A new type of supramolecular assembly consisting of crown ether complex cation and a polyoxometalate anion: Synthesis and crystal structure of [Na(C20H24O6)(CH3CN)2]2[Mo6O19] · 4CH3CN

A novel supramolecular assembly consisting of sodium-dibenzo-18-crown-6(DB18C6) complex cation [Na(C₂₀H₂₄O₆)(CH₃CN)₂]²⁺ and isopolyanion [Mo₆O₁₉]²⁻ has been demonstrated in the 3D structure of [Na(C₂₀H₂₄O₆)(CH₃CN)₂]₂[Mo₆O₁₉] · 4CH₃CN (1). Weak intermolecular forces (C–HO hydrogen bonds) between isopolyanion and crown ether play a significant role in the construction of supramolecular framework in the crystal structure of 1. Compound 1 has been characterized in the solid state by single crystal X-ray diffraction, IR, CHN analysis, and TGA.     

Electrochemical characterization of self-assembly process of nano-scaled polyoxomolybdate (NH4)42[Mo72Mo60O372(CH3COO)30(H2O)72]·ca.300H2O

Cyclic voltammetry and electrochemical admittance were used to characterize the self-assembly process of nano-scaled spheres of polyoxomolybdate (NH₄)₄₂[Mo^VI₇₂Mo^V₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]·ca.300H₂O·ca.10CH₃COONH₄) or {Mo₁₃₂}. Cyclic voltammetry indicated that the self-assembly process could be detected after 8 h and completed after one day. Electrochemical admittance showed that the molybdenum species in the CH₃COONH₄-CH₃COOH buffer (pH 4.46) were totally different from those in the pure (NH₄)₆Mo₇O₂₄ solution (pH 5.54) and the (NH₄)₆Mo₇O₂₄ solution (pH 4.21) acidified by hydrochloric acid. However, the molybdate species in the latter two solutions should be mixtures of non-protonated and/or protonated [Mo₇O₂₄]⁶⁻ and [Mo₈O₂₆]⁴⁻ anions. Detailed analysis of admittance results could support the existence of the molybdate species related to the {Mo^VI₆} fragment which was one of the components of {Mo₁₃₂} clusters. Admittance results on the self-assembly process were coincident with those from cyclic voltammetry.     

An intertwined double chain constructed by [SiMo12O40] clusters and unusual [Cu2(DF)2H2O] dimers

A new compound, {[Cu₂(DF)₂H₂O]₂SiMo₁₂O₄₀} (1) (DF = 4,5-diazafluoren-9-one), has been hydrothermally synthesized and characterized by routine methods and single crystal X-ray diffraction. In 1, all the DF only adopt the unusual bidentate coordination mode for the first time coordinating to Cu atoms to form copper-dimers which link [SiMo₁₂O₄₀]⁴⁻ clusters obtaining an intertwined double chain. Furthermore, the luminescent and electrochemical properties of the title compound have been studied.     

Selective determination of ascorbic acid with a novel hybrid material based 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and the Dawson type ion [P2Mo18O62] immobilized on glassy carbon

