Photoelectron spectroscopic study of the hydrated nucleoside anions: Uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1)

The hydrated nucleoside anions, uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1), have been prepared in beams and studied by anion photoelectron spectroscopy in order to investigate the effects of a microhydrated environment on parent nucleoside anions. Vertical detachment energies (VDEs) were measured for all eight anions, and from these, estimates were made for five sequential anion hydration energies. Excellent agreement was found between our measured VDE value for thymidine(-)(H(2)O)(1) and its calculated value in the companion article by S. Kim and H. F. Schaefer III.     

Ab initio molecular dynamics simulations of an excited state of X(-)(H(2)O)(3) (X = Cl, I) complex

Upon excitation of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) clusters, the electron transfers from the anionic precursor to the solvent, and then the excess electron is stabilized by polar solvent molecules. This process has been investigated using ab initio molecular dynamics (AIMD) simulations of excited states of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) clusters. The AIMD simulation results of Cl(-)(H(2)O)(3) and I(-)(H(2)O)(3) are compared, and they are found to be similar. Because the role of the halogen atom in the photoexcitation mechanism is controversial, we also carried out AIMD simulations for the ground-state bare excess electron -- water trimer [e(-)(H(2)O)(3)] at 300 K, the results of which are similar to those for the excited state of X(-)(H(2)O)(3) with zero kinetic energy at the initial excitation. This indicates that the rearrangement of the complex is closely related to that of e(-)(H(2)O)(3), whereas the role of the halide anion is not as important.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.     

Ab initio study of hydrated sodium halides NaX(H2O)(1-6) (X=F, Cl, Br, and I)

We have studied the dissociation phenomena of sodium halides by water molecules. The structures, binding energies, electronic properties, and IR spectroscopic features have been investigated by using the density-functional theory, second-order Moller-Plesset perturbation theory, and coupled clusters theory with single, double, and perturbative triplet excitations. In the case that the sodium halides are hydrated by three water molecules, the most stable structures show the partial (or half) dissociation feature. The dissociated structures are first found for NaX(H2O)(n=5) for X=BrI, though these structures are slightly higher in energy than the global minimum-energy structure. In the case of hexahydrated sodium halides the global minimum-energy structures (which are different from the structures reported in any previous work) are found to be dissociated (X=F/I) or partially/half dissociated (X=Cl/Br), while other nearly isoenergetic structures are undissociated, and the dissociated cubical structures are higher in energy than the corresponding global minimum-energy structure.     

Vibrational spectroscopy of hydrated electron clusters (H2O)(-)(15-50) via infrared multiple photon dissociation

Infrared multiple photon dissociation spectra for size-selected water cluster anions (H2O)(n)(-), n=15-50, are presented covering the frequency range of 560-1820 cm(-1). The cluster ions are trapped and cooled by collisions with ambient He gas at 20 K, with the goal of defining the cluster temperature better than in previous investigations of these species. Signal is seen in two frequency regions centered around 700 and 1500-1650 cm(-1), corresponding to water librational and bending motions, respectively. The bending feature associated with a double-acceptor water molecule binding to the excess electron is clearly seen up to n=35, but above n=25; this feature begins to blueshift and broadens, suggesting a more delocalized electron binding motif for the larger clusters in which the excess electron interacts with multiple water molecules.     

The mechanism for water exchange in [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-), as studied by quantum chemical methods.

The mechanisms for the exchange of water between [UO(2)(H(2)O)(5)](2+), [UO(2)(oxalate)(2)(H(2)O)](2)(-)(,) and water solvent along dissociative (D), associative (A) and interchange (I) pathways have been investigated with quantum chemical methods. The choice of exchange mechanism is based on the computed activation energy and the geometry of the identified transition states and intermediates. These quantities were calculated both in the gas phase and with a polarizable continuum model for the solvent. There is a significant and predictable difference between the activation energy of the gas phase and solvent models: the energy barrier for the D-mechanism increases in the solvent as compared to the gas phase, while it decreases for the A- and I-mechanisms. The calculated activation energy, Delta U(++), for the water exchange in [UO(2)(H(2)O)(5)](2+) is 74, 19, and 21 kJ/mol, respectively, for the D-, A-, and I-mechanisms in the solvent, as compared to the experimental value Delta H(++) = 26 +/- 1 kJ/mol. This indicates that the D-mechanism for this system can be ruled out. The energy barrier between the intermediates and the transition states is small, indicating a lifetime for the intermediate approximately 10(-10) s, making it very difficult to distinguish between the A- and I-mechanisms experimentally. There is no direct experimental information on the rate and mechanism of water exchange in [UO(2)(oxalate)(2)(H(2)O)](2-) containing two bidentate oxalate ions. The activation energy and the geometry of transition states and intermediates along the D-, A-, and I-pathways were calculated both in the gas phase and in a water solvent model, using a single-point MP2 calculation with the gas phase geometry. The activation energy, Delta U(++), in the solvent for the D-, A-, and I-mechanisms is 56, 12, and 53 kJ/mol, respectively. This indicates that the water exchange follows an associative reaction mechanism. The geometry of the A- and I-transition states for both [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-) indicates that the entering/leaving water molecules are located outside the plane formed by the spectator ligands.     

