Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry

Electrospray ionization (ESI) of uranyl nitrate solutions generates a wide variety of positively and negatively charged ions, including complex adducts of uranyl ions with methoxy, hydroxy, and nitrate ligands. In the positive ion mode, ions detected by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are sensitive to instrumental tuning parameters such as quadrupole operating frequency and trapping time. Positive ions correspond to oligomeric uranyl nitrate species that can be characterized as having a general formula of [(UO(2))(n)(A)(m)(CH(3)OH)(s)](+) or [(UO(2))(n)(O)(A)(m)(CH(3)OH)(s)](+) with n = 1-4, m = 1-7, s = 0 or 1, and A = OH, NO(3), CH(3)O or a combination of these, although the formation of NO(3)-containing species is preferred. In the negative ion mode, complexes of the form [(UO(2))(NO(3))(m)](-) (m = 1-3) are detected, although the formation of the oxo-containing ions [(UO(2))(O)(n)(NO(3))(m)](-) (n = 1-2, m = 1-2) and the hydroxy-containing ions [(UO(2))(OH)(n)(NO(3))(m)](-) (n = 1-2, m = 0-1) are also observed. The extent of coordinative unsaturation of both positive and negative ions can be determined by ligand association/exchange and H/D exchange experiments using D(2)O and CD(3)OD as neutral reaction partners in the gas-phase. Positive ions are of varying stability and reactivity and may fragment extensively upon collision with D(2)O, CD(3)OD and N(2) in sustained off-resonance irradiation/collision-induced dissociation (SORI-CID) experiments. Electron-transfer reactions, presumably occurring during electrospray ionization but also in SORI-CID, can result in reduction of U(VI) to U(V) and perhaps even U(IV).     

Large cluster formation through multiple substitution with lanthanide cations (La, Ce, Nd, Sm, Eu, and Gd) of the polyoxoanion

Several new large polyoxotungstates have been synthesized by reaction of lanthanide cations with the well-known "As(4)W(40)" anion, [(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)](28-) (1). The heteropolyanions [(H(2)O)(11)Ln(III)(Ln(III)(2)OH)(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)](20)(-) (Ln = Ce, Nd, Sm, Gd) (2-4) (Ln(3)As(4)W(40)) and [M(m)()(H(2)O)(10)(Ln(III)(2)OH)(2)(B-alpha-AsO(3)W(9)O(30))(4)(WO(2))(4)]((18-m)(-)) (Ln = La, Ce, Gd and M = Ba, K, none) (5-7) (Ln(4)As(4)W(40)) have been isolated as alkali metal and ammonium salts, respectively, and characterized by single-crystal X-ray analysis, elemental analysis, and IR and (183)W-NMR spectroscopy. The X-ray analyses revealed interanionic W-O-Ln bonds between adjacent Ln(x)()As(4)W(40) units forming a "dimer" for x = 3 and chains for x = 4. Upon dissolving in water these bonds hydrolyze and the monomeric species form. The straightforward syntheses which require the use of concentrated NaCl solutions (1-4 M) and the addition of stoichiometric amounts of Ba(2+) or K(+) reemphasize the importance of the presence of appropriate countercations for the assembly of large polyoxometalate structures.     

应用MALDI-FTICRMS技术研究气相中含钨系列离子簇

以Keggin型磷钨酸为原料, 2,5-二羟基苯乙酮(DHAP)和2,4,6-三羟基苯乙酮(THAP)为基质, 使用基质辅助激光解吸/电离-傅里叶变换离子回旋共振质谱(MALDI-FTICRMS)技术研究气相中金属相关簇的稳定性及气相离子-分子反应. 在气相中获得不同系列的-1价含钨离子簇, 准确确定各系列离子簇的组成及Magic Numbers物种, 并发现基质与钨相互作用生成有机-无机杂化离子簇系列. 结果表明, MALDI-FTICRMS技术适用于研究气相中团簇离子的稳定性及气相离子-分子反应.     

