Photoelectron imaging of hydrated carbon dioxide cluster anions

The effects of homogeneous and heterogeneous solvation on the electronic structure and photodetachment dynamics of hydrated carbon dioxide cluster anions are investigated using negative-ion photoelectron imaging spectroscopy. The experiments are conducted on mass-selected [(CO(2))(n)()(H(2)O)(m)()](-) cluster anions with n and m ranging up to 12 and 6, respectively, for selected clusters. Homogeneous solvation in (CO(2))(n)()(-) has minimal effect on the photoelectron angular distributions, despite dimer-to-monomer anion core switching. Heterogeneous hydration, on the other hand, is found to have the marked effect of decreasing the photodetachment anisotropy. For example, in the [CO(2)(H(2)O)(m)()](-) cluster anion series, the photoelectron anisotropy parameter falls to essentially zero with as few as 5-6 water molecules. The analysis of the data, supported by theoretical modeling, reveals that in the ground electronic state of the hydrated clusters the excess electron is localized on CO(2), corresponding to a (CO(2))(n)()(-).(H(2)O)(m)() configuration for all cluster anions studied. The diminishing anisotropy in the photoelectron images of hydrated cluster anions is proposed to be attributable to photoinduced charge transfer to solvent, creating transient (CO(2))(n)().(H(2)O)(m)()(-) states that subsequently decay via autodetachment.     

Effects of solvation and core switching on the photoelectron angular distributions from (CO2)n(-) and (CO2)(n)(-).H2O

Photoelectron images are recorded in the photodetachment of two series of cluster anions, (CO(2))(n)(-), n=4-9 and (CO(2))(n)(-).H(2)O, n=2-7, with linearly polarized 400 nm light. The energetics of the observed photodetachment bands compare well with previous studies, showing evidence for switching between two anionic core structures: The CO(2)(-) monomer and covalent (CO(2))(2)(-) dimer anions. The systematic study of photoelectron angular distributions (PADs) sheds light on the electronic structure of the different core anions and indicates that solvation by several CO(2) molecules and/or one water molecule has only moderate effect on the excess-electron orbitals. The observed PAD character is reconciled with the symmetry properties of the parent molecular orbitals. The most intriguing result concerns the PADs showing remarkable similarities between the monomer and dimer anion cluster-core types. This observation is explained by treating the highest-occupied molecular orbital of the covalent dimer anion as a linear combination of two spatially separated monomeric orbitals.     

Photodissociation of CO2 - in water clusters via Renner-Teller and conical interactions

The photochemistry of mass selected CO(2) (-)(H2O)(m), m=2-40 cluster anions is investigated using 266 nm photofragment spectroscopy and theoretical calculations. Similar to the previous 355 nm experiment [Habteyes et al., Chem. Phys. Lett. 424, 268 (2006)], the fragmentation at 266 nm yields two types of anionic products: O(-)(H2O)(m-k) (core-dissociation products) and CO(2) (-)(H2O)(m-k) (solvent-evaporation products). Despite the same product types, different electronic transitions and dissociation mechanisms are implicated at 355 and 266 nm. The 355 nm dissociation is initiated by excitation to the first excited electronic state of the CO(2) (-) cluster core, the 1 (2)B(1)(2A") state, and proceeds via a glancing Renner-Teller intersection with the ground electronic state at a linear geometry. The 266 nm dissociation involves the second excited electronic state of CO(2) (-), the 2 (2)A(1)(2A') state, which exhibits a conical intersection with the 3 (2)B(2)(A') state at a bent geometry. The asymptotic O(-) based products are believed to be formed via this 3 (2)B(2)(A') state. By analyzing the fragmentation results, the bond dissociation energy of CO(2) (-) to O(-)+CO in hydrated clusters (m> or =20) is estimated as 2.49 eV, compared to 3.46 eV for bare CO(2) (-). The enthalpy of evaporation of one water molecule from asymptotically large CO(2) (-)(H(2)O)(m) clusters is determined to be 0.466+/-0.001 eV (45.0+/-0.1 kJ/mol). This result compares very favorably with the heat of evaporation of bulk water, 0.456 eV (43.98 kJ/mol).     

