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.     

Modifying electronic communication in dimolybdenum units by linkage isomers of bridged oxamidate dianions

Reactions of Mo(2)(O(2)CCH(3))(DAniF)(3), DAniF = N,N'-di-p-anisylformamidinate, with oxamidate dianions [ArNC(O)C(O)NAr](2-), Ar = C(6)H(5) and p-anisyl, give pairs of isomeric compounds where the [Mo(2)] units are bridged by the oxamidate anions. For the alpha isomers, the C-C unit of the dianion is nearly perpendicular to the Mo-Mo bonds, and these are essentially perpendicular to each other. For the beta isomers, the corresponding C-C unit and the Mo-Mo bonds are essentially parallel to each other. Each type of isomer is stable in solution. The electronic communication as measured by the DeltaE(1/2) for the oxidation of each of the Mo(2) units is significantly better for the beta isomers. This is supported also by the appearance of what is conventionally called an intervalence charge-transfer band in the near infrared region upon oxidation of the beta isomers but not the alpha isomers. Molecular mechanics and DFT calculations help explain the relative conformations in the alpha isomers and the relative energy differences between the alpha and beta isomers.     

Theoretical study of the relative stabilities of the alpha/beta3-[XW11O39](m-) lacunary polyoxometalates (X = P, Si)

A computational study of the relative stability of the monolacunary Keggin polyoxotungstates alpha and beta 3-[XW 11O 39] ( m- ) (X = P, m = 7; X = Si, m = 8) was performed. The influence of the nature of different grafted cations and of the central anion XO 4 ( n- ) on the relative stabilities of the lacunary isomers was analyzed. From these results, an interpretation of the structural difference in the metallic frameworks of alpha-[PW 11O 39{Ru(DMSO) 3(H 2O)}] (5-), alpha-[PW 11O 39{Ru(C 6H 6)(H 2O)}] (5-), and beta 3-[SiW 11O 39{Ru(DMSO) 3(H 2O)}] (6-) is proposed, and conclusions are drawn as to how to favor the formation of beta 3 derivatives in future syntheses.     

Electronic and magnetic properties of alpha-Keggin anions: A DFT study of [XM12O40](n-), (M = W, Mo; X = Al(III), Si(IV), P(V), Fe(III), Co(II), Co(III)) and [SiM11VO40](m- (M = Mo and W).

Calculations based on density functional theory (DFT) have been carried out to investigate the electronic and magnetic properties of the alpha-Keggin anions mentioned in the title. The atomic populations and the distribution of the electron density computed for the studied clusters support the hypothesis that an oxidized Keggin anion is an XO(4)(n-) clathrate inside a neutral M(12)O(36) cage. The energy gap between the band of occupied orbitals, formally delocalized over the oxo ligands, and the unoccupied d-metal orbitals, delocalized over the addenda, has been found to be independent of the central ion. However, substitution of a W or a Mo by V modifies the relative energy of the LUMO and then induces important changes in the redox properties of the cluster. In agreement with the most recent X-ray determination of [Co(III)W(12)O(40)](5-) and with the simplicity of the (183)W NMR and (17)O NMR spectra observed for this anion the calculations suggest that [Co(III)W(12)O(40)](5-) has a slightly distorted T(d ) geometry. For the parent cluster [CoW(12)O(40)](6-) the quadruplet corresponding to the anion encapsulating a Co(II) was found to be approximately 1 eV more stable than the species formed by a Co(III) and 1 e delocalized over the sphere of tungstens. The one-electron reduction of [Co(II)W(12)O(40)](6-) and [Fe(III)W(12)O(40)](5-) leads to the formation of the 1 e blue species [Co(II)W(12)O(40)](7-) and [Fe(III)W(12)O(40)](6-). The blue-iron cluster is considerably antiferromagnetic, and in full agreement with this behavior the low-spin state computed via a Broken Symmetry approach is 196 cm(-1) lower than the high-spin solution. In contrast, the cobalt blue anion has a low ferromagnetic coupling with an S-T energy gap of +20 cm(-1). This blue species is more stable than the alternative reduction product [Co(I)W(12)O(40)](7-) by more than 0.7 eV.     

