Reaction dynamics following electron capture of chlorofluorocarbon adsorbed on water cluster: a direct density functional theory molecular dynamics study

The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF(2)Cl(2) molecule and a cyclic water trimer (H(2)O)(3) were used as halocarbon and water cluster, respectively. The dynamics calculation of CF(2)Cl(2) showed that both C-Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF(2)Cl(2) (-) as a Cl(-) ion. Almost all total available energy was transferred into the internal modes of the parent CF(2)Cl radical on the product state, while the relative translational energy of Cl(-) was significantly low due to the elongation of two C-Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF(2)Cl(2)(H(2)O)(3) showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other Cl atom existed as a dangling Cl atom. After the electron capture, only one C-Cl bond (dangling Cl atom) was rapidly elongated, whereas the other C-Cl bond is silent during the reaction. The dangling Cl atom was directly dissociated from CF(2)Cl(2) (-)(H(2)O)(3) as Cl(-). The fast Cl(-) ion was generated from CF(2)Cl(2) (-)(H(2)O)(3) on the water cluster. The mechanism of the electron capture of halocarbon on water ice was discussed on the basis of the theoretical results.     

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.     

Structure, spectra and stability of a tetrafluoromethane-water complex

The complex formed between water and tetrafluoromethane has been studied by infrared matrix isolation spectroscopy and ab initio calculations. The geometries of the CF4-H2O complexes were optimized in two steps at the MP2/aug-cc-pVTZ level of theory. The structure found at this level was reoptimized on the CP-corrected potential energy surface. The interaction energy was partitioned according to the SAPT scheme and the topological analysis of the electron density was performed. The optimized structure corresponds to the nonhydrogen bonded complex with an oxygen atom of water oriented toward the carbon atom of CF4. The infrared spectra of CF4-H2O /Ne(Ar) matrices demonstrate the presence of a well defined CF4-H2O structure in accord with theoretical prediction. Two complex vibrations were identified in the spectra of neon matrices and four vibrations were observed in the spectra of argon matrices. The available experimental data are in accord with the CP-corrected calculated data.     

Dinuclear calcium complex with weakly NH...O hydrogen-bonded sulfonate ligands

The novel intramolecularly NH...O hydrogen-bonded Ca(II)-aryl sulfonate complex, [Ca2(SO3-2-t-BuCONHC6H4)2(H2O)4]n(2-t-BuCONHC6H4SO3)2n (1), sulfonate anion, (HNEt3)(SO3-2-t-BuCONHC6H4) (2a), (PPh4)(SO3-2-t-BuCONHC6H4) (2b), (n-Bu4N)(SO3-2-t-BuCONHC6H4) (2c), and sulfonic acid, 2-t-BuCONHC6H4SO3H (3), were synthesized. The structures of 1, 2a, and 2b depict the presence of the formation of NH...O hydrogen bonds between the amide NH and S-O oxygen for a series of compounds as determined by IR and 1H NMR analyses both in the solid state and in the solution state. Thus, the NH...O hydrogen bonds with neutral amide groups are available for investigation of the electronic state of the O- anion. The combined data from the IR and 1H NMR spectra indicate that the sulfonic acid, sulfonate anion, and Ca(II) complex have a substantially weak intramolecular NH...O hydrogen bond between the SO3 oxygen and amide NH. In the detailed comparison with the intense NH...O hydrogen bonds for the carboxylate, weak NH...O hydrogen bonds for sulfonate is due to the strong conjugation of the SO3- group with the lower nucleophilicity.     

Photoinduced electron transfer and solvation dynamics in aqueous clusters: comparison of the photoexcited iodide-water pentamer and the water pentamer anion

Upon photoexcitation of iodide-water clusters, I(-)(H(2)O)(n), an electron is transferred from iodide to a diffuse cluster-supported, dipole-bound orbital. Recent femtosecond photoelectron spectroscopy experiments have shown that, for photoexcited I(-)(H(2)O)(n) (n≥ 5), complex excited-state dynamics ultimately result in the stabilization of the transferred electron. In this work, ab initio molecular dynamics simulations of excited-state I(-)(H(2)O)(5) and (H(2)O)(5)(-) are performed, and the simulated time evolution of their structural and electronic properties are compared to determine unambiguously the respective roles of the water molecules and the iodine atom in the electron stabilization dynamics. Results indicate that, driven by the iodine-hydrogen repulsive interactions, excited I(-)(H(2)O)(5) rearranges significantly from the initial ground-state minimum energy configuration to bind the excited electron more tightly. By contrast, (H(2)O)(5)(-) rearranges less dramatically from the corresponding configuration due to the lack of the same iodine-hydrogen interactions. Despite the critical role of iodine for driving reorganization in excited I(-)(H(2)O)(5), excited-electron vertical detachment energies appear to be determined mostly by the water cluster configuration, suggesting that femtosecond photoelectron spectroscopy primarily probes solvent reorganization in photoexcited I(-)(H(2)O)(5).     