Structures of [(CO2)n(H2O)m]- (n=1-4, m=1,2) cluster anions. I. Infrared photodissociation spectroscopy

The infrared photodissociation spectra of [(CO(2))(n)(H(2)O)(m)](-) (n=1-4, m=1, 2) are measured in the 3000-3800 cm(-1) range. The [(CO(2))(n)(H(2)O)(1)](-) spectra are characterized by a sharp band around 3570 cm(-1) except for n=1; [(CO(2))(1)(H(2)O)(1)](-) does not photodissociate in the spectral range studied. The [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2) species have similar spectral features with a broadband at approximately 3340 cm(-1). A drastic change in the spectral features is observed for [(CO(2))(3)(H(2)O)(2)](-), where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm(-1). Ab initio calculations are performed at the MP2/6-311++G(**) level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO(2))(n)(H(2)O)(m)](-) species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO(2))(n)(H(2)O)(m)](-): (1) the incorporated H(2)O is bonded to either CO(2) (-) or C(2)O(4) (-) through two equivalent OH...O hydrogen bonds to form a ring structure in [(CO(2))(n)(H(2)O)(1)](-); (2) two H(2)O molecules are independently bound to the O atoms of CO(2) (-) in [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2); (3) a cyclic structure composed of CO(2) (-) and two H(2)O molecules is formed in [(CO(2))(3)(H(2)O)(2)](-).     

Tetradecanuclear polycarbonatolanthanoid clusters: Diverse coordination modes of carbonate providing access to novel core geometries

The synthesis of two high nuclearity lanthanoid clusters demonstrates the versatility of the carbonate anion as a robust cluster forming agent, potentially allowing for the formation of otherwise inaccessible core topologies. The complexes, [Gd(14)(CO(3))(13)(ccnm)(9)(OH)(H(2)O)(6)(phen)(13)(NO(3))](CO(3))(2.5)·(phen)(0.5) () and [Dy(14)(CO(3))(13)(ccnm)(10)(OH)(H(2)O)(6)(phen)(13)](CO(3))(2.5)·(phen)(0.5) () (ccnm = carbamoylcyanonitrosomethanide, phen = 1,10-phenanthroline), contain a [Ln(14)(CO(3))(13)(OH)] core in which the carbonate anions display four unique coordination modes. The complexes are chiral, and the ccnm ligands also display four unique coordination modes. Extensive intra- and intermolecular π-π stacking between phen ligands leads to the formation of 1D chains in the crystal structure. Both complexes display magnetic properties that are indicative of antiferromagnetic coupling, with complex displaying behaviour consistent with possible single molecule magnet properties.     

Vibrational predissociation spectrum of the carbamate radical anion, C(5)H(5)N-CO(2)(-), generated by reaction of pyridine with (CO(2))(m)(-)

We report the vibrational predissociation spectrum of C(5)H(5)N-CO(2)(-), a radical anion which is closely related to the key intermediates postulated to control activation of CO(2) in photoelectrocatalysis with pyridine (Py). The anion is prepared by the reaction of Py vapor with (CO(2))(m)(-) clusters carried out in an ionized, supersonic entrainment ion source. Comparison with the results of harmonic frequency calculations establishes that this species is a covalently bound molecular anion derived from the corresponding carbamate, C(5)H(5)N-CO(2)(-) (H(+)). These results confirm the structural assignment inferred in an earlier analysis of the cluster distributions and photoelectron spectra of the mixed Py(m)(CO(2))(n)(-) complexes [J. Chem. Phys. 2000, 113 (2), 596-601]. The spectra of the (CO(2))(m)(-) (m = 5 and 7) clusters are presented for the first time in the lower energy range (1000-2400 cm(-1)), which reveal several of the fundamental modes that had only been characterized previously by their overtones and combination bands. Comparison of these new spectra with those displayed by Py(CO(2))(n)(-) suggests that a small fraction of the Py(CO(2))(n)(-) ions are trapped entrance channel reaction intermediates in which the charge remains localized on the (CO(2))(m)(-) part of the cluster.     

