Energetics of cresols and of methylphenoxyl radicals

Combustion calorimetry studies were used to determine the standard molar enthalpies of formation of o-, m-, and p-cresols, at 298.15 K, in the condensed state as Delta(f)H(m) degrees (o-CH(3)C(6)H(4)OH,cr) = -204.2 +/- 2.7 kJ.mol(-1), Delta(f)H(m) degrees (m-CH(3)C(6)H(4)OH,l) = -196.6 +/- 2.1 kJ.mol(-1), and Delta(f)H(m) degrees (p-CH(3)C(6)H(4)OH,cr) = -202.2 +/- 3.0 kJ.mol(-1). Calvet drop calorimetric measurements led to the following enthalpy of sublimation and vaporization values at 298.15 K: Delta(sub)H(m) degrees (o-CH(3)C(6)H(4)OH) = 73.74 +/- 0.46 kJ.mol(-1), Delta(vap)H(m) degrees (m-CH(3)C(6)H(4)OH) = 64.96 +/- 0.69 kJ.mol(-1), and Delta(sub)H(m) degrees (p-CH(3)C(6)H(4)OH) = 73.13 +/- 0.56 kJ.mol(-1). From the obtained Delta(f)H(m) degrees (l/cr) and Delta(vap)H(m) degrees /Delta(sub)H(m) degrees values, it was possible to derive Delta(f)H(m) degrees (o-CH(3)C(6)H(4)OH,g) = -130.5 +/- 2.7 kJ.mol(-1), Delta(f)H(m) degrees (m-CH(3)C(6)H(4)OH,g) = -131.6 +/- 2.2 kJ.mol(-1), and Delta(f)H(m) degrees (p-CH(3)C(6)H(4)OH,g) = -129.1 +/- 3.1 kJ.mol(-1). These values, together with the enthalpies of isodesmic and isogyric gas-phase reactions predicted by the B3LYP/cc-pVDZ, B3LYP/cc-pVTZ, B3P86/cc-pVDZ, B3P86/cc-pVTZ, MPW1PW91/cc-pVTZ, CBS-QB3, and CCSD/cc-pVDZ//B3LYP/cc-pVTZ methods, were used to obtain the differences between the enthalpy of formation of the phenoxyl radical and the enthalpies of formation of the three methylphenoxyl radicals: Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (o-CH(3)C(6)H(4)O*,g) = 42.2 +/- 2.8 kJ.mol(-1), Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (m-CH(3)C(6)H(4)O*,g) = 36.1 +/- 2.4 kJ.mol(-1), and Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (p-CH(3)C(6)H(4)O*,g) = 38.6 +/- 3.2 kJ.mol(-1). The corresponding differences in O-H bond dissociation enthalpies were also derived as DH degrees (C(6)H(5)O-H) - DH degrees (o-CH(3)C(6)H(4)O-H) = 8.1 +/- 4.0 kJ.mol(-1), DH degrees (C(6)H(5)O-H) - DH degrees (m-CH(3)C(6)H(4)O-H) = 0.9 +/- 3.4 kJ.mol(-1), and DH degrees (C(6)H(5)O-H) - DH degrees (p-CH(3)C(6)H(4)O-H) = 5.9 +/- 4.5 kJ.mol(-1). Based on the differences in Gibbs energies of formation obtained from the enthalpic data mentioned above and from published or calculated entropy values, it is concluded that the relative stability of the cresols varies according to p-cresol < m-cresol < o-cresol, and that of the radicals follows the trend m-methylphenoxyl < p-methylphenoxyl < o-methylphenoxyl. It is also found that these tendencies are enthalpically controlled.     

Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

Kinetics of Dissociation of Iron(III) Complexes of Tiron in Aqueous Acid

The kinetics of dissociation of the mono, bis, and tris complexes of Tiron (1,2-dihydroxy-3,5-benzenedisulfonate) have been studied in acidic aqueous solutions in 1.0 M HClO(4)/NaClO(4), as a function of [H(+)] and temperature. In general, the kinetics can be explained by two reactions, (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) + H(+) (k(n), k(-n)) and (HO)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L(n)H) (k(n)', k(-n)'), a rapid equilibrium, (H(2)O)Fe(L(n)H) right arrow over left arrow (H(2)O)Fe(L)(n) + H(+) (K(cn)), and the formation constant (H(2)O)Fe(L)(n)(-1) + H(2)L right arrow over left arrow (H(2)O)Fe(L)(n) + 2H(+). For n = 1, the reaction was observed at 670 nm, and at [H(+)] of 0.05-0.5 M at temperatures of 2.0, 14.0, 25.0, and 36.7 degrees C. For n = 2, the analogous conditions are 562 nm, at [H(+)] of 1.5 x 10(-3) to 1.4 x 10(-2) M at temperatures of 2.0, 9.0, and 14.0 degrees C. For n = 3, the conditions are 482 nm, at pH 4.5-5.7 in 0.02 M acetate buffer at temperatures of 1.8, 8.0, and 14.5 degrees C. The rate or equilibrium constants (25 degrees C) with DeltaH or DeltaH degrees (kcal mol(-1)) and DeltaS or DeltaS degrees (cal mol(-1) K(-1)) in brackets are as follows: for n = 1, k(1) = 2.3 M(-1) s(-1) (8.9, -27.1), k(-1) = 1.18 M(-1) s(-1) (4.04, -44.8), K(c1) = 0.96 M (-9.99, -33.6), K(f1) = 2.01 M (-5.14, -15.85); for n = 2, k(-2)/K(c2) = 1.9 x 10(7) (19.9, 41.5) and k(-2)'/K(c2) = 1.85 x 10(3) (1.4, -38.8) and a lower limit of K(c2) > 0.015 M; for n = 3, k(3) = 7.7 x 10(3) (15.8, 12.3), k(-3) = 1.7 x 10(7) (16.2, 28.9), K(c3) = 7.4 x 10(-5) M (4.1, -5.1), and K(f3) = 3.35 x 10(-8) (3.7, -21.7). From the variations in rate constants and activation parameters, it is suggested that the Fe(L)(2) and Fe(L)(3) complexes undergo substitution by dissociative activation, promoted by the catecholate ligands.     