Inversed stability order in Keggin polyoxothiometalate isomers: a DFT study of 12-electron reduced alpha, beta, gamma, delta, and epsilon [(MoO4)Mo12O12S12(OH)12]2- anions

Density functional theory calculations have been carried out to investigate 12-electron reduced alpha, beta, gamma, delta, and epsilon Keggin-like [(MoO4)Mo12O12S12(OH)12]2- polyoxothiometalates (POTMs), which show that the stability order is alpha < beta < gamma < delta < epsilon that is perfectly inverse to the well-known trend of the classical Keggin polyoxometalates. Energy decomposition analysis reveals that the enhanced stabilities of gamma, delta, and epsilon isomers originate the favorable arrangements of their Mo12O12S12(OH)12 shell, in which the edge-sharing [MoV2(mu-S)2O2] fragment plays a fundamental role in stabilizing the overall structure. Both frontier orbital analysis and Mayer indexes exhibit that a Mo-Mo single bond is formed inside the [MoV2(mu-S)2O2] fragment, which leads to the localization of the two reduced electrons. As compared with experimentally discovered cyclic [(C9H3O6)@Mo12O12S12(OH)12]3-, all Keggin POTM structures are less stable due to their disfavored cage framework and the disadvantageous host-guest interaction. However, the epsilon-type Keggin POTM that has the largest similarity to the cyclic species is possibly available in the presence of appropriate templates.     

Voltammetric Reduction of alpha- and gamma-[S2W18O62]4- and alpha-, beta-, and gamma-[SiW12O40]4-: isomeric dependence of reversible potentials of polyoxometalate anions using data obtained by novel dissolution and conventional solution-phase processes

Comparative studies on the voltammetric reduction of the alpha and gamma isomers of Dawson [S(2)W(18)O(62)](4)(-) and alpha, beta, and gamma forms of Keggin [SiW(12)O(40)](4)(-) polyoxometalate anions have been undertaken. For the six reversible one-electron [S(2)W(18)O(62)](4)(-)(/5)(-)(/6)(-)(/7)(-)(/8)(-)(/9)(-)(/10)(-) processes in acetonitrile, reversible potentials (E(0)(')) were found to be independent of isomeric form within experimental error (+/-5 mV). However, because both the alpha and gamma* isomers of [Bu(4)N](4)[S(2)W(18)O(62)] are insoluble in water, solid-state voltammetric studies with microcrystals adhered to electrode surfaces in contact with aqueous Et(4)NCl and Bu(4)NCl electrolyte media were also possible. Although no isomeric distinction was again detected in the solid-state studies, it was found that reduction of adhered solid by four or more electron equivalents led to rapid dissolution. When Et(4)NCl was the electrolyte, this dissolution process coupled with potential cycling experiments enabled conventional solution-phase data to be obtained in water for the analogous six one-electron reduction steps previously detected in acetonitrile. A strong medium effect attributed to Lewis acidity effects was apparent upon comparison with E(0)(') data obtained in water and acetonitrile. In contrast, with the [SiW(12)O(40)](4)(-) system, E(0)(') values for the [SiW(12)O(40)](4)(-)(/5)(-)(/6)(-)(/7)(-) processes in acetonitrile exhibited a larger (about 70 mV) dependence on isomeric form, and the isomerization step, [gamma-SiW(12)O(40)](6)(-)--> [alpha-SiW(12)O(40)](6)(-), was detected on the voltammetric time scale. The influence of isomeric form on reversible potential data is considered in terms of structural and charge density differences exhibited in the [S(2)W(18)O(62)](4)(-) and [SiW(12)O(40)](4)(-) systems studied in this paper and published data available on the alpha, beta, gamma, and gamma isomers of [As(2)W(18)O(62)](6)(-) and [P(2)W(18)O(62)](6)(-) Dawson anions and Keggin systems.     

