Film-Forming Capacity of Sn(II), Zr(IV), and Hf(IV) Acetylacetonates

Zr(acac)₄, Hf(acac)₄, and SnHacacCl₂ · 2H₂O were prepared in the solid state and in enthanol solutions. The film-forming capacity and thermal stability of these compounds were studied. Films of ZrO₂, HfO₂, and SnO₂ were prepared from film-forming solutions of the corresponding acetylacetonates.     

Polyrotaxane metal-organic frameworks (PMOFs)

Polyrotaxane metal-organic frameworks (PMOFs), a relatively rare branch of entangled networks, have received significant attention due to their unusual entanglement topologies. The PMOFs we described here are still at an early stage of development. This feature article summarizes the recent developments in structural types of PMOFs from our own group and others. We make some generalizations about the various classes of PMOFs, and develop the definitions and nomenclature of these entanglements, including classification into trivial and nontrivial polyrotaxanes, and limits on what constitutes a (nontrivial) polyrotaxane. Finally, the synthetic strategies toward the design and preparation of new PMOFs are elucidated.     

Solvent extraction of Hf(IV) and Zr(IV) with some 1-phenyl-3-methyl-4-acylpyrazolones-5

The distribution of Hf, Zr and Nb between aqueous solutions of mineral acids and solutions of 1-phenyl-3-methyl-4-acylpyrazolones-5 (acyl=acetyl, ethoxycarbonyl, butyryl, capronyl, capryl and benzoyl) in various organic solvents has been studied. The dependence of the distribution ratio of metal on the acidity of the aqueous phase, the analytical concentrations of reagents and metals, and on the organic solvent was investigated. The composition of the complex extracted is MeP₄ for Hf and Zr. The conditions for the separation of Zr, Hf and Nb are defined, and a comparison is made with extractions by means of thenoyltrifluoroacetone.     

Heterometallic metal-organic frameworks based on tris(dipyrrinato) coordination complexes

A novel class of heterometallic metal-organic frameworks (MOFs) has been synthesized and characterized. The MOFs rely on the use of tris(dipyrrinato) coordination complexes as the bridging structure and silver(I) ions as the linking unit. The building blocks and resulting MOFs have been structurally characterized by using single-crystal X-ray diffraction. The modular nature of this approach is demonstrated by the use of both iron(III) and cobalt(III) complexes. The MOFs have strong electronic absorption features originating from the metal-dipyrrin chromophore and have continuous channels throughout the lattice that are occupied by ordered and disordered solvent molecules.     

Proposal of a New Hf(IV)/Zr(IV) Separation System by the Solvent Extraction Method

A liquid-liquid extraction study has been conducted to separate hafnium from zirconium, using Cyanex 301 in kerosene. Noticeably, it is the first time that Cyanex 301 is utilized to separate Hf(IV) from Zr(IV). In this series of experiments, several parameters influencing the separation have been investigated, such as the initial pH, the extractant concentration, the metal ion concentration, the temperature, the type of the diluents and the salt addition. Regarding the aging of the Zr(IV) and Hf(IV) solutions, the solutions with a maximum 3 d aging time could be used with no difficulties. It was observed that the initial pH increase caused an increase in the Zr(IV)/Hf(IV) separation factor. Moreover, the distribution decreased with the temperature increase, suggesting that the reaction is exothermic. In agreement with the resulting data, the optimum separation factor illustrates the value of 7 at a pH of 4.00 in the presence of NaCl as an added salt. The attractive characteristics of the presently designed method are the use of low acidic nitrate solutions, the lack of using thiocyanate and a higher extractability of hafnium-Cyanex 301 relative to zirconium-Cyanex 301 complexes.     

Twelve-connected porous metal-organic frameworks with high H(2) adsorption

The twelve-connected metal-organic frameworks {[Ni(3)(OH)(L)(3)].n(solv)}(infinity) and {[Fe(3)(O)(L)(3)].n(solv)}(infinity) [LH(2) = pyridine-3,5-bis(phenyl-4-carboxylic acid)] have been prepared and characterised: these materials can be desolvated to form porous materials that show adsorption of H(2) up to 4.15 wt% at 77 K.     

Group IV M‐POSS (M=Zr,Hf) Coordination Polymers

The synthesis and characterization of Zr‐POSS and Hf‐POSS coordination polymers were reported. The IR data and the solid‐state ²⁹Si MAS NMR indicated the existence of Si? O? M linkage. The polarized optical microscopy images and the XRD data suggested their crystalline nature.     

