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.     

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.     

Elucidation of the solution structure and water-exchange mechanism of paramagnetic [Fe(II)(edta)(H(2)O)](2-)

The lability and structural dynamics of [Fe(II)(edta)(H(2)O)](2-) (edta = ethylenediaminetetraacetate) in aqueous solution strongly depend on solvent interactions. To study the solution structure and water-exchange mechanism, (1)H, (13)C, and (17)O NMR techniques were applied. The water-exchange reaction was studied through the paramagnetic effect of the complex on the relaxation rate of the (17)O nucleus of the bulk water. In addition to variable-temperature experiments, high-pressure NMR techniques were applied to elucidate the intimate nature of the water-exchange mechanism. The water molecule in the seventh coordination site of the edta complex is strongly labilized, as shown by the water-exchange rate constant of (2.7 +/- 0.1) x 106 s(-1) at 298.2 K and ambient pressure. The activation parameters DeltaH(not equal), DeltaS(not equal), and DeltaV(not equal) were found to be 43.2 +/- 0.5 kJ mol(-1), +23 +/- 2 J K(-1) mol(-1), and +8.6 +/- 0.4 cm(3) mol(-1), respectively, in line with a dissociatively activated interchange (Id) mechanism. The scalar coupling constant (A/h) for the Fe(II)-O interaction was found to be 10.4 MHz, slightly larger than the value A/h = 9.4 MHz for this interaction in the hexa-aqua Fe(II) complex. The solution structure and dynamics of [Fe(II)(edta)(H(2)O)](2-) were clarified by (1)H and (13)C NMR experiments. The complex undergoes a Delta,Lambda-isomerization process with interconversion of in-plane (IP) and out-of-plane (OP) positions. Acetate scrambling was also found in an NMR study of the corresponding NO complex, [Fe(III)(edta)(NO(-))](2-).     

Rates of oxygen exchange between the [H(x)Nb(6)O(19)](8)(-)(x)(a)(q)) Lindqvist ion and aqueous solutions

Oxygen-isotope-exchange rates were measured between sites in the Lindqvist-type [H(x)()Nb(6)O(19)](8)(-)(x)()((aq)) polyoxoanion and aqueous solution as a function of pH and temperature. The ion has a central mu(6)-O that is inert to exchange, 12 mu(2)-O(H), and 6 eta-O. The potassium salt of this ion is recrystallized in (17)O-enriched water to (17)O-label the anion, which is then redissolved into isotopically normal water so that the (17)O NMR signals from structural oxygens can be followed as a function of time. Because the central mu(6)-O retains its (17)O signal throughout the experiments, it is clear that the polyoxoanion remains intact during isotopic equilibration of the other structural oxygens. At pH conditions where the [HNb(6)O(19)](7)(-) ion predominates, the mu(2)-O(H) sites isotopically exchange with solution about an order of magnitude more rapidly than the eta-O sites. Yet, we observe that the terminal and bridging oxo sites react at nearly the same rates when the ion is coordinated to 2-3 protons and possibly when it is unprotonated. On the basis of molecular models and experimental kinetic data, we propose metastable polymorphs of the hexaniobate structure where four of the mu(2)-O(H) and eta-O sites are temporarily equivalent and bonded to a coordinatively unsaturated Nb(V). This hypothesized intermediate allows facile access to bulk water molecules for exchange but cannot fully explain the kinetic results and additional experiments on other Lindvist ions are required.     

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.     

Kinetics and mechanism of the [Ru(III)(edta)(H2O)](-)-mediated oxidation of cysteine by H2O2

