Cl/Cl isotope effects in Rh NMR of [RhCln(H2O)6−n] complex anions in hydrochloric acid solution as a unique ‘NMR finger-print’ for unambiguous speciation

A detailed analysis of the ³⁵Cl/³⁷Cl isotope effects observed in the 19.11 MHz ¹⁰³Rh NMR resonances of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6) in acidic solution at 292.1 K, shows that the ‘fine structure’ of each ¹⁰³Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These ³⁵Cl/³⁷Cl isotope effects in the ¹⁰³Rh NMR resonance of the [Rh^35/37Cl₆]³⁻ species manifest only as a result of the statistically expected ³⁵Cl/³⁷Cl isotopologues, whereas for the aquated species such as for example [Rh^35/37Cl₅(H₂O)]²⁻, cis-[Rh^35/37Cl₄(H₂O)₂]⁻ as well as the mer-[Rh^35/37Cl₃(H₂O)₃] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl₄(H₂O)₂]⁻, trans-[RhCl₄(H₂O)₂]⁻, fac-[RhCl₃(H₂O)₃] and mer-[RhCl₃(H₂O)₃] based on the ¹⁰³Rh NMR line shape, other than on the basis of their very similar δ(¹⁰³Rh) chemical shift. The ¹⁰³Rh NMR resonance structure thus serves as a novel and unique ‘NMR-fingerprint’ leading to the unambiguous assignment of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6), without reliance on accurate δ(¹⁰³Rh) chemical shifts.     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Hydrolysis of ammonium oxofluorotungstates: A F, O and W NMR study

Fluorine-19 and natural abundance ¹⁷O and ¹⁸³W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃. Dissolution of the (NH₄)₂WO₂F₄ complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W₂O₅F₆]⁴⁻, and unreacted cis-[WO₂F₄]²⁻. The cis(fac)-[W₂O₅F₆]⁴⁻ anion is the major soluble product resulting from the alkaline hydrolysis of (NH₄)₂WO₂F₄ along with the isolation of the solid (NH₄)₂WO₃F₂. In addition, the edge-bridging dimer, [W₂O₆F₄]⁴⁻, and the cyclic trimer, [W₃O₉F₆]⁶⁻, are also suggested as hydrolysis products. Decomposition of (NH₄)₃WO₃F₃ occurs in aqueous solution to give NH₄WO₃F.     

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Electrochemical behavior of hexafluoroniobate (Nb(V)F₆⁻), heptafluorotungstate (W(VI)F₇⁻), and oxotetrafluorovanadate (V(V)OF₄⁻) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F₆⁻ anion is reduced to Nb(IV)F₆²⁻ by a one-electron reversible reaction. Electrochemical reductions of W(VI)F₇⁻ and V(V)OF₄⁻ anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F₆⁻, W(VI)F₇⁻ and V(V)OF₄⁻ determined by chronoamperometry are 1.34 × 10⁻⁷, 7.45 × 10⁻⁸ and 2.49 × 10⁻⁷ cm² s⁻¹, respectively. The Stokes radii of Nb(V)F₆⁻, W(VI)F₇⁻, and V(V)OF₄⁻ in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.     

Phase diagram, crystal chemistry and thermoelectric properties of compounds in the Ca-Co-Zn-O system

In the Ca-Co-Zn-O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca₃(Co, Zn)₄O_9−z and Ca₃(Co,Zn)₂O_6−z at 885 °C in air. In Ca₃(Co,Zn)₄O_9−z, which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca₃(Co_3.8Zn_0.2)O_9−z. The compound Ca₃(Co,Zn)₂O_6−z (n=1 member of the homologous series, Ca_n+2(Co,Z_n)_n(Co,Zn)′O_3n+3−z) consists of one-dimensional parallel (Co,Zn)₂O₆⁶⁻ chains that are built from successive alternating face-sharing (Co,Zn)O₆ trigonal prisms and ‘n’ units of (Co,Zn)O₆ octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca₃Co₂O₆ to a small amount of approximately Ca₃(Co_1.95Zn_0.05)O_6−z. In the ZnO-CoO_z system, Zn substitutes in the tetrahedral Co site of Co₃O₄ to the maximum amount of (Co_2.49Zn_0.51)O_4−z and Co substitutes in the Zn site of ZnO to (Zn_0.94Co_0.06)O. The crystal structures of (Co_2.7Zn_0.3)O_4−z, (Zn_0.94Co_0.06)O, and Ca₃(Co_1.95 Zn_0.05)O_6−z are described. Despite the Ca₃(Co, Zn)₂O_6−z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT.     