单空位Keggin结构杂多化合物的相转移化学研究(英文)

利用相转移试剂四庚基溴化铵将含过渡金属单空位Ｋｅｇｇｉｎ结构杂多化合物［ＸＷ１１Ｏ３９Ｚ（Ｈ２Ｏ）］ｎ－（Ｘ＝Ｃｒ，Ｍｎ，Ｆｅ；Ｚ＝Ｃｏ，Ｚｎ，Ｃｒ；ｎ＝６，７），从水相转移至非极性溶剂有机相苯中．并根据电子光谱、ＩＲ谱、ＥＳＲ谱的变化，进一步考察了它们在有机相苯中的配位水脱去，形成配位不饱和杂多阴离子的情况，同时详细研究了该类杂多阴离子所含表面配位水与若干无机阴离子及有机配体的取代反应．实验表明，杂多阴离子由水相转移至有机相苯后，较易脱去配位水形成溶剂配位不饱和离子．当加入Ｌｅｗｉｓ碱时，可迅速恢复饱和配位．ＥＳＲ测定给出某些含过渡金属单空位Ｋｅｇｇｉｎ结构杂多阴离子相转移前后价态变化及电子转移情况．     

Relative stability in alpha- and beta-Wells-Dawson heteropolyanions: a DFT study of [P2M18O62]n- (M = W and Mo) and [P2W15V3O62]n-

To determine the relative stability of alpha and beta rotational isomers of the Wells-Dawson structure, the energies of some fully oxidized, single- and 2-fold-reduced systems were calculated by means of DFT calculations. The thermodynamics of the alpha/beta equilibrium for P(2)M(18) Wells-Dawson anions is slightly shifted toward the alpha structure, but the difference in stability is smaller than in the Keggin anions. Tungstates (2:18) and vanadotungstates (2:3:15) show minimal redox differences between isomers, as the electronic structure of the frontier orbitals appears to be nearly the same. In addition, an alternative arrangement is proposed that have long and short Mo-O bonds in beta-P(2)Mo(18) with an idealized C(3) symmetry. This arrangement was computed to be about 8.2 kcal mol(-1) more stable than the nonalternate framework of C(3)(v)() symmetry. The P(2)Mo(18) is the Wells-Dawson anion for which the alpha/beta equilibrium most resembles that of the Keggin anions.     

骨架金属原子对Keggin阴离子电子结构和物化性质的研究

使用第一原理密度泛函理论中的离散变分方法(DFT-DVM)对(PM~1~2O~4~0)^n^-(M=Mo,W,V),(PMo~9W~3O~4~0)^3^-,(PMo~9V~3O~4~0)^6^-五种Keggin结构杂多阴离子进行了电子结构计算,讨论了骨架金属原子对Keggin结构杂多阴离子的电荷分布、成键作用、热稳定性、氧化还原性等的影响。结果表明,骨架金属原子对Keggin阴离子的电荷分布和成键作用均有一定的影响,以Mo,W,V作骨架金属原子的Keggin阴离子(PM~1~2O~4~0)^n^-的热稳定性顺序为:(PW~1~2O~4~0)~3^->(PMo~1~2O~4~0)^3^->(PV~1~2O~4~0)^1^5^-。提出了判断杂多阴离子氧化性强弱的两因素法---脱出晶格氧的难易程度和LUMO轨道电负性,并根据两因素法得到氧化性强弱顺序为:(PV~1~2O~4~0)^1^5^->(PMo~1~2O~4~0)^3^->(PW~1~2O~4~0)~3^-。同时,讨论了当(PMo~1~2O~4~0)~3^-中的Mo部分被W和V取代后,即(PMo~9W~3O~4~0)^3^-,(PMo~9V~3O~4~0)^6^-,其中取代原子对电子结构的影响,结果表明,W取代使整个阴离子的稳定性增强,但氧化性减弱,V取代,使稳定性减弱,但氧化性增强。     

双帽Keggin型杂多阴离子[PM12O40(VO)2]n-(M=Mo,n=5; M=V, n=9)的离散变分方法研究

使用密度泛函理论的离散变分方法(DFT-DVM)研究了双帽Keggin型杂多阴离子[PM12O40(VO)2]n-(M=Mo, n=5; M=V, n=9),即[PMo12O40(VO)2]5- (a)和[PV12O40(VO)2]9- (b)的电子结构,讨论了双帽的形成对Keggin型杂多阴离子的电子结构和催化性质的影响,并与其Keggin型杂多阴离子(PM12O40)n-(M=Mo, n=3; M=V, n=15)的计算结果进行了对比分析,计算结果表明,双帽的形成对Keggin型杂多阴离子的电子结构产生了很大的影响,因而它们在催化活性上可能会表现出较大的差异.     

