The self-assembly mechanism of the Lindqvist anion [W(6)O(19)](2-) in aqueous solution: a density functional theory study

The formation mechanism is always a fundamental and confused issue for polyoxometalate chemistry. Two formation mechanisms (M1 and M2) of the Lindqvist anion [W(6)O(19)](2-) have been adopted to investigate it's self-assembly reaction pathways at a density functional theory (DFT) level. The potential energy surfaces reveal that both the mechanisms are thermodynamically favorable and overall barrierless at room temperature, but M2 is slightly dominant to M1. The formation of the pentanuclear species [W(5)O(16)](2-) and [W(5)O(15)(OH)](-) are recognized as the rate-determining steps in the whole assembly polymerization processes. These two steps involve the highest energy barriers with 30.48 kcal mol(-1) and 28.90 kcal mol(-1), respectively, for M1 and M2. [W(4)O(13)](2-) and [W(4)O(12)(OH)](-) are proved to be the most stable building blocks. In addition, DFT results reveal that the formation of [W(3)O(10)](2-) experiences a lower barrier along the chain channel.     

杂多阴离子[GeMo12O40]4-α/β异构体的密度泛函研究

采用密度泛函方法，在DND基组水平上，对[GeMo12O40]^4-杂多阴离子最常见的α和β异构体进行了几何构型优化，得到了与X射线晶体衍射实验结果相一致的结构参数，并在此基础上进行了振动频率分析，得到了杂多阴离子的电子结构、热力学特性和振动光谱，通过定义α，β异构体异构化反应的Gibbs函变△Gα-β与温度的关系，研究了这两种异构体的相对稳定性．结果表明：低温时α异构体更稳定，高温时β异构体更稳定些，550K左右为转变点．振动频率分析得到2种异构体的最强峰位于4个频率位置，分别指认为vax(Mo-Od)，vas(Mo-Od)，vas(Mo-Oc-Mo)，vas(Ge-Oa)，vas(Mo-Ob-Mo)振动，与红外光谱(IR)的特征振动峰相对应，观察到了特征频率的振动模式，从理论计算角度说明了Rocchiccioli—Deltcheff关于振动模式的设想是合理的．     

Correlated electrons in the Eu-exchanged Preyssler anion [EuP(5)W(30)O(110)](n-)

The Eu-encrypted Preyssler anion, [EuP5W30O110]n-, demonstrates unusual electronic properties as a function of applied potenial. The Preyssler anion itself, when exchanged with a nonredox active trivalent ion such as La3+, is electroactive in acidic solution, reversibly accepting up to 10 electrons under reducing conditions. Encrypted Eu, which is trivalent at rest potential, is reduced concomitantly with the framework. The details of this reduction are probed with Eu L3-XANES, coulometry, and magnetic susceptibility. The results are interpreted in terms of a bonding interaction between the Eu f-states and the W-O framework band, facilitated by the crossing of the framework Fermi level with the localized states. Such behavior has been previously observed in intermediate-valent and correlated-electron systems. The observation of such behavior in an isolated cluster opens the door for new avenues of research into correlated-electron behavior.     

Solution and solid-state structure of the anion [Ag(2)[closo-CB(11)H(12)](4)](2-)

Addition of the carbene 1,3-dimesitylimidazol-2-ylidene (IMes) to a toluene solution of Ag[closo-CB(11)H(12)] results in the formation of the complex [(IMes)(2)Ag](2)[Ag(2)[closo-CB(11)H(12)](4)], the anionic component of which contains two silver(I) centers bridged by two carboranes in addition to one terminally bound carborane on each metal, in the solid-state. Comparison of the observed (11)B[(1)H] NMR chemical shifts of [(IMes)(2)Ag](2)[Ag(2)[closo-CB(11)H(12)](4)] or Ag[closo-CB(11)H(12)] with [NBu(4)][closo-CB(11)H(12)] in CD(2)Cl(2) demonstrates that the silver ion interacts significantly with the cage in solution. Theoretical investigations using the ab initio/GIAO/NMR method of [closo-CB(11)H(12)](-) and Na[closo-CB(11)H(12)] as model geometries for the silver salts support experimental evidence for these Ag...[BH] interactions in solution.     