Synthetic,structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/fumaric acid/N,N′-chelates tertiary reaction systems

The synthetic investigation of the Cu(ClO₄)₂·6H₂O/fumaric acid (H₂fum)/N,N’-chelates (1,10-phen, 2,2′-bpy) tertiary reaction systems has yielded mononuclear, dinuclear and tetranuclear complexes, and three coordination polymers. The chemical and structural identity of the products depends on the solvent, the absence or presence of external hydroxides in the reaction mixtures and the N,N’-donor. Three fumarato(−2) complexes, i.e. compounds [Cu₂(fum)(phen)₄](ClO₄)₂·2H₂O (1·2H₂O), [Cu(fum)(phen)(H₂O)]_n (3) and [Cu₂(fum)(bpy)₂(H₂O)₂]_n(ClO₄)_2n (6), were isolated and structurally characterized, and four non-fumarato complexes, i.e. compounds [Cu₄(μ₃-ΟΗ)₂(μ₂-ΟΗ)₂(phen)₄(H₂O)₂](ClO₄)₄·2H₂O (2·2H₂O), [Cu(ClO₄)(phen) (MeCN)₂(H₂O)](ClO₄) (4), [Cu(ClO₄)(phen)(MeCN)₂]_n(ClO₄)_n (5) and [Cu(ClO₄)₂(bpy)(MeCN)₂] (7), were simultaneously obtained from the reaction systems investigated. The coordination versatility of the fumarato(−2) ligand is reflected to the three different coordination modes observed in 1·2H₂O, 3 and 6; the monodentate bridging μ₂-κO:κO′ mode in 3, the asymmetric chelating bridging μ₂-κO:κO′:κO′′:κO′′′ mode in 1·2H₂O and 3, and the syn,syn bridging μ₄-κO:κO′:κO′′:κO′′′ mode in 6. The crystal structures of the complexes are stabilized by intra- and inter-molecular hydrogen bonding and π–π stacking interactions leading to interesting supramolecular architectures. Characteristic IR bands of the complexes are discussed in terms of the known structures, and the coordination modes of the fum²⁻ ligands.     

K2B12F12: A rare A2X structure for an ionic compound at ambient conditions

The anhydrous salt K₂B₁₂F₁₂ crystallized from aqueous solution and its structure was determined by single crystal X-ray diffraction. The Ni₂In-type structure it exhibits is rare for an A₂X ionic compound at 25 °C and 1 atm., consisting of an expanded hexagonal close-packed array of B₁₂F₁₂²⁻ centroids (cent?cent distances: 7.204-8.236 Å) with half of the K⁺ ions filling all of the O_h holes and half of the K⁺ ions filling all of the D_3h trigonal holes in the close-packed layers that are midway between two “empty” T_d holes. The structure is also unusual in that the bond-valence sum for the K⁺ ions in O_h holes is less than or equal to 0.73 (the bond-valence sum for the other type of K⁺ ion is 1.16). A variation of the Ni₂In structure is exhibited by the previously published monohydrate Cs₂(H₂O)B₁₂F₁₂, for which an improved structure is also reported here. For K₂B₁₂F₁₂: monoclinic, C2/c, a = 8.2072(8), b = 14.2818(7), c = 11.3441(9) Å, β = 92.832(5)°, Z = 4, T = 120(2) K. For Cs₂(H₂O)B₁₂F₁₂: orthorhombic, P2₁2₁2₁, a = 9.7475(4), b = 10.2579(4), c = 15.0549(5) Å, Z = 4, T = 110(1) K.     

The effect of F-doping and temperature on the structural and textural evolution of mesoporous TiO2 powders

Mesoporous F⁻-doped TiO₂ powders were prepared by hydrolysis of titanium tetraisopropoxide (TTIP) in a mixed NH₄F-H₂O solution. Effects of F⁻ ion content and calcination temperatures on the phase composition and porosity of mesoporous titania were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and BET surface areas. The results showed the BET surface area (S_BET) of the pure and doped powders dried at 100°C ranged from 260 to 310 m²/g as determined by nitrogen adsorption. With increasing calcination temperatures, the S_BET values of the calcined titania powders decreased due to the increase in crystalline size. The pore size distribution was bimodal with fine intra-particle pore and larger inter-particle pore as determined by nitrogen adsorption isotherms. The peak pore diameter of intra-particle pore increases with increasing F⁻ ion content. At 700°C, all the titania powders exhibit monomodal pore size distributions due to the complete collapse of the intra-particle pores. The crystallization of anatase was obviously enhanced due to F⁻-doping at 400°C and 500°C. Moreover, with increasing F⁻ ion concent, F⁻ ions not only suppressed the formation of brookite phase at low temperature, but also prevented phase transition of anatase to rutile at high temperature.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Adsorption of fluoride on synthetic siderite from aqueous solution