Periodic trends in hexanuclear actinide clusters

Four new Th(IV), U(IV), and Np(IV) hexanuclear clusters with 1,2-phenylenediphosphonate as the bridging ligand have been prepared by self-assembly at room temperature. The structures of Th(6)Tl(3)[C(6)H(4)(PO(3))(PO(3)H)](6)(NO(3))(7)(H(2)O)(6)·(NO(3))(2)·4H(2)O (Th6-3), (NH(4))(8.11)Np(12)Rb(3.89)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(24)·15H(2)O (Np6-1), (NH(4))(4)U(12)Cs(8)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(24)·18H(2)O (U6-1), and (NH(4))(4)U(12)Cs(2)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(18)·40H(2)O (U6-2) are described and compared with other clusters of containing An(IV) or Ce(IV). All of the clusters share the common formula M(6)(H(2)O)(m)[C(6)H(3)(PO(3))(PO(3)H)](6)(NO(3))(n)((6-n)) (M = Ce, Th, U, Np, Pu). The metal centers are normally nine-coordinate, with five oxygen atoms from the ligand and an additional four either occupied by NO(3)(-) or H(2)O. It was found that the Ce, U, and Pu clusters favor both C(3i) and C(i) point groups, while Th only yields in C(i), and Np only C(3i). In the C(3i) clusters, there are two NO(3)(-) anions bonded to the metal centers. In the C(i) clusters, the number of NO(3)(-) anions varies from 0 to 2. The change in the ionic radius of the actinide ions tunes the cavity size of the clusters. The thorium clusters were found to accept larger ions including Cs(+) and Tl(+), whereas with uranium and later elements, only NH(4)(+) and/or Rb(+) reside in the center of the clusters.     

Synthesis, crystal structure and optical properties of [Ag(UO2)3(OAc)9][Zn(H2O)4(CH3CH2OH)2]: a novel compound containing closed-shell 3d10, 4d10 and 5d10 metal ions

[Ag(UO(2))(3) (OAc)(9)][Zn(H(2)O)(4)(CH(3)CH(2)OH)(2)] (, OAc = CH(3)COO(-)) crystallized from an ethanol solution and its structure was determined by IR spectroscopy, elemental analysis, (1)H NMR, (13)C NMR and X-ray crystallography; it is composed of [Zn(H(2)O)(4)(CH(3)CH(2)OH)(2)](2+) cations and [Ag(UO(2))(3)(OAc)(9)](2-) anions in which triuranyl [(UO(2))(OAc)(3)](3) clusters are linked by the Ag ion.     

Synthesis of a uranyl persulfide complex and quantum chemical studies of formation and topologies of hypothetical uranyl persulfide cage clusters

The compound Na(4)[(UO(2))(S(2))(3)](CH(3)OH)(8) was synthesized at room temperature in an oxygen-free environment. It contains a rare example of the [(UO(2))(S(2))(3)](4-) complex in which a uranyl ion is coordinated by three bidentate persulfide groups. We examined the possible linkage of these units to form nanoscale cage clusters analogous to those formed from uranyl peroxide polyhedra. Quantum chemical calculations at the density functional and multiconfigurational wave function levels show that the uranyl-persulfide-uranyl, U-(S(2))-U, dihedral angles of model clusters are bent due to partial covalent interactions. We propose that this bent interaction will favor assembly of uranyl ions through persulfide bridges into curved structures, potentially similar to the family of nanoscale cage clusters built from uranyl peroxide polyhedra. However, the U-(S(2))-U dihedral angles predicted for several model structures may be too tight for them to self-assemble into cage clusters with fullerene topologies in the absence of other uranyl-ion bridges that adopt a flatter configuration. Assembly of species such as [(UO(2))(S(2))(SH)(4)](4-) or [(UO(2))(S(2))(C(2)O(4))(4)](4-) into fullerene topologies with ~60 vertices may be favored by use of large counterions.     