Relative energies of alpha and beta isomers of Keggin dodecatungstogallate

The relative energies of beta Keggin heteropolytungstates, X(n+) W12O40(8-n)-, decrease as X(n+) is varied within period 3, from P5+ to Si4+ to Al3+. With heating of alpha-H5Ga3+ W12O40 at 200 degrees C in water, an equilibrated mixture of alpha (T(d); one 183W NMR signal) and beta (C(3v); three signals; 1:2:1 ratio) isomers is obtained. From deltaG(exp) = -RT ln K(beta-->alpha), in which (from 71Ga NMR spectra) K(beta-->alpha) (= [alpha]/[beta]) = 5.0, beta-GaW12O40(5-) is 0.65 kcal mol(-1) higher in energy than alpha-GaW12O40(5-). This finding is evaluated by analysis of the X-ray crystal structure alpha-K2Na3[GaW12O40] x 9.3 H2O [trigonal, space group P3(2)21, a = 18.9201(13) A, b = 18.9201(13) A, c = 12.5108(12) A, Z = 3, T = 100(2)K], comparison of the Shannon and Prewitt radii and Pauling electronegativities of Al3+ and Ga3+, and insight from density functional theory calculations, which predicted Ebeta - Ealpha = 0.32 kcal mol(-1).     

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.     

Photoelectron spectroscopy of free multiply charged Keggin anions alpha-[PM12O40]3- (M = Mo, W) in the gas phase

Two polyoxometalate Keggin-type anions, alpha-PM12O40(3-) (M = Mo, W), were transferred to the gas phase by electrospray; their electronic structure and stability were probed by photoelectron spectroscopy. These triply charged anions were found to be highly stable in the gas phase with large adiabatic electron detachment energies of 1.7 and 2.1 eV for M = Mo and W, respectively. The magnitude of the repulsive Coulomb barrier was measured as approximately 3.4 eV for both anions, providing an experimental estimate for the intramolecular Coulomb repulsion present in these highly charged anions. Density functional theory calculations were carried out and compared with the experimental data, providing insight into the electronic structure and valence molecular orbitals of the two Keggin anions. The calculations indicated that the highest occupied molecular orbital and other frontier orbitals for PM12O40(3-) are localized primarily on the mu2-oxo bridging ligands of the polyoxometalate framework, consistent with the reactivity on the mu2-oxo sites observed in solution. It was shown that the HOMO of PW12O40(3-) is stabilized relative to that of PMo12O40(3-) by approximately 0.35 eV. The experimental adiabatic electron detachment energies of PM12O40(3-) (i.e., the electron affinities of PM12O40(2-)) are combined with recent calculations on the proton affinity of PM12O40(3-) to yield O-H bond dissociation energies in PM12O39(OH)2- as approximately 5.1 eV.     

Structure,stability, and electronic and NMR properties of various oxo- and nitrido-derivatives of [L(Salen)Mn(III)]+, where L = none and imidazole. A density functional study

Structure, stability, and electronic and NMR properties of [(Salen)Mn(III)](+)-derived intermediates/reactants in the epoxidation/amination of unfunctionalized olefins, namely [(Salen)Mn(V)O](+) (1-oxo), [(Salen)Mn(IV)O] (2-oxo), and [(Salen)Mn(V)N] (3), have been studied with the B3LYP density functional method. It has been shown that the (1)A, (3)A, and (5)A states of cationic 1-oxo species are virtually degenerate, while for the neutral 2-oxo species the ground (4)A state lies 6.4 kcal/mol lower than (2)A. In the nitrido species 3, the (1)A state has been shown to be the ground state in agreement with experiment. We have investigated isomerization of 1-oxo and 2-oxo species into unusual [(OSalen)Mn(III)](+) (1-N-oxo and 1-peroxo) and [(OSalen)Mn(II)] (2-N-oxo and 2-peroxo) species, respectively. For cationic species 1, the 1-N-oxo isomers are more stable (by 10-12 kcal/mol) than the 1-oxo isomer and are separated from the latter by 21-22 kcal/mol barriers. On the other hand, 1-peroxo isomers are calculated to be 14-16 kcal/mol higher than the 1-oxo isomer. For neutral species 2, however, both 2-N-oxo and 2-peroxo isomers lie significantly higher in energy than the 2-oxo isomer. It has been shown that coordination of axial imidazole ligand alters relative energies of spin states for 1- and 2-oxo species, destabilizing low-spin states. For singlet states of H(2)Salen, 1-oxo, and 3, we have calculated (1)H, (13)C, (15)N, and (17)O NMR chemical shifts using the gauge-independent-atomic orbital (GIAO) approach.     