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.     

Potential energy surface of O2-(H2O) and factors controlling water-to-O2- binding motifs

The potential energy surface (PES) of O(2)(-)(H(2)O) is investigated by varying the interoxygen distance of O(2)(-) via ab initio calculations with a large basis set. Although two stationary points, C(s) and C(2v) conformers, are found along the interoxygen-distance coordinate, only the C(s) conformer is identified as a minimum-energy species. We find a critical distance, r(c), separating these two conformers in the PES. The C(s) conformer prevails at interoxygen distances of O(2)(-) that are less than r(c), while the C(2v) conformer dominates at the distances larger than r(c). The structural features of these two conformers are also discussed. Although the water deformation energy is shown to be the stabilization source responsible for the prevalence of the C(s) cluster conformer at the interoxygen distances of O(2)(-) less than r(c), the ionic hydrogen bonding is the major driving force for transformation of the water binding motif from C(s) to C(2v) when the interoxygen distance of O(2)(-) increases.     

Theoretical Modeling of Water Exchange on [Pd(H(2)O)(4)](2+), [Pt(H(2)O)(4)](2+), and trans-[PtCl(2)(H(2)O)(2)

Density functional theory is applied to modeling the exchange in aqueous solution of H(2)O on [Pd(H(2)O)(4)](2+), [Pt(H(2)O)(4)](2+), and trans-[PtCl(2)(H(2)O)(2)]. Optimized structures for the starting molecules are reported together with trigonal bipyramidal (tbp) systems relevant to an associative mechanism. While a rigorous tbp geometry cannot by symmetry be the actual transition state, it appears that the energy differences between model tbp structures and the actual transition states are small. Ground state geometries calculated via the local density approximation (LDA) for [Pd(H(2)O)(4)](2+) and relativistically corrected LDA for the Pt complexes are in good agreement with available experimental data. Nonlocal gradient corrections to the LDA lead to relatively inferior structures. The computed structures for analogous Pd and Pt species are very similar. The equatorial M-OH(2) bonds of all the LDA-optimized tbp structures are predicted to expand by 0.25-0.30 ?, while the axial bonds change little relative to the planar precursors. This bond stretching in the transition state counteracts the decrease in partial molar volume caused by coordination of the entering water molecule and can explain qualitatively the small and closely similar volumes of activation observed. The relatively higher activation enthalpies of the Pt species can be traced to the relativistic correction of the total energies while the absolute DeltaH() values for exchange on [Pd(H(2)O)(4)](2+) and [Pt(H(2)O)(4)](2+) are reproduced using relativistically corrected LDA energies and a simple Born model for hydration. The validity of the latter is confirmed via some simple atomistic molecular mechanics estimates of the relative hydration enthalpies of [Pd(H(2)O)(4)](2+) and [Pd(H(2)O)(5)](2+). The computed DeltaH() values are 57, 92, and 103 kJ/mol compared to experimental values of 50(2), 90(2), and 100(2) kJ/mol for [Pd(H(2)O)(4)](2+), [Pt(H(2)O)(4)](2+), and trans-[PtCl(2)(H(2)O)(2)], respectively. The calculated activation enthalpy for a hypothetical dissociative water exchange at [Pd(H(2)O)(4)](2+) is 199 kJ/mol. A qualitative analysis of the modeling procedure, the relative hydration enthalpies, and the zero-point and finite temperature corrections yields an estimated uncertainty for the theoretical activation enthalpies of about 15 kJ/mol.     