The kinetics and mechanism of the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation of cysteine (RSH) by hydrogen peroxide (edta(4-) = ethylenediaminetetraacetate), were studied in detail as a function of both the hydrogen peroxide and cysteine concentrations at pH 5.1 and room temperature. The kinetic traces reveal clear evidence for a catalytic process in which hydrogen peroxide reacts directly with cysteine coordinated to the Ru(III)(edta) complex in the form of [Ru(III)(edta)SR](2-). A parallel process in which [Ru(III)(edta)(H(2)O)](-) first reacts with H(2)O(2) to produce [Ru(V)(edta)O](-) and subsequently oxidizes cysteine, is orders of magnitude slower than the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation in which cysteine rapidly coordinates to [Ru(III)(edta)(H(2)O)](-) prior to the reaction with H(2)O(2). HPLC product analyses revealed the formation of cystine (RSSR) as major product along with cysteine sulfinic acid (RSO(2)H) in the reaction system, and established the catalytic role of [Ru(III)(edta)(H(2)O)](-). Simulations were performed to account for the rather complex kinetic traces in terms of the suggested reaction mechanism. The results of the simulations support the proposed reaction mechanism that involves the oxidation of coordinated cysteine to cysteine sulfenic acid (RSOH), which subsequently rapidly reacts with H(2)O(2) and RSH to form RSO(2)H and RSSR, respectively.     

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.     

Structural, theoretical and spectroscopic studies of the dichloride hexahydrate cube [Cl(2)(H(2)O)(6)](2-)

The structure of the dichloride hexahydrate cube, [Cl(2)(H(2)O)(6)](2-), as a salt with the tris(diisopropylamino)cyclopropenium cation, [C(3)(N(i)Pr(2))(3)](+), has been determined by low-temperature X-ray and neutron-diffraction studies. H atoms not involved in O-HCl bonding are disordered over two 0.5 occupancy sites around the O(6) ring. Calculations of the dianionic cube in the gas phase show remarkably good agreement with the solid-state structures with the exception of short O-H bond distances around the O(6) ring that suggests the involvement of a dynamic process. The cluster was also characterised by single-crystal infrared spectroscopy, and vibrational wavenumbers were found to be in good agreement with hydrogen bonding distances. Dibromide and difluoride hexahydrates were also studied theoretically, and OO distances were found to decrease in the order difluoride > dichloride > dibromide > (H(2)O)(6) and as OOO angles increased towards an almost planar ring in (H(2)O)(6). NMR spectra of a chloroform solution of the hydrated salt at -25 °C is consistent with cluster formation.     

Reaction of [RuIII(edta)(H2O)]- with H2O2 in aqueous solution. Kinetic and mechanistic investigation

The reaction of [Ru(III)(edta)(H(2)O)](-) (1) (edta = ethylenediaminetetraacetate) with hydrogen peroxide was studied kinetically as a function of [H(2)O(2)], temperature (5-35 degrees C) and pressure (1-1300 atm) at a fixed pH of 5.1 using stopped-flow techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru(III)(edta)(OOH)](2-) intermediate which subsequently undergoes parallel heterolytic and homolytic cleavage to produce [(edta)Ru(V)=O](-) (45%) and [(edta)Ru(IV)(OH)](-) (55%), respectively. The water soluble trap, 2,2'-azobis(3-ethylbenzithiazoline-6-sulfonate) (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first conditions for [ABTS] > [HOBr] > [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS* (+). A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed with reference to data reported for the corresponding [Fe(III)(edta)(H(2)O)](-)/H(2)O(2) system.     

Physicochemical properties of the high-field MRI-relevant [Gd(DTTA-Me)(H2O)2]- complex

