Catalytic effect of a second H3PO2 in the mechanism of stabilisation of the unstable pyramidal tautomer of H3PO2 coordinated at [Mo3S4M'] clusters (M' = Ni, Pd)

Kinetic and DFT studies indicate that the stabilization of a single pyramidal H(3)PO(2) molecule at the M' site of [Mo(3)S(4)M'] clusters requires the participation of two tetrahedral H(3)PO(2) molecules, the role of the second one being assisting tautomerization of a previously coordinated tetrahedral H(3)PO(2).     

Template synthesis of [(Mo(V)2O4)(O3PCH2PO3)]n clusters (n = 3, 4, 10): solid state and solution studies

The influence of three exogenous ligands (acetate, formate and carbonate) on the condensation process of the [Mo2O4]2+ dioxocation with the [O3PCH2PO3](4-) group has been investigated. Four cyclic or bicyclic compounds have been isolated and characterized by X-ray diffraction studies. Two closely related acetato and formato ovoidal duodecanuclear compounds, Na24[Na4(H2O)6[(Mo2O4)10(O3PCH2PO3)10(CH3COO)8(H2O)4]].103H2O (1) and Na28[Na2[(Mo2O4)10(O3PCH2PO3)10(HCOO)10]].110H2O (2), respectively, have been obtained. Their structures can be described as two interconnected nonequivalent wheels, delimiting a large cavity. When the condensation is performed in similar conditions but replacing carboxylato groups by carbonato ligands, the ellipsoidal octanuclear Na11[Na(H2O)2[(Mo2O4)4(O3PCH2PO3)4(CO3)2]].70H2O (3) compound is isolated. 31P NMR spectroscopic studies have shown that complexes 1 and 3 are stable in solution at room temperature. Nevertheless, on heating an aqueous solution of 3, the Na8[(Mo2O4)3(O3PCH2PO3)3(MoO4)].18H2O (4) complex, free of carbonato groups, is obtained. 4 is a hexanuclear Mo(V) wheel encapsulating a tetrahedral [Mo(VI)O4](2-) anion. Its rational synthesis using a controlled Mo(V)/Mo(VI) ratio is also presented.     

A complete family of isostructural cluster compounds with cubane-like M(3)S(4)M' cores (M = Mo,W; M' = Ni,Pd, Pt): comparative crystallography and electrochemistry

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.     

Mössbauer spectroscopic studies of cubane-type clusters of [Mo3FeS4(NH3)9(H2O)]Cl4 and [Mo3FeS4(H2O)10](pts)4.7H2O (pts−: CH3(C6H4)SO 3 − )

Mixed-metal cubane-type clusters of [Mo₃FeS₄(NH₃)₉(H₂O)Cl₄ and [Mo₃FeS₄(H₂O)₁₀](pts)₄.7H₂O have been characterized by means of⁵⁷Fe-Mössbauer spectroscopy. The Mössbauer parameters indicate that the oxidation states of iron in the cluster compounds are ascribed to +2.5₄ and +2.3₉, respectively.     

Synthesis and structure of nickel-containing cuboidal clusters derived from [W3Se4(H2O)9]4+. Site-differentiated substitution at the nickel site in the series [W3NiQ4(H2O)10]4+ (Q = S, Se)

New Ni-containing heterometallic cuboidal cluster aqua complex [W3(NiCl)Se4(H2O)9]3+, the missing link in the family of the M3NiQ4 clusters (M = Mo, W; Q = S, Se), has been prepared by the reaction of [W3Se4(H2O)9]4+ with Ni in 2 M HCl. Single crystals of edge-linked double-cuboidal cluster [{W3NiSe4(H2O)9}2](pts)8.18H2O (pts = p-toluenesulfonate) were grown from the solution of the aqua complex in 3 M Hpts, and their structures were determined. The Ni site in the clusters [W3(NiCl)Q4(H2O)9]3+ selectively coordinates typical pi-acceptor ligands such as CO, olefins, acetylenes, phosphines, arsines, or SnCl3-. This allows stabilization by coordination of such elusive species as HP(OH)2 and As(OH)3. The stability constants for coordination of HP(OH)2, As(OH)3, and SnCl3- were determined. The Se for S substitution increases the stability by 1-2 orders of magnitude. Supramolecular adducts with cucurbit[6]uril (Cuc), [W3(Ni(HP(OH)2))Q4(H2O)9]Cl4.Cuc.11H2O and [W3(NiAs(OH)3)S4(H2O)8Cl]Cl3.Cuc.13H2O, were isolated and structurally characterized.     