Reactions of lead cluster ions with acetone

Reactions of lead cluster cations and anions with acetone have been studied using a homemade reflectron time-of-flight mass spectrometer. Association with acetone to form Pb(k)(CH(3)COCH(3))(n)(+), high-energy pathway reactions forming Pb(k)CH(3)(+), and intraheterocluster reaction of Pb(k)(CH(3)COCH(3))(n+1)(+) to give Pb(k)CH(3)(CH(3)COCH(3))(n)(+) were the main reaction pathways for lead cluster cations with acetone. Decomposition of acetone by Pb(k)(-) to give Pb(k)C(m)(-) ions and their further association with acetone, Pb(k)C(m)(CH(3)COCH(3))(-), were the dominant reactions of lead cluster anions with acetone. Pb(7)(-), Pb(10)(-), and Pb(k)C(5)(-) were 'magic numbers' with special structural stabilityin Pb(k)(-) and Pb(k)C(m)(-), respectively. In addition, Pb(k)H(-), CH(2)COCH(3)(CH(3)COCH(3))(n)(-) and Pb(k)CH(2)COCH(3)(CH(3)COCH(3))(n)(-) were also observed in the reaction of lead cluster anions. Some reaction mechanisms are proposed for these reactions. To investigate the isotope effect for the reaction of lead cluster cations and anions with acetone and to verify the structural assignments of the observed ions, reactions of lead cluster cations and anions with deuterated acetone-d(6) were also performed.     

Solvation-induced cluster anion core switching from NNO2(-)(N2O)n-1 to O(-)(N2O)n

We report a photoelectron imaging study of the [O(N(2)O)(n)](-), 0or=4 (and up to at least n=9) signatures of an O(-) core are predominantly observed. Photofragmentation studies at 355 nm support these results.     

Observations of different core water cluster ions Y-(H2O)n (Y = O2, HOx, NOx, COx) and magic number in atmospheric pressure negative corona discharge mass spectrometry

Reliable mass spectrometry data from large water clusters Y(-)(H(2)O)(n) with various negative core ions Y(-) such as O(2)(-), HO(-), HO(2)(-), NO(2)(-), NO(3)(-), NO(3)(-)(HNO(3))(2), CO(3)(-) and HCO(4)(-) have been obtained using atmospheric pressure negative corona discharge mass spectrometry. All the core Y(-) ions observed were ionic species that play a central role in tropospheric ion chemistry. These mass spectra exhibited discontinuities in ion peak intensity at certain size clusters Y(-)(H(2)O)(m) indicating specific thermochemical stability. Thus, Y(-)(H(2)O)(m) may correspond to the magic number or first hydrated shell in the cluster series Y(-)(H(2)O)(n). The high intensity discontinuity at HO(-)(H(2)O)(3) observed was the first mass spectrometric evidence for the specific stability of HO(-)(H(2)O)(3) as the first hydrated shell which Eigen postulated in 1964. The negative ion water clusters Y(-)(H(2)O)(n) observed in the mass spectra are most likely to be formed via core ion formation in the ambient discharge area (760 torr) and the growth of water clusters by adiabatic expansion in the vacuum region of the mass spectrometers (≈1 torr). The detailed mechanism of the formation of the different core water cluster ions Y(-)(H(2)O)(n) is described.     

Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m

Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5 eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5) x 10(4) s(-1) for cluster sizes of 5< or =n< or =16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n+ cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2)(H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed.     

Interaction of Co(m)O(-) (m = 1-3) with water: anion photoelectron spectroscopy and density functional calculations

We investigated the reactions between cobalt-oxides and water molecules using photoelectron spectroscopy and density functional calculations. It has been confirmed by both experimental observation and theoretical calculations that dihydroxide anions, Co(m)(OH)(2)(-) (m = 1-3), were formed when Co(m)O(-) clusters interact with the first water molecule. Addition of more water molecules produced solvated dihydroxide anions, Co(m)(OH)(2)(H(2)O)(n)(-) (m = 1-3). Hydrated dihydroxide anions, Co(m)(OH)(2)(H(2)O)(n)(-), are more stable than their corresponding hydrated metal-oxide anions, Co(m)O(H(2)O)(n+1)(-).     

Electrochemistry of niobium(V) in sulfuric and methanesulfonic acids: formation of the Nb3O2(SO4)6(H2O)(3)(5-) cluster and designed electrochemical generation of "Nb3O2" core clusters by double potential pulse electrolysis