Syntheses, characterization, and magnetic studies of copper(II) complexes with the ligand N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-benzenediamine (1,3-tpbd) and its phenol derivative 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresol] (2,6-Htpcd)

The copper(II) complexes [Cu(4)(1,3-tpbd)(2)(H(2)O)(4)(NO(3))(4)](n)(NO(3))(4n)·13nH(2)O (1), [Cu(4)(1,3-tpbd)(2)(AsO(4))(ClO(4))(3)(H(2)O)](ClO(4))(2)·2H(2)O·0.5CH(3)OH (2), [Cu(4)(1,3-tpbd)(2)(PO(4))(ClO(4))(3)(H(2)O)](ClO(4))(2)·2H(2)O·0.5CH(3)OH (3), [Cu(2)(1,3-tpbd){(PhO)(2)PO(2)}(2)](2)(ClO(4))(4) (4), and [Cu(2)(1,3-tpbd){(PhO)PO(3)}(2)(H(2)O)(0.69)(CH(3)CN)(0.31)](2)(BPh(4))(4)·Et(2)O·CH(3)CN (5) [1,3-tpbd = N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-benzenediamine, BPh(4)(-) = tetraphenylborate] were prepared and structurally characterized. Analyses of the magnetic data of 2, 3, 4, and [Cu(2)(2,6-tpcd)(H(2)O)Cl](ClO(4))(2) (6) [2,6-tpcd = 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresolate] show the occurrence of weak antiferromagnetic interactions between the copper(II) ions, the bis-terdentate 1,3-tpbd/2,6-tpcd, μ(4)-XO(4) (X = As and P) μ(1,2)-OPO and μ-O(phenolate) appearing as poor mediators of exchange interactions in this series of compounds. Simple orbital symmetry considerations based on the structural knowledge account for the small magnitude of the magnetic couplings found in these copper(II) compounds.     

Structures of [(CO2)n(H2O)m]- (n=1-4, m=1,2) cluster anions. I. Infrared photodissociation spectroscopy

The infrared photodissociation spectra of [(CO(2))(n)(H(2)O)(m)](-) (n=1-4, m=1, 2) are measured in the 3000-3800 cm(-1) range. The [(CO(2))(n)(H(2)O)(1)](-) spectra are characterized by a sharp band around 3570 cm(-1) except for n=1; [(CO(2))(1)(H(2)O)(1)](-) does not photodissociate in the spectral range studied. The [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2) species have similar spectral features with a broadband at approximately 3340 cm(-1). A drastic change in the spectral features is observed for [(CO(2))(3)(H(2)O)(2)](-), where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm(-1). Ab initio calculations are performed at the MP2/6-311++G(**) level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO(2))(n)(H(2)O)(m)](-) species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO(2))(n)(H(2)O)(m)](-): (1) the incorporated H(2)O is bonded to either CO(2) (-) or C(2)O(4) (-) through two equivalent OH...O hydrogen bonds to form a ring structure in [(CO(2))(n)(H(2)O)(1)](-); (2) two H(2)O molecules are independently bound to the O atoms of CO(2) (-) in [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2); (3) a cyclic structure composed of CO(2) (-) and two H(2)O molecules is formed in [(CO(2))(3)(H(2)O)(2)](-).     

Assembly of a luminescent core-shell nanocluster featuring a Ag34S26 shell and a W6O21(6-) polyoxoanion core

Bridging between silver clusters and polyoxoanion clusters, the first 1D assembly, [Ag(34)(S(t)Bu)(26)(W(6)O(21))(CF(3)COO)](CF(3)COO)·Et(3)N·20CH(3)OH (1), based on POM-templated silver-thiolate nanoclusters featuring a [Ag(34)(S(t)Bu)(26)(CF(3)COO)](7+) shell and a [W(6)O(21)](6-) core is reported. This novel core-shell nanocluster possesses nanoscopic morphology, displays intense deep-blue emission in solution under ambient conditions and also shows special electrochemical properties.     