About the Keggin isomers: crystal structure of [N(C4H9)4]-gamma-[SiMo2W10O40]n- (n= 4 or 6)

The tetrabutylammonium gamma-dodecatungstosilicate has been crystallized in a 6/1 acetonitrile/water solvent. An X-ray single-crystal analysis was carried out on [N(C4H9)4]4-gamma-[SiW12O40] which crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with a = 19.0881(3) A, b = 21.4435(3) A, c = 26.0799(1) A, V = 10674.9(2) A3, Z = 4, and rho(calcd) = 2.392 g/cm3. The idealized C2v arrangement of the anion results from the rotation of 60 degrees of two trigonal [W3O13] groups in the Keggin anion. Taking as reference the geometrical characteristics of the Keggin anion, it appears that the bond lengths and bonds angles within the four [W3O13] groups are not significantly modified while the mu-oxo junctions between the two rotated groups and those between the two unrotated groups involve more acute and opened W-O-W angles, respectively. The syntheses and 183W NMR characterizations of the mixed gamma-[SiW10Mo2O40]n- compounds corresponding to the oxidized (Mo(VI); n = 4) and to the two electron-reduced (Mo(V); n = 6) anions are reported. Structural analysis by 183W NMR has proved unambiguously that the C2v structure of the gamma-[SiW10O36]8- subunit is retained in both the compounds. The electronic behavior of the series gamma-[SiW10M2E2O36]6- (M = Mo or W; E = O or S) is examined, compared and related to 183W NMR data.     

Synthesis, crystal structure of α-Keggin heteropolymolybdates with pyridine-2,6-dicarboxylate based frameworks, and associated RhB photocatalytic degradation and 2D-IR COS tests

Three α-Keggin heteropolymolybdates with the formula [(C(5)H(4)NH)COOH](3)[PMo(12)O(40)] 1, {[Sm(H(2)O)(4)(pdc)](3)}{[Sm(H(2)O)(3)(pdc)]}[SiMo(12)O(40)]·3H(2)O 2 and {[La(H(2)O)(4)(pdc)](4)}[PMo(12)O(40)]F 3 (H(2)pdc = pyridine-2,6-dicarboxylate), have been synthesized under hydrothermal condition and characterized by single crystal X-ray diffraction analyses, elemental analyses, inductively coupled plasma atomic emission spectroscopy (ICP-AES), IR, thermal gravimetric analyses, thermal infrared spectrum analyses and powder X-ray diffraction (PXRD) analyses. Single crystal X-ray diffraction indicates all three compounds comprise ball-shaped Keggin type [XMo(12)O(40)](n-) polyoxometalates (POMs) (n = 3, X = P; n = 4, X = Si, respectively) with different types of carboxylic ligands derived from H(2)pdc, and these cluster anions are isostructural. In order to explore structural characteristics, Rhodamine B photocatalytic (RhB) degradation and two-dimensional infrared correlation spectroscopy (2D-IR COS) tests, are investigated for 1, 2 and 3. In RhB degradation, all compounds show good photocatalytic activity. For 1, the activity mainly comes from POMs. While in 2 and 3, POMs' photocatalytic activity is enhanced by the Ln(iii)-pdc metal-organic frameworks. Structural properties like POM's stability and magnetic sensitivity are discussed by 2D-IR COS under thermal/magnetic perturbations.     