Aqueous solution chemistry of [Mo3CuSe4]n+ (n = 4, 5) and [W3CuQ4]5+ (Q = S, Se) clusters

The triangular cluster [Mo3Se4(H2O)9]4+ reacts with Cu turnings to give a new heterometallic cuboidal cluster [Mo3CuSe4(H2O)10]4+(purple; UV/Vis lambda(epsilon): 352(3907), 509(2613)). The reaction of [Mo3Se4(H2O)9]4+ with CuCl afforded the 5+ cube [Mo3CuSe4(H2O)10]5+(red; UV/Vis lambda(epsilon): 356(5406), 500(3477)). In contrast, [W3Se4(H2O)9]4+ both with Cu and CuCl gives the 5+ cube, [W3CuSe4(H2O)10]5+(yellow-green; UV/Vis lambda(epsilon): 312(5327), 419(3256) and 628(680)). Cyclic voltammetry of [M3CuQ4(H2O)10]5+ in 2 M HCl (M = Mo, W; Q = S, Se) shows a reversible one-electron reduction wave for the Mo clusters, but no reduction occurs for the W clusters prior to H+ reduction. In HCl solutions, Cl is coordinated to the Cu site of the clusters, alongside some less extensive coordination to Mo and W, and for [W3(CuCl)S4(H2O)6Cl3]+, isolated as the supramolecular adduct with cucurbit[6]uril, [W3(CuCl)S4(H2O)6Cl3]2Cl2 x C36H36N24O12 x 12H2O, the crystal structure was determined (Cu-W 2.856(4) angstroms, W-W 2.7432(15) angstroms, Cu-Cl 2.167(13) angstroms).     

Ab initio studies on vibrational spectra of Ni(II), Pd(II), and Pt(II) complexes of M'X4(2-) and M'OS3(2-) (M' = Mo, W; X = O, S)

The vibrational spectra of MM'2X8(2-) and trans-MM'2S6O2(2-) (M = Ni(II), Pd(II), Pt(II); M' = Mo, W; X = O, S) are calculated using ab initio method at RHF/LanL2DZ level. The calculated vibrational frequencies of MM'2S8(2-) and trans-MM'2O2S6(2-) are evaluated via comparison with experimental data. The results obtained by this method have the deviation <5% for M'S and MS stretching vibrational frequencies, however, relatively higher deviation is obtained for M'O stretching vibrational frequencies. Some vibrational frequencies of these complexes that have not been experimentally reported are also predicted and some of the experimental values are assigned.     

两个具有[Mo~3M'S~4]^5^+(M'=Mo,W)簇芯的原子簇化合物的合 成和晶体结构

以Mo~3S~4(dtp)~4.H~2O和M'(CO)~6(M'=Mo,W)为起始物在羧酸介质下通过[3+1]模式合成,分别得到一个同核和一个异核四核簇[Mo~4S~4(μ-C~2H~5CO~2)~2(dtpH)(dtp)~3]4和[Mo~3WS~4(μ-CH~3CO~2)~2(dtpH)(dtp)~3]5[dtp=(EtO)~2PS~2^-;dtpH=(EtO)~2P(S)(SH)]。两个簇合物以单晶X射线分析和IR谱学进行结构表征,它们均具有[M~4S~4]^5^+类立方烷簇芯。     

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.     

The H and H2 interaction with Pd3Cu,Pd4, and Cu4 fcc (111) clusters: A DFT comparative study

A comparative study of adsorption of H atoms and H₂ molecules on Pd₃Cu, Cu₄, and Pd₄ clusters has been performed through density functional calculations, using the hybrid B3LYP exchange‐correlation functional as implemented in the Gaussian98 program. For Pd atoms the relativistic small‐core effective core potential LANL and LANL2DZ basis set was used and for hydrogen a 6‐31G** basis set was used. The main emphasis is set in the reaction behavior of the different clusters with hydrogen atoms and molecules. We find that full geometry optimization does not appreciably change the metal cluster geometry either for certain reaction modes or the H and H₂ capture parameters, but increases the number of reactive sites of the metal clusters. Also, we found that there is charge transfer competition between H and Cu atoms, which drastically diminishes H₂ adsorption energy, related to the Pd cluster observed value. Edges and threefold sites are the principal hydrogen adsorption sites. Hydrogen has a great mobility over the metal clusters for different minima, especially when Cu is present; many initial pathways end in the same adsorption site. The observed hydrogen adsorption and binding energies are well reproduced by the calculations. Also, the adsorption mechanisms were determined. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Preparation and X-Ray Structure of Cubane-Type Mixed Metal Aqua Ion, [Mo3NiS4(H2O)10]4+