In this study, we synthesized a new hybrid material using well-Dawson K₆[P₂Mo₁₈O₆₂]·nH₂O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). CHN elemental analysis showed that one mole of [P₂Mo₁₈O₆₂]⁶⁻ reacts with 6 moles of [BMIM]⁺ to form [BMIM]₆P₂Mo₁₈O₆₂. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid material compared to the parent Dawson POM. The new hybrid material [BMIM]₆P₂Mo₁₈O₆₂ was immobilized on glassy carbon (GC) electrode and the modified electrode was investigated by cyclic voltammetry and amperometry. Compared to the electrochemical behavior of dissolved [P₂Mo₁₈O₆₂]⁶⁻, a slight shift in the redox peaks towards negative potentials is observed for the immobilized [BMIM]₆P₂Mo₁₈O₆₂. The relationship between the peak currents of the deposited [BMIM]₆P₂Mo₁₈O₆₂ film and scan rate is shown to be linear, which demonstrates a surface-confined electron transfer processes. [BMIM]₆P₂Mo₁₈O₆₂ modified electrode showed high sensitivities towards pH and shown to be active even at neutral pH. [BMIM]₆P₂Mo₁₈O₆₂ modified GC electrode was subjected to cyclic voltammetry and amperometry in the presence of ascorbic acid (AA) and found to exhibit a remarkable catalytic activity towards the oxidation of AA. The catalytic oxidation peak of AA at [BMIM]₆P₂Mo₁₈O₆₂ modified GC electrode occurs at low potential of ∼0 V vs Ag/AgCl at neutral pH and shifts to more positive potentials when pH decreases. Comparison between [BMIM]₆P₂Mo₁₈O₆₂ and [P₂Mo₁₈O₆₂]⁶⁻ modified GC films towards the oxidation of AA suggests that the significant decrease in the overpotentials recorded with [BMIM]₆P₂Mo₁₈O₆₂ film is related to the presence of ionic liquid cation in the hybrid material, which probably plays the role of the redox mediator. The resulting AA sensor [BMIM]₆P₂Mo₁₈O₆₂/GC has a significant sensitivity of ∼63 nA/μM AA, fast response time (<9 s), low detection limit (<0.1 μM), high selectivity towards endogenous interferences such as uric acid, acetaminophen and dopamine, a linear range from 0.1 μM to at least 22 mM AA and was stable for at least 2 weeks. In addition, such AA sensors can operate in a pH range from 0 to at least 7.     

Synthesis and structure of [{As(NBu)3}2Li6] containing an [As(NBu)3] trianion

Attempts to prepare the [As(N^tBu)₃]³⁻ trianion by the reaction of As(NMe₂)₃ with [^tBuNHLi]_n (1:3 monomer equiv.) proved unsuccessful. However, if the reaction is carried out with an excess of ^tBuNH₂ (3 equiv.) the target complex [{As(N^tBu)₃}₂Li₆] (1) is obtained. This is the first example of a complex containing an [As(NR)₃]³⁻ trianion.     

A zirconium-containing sandwich-type dimer based on trivacant α- and β-[GeW9O34] units, [Zr3O(OH)2(α-GeW9O34)(β-GeW9O34)]

A new zirconium-containing sandwich-type dimer based on trivacant α- and β-[GeW₉O₃₄]¹⁰⁻ units, [Zr₃O(OH)₂(α-GeW₉O₃₄)(β-GeW₉O₃₄)]¹²⁻, was synthesized and characterized by IR spectroscopy, UV electronic spectroscopy and single crystal X-ray diffraction. The central bent of the polyanion contains three oxygen atoms alternating with the three zirconium atoms. The polyanion represents a rare example of the sandwich POMs containing two different isomer subunits.     

Synthesis, crystal structure and NMR of [Na(DB18C6)(CH3CN)]3[α-AsM12O40] (M = Mo/W)

Two super-molecular complexes [Na(DB18C6)(CH₃CN)]₃[α-AsM₁₂O₄₀] (M = Mo/W) were obtained by solvothermal reaction and characterized by IR,¹H ¹³C and gUMBC NMR, X-ray. The result reveals that the complex consists of a [α-AsM₁₂O₄₀]³⁻ (M = Mo/W) anion with α-Keggin structure, and three complex [Na (DB18C6)(CH₃CN)]⁺ cations in which every sodium ion is located in the cavity of dibenzo-18-crown-6 with 6 Na–O bonds and coordinated with one of the terminal O atom of [α-AsM₁₂O₄₀]³⁻ (M = Mo/W) and the N atom of CH₃CN from two sides of the distorted DB18C6 plane, respectively. The three terminal O atoms linked with sodium ion are from a single M₃O₁₃ (M = Mo/W) triplet of the α-Keggin metalatoarsenate anion, and M–O_b (M = Mo/W) bonds exhibit alternating single–double bond character.     