Core-crosslinked block copolymer nanorods as templates for grafting [SiMo(12)O(40)](4-) Keggin ions

Core-crosslinked PB-P2VP block copolymer nanorods are used as templates for the synthesis of Keggin-type heteropolyoxometalate (POM) nanostructures by grafting [SiMo(12)O(40)](4-) Keggin ions on the template.     

Microsolvation of the dicyanamide anion: [N(CN)(2)(-)](H(2)O)n (n = 0-12)

Photoelectron spectroscopy is combined with ab initio calculations to study the microsolvation of the dicyanamide anion, N(CN)(2)(-). Photoelectron spectra of [N(CN)(2)(-)](H2O)n (n = 0-12) have been measured at room temperature and also at low temperature for n = 0-4. Vibrationally resolved photoelectron spectra are obtained for N(CN)(2)(-), allowing the electron affinity of the N(CN)2 radical to be determined accurately as 4.135 +/- 0.010 eV. The electron binding energies and the spectral width of the hydrated clusters are observed to increase with the number of water molecules. The first five waters are observed to provide significant stabilization to the solute, whereas the stabilization becomes weaker for n > 5. The spectral width, which carries information about the solvent reorganization upon electron detachment in [N(CN)(2)(-)](H2O)n, levels off for n > 6. Theoretical calculations reveal several close-lying isomers for n = 1 and 2 due to the fact that the N(CN)(2)(-) anion possesses three almost equivalent hydration sites. In all the hydrated clusters, the most stable structures consist of a water cluster solvating one end of the N(CN)(2)(-) anion.     

Electronic properties of polyoxometalates: a DFT study of alpha/beta-[XM(12)O(40)](n-) relative stability (M=W, Mo and X a main group element)

Keggin heteropolyanions [XM(12)O(40)](n-) have various isomeric structures, alpha and beta being the most common. Conventionally, the alpha structure appears to be the most stable, but calculations carried out at the DFT level for X = P(V), Si(IV), Al(III), As(V), Ge(IV), and Ga(III) and M = W(VI) and Mo(VI) show that this stability depends on several factors, particularly on the nature of the heteroatom (X) and the total charge of the cluster. In this paper, we apply the clathrate model to the Keggin molecule to carry out a fragment-interaction study to elucidate when and why the traditional relative stability of various isomers can be inverted. The fully oxidized anions that have inverted the traditional stability trend in this series are [AlW(12)O(40)](5-) and [GaW(12)O(40)](5-), both of which contain a third-group heteroatom and an overall charge of -5. beta-isomers are always more easily reduced than alpha-isomers. This experimental observation suggests that reduction favors the stability of beta-isomers and one of the most important results of this study is that the alpha/beta inversion is achieved in most cases after the second reduction. The alpha- and beta-isomers may have different properties because the energy of the LUMO, a symmetry-adapted d(xy)-metal orbital, is different.     

Dimerization of A-alpha-[SiNb(3)W(9)O(40)](7-) by pH-controlled formation of individual Nb-mu-O-Nb linkages

The reversible, stepwise formation of individual Nb-mu-O-Nb linkages during acid condensation of 2 equiv of A-alpha-[SiNb(3)W(9)O(40)](7-) (1) to the tri-mu-oxo-bridged structure A-alpha-[Si(2)Nb(6)W(18)O(77)](8-) (4) is demonstrated by a combination of X-ray crystallography and variable-pD solution (183)W and (29)Si NMR spectroscopy. Addition of DCl to a pD 8.4 solution of 1 (Li(+) salt in D(2)O) results in formation of a mono-Nb-mu-O-Nb-linked dimer, A-alpha-[Si(2)Nb(6)W(18)O(79)](12-) (2; pD = 3.0-1.3). At pD values between 1.6 and 0.3, two isomers (syn and anti) of the di-mu-oxo-bridged dimer, A-alpha-[Si(2)Nb(6)W(18)O(78)](10-) (3), are observed by (183)W NMR (C(2v) and C(2h) symmetry for the syn and anti isomers, respectively; 5 (183)W NMR signals for each isomer in the ratio 2:2:2:2:1). X-ray-quality crystals of syn-3 were isolated in 53% yield (syn-A-alpha-Cs(8)H(2)[Si(2)Nb(6)W(18)O(78)].18H(2)O, orthorhombic, Cmcm, a = 40.847(2), b = 13.2130(7), and c = 16.8179(9) A at 173K, Z = 4, final R(1) = 0.0685). At the low-pD limit of -0.08 (1.2 M DCl), 4 alone is observed. Additional supporting data are provided by variable-pD (29)Si NMR spectroscopy. Reversibility of the above processes was subsequently demonstrated by acquisition of (183)W NMR spectra after incremental additions of LiOH to D(2)O solutions of 4 to effect its stepwise hydrolysis to 2 equiv of 1.     