Selten‐Erd‐Metall‐Koordinationspolymere: Synthese und Kristallstrukturen von fünf neuen Adipinaten, [M2(Adi)3(H2O)4](AdiH2)(H2O)4 (M = La,Nd), [Er(Adi)(H2O)5]Cl(H2O) und [M(Adi)(H2O)5](NO3)(H2O) (M = Gd,Er)

Rare‐Earth‐Metal Coordination Polymers: Synthesis and Crystal Structures of Five New Adipinates, [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ (M = La, Nd), [Er(Adi)(H₂O)₅]Cl(H₂O) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd, Er) The new rare‐earth compounds [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ (M = La ( 1 ), Nd ( 2 )), [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) were obtained from the reaction of adipinic acid with La(OH)₃·xH₂O, Nd₂O₃, ErCl₃·6H₂O, Gd(NO)₃·xH₂O and Er₂O₃, respectively. Their crystal structures were determined by single‐crystal X‐ray diffraction. The coordination polymers [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ crystallize in the triclinic space group (no. 2) with a = 875.4(1), b = 1000.4(2), c = 1179.0(2) pm, α = 74.70(1), β = 69.85(1), γ = 86.18(2)° and Z = 1 (crystal data for M = La, ( 1 )). The quasi‐isostructural compounds [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) crystallize with monoclinic symmetry, space group C2/c (no. 15) with lattice parameters of a = 1231.5(1), b = 1532.6(1), c = 895.4(1) pm, β = 123.44(1)° and Z = 4 (crystal data for ( 3 )). The rare‐earth cations have the coordination numbers 10 ( 1 , 2 ) and 9 ( 3 , 4 and 5 ), respectively. The compounds [M₂(Adi)₃(H₂O)₄](AdiH₂)(H₂O)₄ are constructed of infinite chains of edge‐sharig [MO₈(H₂O)₂] polyhedra that are cross‐linked by adipinic acid molecules to form framework structures. In [Er(Adi)(H₂O)₅]Cl(H₂O) ( 3 ) and [M(Adi)(H₂O)₅](NO₃)(H₂O) (M = Gd ( 4 ), Er ( 5 )) the central cations are bridged by adipinic acid molecules in a bidentate‐chelating manner to positively charged zigzag chains. Between these the counter ions and crystal water molecules are incorporated.     

A rational basis for the axial ligand effect in C-H oxidation by [MnO(porphyrin)(X)]+ (X = H2O, OH-, O2-) from a DFT study

Oxyl radical character in the MnO group of the title system is shown from a density functional theory study to be essential for efficient C-H cleavage, which is a key step in C-H oxidation. Since oxyl species have elongated Mn-O bonds relative to the more usual oxo species of type MnO, the normal expectation would be that high trans-influence ligands X should facilitate oxyl character by elongating the Mn-O bond and thus enhance both oxyl character and reactivity. Contrary to this expectation, but in line with the experimental data (Jin, N.; Ibrahim, M.; Spiro, T. G.; Groves, J. T. J. Am. Chem. Soc. 2007, 129, 12416), we find that reactivity increases along the series X = O(2-) < OH(-) < H2O for the following reasons. The ground-state singlet (S) is unreactive for all X, and only the higher-energy triplet (T) and quintet (Q) states have the oxyl character needed for reactivity, but the higher trans-influence X ligands are also shown to increase the S/T and S/Q gaps, thus making attainment of the needed T and Q states harder. The latter effect is dominant, and high trans-influence X ligands thus disfavor reaction. The higher reactivity in the presence of acid noted by Groves and co-workers is thus rationalized by the preference for having X = H2O over OH(-) or O(2-).     

Tetranuclear and Pentanuclear Vanadium(IV/V) Carboxylate Complexes: [V(4)O(8)(NO(3))(O(2)CR)(4)](2-) and [V(5)O(9)X(O(2)CR)(4)](2-) (X = Cl(-), Br(-)) Salts