Organically templated Np(IV) coordination polymer with in situ formed oxalate anion (ImidazoleH)[Np(C2O4)(CH3SO3)3(H2O)2]

The reaction of Np(V) methanesulfonate solution with imidazole led to the in situ formation of oxalic acid and the reduction of Np(V) to Np(IV). As a result, the novel organically templated organic polymer, (ImidazoleH)[Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂], was formed. The structure consists of infinite chains of [Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂]⁻ and imidazolium cations. The crystal structure is confirmed by IR and UV–vis spectroscopic data. This complex is the first example of structurally characterized 1:1 An(IV) oxalate.     

Synthesis, crystal structure and magnetic properties of a new three-dimensional porous framework: [Gd2(BDA)3(DMF)2(H2O)4] · 2DMF

The open framework compound of [Gd₂(BDA)₃(DMF)₂(H₂O)₄] · 2DMF (1), prepared by heating GdCl₃ with 2,2′-bipyridyl-4,4′-dicarboxylatic acid (BDA) in mixed solvent, is constructed from BDA linking up polymeric [GdO₅(DMF)(H₂O)₂]_n tethers. The 1D channels are filled with coordinated and uncoordinated DMF molecules hydrogen bonding to terminal aqua ligands. The study of the temperature dependent magnetic susceptibilities revealed that there are ferromagnetic interactions between intra-chain Gd^III atoms and weak antiferromagnetic interactions between inter-chain Gd^III atoms.     

Supramolecular π–π assembly of a neutral [Cu(salen)] complex via the templating effect of an ionic inorganic complex Na2[Cu(mnt)2] forming a framework type material having well-defined channels

A classical ionic inorganic complex Na₂[Cu(mnt)₂] (mnt²⁻ = maleonitriledithiolate = 1,2-dicyanoethylenedithiolate), that acts as a template in assembling neutral [Cu(salen)] (salen = bis(salicylidene)ethylenediamine) complexes forming a framework type arrangement, is accommodated in the channel formed in the crystal structure of a new type of host–guest compound [Cu(salen)]₄ · Na₂[Cu(mnt)₂] (1). The non-covalent supramolecular interactions among [Cu(salen)] complexes and between [Cu(salen)] and [Cu(mnt)₂]²⁻ complexes in the crystal lattice of 1 result in weak antiferromagnetic coupling.     

A new sandwich polyoxometalate based on Keggin-type monolacunary polyoxotungstoborate anion, [Zr(α-BW11O39)2]

A new sandwich-type polyoxometalate based on Keggin-type monolacunary anion, [Zr(α-BW₁₁O₃₉)₂]¹⁴⁻ was synthesized and characterized by IR spectroscopy, UV electronic spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction. This is the first report of crystal structure for the sandwich Keggin-type polyoxotungstoborate.     

Intercluster porous nanocomposites from combination of [AlO4Al12(OH)24(H2O)12]7+ cation and Anderson-type [Al1? x Cr x Mo6O24H6]3? anion: XRD, TG-DTA, SEM-EDAX and EPR studies

The synthesis of intercluster porous nanocomposites obtained from polyoxometallate compounds such as the [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ cation (named Al₁₃) and the Anderson-type [Al_1−x Cr _x Mo₆O₂₄H₆]³⁻ anion (named Al_1−x Cr _x Mo₆) has been performed in order to study the interaction between the two cluster ions, the stability of the XMo₆ planar configuration, the products obtained after thermal treatment, the structure and the local symmetry of the Cr³⁺ species. Chemical, thermal, structural and spectroscopic characterizations of the original and thermally treated phases have been followed by different techniques such as TG-DTA, XRD, SEM-EDAX, and mainly by EPR. All the results have shown that the structure of the intercluster nanocomposites (Al₁₃)(Al_1−x Cr _x Mo₆)₂ precursors is similar to that reported by Son et al. for the chromium-free (Al₁₃)(AlMo₆)₂ intercluster nanocomposite [Son et al., J. Am. Chem. Soc. 122 (2000) 7432]. After thermal treatment in air at several temperatures of the (Al₁₃)(Al_1−x Cr _x Mo₆)₂ nanocomposites the following phases have been observed and characterised: (i) at 400 °C an amorphous phase containing dispersed Cr³⁺ ions; (ii) at 700 °C a crystalline phase corresponding to Cr₂(MoO₄)₃/Al₂(MoO₄)₃ solid solutions; (iii) at 950 °C α-Al₂O₃/Cr₂O₃ solid solutions with a random dispersion of the Cr³⁺ ions.     