Direct observation of triple ions in aqueous solutions of nickel(II) sulfate: a molecular link between the gas phase and bulk behavior

Electrospray ionization of an aqueous solution of nickel(II) sulfate provides direct experimental evidence for the formation of triple ions of the type [Ni(2)(SO(4))(H(2)O)(n)](2+) and [Ni(SO(4))(2)](2-), whose existence in aqueous solution has previously been proposed based on relaxation spectroscopy [Chen et al. J. Sol. Chem. 2005, 34, 1045]. Formally, these triple ions are formed by aggregation of the solvated ions Ni(2+) and SO(4)(2-), respectively, with the neutral ion pair NiSO(4). In addition, also higher adducts are observed, e.g. the "pentuple ions" [Ni(3)(SO(4))(2)(H(2)O)(n)](2+) (n = 7-9) and [Ni(2)(SO(4))(3)](2-), of which the dicationic is extensively hydrated, whereas the anionic is not. The structures of the dinuclear nickel clusters are derived from ab initio calculations and their infrared spectra are compared with experimental data obtained for the gaseous ions [Ni(2)SO(4)(H(2)O)(5)](2+) and [Ni(2)(SO(4))(3)](2-), respectively. The calculations show that the structures are crucially controlled by the degree of solvation of nickel ion. Explicit consideration of solvating water molecules within the first coordination sphere suggest that the dicationic triple ion [Ni(2)SO(4)](aq)(2+) is bent and thus bears a permanent dipole moment, whereas the [Ni(SO(4))(2)](aq)(2-) dianion tends to be quasi-linear. The experimental and theoretical data for the gaseous ions thus support the elegant, but indirect, deductions previously made based on solution-phase studies.     

Oxygen/sulfur substitution reactions of tetraoxometalates effected by electrophilic carbon and silicon reagents

Reactions of [MO(4)](2)(-) (M = Mo, W) with certain carbon and silicon electrophiles were investigated in acetonitrile in order to produce species of potential utility in the synthesis of analogues of the sites in the xanthine oxidoreductase enzyme family. Silylation of [MoO(4)](2)(-) affords [MoO(3)(OSiPh(3))](1)(-), which with Ph(3)SiSH is converted to [MoO(2)S(OSiPh(3))](1)(-). Reaction with (Ph(3)C)(PF(6))/HS(-) yields the tetrahedral monosulfido species [MO(3)S](2)(-), previously obtained only from the aqueous system [MO(4)](2)(-)/H(2)S. Dithiolene chelate rings are readily introduced upon reaction with 1,2-C(6)H(4)(SSiMe(3))(2), leading to the square pyramidal trioxo complexes [MO(3)(bdt)](2)(-), a previously unknown dithiolene molecular type. Further ring insertion occurs upon reaction of [WO(3)(bdt)](2)(-) with 1,2-C(6)H(4)(SSiMe(3))(2), giving [WO(2)(bdt)(2)](2)(-). Related reactions occur with [ReO(4)](1)(-). Treatment with 1 equiv of (Me(3)Si)(2)S produces [ReO(3)S](1)(-); with 3 equiv of 1,2-C(6)H(4)(SSiMe(3))(2), [ReO(bdt)(2)](1)(-) is obtained with concomitant Re(VII) --> Re(V) reduction. X-ray structures are reported for [MO(3)S](z)(-) (M = Mo, W, z = 2; M = Re, z = 1), [MO(3)(bdt)](2)(-), and [WO(2)(OSiPh(3))(bdt)](1)(-), a silylation product of [WO(3)(bdt)](2)(-). [MoO(3)(bdt)](2)(-) is related to the site of inactive sulfite oxidase, and [WO(2)(OSiPh(3))(bdt)](1)(-) should closely approximate the metric features of the [(dithiolene)MoO(2)(OH)] site in inactive aldehyde/xanthine oxidoreductase. This work provides convenient syntheses of known and new derivatives of tetraoxometalates, among which is entry to a unique class of oxo-monodithiolene complexes.     