The electrochemical and spectroelectrochemical properties of niobium(V) and the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster in sulfuric acid and methanesulfonic acid were investigated using cyclic voltammetry, constant potential electrolysis, and spectroelectrochemistry. These chemical systems were suitable to probe the formation of "Nb(3)O(2)" core trinuclear clusters. In 9 M H(2)SO(4) the cluster Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) exhibited a reversible 1-electron reduction peak at E(pc) = -1.30 V vs Hg/Hg(2)SO(4) electrode, as well as a 4-electron irreversible oxidation peak at E(pa) = -0.45 V. Controlled potential reduction at E = -1.40 V produced the green Nb(3.33+) cluster anion Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(6-). In 12 M H(2)SO(4) Nb(V) displayed two reduction peaks at E(pc) = -1.15 V and E(pc) = -1.30 V. It was determined that the first process involves a quasi-reversible 2-electron reduction. After reduction of Nb(V) to Nb(III) the following chemical step involves formation of [Nb(III)](2) dimer, which further reacts with Nb(V) to produce the Nb(3)O(2)(SO(4))(6(H(2)O)(3)(5-) cluster (ECC process). The second reduction peak at E(pc) = -1.30 V corresponds to further 2-electron reduction of Nb(III) to Nb(I). The electrogenerated Nb(I) species also chemically reacts with starting material Nb(V) to produce additional [Nb(III)](2). In 5 M H(2)SO(4), the rate of the second chemical step in the ECC process is relatively slower and reduction of Nb(V) at E = -1.45 V/-1.2 V produces a mixture of Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) and [Nb(III)](2) dimer. [Nb(III)](2) can be selectively oxidized by two 2-electron steps at E = -0.65 V to Nb(V). However, if the oxidation is performed at E = -0.86 V, the product is Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-). A double potential pulse electrolysis waveform was developed to direct the reduction of Nb(V) toward selective formation of the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster. Proper application of dc-voltage pulses alternating between E(1) = -1.45 V and E(2) = -0.86 V yields only the target trinuclear cluster. Analogous double potential pulse electrolysis of Nb(V) in methanesulfonic acid generates the "Nb(3)O(2)" core cluster Nb(3)O(2)(CH(3)SO(3))(6)(H(2)O)(3)(+).     

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.     

Oxygen cluster anions revisited: solvent-mediated dissociation of the core O4(-) anion

The electronic structure and photochemistry of the O(2n)(-)(H(2)O)(m), n = 1-6, m = 0-1 cluster anions is investigated at 532 nm using photoelectron imaging and photofragment mass-spectroscopy. The results indicate that both pure oxygen clusters and their hydrated counterparts with n ≥ 2 form an O(4)(-) core. Fragmentation of these clusters yields predominantly O(2)(-) and O(2)(-)·H(2)O anionic products, with the addition of O(4)(-) fragments for larger parent clusters. The fragment autodetachment patterns observed for O(6)(-) and larger O(2n)(-) species, as well as some of their hydrated counterparts, indicate that the corresponding O(2)(-) fragments are formed in excited vibrational states (v ≥ 4). Yet, surprisingly, the unsolvated O(4)(-) anion itself does not show fragment autodetachment at 532 nm. It is hypothesized that the vibrationally excited O(2)(-) is formed in the intra-cluster photodissociation of the O(4)(-) core anion via a charge-hopping electronic relaxation mechanism mediated by asymmetric solvation of the nascent photofragments: O(4)(-) → O(2)(-)(X(2)Π(g)) + O(2)(a(1)Δ(g)) → O(2)(X(3)Σ(g)(-)) + O(2)(-)(X(2)Π(g)). This process depends on the presence of solvent molecules and leads to vibrationally excited O(2)(-)(X(2)Π(g)) products.     

Kinetics of Formation and Dissociation of [Cr(3)O(O(2)CCH(3))(6)(urea)(3)](+): An Example of Statistically Controlled Kinetics and Equilibrium

Kinetics of the overall reaction [Cr(3)O(O(2)CCH(3))(6)(H(2)O)(3)](+) + 3 urea right harpoon over left harpoon [Cr(3)O(O(2)CCH(3))(6)(urea)(3)](+) + 3H(2)O have been studied spectrophotometrically. Monophasic kinetics were observed in both directions. The reverse steps, of urea dissociation, were monitored using an analytical technique which permits direct determination of the concentration of liberated urea and does not require knowledge of extinction coefficients of intermediate species. Results imply that consecutive steps occur with rate constants in close to the statistical ratios of k(1):k(2):k(3) = 3:2:1 and k(-)(1):k(-)(2):k(-)(3) = 1:2:3. Rates indicate strong labilization of urea, compared to the case of mononuclear complex [Cr(urea)(6)](3+).     