To study the physicochemical properties of the DTTA chelating moiety (H4DTTA = diethylenetriaminetetraacetic acid = N,N'-[iminobis(ethane-2,1-diyl)]bis[N-(carboxymethyl)glycine]), used in several compounds proposed as magnetic resonance imaging (MRI) contrast agents, the methylated derivative H4DTTA-Me (N,N'-[(methylimino)bis(ethane-2,1-diyl)]bis[N-(carboxymethyl)glycine]) was synthesized. Protonation constants of the ligand were determined in an aqueous solution by potentimetry and (1)H NMR pH titration and compared to various DTTA derivatives. Stability constants were measured for the chelates formed with Gd(3+) (log K(GdL) = 18.60 +/- 0.10) and Zn(2+) (log K(ZnL) = 17.69 +/- 0.10). A novel approach of determining the relative conditional stability constant of two paramagnetic complexes in a direct way by (1)H NMR relaxometry is presented and was used for the Gd(3+) complexes [Gd(DTTA-Me)(H2O)2](-) (L1) and [Gd(DTPA-BMA)(H2O)] (L2) [K(L1/L2)*(at pH 8.3, 25 degrees C) = 6.4 +/- 0.3]. The transmetalation reaction of the Gd(3+) complex with Zn(2+) in a phosphate buffer solution (pH 7.0) was measured to be twice as fast for [Gd(DTTA-Me)(H2O)2](-) in comparison to that for [Gd(DTPA-BMA)(H2O)]. This can be rationalized by the higher affinity of Zn(2+) toward DTTA-Me(4-) if compared to DTPA-BMA(3-). The formation of a ternary complex with L-lactate, which is common for DO3A-based heptadentate complexes, has not been observed for [Gd(DTTA-Me)(H2O)2](-) as monitored by (1)H NMR relaxometric titrations. From the results, it was concluded that the heptadentate DTTA-Me(4-) behaves similarly to the commercial octadentate DTPA-BMA(3-) with respect to stability. The use of [Gd(DTTA-Me)(H2O)2](-) as an MRI contrast agent in vitro and in animal studies is conceivable, mainly at high magnetic fields, where an increase of the inner-sphere-coordination water actually seems to be the most certain way to increase the relaxivity.     

Excited-state interactions for [Au(CN)(2)(-)](n) and [Ag(CN)(2)(-)](n) oligomers in solution. Formation of luminescent gold-gold bonded excimers and exciplexes.

Solutions of K[Au(CN)(2)] and K[Ag(CN)(2)] in water and methanol exhibit strong photoluminescence. Aqueous solutions of K[Au(CN)(2)] at ambient temperature exhibit luminescence at concentration levels of > or =10(-2) M, while frozen methanol glasses (77 K) exhibit strong luminescence with concentrations as low as 10(-5) M. The corresponding concentration limits for K[Ag(CN)(2)] solutions are 10(-1) M at ambient temperature and 10(-4) M at 77 K. Systematic variations in concentration, solvent, temperature, and excitation wavelength tune the luminescence energy of both K[Au(CN)(2)] and K[Ag(CN)(2)] solutions by >15 x 10(3) cm(-1) in the UV-visible region. The luminescence bands have been individually assigned to *[Au(CN)(2)(-)](n) and *[Ag(CN)(2)(-)](n) excimers and exciplexes that differ in "n" and geometry. The luminescence of Au(I) compounds is related for the first time to Au-Au bonded excimers and exciplexes similar to those reported earlier for Ag(I) compounds. Fully optimized unrestricted open-shell MP2 calculations for the lowest-energy triplet excited state of staggered [Au(CN)(2)(-)](2) show the formation of a Au-Au sigma single bond (2.66 A) in the triplet excimer, compared to a weaker ground-state aurophilic bond (2.96 A). The corresponding frequency calculations revealed Au-Au Raman-active stretching frequencies at 89.8 and 165.7 cm(-1) associated with the ground state and lowest triplet excited state, respectively. The experimental evidence of the exciplex assignment includes the extremely large Stokes shifts and the structureless feature of the luminescence bands, which suggest very distorted excited states. Extended Hückel (EH) calculations for [M(CN)(2)(-)](n) and *[M(CN)(2)(-)](n) models (M = Au, Ag; n = 2, 3) indicate the formation of M-M bonds in the first excited electronic states. From the average EH values for staggered dimers and trimers, the excited-state Au-Au and Ag-Ag bond energies are predicted to be 104 and 112 kJ/mol, respectively. The corresponding bond energies in the ground state are 32 and 25 kJ/mol, respectively.     

Thermochemistry of rare earth complexes [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr, Gd)

The two complexes, [Ln(Ala)₂(Im)(H₂O)](ClO₄)₃ (Ln=Pr, Gd), were synthesized and characterized. Using a solution-reaction isoperibol calorimeter, standard enthalpies of reaction of two reactions: LnCl₃⋅6H₂O(s)+2Ala(s)+Im(s)+3NaClO₄(s)=[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)+3NaCl(s)+5H₂O(l) (Ln=Pr, Gd), at T=298.15 K, were determined to be (39.26±0.10) and (5.33±0.12) kJ mol^–1 , respectively. Standard enthalpies of formation of the two complexes at T=298.15 K, Δ_fH^Θ_m {[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)} (Ln=Pr, Gd), were calculated as –(2424.2±3.3) and –(2443.4±3.3) kJ mol^–1 , respectively.     