双帽Keggin型杂多阴离子[H4As3Mo12O40]-和Keggin型杂多酸H3PM12O40(M=Mo,W)质子化的DFT研究

选用B3LYP方法在LanL2MB水平下,对双帽α-Keggin型杂多阴离子[H4As3Mo12O40]-的电子结构和质子的定位进行了密度泛函理论(DFT)研究.结果表明,双帽的形成大大影响了杂多阴离子[As3Mo12O40]5-的电子结构和性质,NBO分析显示参与成帽的三桥氧上的电子密度比双桥氧上的要大,简单地从电荷密度来看,质子将首先在三桥氧上定域成键,但通过比较质子定域在几种桥氧上质子化稳定化能的大小,发现[H4As3Mo12O40]-中的四个质子将在八个双桥氧中的其中四个氧原子上定位,而不是如文献中报道的在四个三桥氧上定域成键.对杂多酸H3PM12O40(M=Mo,W)中质子的定位也进行了理论计算并与文献进行了比较,结果显示,H3PMo12O40中质子是定位在双桥氧上;而H3PW12O40中质子将优先在双桥氧上定位,但也可在端氧上定位;这一结果与文献报道的相一致.     

用密度泛函方法研究α-[XMo12O40]n-杂多阴离子的振动光谱

采用第一性原理密度泛函方法,在考虑极化函数的双数字(DND)基组水平上,对α-[XMo12O40]n-(X=P,Si,Ge)杂多阴离子进行了几何构型优化,得到了与X-ray晶体衍射实验结果相一致的结构参数;并在优化几何构型基础上进行了振动频率分析,首次得到了非经验计算的杂多阴离子的振动光谱,计算的频率及强度与实验结果总体上吻合得较好.对全部22个有红外活性(IR)和44个有拉曼(R)活性的频率进行了指认,并与经验方法得到的结果进行了比较,同时,对部分频率的归属加以进一步的澄清与确认.     

ChemInform Abstract: Crystal Structures of α-(Co(II)W12O40)6- and Its Heteropoly Blue 2e Reduction Product, α-(Co(II)W12O40)8-. Structural,Electronic, and Chemical Consequences of Electron Delocalization in a Multiatom Mixed-Valence System.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Assignment of the electronic spectra of [Mo(CN)(8)](4)(-) and [W(CN)(8)](4)(-) by Ab initio calculations

CASPT2 calculations are performed on the dodecahedral and square antiprismatic isomers of the [Mo(CN)(8)](4)(-) and [W(CN)(8)](4)(-) complexes. The high-energy experimental bands above 40000 cm(-)(1) are assigned to MLCT transitions. The experimental observed trend of the extinction coefficients for the molybdenum and tungsten complex is reproduced by our CASSCF oscillator strengths. All bands below 40000 cm(-)(1) can be ascribed to ligand-field transitions, although small contributions from forbidden MLCT transitions cannot be excluded. In order to account for all experimental bands in the electronic spectrum of these octacyanocomplexes, a dynamic equilibrium in solution between the two isomeric forms must be hypothesized. Spin-orbit coupling effects are found to be more important for the square antiprismatic isomers; in particular, large singlet-triplet mixings are calculated for this isomer of [W(CN)(8)](4)(-). Ligand-field and Racah parameters as well as spin-orbit coupling constants are determined on the basis of the calculated transition energies. The obtained values for these parameters support the recently proposed model for exchange interactions in magnetic clusters and networks containing pentavalent octocyanometalates of molybdenum and tungsten.     