New ionic crystals of oppositely charged cluster ions and their characterization

By reacting Keggin-type polyoxometalate cluster anions H(2)W(12)O(40)(6)(-) (metatungstate) or Co(II)W(12)O(40)(6)(-) (tungstocobaltate) with the large aluminum cluster polycation [Al(30)O(8)(OH)(56)(H(2)O)(26)](18+), Keggin ion based molecular ionic compounds [delta-Al(13)O(4)(OH)(24)(H(2)O)(12)][XW(12)O(40)](OH).nH(2)O (X = H(2) (1) and Co (2); n congruent with 20) and [W(2)Al(28)O(18)(OH)(48)(H(2)O)(24)][H(2)W(12)O(40)](2).55H(2)O (3) were obtained. The polygon-shaped cluster ions are packed alternately through intercluster hydrogen bonds as well as electrostatic interactions, leaving large pores, which result from the packing of large clusters. The clusters are arranged in square pyramidal geometries, showing face-to-face interactions between them. The isolation of metastable [delta-Al(13)O(4)(OH)(24)(H(2)O)(12)](7+) and the formation of a new transition metal substituted aluminum heteropolycation [W(2)Al(28)O(18)(OH)(48)(H(2)O)(24)](12+) in 1-3 result from the slow fragmentation and recombination of Al(30) in the presence of suitable counter cluster anions with similar shape and charge.     

Methoxide of an Anderson-type polyoxometalate and its conversion to a new type of species, [IMo9O32(OH)(OH2)3]4-

A totally new type of polyoxometalate, [IMo(9)O(32)(OH)(OH(2))(3)](4)(-), has been synthesized by reacting [IMo(6)O(22)(OMe)(2)](3)(-) with water. The [IMo(9)O(32)(OH)(OH(2))(3)](4)(-) anion further transforms into [(IMo(7)O(26))(2)](6)(-), a molecular oxide that has a rutile core, in dry acetonitrile, while it stays intact for several hours in wet acetonitrile.     

Solid-state coordination chemistry of the oxomolybdate-organodiphosphonate/nickel-organoimine system: structural influences of the secondary metal coordination cation and diphosphonate tether lengths

The hydrothermal reactions of a molybdate source, a nickel(II) salt, tetra-2-pyridylpyrazine (tpyprz), and organodiphosphonic acids H(2)O(3)P(CH(2))(n)()PO(3)H(2) (n = 1-5) of varying tether lengths yielded a series of organic-inorganic hybrid materials of the nickel-molybdophosphonate family. A persistent characteristic of the structural chemistry is the presence of the [Mo(5)O(15)(O(3)PR)(2)](4)(-) cluster as a molecular building block, as noted for the one-dimensional materials [[Ni(2)(tpyprz)(2)]Mo(5)O(15)[O(3)P(CH(2))(4)PO(3)]]x6.65H(2)O (6x6.65H(2)O) and [[Ni(2)(tpyprz)(2)]Mo(5)O(15)[O(3)P(CH(2))(5)PO(3)]]x3.75H(2)O (8x3.75H(2)O), the two-dimensional phases [[Ni(4)(tpyprz)(3)][Mo(5)O(15)(O(3)PCH(2)CH(2)PO(3))](2)]x23H(2)O (3x23H(2)O) and [[Ni(3)(tpyprz)(2)(H(2)O)(2)](Mo(5)O(15))(Mo(2)O(4)F(2))[O(3)P(CH(2))(3)PO(3)](2)]x8H(2)O (5x8H(2)O), and the three-dimensional structures [[Ni(2)(tpyprz)(H(2)O)(3)]Mo(5)O(15)[O(3)P(CH(2))(3)PO(3))]]xH(2)O (4xH(2)O) and [[Ni(2)(tpyprz)(H(2)O)(2)]Mo(5)O(15) [O(3)P(CH(2))(4)PO(3)]]x2.25H(2)O (7x2.25H(2)O). In the case of methylenediphosphonic acid, the inability of this ligand to tether adjacent pentanuclear clusters precludes the formation of the common molybdophosphonate building block, manifesting in contrast a second structural motif, the trinuclear [(Mo(3)O(8))(x)(O(3)PCH(2)PO(3))(y)] subunit of [[Ni(tpyprz)(H(2)O)(2)](Mo(3)O(8))(2) (O(3)PCH(2)PO(3))(2)] (1) which had been previously observed in the corresponding methylenediphosphonate phases of the copper-molybdophosphonate family. Methylenediphosphonic acid also provides a second phase, [Ni(2)(tpyprz)(2)][Mo(7)O(21)(O(3)PCH(2)PO(3))]x3.5H(2)O (9x5H(2)O), which contains a new heptamolybdate cluster [Mo(7)O(21)(O(3)PCH(2)PO(3))](4)(-) and a cationic linear chain [Ni(tpyprz)](n)(4n+) substructure. The structural chemistry of the nickel-molybdophosphonate series contrasts with that of the corresponding copper-molybdophosphonate materials, reflecting in general the different coordination preferences of Ni(II) and Cu(II). Consequently, while the Cu(II)-organic complex building block of the copper family is invariably the binuclear [Cu(2)(tpyprz)](4+) subunit, the Ni(II) chemistry with tpyprz exhibits a distinct tendency toward catenation to provide [Ni(3)(tpyprz)(2)](6+), [Ni(4)(tpyprz)(3)](8+), and [Ni(tpyprz)](n)(4n+) building blocks as well as the common [Ni(2)(tpyprz)](4+) moiety. This results in a distinct structural chemistry for the nickel(II)-molybdophosphonate series with the exception of the methylenediphosphonate derivative 1 which is isostructural with the corresponding copper compound [[Cu(2)(tpyprz)(H(2)O)(2)](Mo(3)O(8))(2)(O(3)PCH(2)PO(3))] (2). The structural chemistry of the nickel(II) series also reflects variability in the number of attachment sites at the molybdophosphonate clusters, in the extent of aqua ligation to the Ni(II) tpyprz subunit, and in the participation of phosphate oxygen atoms as well as molybdate oxo groups in linking to the nickel sites.     