Ten-vertex osmamonocarbaboranes via arachno and nido {CB9} monocarbaboranes. Polyhedral contraction promoted by [OsCl2(PPh3)3] in MeOH and the crystal and molecular structure of [1-H-1,1-(PPh3)2-2-Ph-3-(OMe)-isocloso-1,2-OsCB8H7]

Reactions of [OsCl₂(PPh₃)₃] 1 with the [NEt₄]⁺ salts of the [6-Ph-nido-6-CB₉H₁₁]⁻ anion 2 and the [arachno-6-CB₉H₁₄]⁻ anion 3 each proceed selectively in methanol solution with the elimination of one boron-containing fragment from the starting cluster polyhedron, yielding together a short series of three novel 10-vertex hydridoosmamonocarbaboranes of isocloso {OsCB₈} cluster geometry.     

Two novel isomeric complexes supported by vanadates {V4O12}: [{Cu(dpa)2}2V4O12] (dpa = 2,2′-dipyridylamine)

Two Cu(II) complexes supported by tetravanadates, [{Cu(dpa)₂}₂V₄O₁₂] (1 and 2), have been synthesized under hydrothermal reactions. Structural analysis indicates that complexes 1 and 2 are isomeric and consist of a cyclic [V₄O₁₂]^4- anion bridged to two [Cu(dpa)₂]²⁺ moieties. Close inspection of complexes 1 and 2 reveals that the [V₄O₁₂]^4- anions adopt chair-like and boat-like configurations respectively, and are coordinated to each Cu(II) ions through a single terminal oxygen atom of two cross vanadium sites. Moreover, Complexes 1 and 2 exhibit trans- and cis-configurations, respectively.     

Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)₃]₃[P₂W₁₈O₆₂] has been synthesised and characterised by elemental analysis, spectroscopic (UV-vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu₄NPF₆ DMSO the complex shows a series of redox couples associated with the Os^3+/2+ and bipyridine ligands of the cationic [Os(bpy)₃]²⁺ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P₂W₁₈O₆₂]⁶⁻. At this electrolyte concentration, the Os³⁺ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu₄NPF₆ in addition to the Os^3+/2+ redox couple, the redox process associated with the [P₂W₁₈O₆₂]^8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os^2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.     

Ferromagnetic coupling in a novel dicyanamide-bridged dinuclear gadolinium(III) complex [Gd2(dca)4(OH)2 (NITpPy)4] (NITpPy = 4-pyridyl-nitronyl nitroxide radical)

The novel six-coordinated gadolinium(III) complex of formula [Gd₂(dca)₄(OH)₂(NITpPy)₄] (1) (dca = dicyanamide, NITpPy = 4-pyridyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-oxy-3-oxide) has been prepared and characterized by X-ray crystallography. Compound 1 is a dimer structure made up of double μ_1,5-dca-bridged gadolinium(III) ions and one terminal dca ligand; variable-temperature magnetic susceptibility measurements reveal the occurrence of a significant ferromagnetic interaction directly spin polarization through the NITpPy–Gd(III)–NITpPy pathway with J = 11.56 cm⁻¹.     

Synthesis, structure and photoluminescence of a novel palladium(I) compound: [Pd3(μ3-Cl)2(dppp)3][Pd2(μ2-Cl)3(PPh3)2](PPh3)2

Pd(PPh₃)₂Cl₂ reacts with PdCl₂ and 1,3-bis(diphenylphosphine)propane (dppp) in ethanol–DMF–pyridine mixed solvent to yield a novel palladium(I) compound [Pd₃(μ₃-Cl)₂(dppp)₃][Pd₂(μ₂-Cl)₃(PPh₃)₂](PPh₃)₂. It features an isolated structure based on [Pd₃(μ₃-Cl)₂(dppp)₃]⁺ cations having triangulo-palladium clusters and [Pd₂(μ₂-Cl)₃(PPh₃)₂]⁻ anions in which the coordination environment of palladium is an unusual tetrahedral geometry. Its photoluminescence is measured.     