Synthesis,structure, and magnetic properties of the single-molecule magnet [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-)

The preparation of two new compounds containing the cluster [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-) is presented, together with a detailed magnetic investigation of one of the compounds. We found that this cluster shows an unexpected stability and that it exists as different stereoisomers. Compound 1 contains the achiral cluster with a Delta-Lambda configuration, and compound 2 contains a pair of enantiomeric clusters with the configurations Delta-Delta and Lambda-Lambda, respectively. Magnetic measurements of 1 in the millikelvin range were necessary to determine the spin ground state of S = 3, and they also revealed a magnetic anisotropy within the ground state. A frequency-dependent out-of-phase signal was found in alternating current susceptibility measurements at very low temperatures, which indicates a slow relaxation of the magnetization. Thus, individual molecules are acting as single magnetic units, which is a rare phenomenon for nickel clusters. The energy barrier exhibited by compound 1 has been calculated to be 2.9 K.     

Preparation and Properties of the Corner-Shared Double Cube [Mo(6)BiS(8)(H(2)O)(18)](8+) as a Derivative of [Mo(3)S(4)(H(2)O)(9)](4+) in Aqueous Acidic Solutions

The reaction of [Mo(3)S(4)(H(2)O)(9)](4+) with Bi(III) in the presence of BH(4)(-) (rapid), or with Bi metal shot (3-4 days), gives a heterometallic cluster product. The latter has been characterized as the corner-shared double cube [Mo(6)BiS(8)(H(2)O)(18)](8+) by the following procedures. Analyses by ICP-AES confirm the Mo:Bi:S ratio as 6:1:8. Elution from a cation-exchange column by 4 M Hpts (Hpts = p-toluenesulfonic acid), but not 2 M Hpts (or 4 M HClO(4)), is consistent with a high charge. The latter is confirmed as 8+ from the 3:1 stoichiometries observed for the oxidations with [Co(dipic)(2)](-) or [Fe(H(2)O)(6)](3+) yielding [Mo(3)S(4)(H(2)O)(9)](4+) and Bi(III) as products. Heterometallic clusters [Mo(6)MS(8)(H(2)O)(18)](8+) are now known for M = Hg, In, Tl, Sn, Pb, Sb, and Bi and are a feature of the P-block main group metals. The color of [Mo(6)BiS(8)(H(2)O)(18)](8+) in 2.0 M Hpts (turquoise) is different from that in 2.0 M HCl (green-blue). Kinetic studies (25 degrees C) for uptake of a single chloride k(f) = 0.80 M(-)(1) s(-)(1), I = 2.0 M (Hpts), and the high affinity for Cl(-) (K > 40 M(-)(1)) exceeds that observed for complexing at Mo. A specific heterometal interaction of the Cl(-) not observed in the case of other double cubes is indicated. The Cl(-) can be removed by cation-exchange chromatography with retention of the double-cube structure. Kinetic studies with [Co(dipic)(2)](-) and hexaaqua-Fe(III) as oxidants form part of a survey of redox properties of this and other clusters. The Cl(-) adduct is more readily oxidized by [Co(dipic)(2)](-) (factor of approximately 10) and is also more air sensitive.     

Structure and magnetism of the tetra-copper(II)-substituted heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8-)