The study has investigated the feasibility of using synthetic siderite for F⁻ removal from aqueous solution. Batch experiments were performed to test effects of adsorbent dosage, contact time, initial F⁻ concentration, temperature, solution pH, and coexisting anions on F⁻ removal. Results show that the kinetic rate of F⁻ adsorption was high in the first 2 h, and thereafter significantly decreased. The kinetic data was better fitted to the pseudo-second order kinetic model than the pseudo-first order kinetic model. In comparison with Langmuir isotherm, both Freundlich and Redlich-Peterson isotherms better described the adsorption process, which indicates that the multilayer adsorption should be involved in the process of F⁻ removal. Thermodynamic study manifests that F⁻ adsorption on synthetic siderite was spontaneous and exothermic in nature. The synthetic siderite had high adsorption capacity for F⁻ removal, which was up to 1.775 mg/g in the batch with an adsorbent dosage of 5 g/L and an initial F⁻ concentration of 20 mg/L at 25 °C. The adsorption was relatively independent on solution pH between 4 and 9. The presence of Cl⁻ and NO₃⁻ had less impact on F⁻ adsorption, while PO₄³⁻ significantly affected F⁻ removal from aqueous solution. Results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) suggest that the high adsorption capacity possibly arose from both coprecipitation of ferric hydroxide with F⁻ and adsorption of F⁻ on the fresh goethite.     

Complexes derived from the copper(II)/succinamic acid/N,N′,N″-chelate tertiary reaction systems: Synthesis,structural and spectroscopic studies

The use of succinamic acid (H₂sucm) in Cu^II/N,N′,N″-donor [2,2′:6′,2″-terpyridine (terpy), 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (dmbppy)] reaction mixtures yielded compounds [Cu(Hsucm)(terpy)]_n(ClO₄)_n (1), [Cu(Hsucm)(terpy)(MeOH)](ClO₄) (2), [Cu₂(Hsucm)₂(terpy)₂](ClO₄)₂ (3), [Cu(ClO₄)₂(terpy)(MeOH)] (4), [Cu(Hsucm)(dmbppy)]_n(NO₃)_n·3nH₂O (5^.3nH₂O), and [CuCl₂(dmbppy)]·H₂O (6·H₂O). The succinamate(−1) ligand exists in four different coordination modes in the structures of 1–3 and 5, i.e., the μ₂-κO:κO′:κO″ in 1 and 5 which involves asymmetric chelating coordination of the carboxylato group and ligation of the amide O-atom leading to 1D coordination polymers, the μ₂-κ²O:κO′ in 3 which involves asymmetric chelating and bridging coordination of the carboxylato group, and the asymmetric chelating mode in 2. The primary amide group, either coordinated in 1 and 5, or uncoordinated in 2 and 3, participate in hydrogen bonding interactions, leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of complex 5·3nH₂O was monitored by TG/DTG and DTA measurements.     

Crystal chemistry of M[PO2(OH)2]2·2H2O compounds (M=Mg, Mn, Fe, Co, Ni, Zn, Cd): Structural investigation of the Ni, Zn and Cd salts