The syntheses and properties of tetra- and pentanuclear vanadium(IV,V) carboxylate complexes are reported. Reaction of (NBzEt(3))(2)[VOCl(4)] (1a) with NaO(2)CPh and atmospheric H(2)O/O(2) in MeCN leads to formation of (NBzEt(3))(2)[V(5)O(9)Cl(O(2)CPh)(4)] 4a; a similar reaction employing (NEt(4))(2)[VOCl(4)] (1b) gives (NEt(4))(2)[V(5)O(9)Cl(O(2)CPh)(4)] (4b). Complex 4a.MeCN crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -148 degrees C: a = 13.863(13) ?, b = 34.009(43) ?, c = 12.773(11) ?, and Z = 4. The reaction between (NEt(4))(2)[VOBr(4)] (2a) and NaO(2)CPh under similar conditions gives (NEt(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6a), and the use of (PPh(4))(2)[VOBr(4)] (2b) likewise gives (PPh(4))(2)[V(5)O(9)Br(O(2)CPh)(4)] (6b). Complex 6b crystallizes in space group P2(1)2(1)2(1) with the following unit cell dimensions at -139 degrees C: a = 18.638(3) ?, b = 23.557(4) ?, c = 12.731(2) ?, and Z = 4. The anions of 4a and 6b consist of a V(5) square pyramid with each vertical face bridged by a &mgr;(3)-O(2)(-) ion, the basal face bridged by a &mgr;(4)-X(-) (X = Cl, Br) ion, and a terminal, multiply-bonded O(2)(-) ion on each metal. The RCO(2)(-) groups bridge each basal edge to give C(4)(v)() virtual symmetry. The apical and basal metals are V(V) and V(IV), respectively (i.e., the anions are trapped-valence). The reaction of 1b with AgNO(3) and Na(tca) (tca = thiophene-2-carboxylate) in MeCN under anaerobic conditions gives (NEt(4))(2)[V(4)O(8)(NO(3))(tca)(4)] (7). Complex 7.H(2)O crystallizes in space group C2/c with the following unit cell dimensions at -170 degrees C: a = 23.606(4) ?, b = 15.211(3) ?, c = 23.999(5) ?, and Z = 4. The anion of 7 is similar to those of 4a and 6b except that the apical [VO] unit is absent, leaving a V(4) square unit, and the &mgr;(4)-X(-) ion is replaced with a &mgr;(4),eta(1)-NO(3)(-) ion. The four metal centers are now at the V(IV), 3V(V) oxidation level, but the structure indicates four equivalent V centers, suggesting an electronically delocalized system. Variable-temperature magnetic susceptibility data were collected on powdered samples of 4b, 6a, and 7 in the 2.00-300 K range in a 10 kG applied field. 4b and 6a both show a slow increase in effective magnetic moment (&mgr;(eff)) from approximately 3.6-3.7 &mgr;(B) at 320 K to approximately 4.5-4.6 &mgr;(B) at 11.0 K and then a slight decrease to approximately 4.2 &mgr;(B) at 2.00 K. The data were fit to the theoretical expression for a V(IV)(4) square with two exchange parameters J = J(cis)() and J' = J(trans)() (H = -2JS(i)()S(j)()): fitting of the data gave, in the format 4b/6a, J= +39.7/+46.4 cm(-)(1), J' = -11.1/-18.2 cm(-)(1) and g = 1.83/1.90, with the complexes possessing S(T) = 2 ground states. The latter were confirmed by magnetization vs field studies in the 2.00-30.0 K and 0.500-50.0 kG ranges: fitting of the data gave S(T) = 2 and D = 0.00 cm(-)(1) for both complexes, where D is the axial zero-field splitting parameter. Complex 7 shows a nearly temperature-independent &mgr;(eff) (1.6-2.0 &mgr;(B)) consistent with a single d electron per V(4) unit. The (1)H NMR spectra of 4b and 6a in CD(3)CN are consistent with retention of their pentanuclear structure on dissolution. The EPR spectrum of 7 in a toluene/MeCN (1:2) solution at approximately 25 degrees C yields an isotropic signal with a 29-line hyperfine pattern assignable to hyperfine interactions with four equivalent I = (7)/(2) (51)V nuclei.     

Trichloro-bridged diruthenium (III,III) complexes: X-ray isomorphous structures of [Ph3X=O···H···O=XPh3][Ru2Cl7(XPh3)2]·0.5(CH2Cl2)(H2O)(X = As or P)

The triply chloro-bridged binuclear complexes [Ph₃X=O···H···O=XPh₃][Ru₂Cl₇(XPh₃)₂]·0.5(CH₂Cl₂)(H₂O) (X = As or P) were obtained from [RuCl₃(XPh₃)₂DMA]·DMA (DMA = dimethylacetamide) CH₂Cl₂/Et₂O solution. The structures were characterized by X-ray diffraction studies. The complexes are formed from two Ru atoms bridged by three chloride anions. The two ruthenium atoms are also coordinated to two non-bridging Cl atoms and an AsPh₃ or PPh₃ ligand respectively. As an interesting feature, the cations of these complexes are protons, trapped in a very short hydrogen bond between two triphenylarsine or triphenylphosphine oxide molecules.     