Preparation and Tungsten-183 NMR Characterization of [alpha-1-P(2)W(17)O(61)](10)(-), [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-), and [alpha-2-Zn(H(2)O)P(2)W(17)O(61)](8)(-)

The preparation of the alpha-1 and alpha-2 isomers of the Wells-Dawson 17 tungsto derivatives by standard methods is accompanied by a significant proportion of the other isomer present as an impurity. In this study, the alpha-1 and alpha-2 isomers of [Zn(H(2)O)P(2)W(17)O(61)](8)(-) have been prepared in >98% purity by reacting isomerically pure K(9)Li[alpha-1-P(2)W(17)O(61)] and K(10)[alpha-2-P(2)W(17)O(61)], respectively, with ZnCl(2), while rigorously controlling the pH at 4.7. The molecules were isolated as potassium salts. For (183)W NMR and (31)P NMR characterization, both molecules were ion exchanged by cation-exchange chromatography, maintaining the pH at 4.7, to obtain the lithium salts. Removal of water and isolation of a solid sample of [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) was achieved by lyophilization at -40 degrees C. The chemical shift data from (31)P and (183)W NMR spectroscopy of the isolated [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) and [alpha-2-Zn(H(2)O)P(2)W(17)O(61)](8)(-) isomers are consistent with a mixture of the alpha-1 and alpha-2 isomers reported previously;(1) the molecules have the expected C(1) and C(s)() symmetry, respectively. The [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) isomer is stable in the pH range of 4.6-6 at temperatures <35 degrees C. Using the same ion exchange and lyophilization techniques, the lacunary [alpha-1-P(2)W(17)O(61)](10)(-) isomer was isolated as the lithium salt; characterization by (183)W NMR spectroscopy confirms the C(1) symmetry.     

Novel octahedral tungsten sulfidocyanide cluster anion [W6S8(CN)6]6-

Novel tungsten octahedral sulfidocyanide cluster compounds Na6[W6S8(CN)6].18DMSO 1 and K6[W6S8(CN)6] 2 have been synthesized and characterized by X-ray crystallography and NMR spectroscopy.     

Synthesis, structure, and theoretical study of the nonclassical [CuTe(7)](3-) anion

The compound [PPh(4)](2)[NEt(4)][CuTe(7)] has been synthesized from the reaction of CuCl with a polytelluride solution in dimethylformamide at room temperature. The compound crystallizes with two formula units in the triclinic space group P(-)1 in a cell with dimensions a = 8.9507(18) A, b = 14.714(3) A, and c = 23.277(5) A and alpha= 86.32(3) degrees, beta= 80.17(3) degrees, and gamma= 75.63(3) degrees (T = -120 degrees C). Ab initio calculations indicate that the nonclassical [CuTe(7)](3)(-) anion is the result of joining Te(3)(2-) and [CuTe(4)](1-) fragments through donor-acceptor interactions.     

DFT study on the five isomers of PW(12)O(40)(3)(-): relative stabilization upon reduction

The electronic characteristics and the redox properties of each isomer of PW(12)O(40)(3)(-) depend on the arrangement adopted by the metal-oxide framework. At the DFT/BP86 level, we computed the structures of the five isomers of PW(12)O(40)(3)(-) in oxidized form. The energy scale fits the experimental findings as well as the number of rotated triads of the metal-oxide core since the energy grows as follows: alpha < beta < gamma < delta < epsilon. The reduced clusters behave differently as long as the beta form becomes the most stable isomer after the second reduction. The gamma isomer also gains stability upon reduction, but not enough to be competitive with beta. For the 4-fold reduced PW(12) cluster, the energy difference computed between beta and gamma in solution is 11 kcal mol(-)(1). This large difference proves that the beta --> gamma isomerization is not favored upon simple reduction. The other isomers, delta and epsilon, are much more unstable than alpha or beta in any reduction state.     

Magnetism in polyoxometalates: anisotropic exchange interactions in the Co3II moiety of [Co3W(D2O)2(ZnW9O34)2](12-)--A magnetic and inelastic neutron scattering study

The ground-state properties of a Co3II moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2].40D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin-orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as H = -2 sigma a = x,y,z (Ja12 S1a S2a + Ja23 S2a S3a), where Ja are the components of the exchange interactions between the CoII ions. To reproduce the INS data, different orientations of the two anisotropic J tensors must be considered, and the following conditions had to be introduced: Jx12 = Jy23, Jy12 = Jx23, Jz12 = Jz23. This result was correlated with the molecular symmetry of the complex. The following set of parameters was obtained: Jx12 = Jy23 = 1.37, Jy12 = Jx23 = 0.218, and Jz12 = Jz23 = 1.24 meV. This set also reproduces in a satisfactory manner the specific heat, susceptibility, and magnetization properties of Co3.