The compounds M[PO₂(OH)₂]₂·2H₂O (M=Mg, Mn, Fe, Co, Ni, Zn, Cd) were prepared from super-saturated aqueous solutions at room temperature. Single-crystal X-ray structure investigations of members with M=Ni, Zn, Cd were performed at 295 and 120 K. The space-group symmetry is P2₁/n, Z=2. The unit-cell parameters are at 295/120 K for M=Ni: a=7.240(2)/7.202(2), b=9.794(2)/9.799(2), c=5.313(1)/5.285(1) Å, β=94.81(1)/94.38(1)°, V=375.4/371.9 Å³; M=Zn: a=7.263(2)/7.221(2), b=9.893(2)/9.899(3), c=5.328(1)/5.296(2) Å, β=94.79(1)/94.31(2)°, V=381.5/377.5 Å³; M=Cd: a=7.356(2)/7.319(2), b=10.416(2)/10.423(3), c=5.407(1)/5.371(2) Å, β=93.85(1)/93.30(2)°, V=413.4/409.1 Å³. Layers of corner-shared MO₆ octahedra and phosphate tetrahedra are linked by three of the four crystallographically different hydrogen bonds. The fourth hydrogen bond (located within the layer) is worth mentioning because of the short O_h?O bond distance of 2.57-2.61 Å at room temperature (2.56-2.57 Å at 120 K); only for M=Mg it is increased to 2.65 Å. Any marked temperature-dependent variation of the unit-cell dimension is observed only vertical to the layers. The analysis of the infrared (IR) spectroscopy data evidences that the internal PO₄ vibrations are insensitive to the size and the electronic configuration of the M²⁺ ions. The slight strengthening of the intra-molecular P-O bonds in the Mg salt is caused by the more ionic character of the Mg-O bonds. All IR spectra exhibit the characteristic “ABC trio” for acidic salts: 2900-3180 cm⁻¹ (A band), 2000-2450 cm⁻¹ (B band) and 1550-1750 cm⁻¹ (C band). Both the frequency and the intensity of the A band provide an evidence that the PO₂(OH)₂ groups in M[PO₂(OH)₂]₂·2H₂O compounds form weaker hydrogen bonds as compared with other acidic salts with comparable O?O bond distances of about 2.60 Å. The observed shift of the O-H stretching vibrations of the water molecule in the order M=Mg>Mn≈Fe≈Co>Ni>Zn≈Cd has been discussed with respect to the influence of both the character and the strength of M↔H₂O interactions.     

Synthesis and characterization of sulfate and dodecylbenzenesulfonate intercalated zinc-iron layered double hydroxides by one-step coprecipitation route

Inorganic sulfate- and organic dodecylbenzenesulfonate (DBS)-intercalated zinc-iron layered double hydroxides (LDHs) materials were prepared by one-step coprecipitation method from a mixed salt solutions containing Zn(II), Fe(II) and Fe(III) salts. The as-prepared samples have been characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption, scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), and Mössbauer spectroscopy (MS). The XRD analyses demonstrate the typical LDH-like layered structural characteristics of both products. The room temperature MS results reveal the characteristics of both the Fe(II) and Fe(III) species for SO₄²⁻-containing product, while only the Fe(III) characteristic for DBS-containing one. The combination characterization results and Rietveld analysis illustrate that the SO₄²⁻-containing product possesses the Green Rust two (GR2)-like crystal structure with an approximate chemical composition of [Zn_0.435·Fe^II_0.094·Fe^III_0.470·(OH)₂]·(SO₄²⁻)_0.235·1.0H₂O, while the DBS-containing one exhibits the common LDH compound-like structure. The contact angle measurement indicates the evident hydrophobic properties of DBS-containing nanocomposite, compared with SO₄²⁻-containing product, due to the modification of the internal and external surface of LDHs by the organic hydrophobic chain of DBS.     

Synthesis, structure and magnetic properties of the S=1/2, one-dimensional antiferromagnet, Y5Re2O12

Single crystals of Y₅Re₂O₁₂ have been grown, and the crystal structure has been determined by X-ray diffraction. This compound crystallizes in space group C2/m with cell dimensions of a=12.4081(10) Å b=5.6604(5)Å, c=7.4951(6) Å, β=107.837(3)°, Z=2. The final refinement led to R1=0.0238, WR2=0.0459 for 1053 observed reflections with F>4σ(F₀). Edge-sharing ReO₆ octahedra form infinite linear [ReO₂O_4/2]_n chains along the b direction with alternating short and long Re-Re distances. Three crystallographically independent yttrium atoms surround O2 to form OY₄ tetrahedra, which share edges and corners in the ab plane to form a two-dimensional Y₅O₄ network which separates the [ReO₂O_4/2]_n magnetic chains. This compound is therefore isostructural with the series Ln₅Re₂O₁₂Ln=Gd-Lu, which have been known since 1969. The average Re oxidation state is +4.5 in the chains and a reasonable, if qualitative MO scheme results in one unpaired electron per Re dimer. Consistent with this, magnetic susceptibility data can be fitted to the one-dimensional antiferromagnetic Heisenberg model with S=1/2 and parameters J^intra/k=−89(1)K, g=2.15(4) and χ(TIP)=5(1)×10⁻⁴ emu/mol. There is no sign of long-range magnetic order down to 2 K. These results are contrasted with those for the isostructural Y₅Mo₂O₁₂.     