Structure and H(2)-Loss Energies of OsHX(H(2))(CO)L(2) Complexes (L = P(t-Bu)(2)Me, P(i-Pr)(3); X = Cl, I, H): Attempted Correlation of (1)J(H-D), T(1min), and DeltaG()

1J(H-D), T(1min) and k(1) for H(2) dissociation from OsHX(H(2))(CO)L(2) have been measured for X = Cl, I, H (L = P(t-Bu)(2)Me or P(i-Pr)(3)), as well as for OsCl(2)(H(2))(CO)(P(i-Pr)(3))(2). For comparison, new data (including previously unobserved coupling constants) have been reported for W(HD)(CO)(3)(P(i-Pr)(3))(2). A comprehensive consideration of T(1min) data for over 20 dihydrogen complexes containing only 1-2 phosphines cis to H(2), together with a consideration of the shortest "conceivable" H-H distance for H(2) bound to a d(4) or d(6) metal, is used to argue that the "fast spinning" model is not appropriate for determining r(H-H) in such complexes. Regarding OsHX(H(2))(CO)L(2), the stronger electron-donor (lighter) halide, when cis to H(2), facilitates loss of H(2). The complete absence of pi-donor ability when X = H renders H(2) loss most difficult. However, a pi-donor trans to H(2) also makes H(2) loss unobservable. Within the series of isoelectronic, structurally analogous Os complexes, a longer H-H bond shows a larger DeltaG() for H(2) loss. However, this correlation does not continue to W(H(2))(CO)(3)(P(i-Pr)(3))(2), which has r(H-H) comparable to that of OsH(halide)(H(2))(CO)(P(i-Pr)(3))(2), but a significantly higher DeltaG(). This may originate from lack of a pi-donor ligand to compensate as H(2) leaves W.     

Crown ethers as ancillary ligands in the assembly of silver(i) aggregates containing embedded acetylenediide

Five silver(I) double salts containing embedded acetylenediide, [Ag([12]crown-4)(2)][Ag(10)(C(2))(CF(3)CO(2))(9)([12]crown-4)(2)(H(2)O)(3)] x H(2)O (2), [Ag(2)C(2) x 5 AgCF(3)CO(2) x (benzo[15]crown-5) x 2 H(2)O] x 0.5 H(2)O (3), [Ag(4)([18]crown-6)(4)(H(2)O)(3)][Ag(18)(C(2))(3)(CF(3)CO(2))(16)(H(2)O)(2.5)] x 2.5 H(2)O (4), [Ag(2)C(2) x 6 AgC(2)F(5)CO(2) x 2([15]crown-5)](2) (5), and [(Ag(2)C(2))(2) x (AgC(2)F(5)CO(2))(9) x ([18]crown-6)(2) x (H(2)O)(3.5)] x H(2)O (6), have been isolated by varying the types of crown ethers and anions employed. Single-crystal X-ray analysis has shown that complex 2 is composed of winding anionic chains with sandwiched [Ag([12]crown-4)(2)](+) ions accommodated in the concave cavities between them. In 3, silver(I) double cages each sandwiched by a couple of benzo[15]crown-5 ligands are linked by [Ag(2)(CF(3)CO(2))(2)] bridges to form a one-dimensional structure. For 4, an anionic silver column is generated through fusion of two kinds of silver polyhedra (triangulated dodecahedron and bicapped trigonal antiprism), and the charge balance is provided by aqua-ligated [Ag([18]crown-6)](+) ions. Complex 5 is a centrosymmetric hexadecanuclear supermolecule composed of two [(eta(5)-[15]crown-5)(2)(C(2)@Ag(7))(mu-C(2)F(5)CO(2))(5)] moieties connected through a [Ag(2)(C(2)F(5)CO(2))(2)] bridge. Compound 6 is a discrete supermolecule containing an asymmetric (C(2))(2)@Ag(13) cluster core capped by two [18]crown-6 ligands in mu(3)-eta(5) and mu(4)-eta(6) ligation modes.     

Dinuclear nickel complexes with a Ni(2)O(2) core: a structural and magnetic study

The acetylacetonate complexes [Ni(2)L(1)(acac)(MeOH)] x H(2)O, 1 x H(2)O and [Ni(2)L(3)(acac)(MeOH)] x 1.5H(2)O, 2 x 1.5H(2)O (H(3)L(1) = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H(3)L(3) = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni(2)HL(x)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x n MeOH and [Ni(2)HL(x)(O(2)CCH(2)CO(2))(H(2)O)]x nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni(2)HL(1)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x MeOH, 3 x MeOH, [Ni(2)HL(3)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x 3 MeOH, 4 x 3 MeOH and [Ni(2)HL(1)(O(2)CCH(2)CO(2))(H(2)O)] x 2.5H(2)O x 0.25 MeOH x MeCN, 5 x 2.5H(2)O x 0.25 MeOH x MeCN, were solved. Complexes 3-5 show dinuclear [Ni(2)HL(x)(dicarboxylate)(H(2)O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.     