Syntheses, structures and properties of a series of non-heme alkoxide-Fe(III) complexes of a benzimidazolyl-rich ligand as models for lipoxygenase

The treatment of Fe(ClO(4))(2)·6H(2)O or Fe(ClO(4))(3)·9H(2)O with a benzimidazolyl-rich ligand, N,N,N',N'-tetrakis[(1-methyl-2-benzimidazolyl)methyl]-1,2-ethanediamine (medtb) in alcohol/MeCN gives a mononuclear ferrous complex, [Fe(II)(medtb)](ClO(4))(2)·?CH(3)CN·?CH(3)OH (1), and four non-heme alkoxide-iron(III) complexes, [Fe(III)(OMe)(medtb)](ClO(4))(2)·H(2)O (2, alcohol = MeOH), [Fe(III)(OEt)(Hmedtb)](ClO(4))(3)·CH(3)CN (3, alcohol = EtOH), [Fe(III)(O(n)Pr)(Hmedtb)](ClO(4))(3)·(n)PrOH·2CH(3)CN (4, alcohol = n-PrOH), and [Fe(III)(O(n)Bu)(Hmedtb)](ClO(4))(3)·3CH(3)CN·H(2)O (5, alcohol = n-BuOH), respectively. The alkoxide-iron(III) complexes all show 1) a Fe(III)-OR center (R = Me, 2; Et, 3; (n)Pr, 4; (n)Bu, 5) with the Fe-O bond distances in the range of 1.781-1.816 ?, and 2) a yellow color and an intense electronic transition around 370 nm. The alkoxide-iron(III) complexes can be reduced by organic compounds with a cis,cis-1,4-diene moiety via the hydrogen atom abstraction reaction.     

Organic-soluble lacunary {M(2)(P(2)W(15))(2)} polyoxometalate sandwiches showing a previously unseen αββα isomerism

New polyoxometalate 'sandwiches' have been formed where two [P(2)W(15)O(56)](12-) lacunary Dawson clusters encapsulate two transition metal ions to give clusters with the general formula [M(II)(2)(P(2)W(15)O(56))(2)](20-) (where M = Mn, Co, and Ni respectively), [Fe(III)(2)(P(2)W(15)O(56))(2)](18-), and [Cu(II)(4)(P(2)W(15)O(56))(2)](16-). The Mn, Co, and Ni clusters exhibit a hitherto unseen αββα isomeric geometry and all five compounds are associated with tetrabutylammonium cations which allow for their dissolution in non-aqueous solvent.     