Extraction-chromatographic behavior of Zr(IV) and Hf(IV) on TRU and LN resins in mixtures of HNO3 and HF

The behavior of group-4 homologs Zr and Hf on extraction-chromatographic sorbents LN resin and TRU resin in mixtures of HF and HNO₃ is considered. Distribution coefficients of the elements in the mixtures of 5·10⁻⁴ M–1 M HF and 0.01 M–5 M HNO₃ are determined. Strong retention of both elements was found on LN resin in the range of concentrations c(HF) ≤ 0.01 M for all concentrations of HNO₃. Retention tends to gradually disappear while increasing c(HF) to 0.5 M. On TRU resin retention is observed only in solutions with c(HNO₃) ≥ 2 M and c(HF) ≤ 0.01 M. The possibility of separating Zr(IV) and Hf(IV) on LN resin is illustrated in two different acid mixtures, whereas their separation on TRU resin under the conditions studied in this work is difficult. The results obtained can be used to isolate analytes from multicomponent mixtures during analytical tasks, as well as to separate them from each other.

     

Copper(II) camphorates with tunable pore size in metal-organic frameworks

Three new homochiral metal-organic coordination polymers [Cu₂camph₂dabco] · DMF•2H₂O, [Cu₂camph₂bipy] · 3DMF•2H₂O, and [Cu₂camph₂bpe] · 4DMF•2H₂O (H₂camph is (+)-camphoric acid, bipy is 4,4’-bipyridyl, bpe is trans-bis(4-pyridyl)ethylene) were synthesized by heating copper(II) nitrate, (+)-camphoric acid, and N-donor ligands of different length (dabco, bipy, bpe) in DMF and characterized by powder X-ray diffraction, IR spectroscopy, and TGA. The obtained compounds are isostructural with the previously reported porous zinc(II) camphorates.     

Synthesis, structure and luminescence properties of metal-organic frameworks based on benzo-bis(imidazole)

Metal-organic frameworks(MOFs)constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications.Compared to that from the ligands only,the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework.In this report,by using an organic ligand with azolate moiety,benzo-bis(imidazole)(H2BBI),we synthesized two new MOF structures.Framework 1([Co(H2BBI)(DMSO)2Cl2]n,DMSO=dimethyl sulfoxide),constructed from tetrahedral Co(II)and H2BBI,exhibits zigzag 1D structure.Meanwhile,framework 2([Cu2(H2BBI)3(DMSO)6(NO3)4]n),a layered structure with hcb topology,was assembled from tetragonal pyramidal Cu(II)and H2BBI.Furthermore,2 exhibits strong luminescence emission(ex=280 nm).A blue shift of 40 nm(from 359 nm to 319 nm)was observed in framework 2 compared to the free ligand,which could be explained by the ligand-to-metal charge transfer in the network.     

Simultaneous determination of Zr(IV) and Hf(IV) by CE using precolumn complexation with a [PW(11)O(39)](7-) ligand

A CE method was developed for the simultaneous determination of Zr(IV) and Hf(IV) at trace levels. A lacunary Keggin-type [PW(11)O(39)](7-) ligand reacted quantitatively with a mixture of trace amounts of Zr(IV) and Hf(IV) to form the so-called ternary Keggin-type anions [P(Zr(IV)W(11))O(40)](5-) and [P(Hf(IV)W(11))O(40)](5-) in 0.010 M monochloroacetate buffer (pH 2.2). Since both ternary anions possessed different electrophoretic mobilities and high molar absorptivities in the UV region, Zr(IV) and Hf(IV) were determined simultaneously with direct UV detection at 258 nm. Each peak height was linearly dependent on the concentration of Zr(IV) or Hf(IV) in the range of 5.0x10(-7)-1.0x10(-5) M; a detection limit of 2x10(-7) M was achieved. The utility of the proposed CE method was demonstrated for the simultaneous determination of Zr(IV) and Hf(IV) in natural water samples with satisfactory results.     