Infrared spectroscopy of Mn+ (H2O) and Mn2+ (H2O) via argon complex predissociation

Singly and doubly charged manganese-water cations, and their mixed complexes with attached argon atoms, are produced by laser vaporization in a pulsed nozzle source. Complexes of the form Mn(+)(H(2)O)Ar(n) (n = 1-4) and Mn(2+)(H(2)O)Ar(4) are studied via mass-selected infrared photodissociation spectroscopy, detected in the mass channels corresponding to the elimination of argon. Sharp resonances are detected for all complexes in the region of the symmetric and asymmetric stretch vibrations of water. With the guidance of density functional theory computations, specific vibrational band resonances are assigned to complexes having different argon attachment configurations. In the small singly charged complexes, argon adds first to the metal ion site and later in larger clusters to the hydrogens of water. The doubly charged complex has argon only on the metal ion. Vibrations in all of these complexes are shifted to lower frequencies than those of the free water molecule. These shifts are greater when argon is attached to hydrogen and also greater for the dication compared to the singly charged species. Cation binding also causes the IR intensities for water vibrations to be much greater than those of the free water molecule, and the relative intensities are greater for the symmetric stretch than the asymmetric stretch. This latter effect is also enhanced for the dication complex.     

Dynamics of a cis-dihydrogen/hydride complex of iridium

Insertion of CS2 into one of the Ir-H bonds of [Ir(H)5(PCy3)2] takes place to afford the dihydrido dithioformate complex cis-[Ir(H)2(eta2-S2CH)(PCy3)2] accompanied by the elimination of H2. Protonation of the dithioformate complex using HBF4.Et2O gives cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4] wherein the H atom undergoes site exchange between the dihydrogen and the hydride ligands. The dynamics was found to be so extremely rapid with respect to the NMR time scale that the barrier to exchange could not be measured. Partial deuteration of the hydride ligands resulted in a J(H,D) of 6.5 and 7.7 Hz for the H2D and the HD2 isotopomers of cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4], respectively. The H-H distance (d(HH)) for this complex has been calculated to be 1.05 A, which can be categorized under the class of elongated dihydrogen complexes. The cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4] complex undergoes substitution of the bound H2 moiety with CH(3)CN and CO resulting in new hydride derivatives, cis-[Ir(H)(L)(eta2-S2CH)(PCy3)2][BF4] (L = CH3CN, CO). Reaction of cis-[Ir(H)2(eta2-S2CH)(PCy3)2] with electrophilic reagents such as MeOTf and Me3SiOTf afforded a new hydride aquo complex cis-[Ir(H)(H2O)(eta2-S2CH)(PCy3)2][OTf] via the elimination of CH4 and Me3SiH, respectively, followed by the binding of a water molecule (present in trace quantities in the solvent) to the iridium center. The X-ray crystal structures of cis-[Ir(H)2(eta2-S2CH)(PCy3)2] and cis-[Ir(H)(H2O)(eta2-S2CH)(PCy3)2][OTf] have been determined.     

On the influence of microsolvation by argon atoms on the electron affinity properties of water dimer

This work provides a comparison of neutral (H2O)2Ar(n) and negatively charged (H2O)(2-)Ar(n) complexes. The excess electron stabilizes the complexes and leads to the trans to cis rearrangement within the water dimer core. In the case of small complexes (n < or = 4) the microsolvation of the dimer by argon atoms arises on the trans side with respect to the donor water molecule. The stabilization of an excess electron is enhanced by the delocalization of the electronic charge density due to microsolvation. The process of cis to trans rotation is induced by the electric field of the approaching negative charge. The interaction energy decomposition suggests a more ionic character of binding in the negatively charged complexes. The attachment of an electron is controlled by the correlation energy.     