Electron binding motifs of (H2O)n- clusters

It is has been established that the excess electrons in small (i.e., n < or = 7) (H2O)n- clusters are bound in the dipole field of the neutral cluster and, thus, exist as surface states. However, the motifs for the binding of an excess electron to larger water clusters remain the subject of considerable debate. The prevailing view is that electrostatic interactions with the "free" OH bonds of the cluster dominate the binding of the excess electron in both small and large clusters. In the present study, a quantum Drude model is used to study selected (H2O)n- clusters in the n = 12-24 size range with the goal of elucidating different possible binding motifs. In addition to the known surface and cavity states, we identify a new binding motif, where the excess electron permeates the hydrogen-bonding network. It is found that electrostatic interactions dominate the binding of the excess electron only for isomers with large dipole moments, whereas in isomers without large dipole moments polarization and correlation effects dominate. Remarkably, for the network-permeating states, the excess electron binds even in the absence of electrostatic interactions.     

Di-tert-butyl phosphate as synthon for metal phosphate materials via single-source coordination polymers [M(dtbp)(2)](n) (M = Mn,Cu) and [Cd(dtbp)(2)(H2O)](n) (dtbp-H = (tBuO)(2)P(O)OH)

Reaction of M(OAc)(2).xH(2)O (M = Mn, Cu, or Cd) with di-tert-butyl phosphate (dtbp-H) in a 1:2 molar ratio in methanol followed by slow crystallization of the resultant solid in MeOH/THF medium results in the formation of three new polymeric metal phosphates [M(dtbp)(2)](n)() [M = Mn, 1 (beige); M = Cu, 2 (blue)] and [Cd(dtbp)(2)(H(2)O)](n)(), 3 (colorless)] in good yields. The formation of [Mn(dtbp)(2)](n) (1) proceeds via tetrameric manganese phosphate [Mn(4)(O)(dtbp)(6)] (4), which has been isolated in an analytically pure form. Perfectly air- and moisture-stable compounds 1-4 were characterized with the aid of analytical, thermoanalytical, and spectroscopic techniques. The molecular structures of 1-3 were further established by single-crystal X-ray diffraction studies. Crystal data for 1: C(32)H(72)Mn(2)O(16)P(4), monoclinic, P2(1)/c, a = 19.957(4) A, b = 13.419(1) A, c = 18.083(2) A, beta = 91.25(2) degrees, Z = 4. Crystal data for 2: C(16)H(36)CuO(8)P(2), orthorhombic, Pccn, a = 23.777(2) A, b = 10.074(1) A, c = 10.090(1) A, Z = 4. Crystal data for 3: C(48)H(114)Cd(3)O(27)P(6), triclinic, P1, a = 12.689(3) A, b = 14.364(3) A, c = 22.491(5) A, alpha = 84.54(3) degrees, beta = 79.43(3) degrees, gamma = 70.03(3) degrees, Z = 2. The diffraction studies reveal three different structural forms for the three compounds investigated, each possessing a one-dimensional coordination polymeric structure. While alternating triple and single dtbp bridges are found between the adjacent Mn(2+) ions in 1, uniform double dtbp bridges across the adjacent Cu(2+) ions are present in 2. The cadmium ions in the structure of 3 are pentacoordinated. Thermal analysis (TGA and DSC) indicates that compounds 1-3 convert to the corresponding crystalline metaphosphate materials M(PO(3))(2), in each case at temperatures below 500 degrees C. Similarly, the thermal decomposition of 4 results in the formation of Mn(PO(3))(3) and Mn(2)P(2)O(7). The final materials obtained by independent thermal decomposition of bulk samples have been characterized using IR spectroscopic, powder diffraction, and N(2) adsorption studies.     