Multi-iron silicotungstates: synthesis, characterization, and stability studies of polyoxometalate dimers

The reaction of Fe(III) with Na(+) and K(+) salts of the trivacant [alpha-SiW(9)O(34)](10)(-) ligand have been investigated at pH 6 and pH 1. A new dimer, [(alpha-SiFe(3)W(9)(OH)(3)O(34))(2)(OH)(3)](11-) (1), is synthesized by reacting Na(7)H(3)[alpha-SiW(9)O(34)] or K(10)[alpha-SiW(9)O(34)] with exactly 3 equiv of Fe(III) in a 0.5 M sodium acetate solution (pH 6). The structure of 1, determined by single-crystal X-ray diffraction (a = 22.454(2) A, b = 12.387(2) A, c = 37.421(2), beta = 100.107(8) degrees , monoclinic, C2/c, Z = 4, R(1) = 5.11% based on 12739 independent reflections), consists of two [alpha-SiFe(3)W(9)(OH)(3)O(34)](4-) units linked by three Fe-mu-OH-Fe bonds. Reaction of K(10)[alpha-SiW(9)O(34)] with 3 equiv of Fe(III) in water (pH 1) yields [(alpha-Si(FeOH(2))(2)FeW(9)(OH)(3)O(34))(2)](8)(-2). The structure of 2 was also determined by single-crystal X-ray diffraction (a = 36.903(2) A, b = 13.9868(9) A, c = 21.7839(13) A, beta = 122.709(1) degrees , monoclinic, C2/c, Z = 4, R(1) = 4.57% based on 11787 independent reflections). It consists of two [alpha-Si(FeOH(2))(2)FeW(9)(OH)(3)O(34)](4-) Keggin units linked by a single edge. The terminal ligand on Fe1 in each trisubstituted Keggin unit becomes a mu(2) oxo ligand bridging to a [WO(6)](2-) moiety. The UV-vis spectra of both complexes show the characteristic oxygen-to-metal-charge-transfer bands of polyoxometalates as well as an Fe(III)-centered band at 436 nm (epsilon = 146 M(-1) cm(-1)) and 456 nm (epsilon = 104 M(-1) cm(-1)) for complexes 1 and 2, respectively. Differential scanning calorimetry data show that complex 1 decomposes between 575 and 600 degrees C whereas no decomposition is observed for complex 2 up to temperatures of 600 degrees C.     

Syntheses, characterizations and properties of [Mo2O2S2]-based oxothiomolybdenum wheels incorporating bisphosphonate ligands

We report the syntheses and characterizations of the first polyoxothiometalate complexes isolated from the reaction of the oxothiocationic [Mo(V)(2)O(2)S(2)](2+) precursor and bisphosphonate ligands H(2)O(3)PCR(OH)PO(3)H(2) (R = C(4)H(5)N(2), zoledronic acid; R = C(3)H(6)NH(2), alendronic acid). [(Mo(2)O(2)S(2)(H(2)O))(4)(O(3)PC(O)(C(4)H(6)N(2))PO(3))(4)](8-) (Mo(8)S(8)(Zol)(4)) and [(Mo(2)O(2)S(2)(H(2)O))(4)(O(3)PC(O)(C(3)H(6)NH(3))PO(3))(4)](8-) (Mo(8)S(8)(Ale)(4)) contain four Mo(V) dimers connected via bisphosphonate ligands. These compounds offer a unique opportunity to compare the structures and properties of cyclic compounds obtained with [Mo(2)O(2)S(2)](2+) and with [Mo(2)O(4)](2+). The oxothio compounds appear less stable in solution than the oxo analogue, confirming the higher lability and versatility of [Mo(2)O(2)S(2)]-based compounds compared to [Mo(2)O(4)]-based POMs. Multinuclear and multidimensional solid-state NMR studies were carried out to complement X-ray diffraction analysis. Information on short-range interactions, dynamic behaviors, and local disorder within the crystalline materials are therefore reported. Furthermore, the electrocatalytic properties of Mo(8)S(8)(Ale)(4) and of the analogous [(Mo(2)O(4)(H(2)O))(4)(O(3)PC(O)(C(3)H(6)NH(3))PO(3))(4)](8-) (Mo(8)O(8)(Ale)(4)) immobilized onto the surface of a glassy carbon electrode were studied, thus evidencing the ability of [Mo(2)O(2)S(2)]-based cycles to promote the reduction of protons into hydrogen, whereas the oxo analogue appeared inactive.     