Effect of matrix on IR frequencies of acetylene and acetylene-methanol complex: infrared matrix isolation and ab initio study

Effect of nitrogen and argon matrices on the C-H asymmetric stretching and bending infrared frequencies of the acetylene molecule, C(2)H(2), has been studied by matrix isolation experiments as well as by calculations at MP2 level of theory. The complexes of C(2)H(2) in nitrogen and argon matrices, viz., C(2)H(2)(N(2))(m) (with m=2-8) and C(2)H(2)(Ar)(n) (with n=2-10) are theoretically explored. The computed acetylenic C-H asymmetric stretch in C(2)H(2)-nitrogen complexes shows a redshift of 3.0 to 11.9 cm(-1) compared with the frequencies of the free acetylene molecule, and a corresponding blueshift of 7.4 to 26.2 cm(-1) when C(2)H(2) is complexed with argon atoms. The trends in the computed shifts are in good agreement with the experiments. The molecular electrostatic potential minimum of C(2)H(2) becomes more negative when complexed with nitrogen than on complexation with argon. This observation implies a greater basic character for C(2)H(2) in the nitrogen matrix, favoring the formation of H-pi(C(2)H(2)-MeOH) complex as compared to that in the Ar matrix. Experimentally the preferential formation of H-pi(C(2)H(2)-MeOH) complex in the N(2) matrix has indeed been observed.     

Reactions of in situ generated hydrated organotin cations with chelating O,O- or O,N-ligands: a possible structure-directing influence of the organic substituent on tin

The reaction of [n-Bu(2)SnO](n) with 1,5-naphthalenedisulfonic acid tetrahydrate in a 1:1 stoichiometry followed by reaction with 2,2'-bipyridine-N,N'-dioxide (BPDO-I) afforded a 1D-coordination polymer [n-Bu(2)Sn(BPDO-I)(1,5-C(10)H(6)(SO(3))(2))](n) (1) where the disulfonate ligand acts as a bridging ligand between two tin centers. An analogous reaction involving [Ph(2)SnO](n) afforded a trihydrated O,O'-chelated diorganotin cation [{Ph(2)Sn(BPDO-I)(H(2)O)(3)}(2+)][C(10)H(6)(SO(3)(-))(2)]·2CH(3)OH (2·2CH(3)OH). Utilizing two equivalents of BPDO-I in this reaction resulted in the ionic complex [{Ph(2)Sn(BPDO-I)(2)(H(2)O)}(2+)][C(10)H(6)(SO(3)(-))(2)]·3H(2)O (3·3H(2)O). In 2 and 3 the sulfonate ligands are not present in the coordination sphere of tin. Reaction of [n-Bu(2)SnO](n) and 1,5-naphthalenedisulfonic acid tetrahydrate, followed by reaction with [bis(diphenylphosphoryl)methane (DPPOM)] resulted in the formation of, [{n-Bu(2)Sn(DPPOM)(2)(H(2)O)(1,5-C(10)H(6)(SO(3))(SO(3)(-))}]·H(2)O (4·H(2)O). Of the two coordinating groups present in DPPOM, only one P=O group is coordinated to the tin atom. The remaining P=O motif is free and is involved in intramolecular H-bonding with the tin-bound water molecule. Using [Ph(2)SnO](n) instead of [n-Bu(2)SnO](n) afforded the ionic complex [{Ph(2)Sn(DPPOM)(2)}(2+){1,5-C(10)H(6)(SO(3)(-))(2)}] (5) where the DPPOM functions as a chelating ligand. The reaction of [n-Bu(2)SnO](n) with 1,5-naphthalenedisulfonic acid tetrahydrate followed by addition of one equivalent of 8-hydroxyquinoline (8-HQ) in presence of triethylamine afforded the neutral dinuclear complex, [(H(2)O)(8-Q)n-Bu(2)Sn(μ-1,5-C(10)H(6)(SO(3))(2))n-Bu(2)Sn(8-Q)(H(2)O)] (6) where the two tin atoms are bridged by the disulfonate ligand. Compounds 1-6 are thermally stable as shown by their thermogravimetric analyses.     