Structure of a methylamine sorption complex of fully dehydrated Cd-exchanged zeolite X, Cd46(CH3NH2)16[Si100Al92O384]-FAU

The structure of a methylamine sorption complex of fully dehydrated, fully Cd²⁺-exchanged zeolite X, Cd₄₆(CH₃NH₂)₁₆[Si₁₀₀Al₉₂O₃₈₄]-FAU (a = 24.863(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1) °C. An aqueous exchange solution 0.05 M in Cd²⁺ was allowed to flow past the crystal for 5 days. The crystal was then dehydrated at 480 °C and 2 × 10⁻⁶ Torr for 2 days (colorless), and exposed to 160 Torr of methylamine gas at 21(1) °C for 2 h (yellow). Diffraction data were then gathered in this atmosphere and were refined using all data to the final error indices (based upon the 524 reflections for which F_o > 4σ(F_o)) of R₁ = 0.069 and wR₂ = 0.200. In this structure, Cd²⁺ ions occupy three crystallographic sites. The octahedral sites I at the centers of the hexagonal prisms are filled with 16 Cd²⁺ ions per unit cell (Cd–O = 2.369(8) Å). The remaining 30 Cd²⁺ ions are located at two non-equivalent sites II with occupancies of 14 and 16. The 16 methylamine molecules per unit cell lie in the supercage where each interacts with one of the latter 16 site-II Cd²⁺ ions: N–Cd = 2.11(8) Å. The imprecisely determined N–C bond length, 1.49(22) Å, agrees with that in gaseous methylamine, 1.474 Å. The positions of the hydrogen atoms were calculated. It appears that one of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and that the other forms a bifurcated hydrogen bond to this and another 6-ring oxygen. The methyl group is not involved in hydrogen bonding.     

New ferrocene-derived hydroxymethylphosphines: FcP(CH2OH)2 [Fc=(η-C5H5)Fe(η-C5H4)] and the dppf analogue 1,1-Fc[P(CH2OH)2]2 [Fc=Fe(η-C5H4)2]

Reactions of the ferrocene-phosphines FcPH₂ and 1,1^′-Fc^′(PH₂)₂ with excess formaldehyde gives the new hydroxymethylphosphines FcP(CH₂OH)₂ 1 and 1,1^′-Fc^′[P(CH₂OH)₂]₂ 2, respectively. Phosphine 1 is an air-stable crystalline solid, whereas 2 is isolated as an oil. Reaction of 1 with H₂O₂, S₈ or Se gives the chalcogenide derivatives FcP(E)(CH₂OH)₂ (E=O, S or Se), whilst reaction of 2 with S₈ gives 1,1^′-Fc^′[P(S)(CH₂OH)₂]₂, which were fully characterised. Phosphine 1 was also characterised by an X-ray crystal structure determination.     

Synthesis, structural characterization and third-order non-linear optical property of new three-dimensional metal-organic polymer [Fe2(μ10-btc)0.5(μ2-ox)0.5(μ2-O)1.5]n

One new metal-organic polymer formulated as [Fe₂(μ₁₀-btc)_0.5(μ₂-ox)_0.5(μ₂-O)_1.5]_n 1 (btc = 1,2,4,5-benzenetetracarboxylate, pyramellitate; ox = oxalate) has been synthesized by low-temperature solid-state reaction and characterized by single-crystal X-ray diffraction, elemental analyses, TGA, IR spectra and UV–visible spectra. Complex 1 presents the first 3D coordination network structure constructed by bridging btc, ox and O mixed ligands. In 1, carboxyl groups of btc are all deprotonated and they have a new type of μ₁₀-btc coordination mode. The third-order non-linear optical (NLO) properties of the title compound 1 were also investigated and they exhibit the reverse saturable absorption and self-defocusing performance with modulus of the hyperpolarizability (γ) 5.98 × 10⁻³⁰ esu for 1 in a 7.45 × 10⁻⁴ mol dm⁻³ DMF solution.