Reactivity of the organometallic fac-[(CO)3ReI(H2O)3]+ aquaion. Kinetic and thermodynamic properties of H2O substitution

The water exchange process on [(CO)(3)Re(H(2)O)(3)](+) (1) was kinetically investigated by (17)O NMR. The acidity dependence of the observed rate constant k(obs) was analyzed with a two pathways model in which k(ex) (k(ex)(298) = (6.3 +/- 0.1) x 10(-3) s(-1)) and k(OH) (k(OH)(298)= 27 +/- 1 s(-1)) denote the water exchange rate constants on 1 and on the monohydroxo species [(CO)(3)Re(I)(H(2)O)(2)(OH)], respectively. The kinetic contribution of the basic form was proved to be significant only at [H(+)] < 3 x 10(-3) M. Above this limiting [H(+)] concentration, kinetic investigations can be unambiguously conducted on the triaqua cation (1). The variable temperature study has led to the determination of the activation parameters Delta H(++)(ex) = 90 +/- 3 kJ mol(-1), Delta S(++)(ex) = +14 +/- 10 J K(-1) mol(-1), the latter being indicative of a dissociative activation mode for the water exchange process. To support this assumption, water substitution reaction on 1 has been followed by (17)O/(1)H/(13)C/(19)F NMR with ligands of various nucleophilicities (TFA, Br(-), CH(3)CN, Hbipy(+), Hphen(+), DMS, TU). With unidentate ligands, except Br(-), the mono-, bi-, and tricomplexes were formed by water substitution. With bidentate ligands, bipy and phen, the chelate complexes [(CO)(3)Re(H(2)O)(bipy)]CF(3)SO(3) (2) and [(CO)(3)Re(H(2)O)(phen)](NO(3))(0.5)(CF(3)SO(3))(0.5).H(2)O (3) were isolated and X-ray characterized. For each ligand, the calculated interchange rate constants k'(i) (2.9 x 10(-3) (TFA) < k'(I) < 41.5 x 10(-3) (TU) s(-1)) were found in the same order as the water exchange rate constant k(ex), the S-donor ligands being slightly more reactive. This result is indicative of I(d) mechanism for water exchange and complex formation, since larger variations of k'(i) are expected for an associatively activated mechanism.     

Unusual syntheses, structures, and electronic properties of compounds containing ternary, T3-type supertetrahedral M/Sn/S anions [M5Sn(mu3-S)4(SnS4)4](10- (M = Zn, Co)

A recently discovered series of quaternary compounds of the general type [K(m)(ROH)(n)()][M(x)Sn(y)()Se(z)] (R = H, Me), containing ternary anions with [SnSe(4)](4-)-coordinated transition metal centers (M = Co, Mn, Zn, Cd, Hg) has now been extended by the synthesis and characterization of the two ortho-thiostannate-coordinated species, [Na(10)(H(2)O)(32)][M(5)Sn(mu(3)-S)(4)(SnS(4))(4)].2H(2)O (M = Zn (1), Co (2)). The central structural motifs of compounds 1 and 2 are highly charged [M(5)Sn(mu(3)-S)(4)(SnS(4))(4)](10-) anions, being the first T3-type supertetrahedral ternary anions reported to date. The exposure of single crystals of 2 to a dynamic vacuum for several hours resulted in the reversible formation of a partially dehydrated, but still monocrystalline material of the composition [Na(10)(H(2)O)(6)][Co(5)Sn(mu(3)-S)(4)(SnS(4))(4)] (3). The loss of 28 of the 34 water molecules only slightly affects the internal structure of the ternary anion in 3 and leads to a significant compacting of the crystal structure with closer linkage of the [Co(5)Sn(5)S(20)](10-) cluster units via the Na(+) cations. Magnetic measurements on 3 show that the ground state of the Co/Sn/S cluster is S = 1/2, indicating a significant antiferromagnetic coupling between the Co centers, which has also been rationalized by DFT investigations of the electronic situation in the ternary subunits of 1-3.