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Syntheses and structural characterizations of 24-membered dimetal (Mn, Ni, Fe) macrocyclic complexes and the C-S bond formation between acetylacetone and a mercapto N-heterocycle

An organic ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L) reacts with metal (Mn, Ni, Fe) salts, resulting in 24-membered dimetal macrocyclic complexes [MnL(H2O)(dmso)](2).2dmso, [NiL(H2O)(dmf)](2).2dmf, [MnL(dmf)2]2 and [Fe2L2(solvent)2(SO4)] (solvent=dmso; H2O ; dmf). Di-manganese macrocyclic complexes [MnL(dmf)(dmso)]2 and [MnL(H2O)2](2).6H2O can also be obtained directly by aerobic assembly reaction of MnCl2, dipotassium 1,3,4-thiadiazole-2,5-dithiolate (K2tdadt) and acetylacetone (H2acac) in various solvents, accompanying a C-S bond formation between acetylacetone and the mercapto N-heterocycle. Disulfide has been considered as the intermediate in the assembly reaction. Meanwhile an assembly reaction including MnCl2, 2-mercaptobenzimidazole and H2acac has produced an organic compound 2-(3-pentanedionylthio)benzimidazole with a new C-S bond. These dimetal complexes have similar macrocyclic structures, in which solvent molecules and sulfate coordinate to the octahedral metal in trans-configuration, whereas a pair of water molecules are located in octahedral cis-positions for owing to a small steric effect. A host cavity of sufficiently large size exists in the macrocyclic structure to trap the solvent molecules and the sulfate anion. The IR spectra have been used to assign the solvent molecules trapped and the sulfate anion which is shown as a bridged bidentate ligand. Thermal analyses show the stability of the macrocyclic backbone below 200 degrees C and gradual release processes of the trapped solvent molecules. Decomposition and oxidation of the dimetal macrocycle backbone occur at 300-500 degrees C, resulting in a metal sulfate. Further decomposition led to metal oxide at 500-600 degrees C.     

Theoretical study of negatively charged Fe(-)-(H2O)(n ≤ 6) clusters

Interactions of a singly negatively charged iron atom with water molecules, Fe(-)-(H(2)O)(n≤6), in the gas phase were studied by means of density functional theory. All-electron calculations were performed using the B3LYP functional and the 6-311++G(2d,2p) basis set for the Fe, O, and H atoms. In the lowest total energy states of Fe(-)-(H(2)O)(n), the metal-hydrogen bonding is stronger than the metal-oxygen one, producing low-symmetry structures because the water molecules are directly attached to the metal by basically one of their hydrogen atoms, whereas the other ones are involved in a network of hydrogen bonds, which together with the Fe(δ-)-H(δ+) bonding accounts for the nascent hydration of the Fe(-) anion. For Fe(-)-(H(2)O)(3≤n), three-, four-, five-, and six-membered rings of water molecules are bonded to the metal, which is located at the surface of the cluster in such a way as to reduce the repulsion with the oxygen atoms. Nevertheless, internal isomers appear also, lying less than 3 or 5 kcal/mol for n = 2-3 or n = 4-6. These results are in contrast with those of classical TM(+)-(H(2)O)(n) complexes, where the direct TM(+)-O bonding usually produces high symmetry structures with the metal defining the center of the complex. They show also that the Fe(-) anions, as the TM(+) ions, have great capability for the adsorption of water molecules, forming Fe(-)-(H(2)O)(n) structures stabilized by Fe(δ-)-H(δ+) and H-bond interactions.     

Binding of polyanions by biogenic amines. I. Formation and stability of protonated putrescine and cadaverine complexes with inorganic anions

The formation and stability of proton diamine-inorganic anion [Cl(-), SO(4)(2-), HPO(4)(2-), P(2)O(7)(4-) and Fe(CN)(6)(4-)] complexes was studied potentiometrically [(H(+))-glass electrode] at 25 degrees C. Several general formula ALH(r) complexes are formed in these various systems. The stability of complexes formed between H(2)A(2+) and different anions ranges from one to six (log formation constants). The formation constants are slightly dependent on the length of the alkylic chain whilst they strongly depend on the anion charge. A general relationship [logK=-0.85+1.81z-0.055n] was found for the reaction H(2)A(2+)+L(z-)=ALH(2)((2-z)) [L=inorganic anions, A=NH(2)-(CH(2))(n)-NH(2) diamines with n=2...8].     