Abstract

We have recently reported that the incomplete cubane-type aqua ion, [Mo₃S₄(H₂O)₉]⁴⁺ (A), reacts with metals (Fe,¹ Cu,², and Hg³) to give cubane-type mixed metal aqua ions, the core structures of which have been verified by the X-ray structure analyses of the complexes derived from the aqua ions. In addition, it was found that the reaction of A with metallic magnesium gave a double cubane-type aqua ion.⁴ We now present the preparation, properties, and X-ray structure of a new cubane-type molybdenum-nickel-sulfur mixed metal cluster compound, [Mo₃NiS₄(H₂O)₁₀](CH₃°C₆H₄·SO₃)₄·6H₂O (B), prepared from the aqua ion A and metallic nickel. Mo₂Ni₂Cp₂(CO)₂ is the only compound so far reported to have the cubane-type Mo-Ni-S core.⁵     

一个新颖镍配位阳离子修饰的还原型钼磷酸盐：Ni[Mo6O12(OH)3(PO4)(HPO4)3]2][Ni(H2O)2][Ni(H2O)(bipy)2]4·5H2O

水热合成并通过红外、热重、单晶X-射线衍射表征了一个新颖镍配位阳离子修饰的还原型钼磷酸盐,Ni[Mo₆O₁₂(OH)₃(PO₄)(HPO₄)₃]₂][Ni(H₂O)₂][Ni(H₂O)(bipy)₂]₄·5H₂O。单晶X-射线衍射研究表明,两个{Mo₆P₄}簇单元通过一个镍离子连接形成一个Ni[Mo₆P₄]₂二聚结构单元,其进一步和其他的镍配位阳离子连接成钼磷酸盐一维链状结构。在H₂O₂存在下的液－固体系中,使用该化合物催化氧化苯甲醛的探针反应结果表明,该化合物具有较高的催化氧化活性。     

Ni(3)(Mo(2)O(8))(XO(3)) (X = Se, Te): the first nickel selenite- and tellurite-containing Mo4 clusters

Two new nickel(II) molybdenum(VI) selenium(IV) and tellurium(IV) oxides generally formulated as Ni3(Mo2O8)(XO3) (X = Se, Te) have been synthesized by solid-state reactions of NiO, MoO3, and SeO2 (or TeO2). Both compounds feature 3D network structures built of [Mo4O16]8- tetranuclear cluster units and 2D nickel(II) selenite or tellurite layers. The nickel(II) selenite layer in Ni3(Mo2O8)(SeO3) is formed by [Ni6O22]32- hexanuclear clusters interconnected by selenite groups whereas the thick nickel(II) tellurite layer in Ni3(Mo2O8)(TeO3) is constructed by corrugated nickel(II) oxide chains bridged by the tellurite groups. The results of magnetic property measurements indicate that there are considerable ferromagnetic interactions between nickel(II) centers in both compounds. Their optical properties and band structures have been also studied.     

A DFT and TD-DFT approach to the understanding of statistical kinetics in substitution reactions of M3Q4 (M = Mo, W; Q = S, Se) cuboidal clusters

For many years it has been known that the nine water molecules in [M(3)Q(4)(H(2)O)(9)](4+) cuboidal clusters (M = Mo, W; Q = S, Se) can be replaced by entering ligands, such as chloride or thiocyanate, and kinetic studies carried out mainly on the substitution of the first water molecule at each metal centre reveal that the reaction at the three metal centres occurs with statistical kinetics; that is, a single exponential with a rate constant corresponding to the reaction at the third centre is observed instead of the expected three-exponential kinetic trace. Such simplification of the kinetic equations requires the simultaneous fulfilment of two conditions: first that the three consecutive rate constants are in statistical ratio, and second that the metal centres behave as independent chromophores. The validity of those simplifications has been checked for the case of the reaction of [Mo(3)S(4)(H(2)O)(9)](4+) with Cl(-) by using DFT and TD-DFT theoretical calculations. The results of those calculations are in agreement with the available experimental information, which indicates that the H(2)O ligands trans to the μ-S undergo substitution much faster than those trans to the μ(3)-S. Moreover, the energy barriers for the substitution of the first water molecule at the three metal centres are close to each other, the differences being compatible with the small changes in the numerical values of the rate constants required for observation of statistical kinetics. TD-DFT calculations lead to calculated electronic spectra, which are in reasonable agreement with those experimentally measured, but the calculations do not indicate that the three metal centres behave as independent chromophores, although the mathematical conditions required for simplification of the kinetic traces to a single exponential are reasonably well fulfilled at certain wavelengths. A re-examination of the kinetics of the reaction by using global fitting procedures yields results, which are compatible with statistical kinetics, although an alternative interpretation in which substitution only occurs at a single metal centre under reversible conditions is also possible.     