Fluoride-selective sensors based on polyurethane membranes doped with Zr(IV)-porphyrins

The feasibility of using Tecoflex polyurethane as a polymeric matrix for fluoride-selective membranes doped with Zr(IV)-octaethyl-(OEP) or Zr(IV)-tetraphenylporphyrins (TPP) is examined. Membranes containing cationic or anionic additives were prepared, with ionophore working according to neutral or charged carrier mechanism, respectively. Results are compared to those found previously using conventional poly(vinyl chloride) (PVC) as the membrane matrix. It was found that this polymer does not affect significantly the properties of these porphyrins, compared to poly(vinyl chloride) matrix. A dimer-monomer equilibrium determined recently to occur for Zr(IV)-porphyrins in PVC/o-NPOE membranes containing lipophilic anionic additives is also observed to occur (via UV-vis spectrophotometry) in the PU matrix. However, the equilibrium constants for dimer-monomer reactions appear to be lower in PU membranes compared to PVC films, as determined from the degree of super-Nernstian responses towards fluoride as well as the anion concentration ranges required to break the dimer as determined spectroscopically. Due to reduced dimerization of Zr(IV)[OEP]Cl₂ it was possible to obtain electrodes with PU/o-NPOE/KTFPB membranes exhibiting only slightly super-Nernstian (−64.6 mV/dec) response towards fluoride and response time (t₉₅ < 120 s) faster than observed for PVC-based membranes. Good working parameters were also obtained for this metalloporphyrin in PU membrane that forces neutral carrier mechanism (PU/DOS/TDMACl): F⁻ calibration slope −58.3 mV/dec and response time t₉₅ < 12 s. Tested membranes were subsequently applied for construction of miniaturized silicon-based sensors. Better fluoride selectivity was observed for sensors with Zr(IV)[OEP]Cl₂/PU/o-NPOE/KTFPB membranes (: ClO₄⁻ 0.7; Br⁻ −1.9; NO₃⁻ −1.9; Cl⁻ −3.1), compared to Zr(IV)[OEP]Cl₂/PU/DOS/TDMACl matrix (: ClO₄⁻ −0.8; Br⁻ −1.3; NO₃⁻ −1.5; Cl⁻ −2.1). However, latter composition was chosen to be better for flow measurement mode, as dimer formation can be totally prevented within this membrane. Sensors with Zr(IV)[OEP]Cl₂/PU/DOS/TDMACl maintained their characteristics at least for 2 months.     

Template induced structural isomerism and enhancement of porosity in manganese(II) based metal-organic frameworks (Mn-MOFs)

Three new metal-organic framework isomers have been synthesized by using the organic linker 5-triazole isophthalic acid and Mn(NO(3))(2)·xH(2)O. Structural conversions from non-porous to porous MOFs due to the template effect have been observed. The cross-sectional pore apertures of the resulting Mn-MOFs are comparable to the molecular dimensions of the template (pyrazine and 4,4'-bipyridine). The periodic increased porosity in Mn-MOFs depending on the size of the template used has been further confirmed by the CO(2) adsorption isotherms.     

Functional mixed metal-organic frameworks with metalloligands

Immobilization of functional sites within metal-organic frameworks (MOFs) is very important for their ability to recognize small molecules and thus for their functional properties. The metalloligand approach has enabled us to rationally immobilize a variety of different functional sites such as open metal sites, catalytic active metal sites, photoactive metal sites, chiral pore environments, and pores of tunable sizes and curvatures into mixed metal-organic frameworks (M'MOFs). In this Minireview, we highlight some important functional M'MOFs with metalloligands for gas storage and separation, enantioselective separation, heterogeneous asymmetric catalysis, sensing, and as photoactive and nanoscale drug delivery and biomedical imaging materials.     

CH(4) storage and CO(2) capture in highly porous zirconium oxide based metal-organic frameworks

A series of porous Zr oxoclusters-based MOFs was computationally explored for their gas storage/capture performances. The highly porous UiO-67(Zr) and UiO-68(Zr) solids show exceptionally high CH(4) and CO(2) adsorption capacities under operating conditions that make these thermal, water and mechanical resistant materials very promising for physisorption-based processes.     

Methanolysis of tetraphenylborate (BPh4(-)) as a reaction unit in halotris(2,4-pentadianato) complexes of Zr(IV) and Hf(IV)

The complexes {(C5H8O2)2Zr[(OCH3)2B(C6H5)2]2.1/2C12H10} (M = Zr (1) or Hf (2)) have been obtained from the reaction of [M(acac)3Cl] with sodium tetraphenylborate (BPh4(-)) in methanol. Crystal structures show 8-coordinate complexes with two 2,4-pentanedionato groups and two dimethoxydiphenylborate groups each coordinated through methoxy groups to the metal centre.