Structure and energetics of nanometer size clusters of sulfuric acid with ammonia and dimethylamine

The structures of positively and negatively charged clusters of sulfuric acid with ammonia and/or dimethylamine ((CH(3))(2)NH or DMA) are investigated using a combination of Monte Carlo configuration sampling, semiempirical calculations, and density functional theory (DFT) calculations. Positively charged clusters of the formula [(NH(4)(+))(x)(HSO(4)(-))(y)](+), where x = y + 1, are studied for 1 ≤ y ≤ 10. These clusters exhibit strong cation-anion interactions, with no contribution to the hydrogen-bonding network from the bisulfate ion protons. A similar hydrogen-bonding network is found for the [(DMAH(+))(5)(HSO(4)(-))(4)](-) cluster. Negatively charged clusters derived from the reaction of DMA with [(H(2)SO(4))(3)(NH(4)(+))(HSO(4)(-))(2)](-) are also studied, up to the fully reacted cluster [(DMAH(+))(4)(HSO(4)(-))(5)](-). These clusters exhibit anion-anion and ion-molecule interactions in addition to cation-anion interactions. While the hydrogen-bonding network is extensive for both positively and negatively charged clusters, the binding energies of ions and molecules in these clusters are determined mostly by electrostatic interactions. The thermodynamics of amine substitution is explored and compared to experimental thermodynamic and kinetic data. Ammonia binds more strongly than DMA to sulfuric acid due to its greater participation in hydrogen bonding and its ability to form a more compact structure that increases electrostatic attraction between oppositely charged ions. However, the greater gas-phase basicity of DMA is sufficient to overcome the stronger binding of ammonia, making substitution of DMA for ammonia thermodynamically favorable. For small clusters of both polarities, substitutions of surface ammonium ions are facile. As the cluster size increases, an ammonium ion becomes encapsulated in the center of the cluster, making it inaccessible to substitution.     

Di- and tricobalt Dawson sandwich complexes: synthesis,spectroscopic characterization,and electrochemical behavior of Na(18)[(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)] and Na(17)[(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)

The reaction of the trivacant Dawson anion alpha-[P(2)W(15)O(56)](12-) and the divalent cations Co(2+) is known to form the tetracobalt sandwich complex [Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) (Co(4)P(4)W(30)). Two new complexes, with different Co/P(2)W(15) stoichiometry, [(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)](18-) (Na(2)Co(2)P(4)W(30)) and [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)](17-) (NaCo(3)P(4)W(30)), have been synthesized as aqueous-soluble sodium salts, by a slight modification of the reaction conditions. Both compounds were characterized by IR, elemental analysis, and (31)P solution NMR spectroscopy. These species are "lacunary" sandwich complexes, which add Co(2+) cations according to Na(2)Co(2)P(4)W(30) + Co(2+) --> NaCo(3)P(4)W(30) + Na(+) followed by NaCo(3)P(4)W(30) + Co(2+) --> Co(4)P(4)W(30) + Na(+). A Li(+)/Na(+) exchange in the cavity was evidenced by (31)P dynamic NMR spectroscopy. The electrochemical behaviors of the sandwich complexes [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)](17-) and [(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)](18-) were investigated in aqueous solutions and compared with that of [Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-). These complexes showed an electrocatalytic effect on nitrite reduction.