Structure,magnetism, and electrochemistry of the multinickel polyoxoanions [Ni6As3W24O94(H2O)2]17-, [Ni3Na(H2O)2(AsW9O34)2]11-, and [Ni4Mn2P3W24O94(H2O)2]17-

The three novel, multi-nickel-substituted heteropolytungstates [Ni(6)As(3)W(24)O(94)(H(2)O)(2)](17)(-) (1), [Ni(3)Na(H(2)O)(2)(AsW(9)O(34))(2)](11)(-) (2), and [Ni(4)Mn(2)P(3)W(24)O(94)(H(2)O)(2)](17)(-) (3) have been synthesized and characterized by IR, elemental analysis, electrochemistry, and magnetic studies. Single-crystal X-ray analysis was carried out on Na(16.5)Ni(0.25)[Ni(6)As(3)W(24)O(94)(H(2)O)(2)].54H(2)O, which crystallizes in the triclinic system, space group P1, with a = 17.450(4) A, b = 17.476(4) A, c = 22.232(4) A, alpha = 85.73(3) degrees, beta = 89.74(3) degrees, gamma = 84.33(3) degrees, and Z = 2, Na(11)[Ni(3)Na(H(2)O)(2)(AsW(9)O(34))(2)].30.5H(2)O, which crystallizes in the triclinic system, space group P1, with a = 12.228(2) A, b = 16.743(3) A, c = 23.342(5) A, alpha = 78.50(3) degrees, beta = 80.69(3) degrees, gamma = 78.66(3) degrees, and Z = 2, and Na(17)[Ni(4)Mn(2)P(3)W(24)O(94)(H(2)O)(2)].50.5H(2)O, which crystallizes in the monoclinic system, space group P2(1)/c, with a = 17.540(4) A, b = 22.303(5) A, c = 35.067(7) A, beta = 95.87(3) A, and Z = 4. Polyanion 1 consists of two B-alpha-(Ni(3)AsW(9)O(40)) Keggin moieties linked via a unique AsW(6)O(16) fragment, leading to a banana-shaped structure with C(2)(v)() symmetry. The mixed-metal tungstophosphate 3 is isostructural with 1. Polyanion 2 consists of two lacunary B-alpha-[AsW(9)O(34)](9)(-) Keggin moieties linked via three nickel(II) centers and a sodium ion. Electrochemical studies show that 1-3 exhibit a unique and reproducible voltammetric pattern and that all three compounds are stable in a large pH range. An investigation of the magnetic properties of 1-3 indicates that the exchange interactions within the trimetal clusters are ferromagnetic. However, for 1 and 3 intra- and intermolecular interactions between different trinuclear clusters are also present.     

Electronic properties of Strandberg anions: A DFT study of [X2Mo5O23]n−, (X = PV,SVI, AsV,SeVI), and [(RP)2Mo5O21]4− (R = H,CH3, C2H5)

The electronic properties of the anions mentioned in the title polyanions were calculated by means of Density Functional Theory (DFT). The redox properties and the basicity of the external oxygen sites of those polyanions were analyzed. The results show that the redox properties of Strandberg anions depend on the nature of heteroatom X. The organic group bonded to the heteroatom modifies the redox property of the cluster. The oxygen basicities of the polyanions were analyzed by virtue of molecular electrostatic potential (MEP). The MEP distribution suggests that the most basic centers are triple‐bridging oxygen atoms, one of which is shared with two metal atoms and one heteroatom X in [P₂Mo₅O₂₃]^6? and [As₂Mo₅O₂₃]^6?. In [(RP)₂Mo₅O₂₁]^4?, the triple‐bridging oxygen atoms and the double‐bridging oxygen atoms bonded to two Mo atoms identified as the most basic centers. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005