing simultaneously in the crystal lattice (1D), (3) a two-dimensional network of the (4,4) net structure (2D), and (4) an unusual chiral three-dimensional framework with 5-fold interpenetrating diamond (dia) topology (3D). In these complexes, the ligands exhibit different coordination modes and construct various architectures by bridging Cd(NO3)2 inorganic building blocks. These results suggest that structural diversity of the complexes is tunable by ligand modifications, that is, varying the ligand spacer bulkiness or substituent position of terminal group. Furthermore, gas adsorption measurements indicate that 4 possesses moderate CO2 uptake and some adsorption selectivity for CO2 over N2.

Construction of 0D to 3D cadmium complexes from different pyridyl diimide ligands

Three new zinc coordination polymers, namely {[Zn(4-pmntd)Cl2]·H2O}n (1), {[Zn(4-pmntd)(CH3CN)4]·(ClO4)2·H2O}n (2), and {[Zn(4-pmntd)(H2O)4]·(CF3SO3)2·3H2O}n (3) (4-pmntd = N,N′-bis(4-pyridylmethyl)-naphthalene diimide) have been synthesized by reactions of 4-pmntd with ZnCl2, Zn(ClO4)2, and Zn(CF3SO3)2, respectively. Compound 1 is an unusual one-dimensional (1D) single-stranded double helical chain containing tubular channels; 2 is an uncommon 1D zigzag chain arranged in a cross-like fashion to generate a 3D plywood-like array; 3 is a typical 1D zigzag chain arranged in a parallel array containing 1D quadrangle channels to accommodate the counter anions and water molecules. The structural diversity in these compounds is attributed to different coordination abilities, sizes, and geometries of counter anions. The anion exchange property of 3 was investigated.

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Anion effect on the structural diversity of three 1D coordination polymers based on a pyridyl diimide ligand

A series of organically directed bimetallic sulfates with one- and two-dimensional structures have been synthesized hydrothermally. The 2D structures with formulas (C2H10N2)2[FeIII2FeII(SO4)6(H2O)4]·2H2O, I, (C2H10N2)2[FeIII2CdII(SO4)6(H2O)4]·2H2O, II, and (C2H10N2)2[FeIII2NiII(SO4)6(H2O)4]·2H2O, III, have identical brick-wall layers constructed from infinite ferrinatrite-type {Fe2(SO4)3}n chains jointed by transition metal ions M2+ (M = Fe, Cd, Ni); the 1D structures with the compositions [C2N2H10][Fe3O(SO4)6La(H2O)6]·3H2O, IV, [C2N2H10][Fe3O(SO4)6Ce(H2O)6]·3H2O, V, and [C4N2H12]1.5[Fe3O(SO4)6Cd(H2O)5]·2H2O, VI, possess sulfated trinuclear iron oxo clusters that are interconnected by Ln3+ or Cd2+cations to extended straight or zigzag chains. The assembly of iron sulfate, resulting from the increase of the radii and coordination numbers of second metal centers, was modulated to afford a 1D chain or 0D cluster and further extended to form distinct 2D layer or 1D cluster-containing chain. The magnetic measu...

Organically Directed Bimetallic Sulfates Based on the Radii and Coordination Number: Synthesis, Structure and Characterization

The Ca and Zr atoms in the title compound, poly[octa­aqua­tetra-μ-oxalato-calciumdipotassiumzirconate(IV)], [CaK2Zr(C2O4)4(H2O)8], are chelated by bridging oxalate groups to form a three-dimensional network; the two independent water-coordinated K atoms occupy the space within the network and also inter­act with the oxalate O atoms to result in eight-coordination for the K atoms. The title compound is isostructural with [CdK2Zr(C2O4)4(H2O)8] [Jeanneau, Audebrand & Louer (2002). J. Mater. Chem. 12, 2383–2389]. All the metal ions occupy special positions with \overline{4} site symmetry.

Calcium dipotassium tetra­oxalatozirconate(IV) octa­hydrate

In the crystal structure of the title compound, poly[ammonium di-μ2-oxalato-bis­muthate(III) 3.72-hydrate], NH4[Bi(C2O4)2]·3.72H2O, the Bi3+ ion and the centre of the [NH4]+ ion lie on different special positions of \overline{4}m2 site symmetry, and the oxalate group and one water mol­ecule on different special positions of m site symmetry; the second water mol­ecule lies on a special position of 2/m site symmetry. The Bi atom is eight-coordinate in a slightly distorted dodeca­hedral environment. This single-crystal redetermination improves the precision of the previous powder diffraction study [Vanhoyland et al. (2004). Inorg. Chem. 43, 785–789], as all non-H atoms have been refined anisotropically.

Redetermination of ammonium bisoxalatobismuthate(III)x-hydrate from single-crystal data

# 2007 International Union of Crystallography All rights reserved The La atom in the title compound, Na4[La2(C2O4)5] 2H2O, is chelated by five oxalate groups in a bicapped squareantiprismatic geometry; one oxalate ligand is located on a centre of inversion. All oxalate groups function in a 2bridging mode, resulting in a three-dimensional network architecture. The Na cations are octahedrally coordinated by oxalate O atoms and water molecules, the latter bridging pairs of cations.

Tetrasodium(I) pentaoxalatodilanthanate(III) dihydrate

CO2 reduction by H2 using metal-free catalysts is highly challenging. Frustrated Lewis pairs (FLPs) have been considered potential metal-free catalysts for this reaction. However, most FLPs are unstable, which limits their practical applications. In this study, a class of novel metal-free catalysts composed of K3-nHnPO4 (n = 0, 1, 2) and B(C6F5-mHm)3 (m = 0, 3, 5) were prepared and identified as effective catalysts for CO2 hydrogenation to formate by density functional theory (DFT) calculations. The simulations show that the B-H bond formation is the rate-determining step (RDS). The acid/base strength and repulsive steric interactions affect the corresponding energy barrier. Therefore, the catalytic performance can be improved by choosing a suitable Lewis acid or base. Among these catalysts, the B(C6H5)3-KH2PO4 pair, with the lowest barrier height (26.3 kcal mol-1) in RDS, is suggested as a promising metal-free catalyst for CO2 hydrogenation. This study may provide strategies for designing new LP-based metal-free catalysts.

Jun-Ying Yang

Papers

Organically Directed Bimetallic Sulfates Based on the Radii and Coordination Number: Synthesis, Structure and Characterization

Calcium dipotassium tetraoxalatozirconate(IV) octahydrate

Redetermination of ammonium bisoxalatobismuthate(III)x-hydrate from single-crystal data

Tetrasodium(I) pentaoxalatodilanthanate(III) dihydrate

In silico design of metal-free hydrophosphate catalysts for hydrogenation of CO2 to formate.

Jun-Ying Yang

Papers

Organically Directed Bimetallic Sulfates Based on the Radii and Coordination Number: Synthesis, Structure and Characterization

Calcium dipotassium tetra­oxalatozirconate(IV) octa­hydrate

Redetermination of ammonium bisoxalatobismuthate(III)x-hydrate from single-crystal data

Tetrasodium(I) pentaoxalatodilanthanate(III) dihydrate

In silico design of metal-free hydrophosphate catalysts for hydrogenation of CO2 to formate.

Calcium dipotassium tetraoxalatozirconate(IV) octahydrate