The novel heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8)(-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and magnetic studies. Single-crystal X-ray analysis was carried out on [K(7)Na[Cu(4)K(2)(H(2)O)(6)(alpha-AsW(9)O(33))(2)].5.5H(2)O](n)(K(7)Na-1), which crystallizes in the tetragonal system, space group P42(1)m, with a = 16.705(4) A, b = 16.705(4) A, c = 13.956(5) A, and Z = 2. Interaction of the lacunary [alpha-AsW(9)O(33)](9)(-) with Cu(2+) ions in neutral, aqueous medium leads to the formation of the dimeric polyoxoanion 1 in high yield. Polyanion 1 consists of two alpha-AsW(9)O(33) units joined by a cyclic arrangement of four Cu(2+) and two K(+) ions, resulting in a structure with C(2)(v)() symmetry. All copper ions have one terminal water molecule, resulting in square-pyramidal coordination geometry. Three of the copper ions are adjacent to each other and connected via two micro(3)-oxo bridges. EPR studies on K(7)Na-1 and also on Na(9)[Cu(3)Na(3)(H(2)O)(9)(alpha-AsW(9)O(33))(2)].26H(2)O (Na(9)-2) over 2-300 K yielded g values that are consistent with a square-pyramidal coordination around the copper(II) ions in 1 and 2. No hyperfine structure was observed due to the presence of strong spin exchange, but fine structure was observed for the excited (S(T) = 3/2) state of Na(9)-2 and the ground state (S(T) = 1) of K(7)Na-1. The zero-field (D) parameters have also been determined for these states, constituting a rare case wherein one observes EPR from both the ground and the excited states. Magnetic susceptibility data show that Na(9)-2 has antiferromagnetically coupled Cu(2+) ions, with J = -1.36 +/- 0.01 cm(-)(1), while K(7)Na-1 has both ferromagnetically and antiferromagnetically coupled Cu(2+) ions (J(1) = 2.78 +/- 0.13 cm(-)(1), J(2) = -1.35 +/- 0.02 cm(-)(1), and J(3) = -2.24 +/- 0.06 cm(-)(1)), and the ground-state total spins are S(T) = 1/2 in Na(9)-2 and S(T) = 1 in K(7)Na-1.     

Cyanide-limited complexation of molybdenum(III): synthesis of octahedral [Mo(CN)(6)](3-) and cyano-bridged [Mo(2)(CN)(11)](5-)

Octahedral coordination of molybdenum(III) is achieved by limiting the amount of cyanide available upon complex formation. Reaction of Mo(CF(3)SO(3))(3) with LiCN in DMF affords Li(3)[Mo(CN)(6)] x 6DMF (1), featuring the previously unknown octahedral complex [Mo(CN)(6)](3-). The complex exhibits a room-temperature moment of mu(eff) = 3.80 mu(B), and assignment of its absorption bands leads to the ligand field parameters Delta(o) = 24800 cm(-1) and B = 247 cm(-1). Further restricting the available cyanide in a reaction between Mo(CF(3)SO(3))(3) and (Et(4)N)CN in DMF, followed by recrystallization from DMF/MeOH, yields (Et(4)N)(5)[Mo(2)(CN)(11)] x 2DMF x 2MeOH (2). The dinuclear [Mo(2)(CN)(11)](5-) complex featured therein contains two octahedrally coordinated Mo(III) centers spanned by a bridging cyanide ligand. A fit to the magnetic susceptibility data for 2, gives J = -113 cm(-1) and g = 2.33, representing the strongest antiferromagnetic coupling yet observed through a cyanide bridge. Efforts to incorporate these new complexes in magnetic Prussian blue-type solids are ongoing.     

Fast catalytic epoxidation with H(2)O(2) and [gamma-SiW(10)O(36)(PhPO)(2)](4-) in ionic liquids under microwave irradiation

Olefin epoxidation by [gamma-SiW10O36(PhPO)2]4- and H2O2 occurs in hydrophobic ionic liquids (ILs), with yields and selectivity up to >99%. The catalytic IL phase is recyclable. Under MW irradiation the reaction occurs with up to 200 turnovers per minute. Simultaneous cooling is instrumental for quantitative H2O2 conversion.     

Two sandwich arsenomolybdates based on the new building block As(iii)Mo(7)O(27)(9-): [Cr(2)(AsMo(7)O(27))(2)](12-) and [Cu(2)(AsMo(7)O(27))(2)](14-)

The polyanions [Cr(2)(AsMo(7)O(27))(2)](12-) () or [Cu(2)(AsMo(7)O(27))(2)](14-) () have sandwich-like structures wrapping two transition metals between two [As(iii)Mo(7)O(27)](9-) fragments, and the fragment is unprecedented and can be viewed as a mono-capped hexavacant B-alpha-Keggin subunit with a central AsO(3) group.