Influence of fluoride on the reversible binding of NO by [Fe(II)(EDTA)(H2O)]2-. Inhibition of autoxidation of [Fe(II)(EDTA)(H2O)]2-

The promising BioDeNO(x) process for NO removal from gaseous effluents suffers from an unsolved problem that results from the oxygen sensitivity of the Fe(II)-aminopolycarboxylate complexes used in the absorber unit to bind NO(g). The utilized [Fe(II)(EDTA)(H2O)](2-) complex is extremely oxygen sensitive and easily oxidized to give a totally inactive [Fe(III)(EDTA)(H2O)](-) species toward the binding of NO(g). We found that an in situ formed, less-oxygen-sensitive mixed-ligand complex, [Fe(II)(EDTA)(F)](3-), still reacts quantitatively with NO(g). The formation constant for the mixed ligand complex was determined spectrophotometrically. For [Fe(III)(EDTA)(F)](2-) we found log K(MLF)(F) = 1.7 +/- 0.1. The [Fe(II)(EDTA)(F)](3-) complex has a smaller value of log K(MLF)(F) = 1.3 +/- 0.2. The presence of fluoride does not affect the reversible binding of NO(g). Even over extended periods of time and fluoride concentrations of up to 1.0 M, the nitrosyl complex does not undergo any significant decomposition. The [Fe(III)(EDTA)(NO(-))](2-) complex releases bound NO on passing nitrogen through the solution to form [Fe(II)(EDTA)(H2O)](2-) almost completely. A reaction cycle is feasible in which fluoride inhibits the autoxidation of [Fe(II)(EDTA)(H2O)](2-) during the reversible binding of NO(g).     

Synthesis and characterization of iron(III)-substituted, dimeric polyoxotungstates, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](n-) (n = 6, X = As(III), Sb(III); n = 4, X = Se(IV), Te(IV))

Interaction of the lacunary [alpha-XW(9)O(33)](9-) (X = As(III), Sb(III)) with Fe(3+) ions in acidic, aqueous medium leads to the formation of dimeric polyoxoanions, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)) in high yield. X-ray single-crystal analyses were carried out on Na(6)[Fe(4)(H(2)O)(10)(beta-AsW(9)O(33))(2)] x 32H(2)O, which crystallizes in the monoclinic system, space group C2/m, with a = 20.2493(18) A, b = 15.2678(13) A, c = 16.0689(14) A, beta = 95.766(2) degrees, and Z = 2; Na(6)[Fe(4)(H(2)O)(10)(beta-SbW(9)O(33))(2)] x 32H(2)O is isomorphous with a = 20.1542(18) A, b = 15.2204(13) A, c = 16.1469(14) A, and beta = 95.795(2) degrees. The selenium and tellurium analogues are also reported, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](4-) (X = Se(IV), Te(IV)). They are synthesized from sodium tungstate and a source of the heteroatom as precursors. X-ray single-crystal analysis was carried out on Cs(4)[Fe(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)] x 21H(2)O, which crystallizes in the triclinic system, space group P macro 1, with a = 12.6648(10) A, b = 12.8247(10) A, c = 16.1588(13) A, alpha = 75.6540(10) degrees, beta = 87.9550(10) degrees, gamma = 64.3610(10) gamma, and Z = 1. All title polyanions consist of two (beta-XW(9)O(33)) units joined by a central pair and a peripheral pair of Fe(3+) ions leading to a structure with idealized C(2h) symmetry. It was also possible to synthesize the Cr(III) derivatives [Cr(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)), the tungstoselenates(IV) [M(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)]((16)(-)(4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Hg(2+)), and the tungstotellurates(IV) [M(4)(H(2)O)(10)(beta-TeW(9)O(33))(2)]((16-4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)), as determined by FTIR. The electrochemical properties of the iron-containing species were also studied. Cyclic voltammetry and controlled potential coulometry aided in distinguishing between Fe(3+) and W(6+) waves. By variation of pH and scan rate, it was possible to observe the stepwise reduction of the Fe(3+) centers.     

Exploring the rich energy landscape of sulfate-water clusters SO4(2-) (H2O)(n=3-7): an electronic structure approach

We present a reinvestigation of sulfate-water clusters SO4(2-) (H2O)(n=3-7), which involves several new aspects. Using a joint molecular mechanics/first principles approach, we perform exhaustive searches for stable cluster geometries, showing that the sulfate-water landscape is much richer than anticipated previously. We check the compatibility of the new structures with experiment by comparing vertical detachment energies (VDEs) calculated at the B3LYP/6-311++G** level of theory and determine the energetic ordering of the isomers at the RI-MP2/aug-cc-pVTZ level. Our results are bench-marked carefully against reference energies of estimated CCSD(T)/aug-cc-VTZ quality and VDEs of CCSD(T)/aug-cc-pVDZ quality. Furthermore, we calculate anharmonic vibrational corrections for up to the n = 6 clusters, which are shown to be significant for isomer energy ordering. We use energy decomposition analysis (EDA) based on the absolutely localized fragment (ALMO) expansion to gain chemical insight into the binding motifs.