Density functional theory and Hartree-Fock studies: geometry, vibrational frequencies and electronic properties of Anderson-type heteropolyanion, [XM6O24]n- (X=TeVI, IVII and M=Mo, W) and [SbVW6O24]7-

The geometry, IR and Raman spectra and electronic properties of Anderson-type heteropolyanions with main-group high oxidation state heteroatom, [Te(VI)Mo(6)O(24)](6-), [I(VII)Mo(6)O(24)](5-), [Sb(V)W(6)O(24)](7-), [Te(VI)W(6)O(24)](6-) and [I(VII)W(6)O(24)](5-) have been investigated using Hartree-Fock (HF) and density functional theory (DFT) methods. HF method has good results in geometry parameters but poorer than DFT method in the results of vibrational frequencies. Also we have investigated the effect of LanL2DZ augmented in the vibrational frequencies. With attention to relative charge and size of the cavity occupied by XO(6) subunit in these anions, we suggest that the general formula [XO(6)(n-)@M(6)O(18)] to describe electronic properties of these anions.     

Mechanistic analysis of the electrocatalytic properties of dissolved alpha and beta isomers of [SiW12O40]4- and solid [Ru(bipy)3]2[alpha-SiW12O40] on the reduction of nitrite in acidic aqueous media

Voltammetric studies on the reduction of alpha and beta isomers of the Keggin polyoxometalate anion [SiW12O40]4- reveal a series of electrochemically reversible processes in acidic aqueous media. In the presence of NO2-, catalytic current is detected in the potential region of the [SiW12O40]4-/5- process. Electronic spectroscopy and simulation of voltammetric data undertaken at variable [NO2-] and [H+] allow the following mechanism to be postulated, [SiW12O40]4- + e- <-->[SiW12O40]5-, H+ + HNO2 <--> NO+ + H2O, NO+ + [SiW12O40]5- --> NO + [SiW12O40]4-. The second-order rate constant for the rate-determining step is faster for the alpha isomer than for the beta one. This may be attributed to the different reversible potentials of -0.144 V (alpha isomer) and -0.036 V vs Ag/AgCl (beta isomer) and, hence, smaller driving force for an assumed outer sphere electron-transfer reaction in the case of beta isomer. A stable, water-insoluble, thin-film [Ru(bipy)3]2[alpha-SiW12O40] chemically modified electrode was generated electrochemically via ion-exchange of [Ru(bipy)3]2+ with Bu4N+ in the [Bu4N]4[alpha-SiW12O40] solid. The first reduction process with this modified electrode gives rise to the reaction [Ru(bipy)3]2[alpha-SiW12O40](solid) + H+(soln) + e- <--> H[Ru(bipy)3]2[alpha-SiW12O40](solid). The need to transfer a proton from the solution to the solid phase for charge neutralization purposes introduces a hydrogen-ion concentration dependence into this reaction, which is not found in the solution-phase study. Nevertheless, the voltammetric catalytic activity with respect to nitrite reduction is retained with the chemically modified electrode. However, nitrite catalysis with the [Ru(bipy)3]2[alpha-SiW12O40]-modified electrode is now independent of concentration of H+, rather than exhibiting a first-order dependence, and full mechanistic details for this process are unknown.     

Core molecular orbital contribution to N2O isomerization as studied using theoretical electron momentum spectroscopy

Core molecular orbital contribution to the electronic structure of N2O isomers has been studied using quantum mechanical density functional theory combined with a plane wave impulse approximation method. Momentum distributions of wave functions for inner shell molecular orbitals of the linear NNO, cyclic and linear NON isomers of N2O are calculated through the (e, 2e) differential cross sections in momentum space. This is possible because this momentum distribution is directly proportional to the modulus squared of the momentum space wave function for the molecular orbital in question. While the momentum distributions of the NNO and cyclic N2O isomers demonstrate strong atomic orbital characteristics in their core space, the outer core molecular orbitals of the linear NON isomer exhibit configuration interactions between them and the valence molecular orbitals. It is suggested that the frozen core approximation breaks down in the prediction of the electronic structure of such an isomer. Core molecular orbital contributions to the electronic structure can alter the order of total energies of the isomers and lead to incorrect conclusions of the stability among the isomers. As a result, full electron calculations should be employed in the study of N2O isomerization.     

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.