Hydrido phosphanido bridged polynuclear complexes obtained by protonation of a phosphinito bridged Pt(I) complex with HBF4 and HF

The protonation of the phosphinito-bridged Pt(I) complex [(PHCy(2))Pt(μ-PCy(2)){κ(2)P,O-μ-P(O)Cy(2)}Pt(PHCy(2))](Pt-Pt) (1) by aqueous HBF(4) or hydrofluoric acid leads selectively to the hydrido-bridged solvento species syn-[(PHCy(2))(H(2)O)Pt(μ-PCy(2))(μ-H)Pt(PHCy(2)){κP-P(OH)Cy(2)}](Y)(2)(Pt-Pt) ([2-H(2)O]Y(2)) {Y = BF(4), F(HF)(n)} when an excess of acid was used. On standing in halogenated solvents, complex [2-H(2)O](BF(4))(2) undergoes a slow but complete isomerization to [(PHCy(2))(2)Pt(μ-PCy(2))(μ-H)Pt{κP-P(OH)Cy(2)}(H(2)O)](BF(4))(2)(Pt-Pt) ([4-H(2)O][BF(4)](2)) having the P(OH)Cy(2) ligand trans to the hydride. The water molecule coordinated to platinum in [2-H(2)O][BF(4)](2) is readily replaced by halides, nitriles, and triphenylphosphane, and the acetonitrile complex [2-CH(3)CN][BF(4)](2) was characterized by XRD analysis. Solvento species other than aqua complexes, such as [2-acetone-d(6)](2+) or [2-CD(2)Cl(2)](2+) were obtained in solution by the reaction of excess etherate HBF(4) with 1 in the relevant solvent. The complex [2-H(2)O](Y)(2) [Y = F(HF)(n)] spontaneously isomerizes into the terminal hydrido complexes [(PHCy(2))Pt(μ-PCy(2)){κ(2)P,O-μ-P(O)Cy(2)}Pt(H)(PHCy(2))](Y)(Pt-Pt) ([6](Y)). In the presence of HF, complex [6](Y) transforms into the bis-phosphanido-bridged Pt(II) dinuclear complex [(PHCy(2))(H)Pt(μ-PCy(2))(2)Pt{κP-P(OH)Cy(2)}](Y)(Pt-Pt) ([7](Y)). When the reaction of 1 with HF was carried out with diluted hydrofluoric acid by allowing the HF to slowly diffuse into the dichloromethane solution, the main product was the linear 60e tetranuclear complex [(PHCy(2)){κP-P(O)Cy(2)}Pt(1)(μ-PCy(2))(μ-H)Pt(2)(μ-PCy(2))](2)(Pt(1)-Pt(2)) (8). Insoluble compound 8 is readily protonated by HBF(4) in dichloromethane, forming the more soluble species [(PHCy(2)){κP-P(OH)Cy(2)}Pt(1)(μ-PCy(2))(μ-H)Pt(2)(μ-PCy(2))](2)(BF(4))(2)(Pt(1)-Pt(2)) {[9][BF(4)](2)}. XRD analysis of [9][BF(4)](2)·2CH(2)Cl(2) shows that [9](2+) is comprised of four coplanar Pt atoms held together by four phosphanido and two hydrido bridges. Both XRD and NMR analyses indicate alternate intermetal distances with peripheral Pt-Pt bonds and a longer central Pt···Pt separation. DFT calculations allow tracing of the mechanistic pathways for the protonation of 1 by HBF(4) and HF and evaluation of their energetic aspects. Our results indicate that in both cases the protonation occurs through an initial proton transfer from the acid to the phosphinito oxygen, which then shuttles the incoming proton to the Pt-Pt bond. The different evolution of the reaction with HF, leading also to [6](Y) or 8, has been explained in terms of the peculiar behavior of the F(HF)(n)(-) anions and their strong basicity for n = 0 or 1.     

Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.     

Microhydration of the guanine-cytosine (GC) base pair in the neutral and anionic radical states: a density functional study