Naked eye sensing of anions using thiourea based chemosensors with real time application

Novel chromogenic sensors with thiourea moiety as receptor unit were synthesized and characterized using IR and NMR spectroscopic techniques. The receptors 1 and 2 bearing hydrogen bonding site demonstrate visually striking color change, UV–vis, and fluorescence responses for F⁻, AcO⁻, and OH⁻ over other anions such as Cl⁻, Br⁻, H₂PO₄⁻ and HSO₄⁻. Both the receptors 1 and 2 demonstrate detection limit at micro molar level. Further insight to the nature of interaction between receptors and anions was studied using ¹H NMR titration experiment. In particular, the fluoride of tooth paste and mouthwash in water phase can be detected by receptor 2.     

Synthesis and characterization of three new fluorovanadate complexes: N(C2H5)4[VOF4], N(CH3)4[VOF3Cl], N(C4H9)4[VOF3Br] and theoretical calculations of VOF4, VOF3Cl and VOF3Br ions

The reaction of VOF₃ with (C₂H₅)₄NF, (CH₃)₄NCl and (C₄H₉)₄NBr salts in anhydrous CH₃CN produced new complexes with the anion general formula [VOF₃X]⁻ in that (X = F⁻, Cl⁻, Br⁻). These were characterized by elemental analysis, IR, UV/Visible and ¹⁹F NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the VX (X = F, Cl, Br) bond length values for the [VOF₃X]⁻ in compounds 1-3 are 1.8247, 2.4031 and 2.5595 Å, respectively. Also, the VF₅ bond length values in [VOF₃X]⁻ are 1.824, 1.812 and 1.802 Å, respectively. These results reveal that the bond order for VX bonds decrease from compounds 1 to 3, while for VF₅ bonds, the bond orders increase. It can be concluded that the decrease of VX bonds lengths and the increase of VF₅ bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF₄⁻, VOF₃Cl⁻ and VOF₃Br⁻ are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site.     

Structural, spectroscopic and photoluminescence studies of LiEu(WO4)2−x(MoO4)x as a near-UV convertible phosphor

A series of lithium europium double tungsto-molybdate phosphors LiEu(WO₄)_2−x(MoO₄)_x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the ⁵D₀→⁷F₂ emission of Eu³⁺ activated at wavelength of 396 nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the ⁵D₀→⁷F₂ transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO₄)_2−x(MoO₄)_x is investigated and discussed.     

The tunable coordination architectures of a flexible multicarboxylate N-(4-carboxyphenyl)iminodiacetic acid via different metal ions, pH values and auxiliary ligand

{[Pb₃(CPIDA)₂(H₂O)₃]·H₂O}_n1, {[Cd₃(CPIDA)₂(H₂O)₄]·5H₂O}_n2, [Cd(HCPIDA)(bpy)(H₂O)]_n3 (bpy=4,4′-bipyridine) and {[Co₃(CPIDA)₂(bpy)₃(H₂O)₄]·2H₂O}_n4 were synthesized with N-(4-carboxyphenyl) iminodiacetic acid (H₃CPIDA). In 1, the CPIDA³⁻ ligands adopt chelating and bridging modes with Pb(II) to possess a 3D porous framework. In 2D-layer 2, the CPIDA³⁻ ligands display a simple bridging mode with Cd(II). The 2D layers have parallelogram-shaped channels along a axis. With bpy ligands, the HCPIDA²⁻ ligands in 3 show more abundant modes, but 3 still displays a 2D sheet on bc plane for the unidentate bpy molecules. However, in 3D-framework 4, the bpy ligands adopt bridging bidentate at a higher pH value and the CPIDA³⁻ ligands show bis-bidentate modes with Co(II). Additionally, 2D correlation analysis of FTIR was introduced to ascertain the characteristic adsorptions location of the carboxylate groups with different coordination modes in 4 with thermal and magnetic perturbation. Compounds 1, 2 and 4 exhibit the fluorescent emissions at room temperature.     

Zr1−xLnxW2O8−x/2 (Ln=Eu, Er, Yb): Solid solutions of negative thermal expansion-synthesis, characterization and limited solid solubility

Zr_1−xLn_xW₂O_8−x/2 solid solutions (Ln=Eu, Er, Yb) of different substitution fractions x have been synthesized. Their X-ray diffraction (XRD) patterns have been indexed and lattice parameters calculated based on the α-ZrW₂O₈ structure. The coefficients of thermal expansion (CTEs) of these solid solutions were estimated to be −10.3×10⁻⁶ K⁻¹ in temperature range of 30-100 °C. The solubility of lanthanide ions in these solid solutions decreases linearly with the increase in the radius of substituted lanthanide ions. Based on the concentration dependence of phase transition temperatures, a novel method for determination of solubility of the lanthanide ions in Zr_1−xLn_xW₂O_8−x/2 solid solutions has been developed. This method seems to be more sensitive as compared with that based on XRD technique.