A density functional study of the effects of microhydration on the guanine-cytosine (GC) base pair and its anion radical is presented. Geometries of the GC base pair in the presence of 6 and 11 water molecules were fully optimized in the neutral (GC-nH2O) and anion radical [(GC-nH2O)*-] (n = 6 and 11) states using the B3LYP method and the 6-31+G** basis set. Further, vibrational frequency analysis at the same level of theory (B3LYP/6-31+G**) was also performed to ensure the existence of local minima in these hydrated structures. It was found that water molecules surrounding the GC base pair have significant effects on the geometry of the GC base pair and promote nonplanarity in the GC base pair. The calculated structures were found to be in good agreement with those observed experimentally and obtained in molecular dynamics (MD) simulation studies. The water molecules in neutral GC-nH2O complexes lie near the ring plane of the GC base pair where they undergo hydrogen bonding with both GC and each other. However, in the GC anion radical complexes (GC-nH2O, n = 6, 11), the water molecules are displaced substantially from the GC ring plane. For GC-11H2O*-, a water molecule is hydrogen-bonded with the C6 atom of the cytosine base. We found that the hydration shell initially destabilizes the GC base pair toward electron capture as a transient anion. Energetically unstable diffuse states in the hydration shell are suggested to provide an intermediate state for the excess electron before molecular reorganization of the water molecules and the base pair results in a stable anion formation. The singly occupied molecular orbital (SOMO) in the anion radical complexes clearly shows that an excess electron localizes into a pi orbital of cytosine. The zero-point-energy (ZPE-) corrected adiabatic electron affinities (AEAs) of the GC-6H2O and GC-11H2O complexes, at the B3LYP/6-31+G** level of theory, were found to be 0.74 and 0.95 eV, respectively. However, the incorporation of bulk water as a solvent using the polarized continuum model (PCM) increases the EAs of these complexes to 1.77 eV.     

Ruthenium(II) 2,2'-bibenzimidazole complex as a second-sphere receptor for anions interaction and colorimeter

A ruthenium(II) complex [Ru(bpy) 2(H 2bbim)](PF 6) 2 ( 1) as anions receptor has been exploited, where Ru(II)-bpy moiety acts as a chromophore and the H 2bbim ligand as an anion binding site. A systematic study suggests that 1 interacts with the Cl (-), Br (-), I (-), NO 3 (-), HSO 4 (-), and H 2PO 4 (-) anions via the formation of hydrogen bonds. Whereas 1 undergoes a stepwise process with the addition of F (-) and OAc (-) anions: formation of the monodeprotonated complex [Ru(bpy) 2(Hbbim)] with a low anion concentration, followed by the double-deprotonated complex [Ru(bpy) 2(bbim)], in the presence of a high anion concentration. These stepwise processes concomitant with the changes of vivid colors from yellow to orange brown and then to violet can be used for probing the F (-) and OAc (-) anions by naked eye. The deprotonation processes are not only determined by the basicity of the anion but also related to the strength of hydrogen bonding, as well as the stability of the formed compounds. Moreover, a double-deprotonated complex [Ru(bpy) 2(bbim)].CH 3OH.H 2O ( 3) has been synthesized, and the structural changes induced by the deprotonation has also been investigated. In addition, complexes [Ru(bpy) 2(Hbbim)] 2(HOAc) 3Cl 2.12H 2O ( 2), [Ru(bpy) 2(Hbbim)](HCCl 3CO 2)(CCl 3CO 2).2H 2O ( 4), and [Ru(bpy) 2(H 2bbim)](CF 3CO 2) 2.4H 2O ( 5) have been synthesized to observe the second sphere coordination between the Ru(II)-H 2bbim moiety and carboxylate groups via hydrogen bonds in the solid state.     

H-bonding dependent structures of (NH4+)3H+(SO4 2-)2. Mechanisms of phase transitions

The role of different H-bonds in phases II, III, IV, and V of triammonium hydrogen disulfate, (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), has been studied by X-ray diffraction and (1)H solid-state MAS NMR. The proper space group for phase II is C2/c, for phases III and IV is P2/n, and for phase V is P onemacr;. The structures of phases III and IV seem to be the same. The hydrogen atom participating in the O(-)-H(+).O(-) H-bond in phase II of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) at room temperature is split at two positions around the center of the crucial O(-)-H(+).O(-) H-bonding, joining two SO(4)(2)(-) tetrahedra. With decreasing temperature, it becomes localized at one of the oxygen atoms. Further cooling causes additional differentiation of possibly equivalent sulfate dimers. The NH(4)(+) ions participate mainly in bifurcated H-bonds with two oxygen atoms from sulfate anions. On cooling, the major contribution of the bifurcated H-bond becomes stronger, whereas the minor one becomes weaker. This is coupled with rotation of sulfate ions. In all the phases of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), some additional, weak but significant, reflections are observed. They are located between the layers of the reciprocal lattice, suggesting possible modulation of the host (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) structure(s). According to (1)H MAS NMR obtained for phases II and III, the nature of the acidic proton disorder is dynamic, and localization of the proton takes place in a broader range of temperatures, as can be expected from the X-ray diffraction data.