Photochemistry of peroxoborates: borate inhibition of the photodecomposition of hydrogen peroxide

The UV absorbance and photochemical decomposition kinetics of hydrogen peroxide in borate/boric acid buffers were investigated as a function of pH, total peroxide concentration, and total boron concentration. At higher pH borate/boric acid inhibits the photodecomposition of hydrogen peroxide (molar absorptivity and quantum yield of H(2)O(2) and HO(2) (-), (19.0+/-0.3) M(-1) cm(-1) and 1, and (237+/-7) M(-1) cm(-1) and 0.8+/-0.1, respectively). The results are consistent with the equilibrium formation of the anions monoperoxoborate, K(BOOH)=[H(+)][HOOB(OH)(3) (-)]/([B(OH)(3)][H(2)O(2)]), 2.0 x 10(-8), R. Pizer, C. Tihal, Inorg. Chem. 1987, 26, 3639-3642, and monoperoxodiborate, K(BOOB)=[BOOB(2-)]/([B(OH)(4) (-)][HOOB(OH)(3) (-)]), 1.0+/-0.3 or 4.3+/-0.9, depending upon the conditions, with molar absorptivity, (19+/-1) M(-1) cm(-1) and (86+/-15) M(-1) cm(-1), respectively, and respective quantum yields, 1.1+/-0.1 and 0.04+/-0.04. The low quantum yield of monoperoxodiborate is discussed in terms of the slower diffusion apart of incipient (.)OB(OH)(3) (-) radicals than may be possible for (.)OH radicals, or a possible oxygen-bridged cyclic structure of the monoperoxodiborate.     

Theoretical study of isomerization and decomposition of propenal

We investigated the dynamics of isomerization and multi-channel dissociation of propenal (CH(2)CHCHO), methyl ketene (CH(3)CHCO), hydroxyl propadiene (CH(2)CH(2)CHOH), and hydroxyl cyclopropene (cyclic-C(3)H(3)-OH) in the ground potential-energy surface using quantum-chemical calculations. Optimized structures and vibrational frequencies of molecular species were computed with method B3LYP∕6-311G(d,p). Total energies of molecules at optimized structures were computed at the CCSD(T)∕6-311+G(3df,2p) level of theory. We established the potential-energy surface for decomposition to CH(2)CHCO + H, CH(2)CH + HCO, CH(2)CH(2)∕CH(3)CH + CO, CHCH∕CH(2)C + H(2)CO, CHCCHO∕CH(2)CCO + H(2), CHCH + CO + H(2), CH(3) + HCCO, CH(2)CCH + OH, and CH(2)CC∕cyclic-C(3)H(2) + H(2)O. Microcanonical rate coefficients of various reactions of trans-propenal with internal energies 148 and 182 kcal mol(-1) were calculated using Rice-Ramsperger-Kassel-Marcus and Variational transition state theories. Product branching ratios were derivable using numerical integration of kinetic master equations and the steady-state approximation. The concerted three-body dissociation of trans-propenal to fragments C(2)H(2) + CO + H(2) is the prevailing channel in present calculations. In contrast, C(3)H(3)O + H, C(2)H(3) + HCO and C(2)H(4) + CO were identified as major channels in the photolysis of trans-propenal. The discrepancy between calculations and experiments in product branching ratios indicates that the three major photodissociation channels occur mainly on an excited potential-energy surface whereas the other channels occur mainly on the ground potential-energy surface. This work provides profound insight in the mechanisms of isomerization and multichannel dissociation of the system C(3)H(4)O.     

Protonation of gas-phase aromatic molecules: IR spectrum of the fluoronium isomer of protonated fluorobenzene

The IR spectrum of the fluoronium isomer of protonated fluorobenzene (F-C(6)H(6)F(+), phenylfluoronium) is recorded in the vicinity of the C-H and F-H stretch fundamentals to obtain the first structured spectrum of an isolated protonated aromatic molecule in the gas phase. Stable F-C(6)H(6)F(+) ions are produced via proton transfer from CH(5)(+) to fluorobenzene (C(6)H(5)F) in a supersonic plasma expansion. The F-C(6)H(6)F(+) spectrum recorded between 2,540 and 4,050 cm(-1) is consistent with a weakly bound ion-dipole complex composed of HF and the phenyl cation, HF-C(6)H(5)(+). The strongest transition occurs at 3,645 cm(-1) and is assigned to the F-H stretch (sigma(FH)). The antisymmetric C-H stretch of the two ortho hydrogen atoms, sigma(CH) = 3,125 cm(-1), is nearly unshifted from bare C(6)H(5)(+), indicating that HF complexation has little influence on the C-H bond strength of C(6)H(5)(+). Despite the simultaneous production of the more stable ring protonated carbenium isomers of C(6)H(6)F(+) (fluorobenzenium) in the electron ionization source, F-C(6)H(6)F(+) can selectively be photodissociated into C(6)H(5)(+) and HF under the present experimental conditions, because it has a much lower dissociation energy than all carbenium isomers. Quantum chemical calculations at the B3LYP and MP2 levels of theory using the 6-311G(2df,2pd) basis support the interpretation of the experimental data and provide further details on structural, energetic, and vibrational properties of F-C(6)H(6)F(+), the carbenium isomers of C(6)H(6)F(+), and other weakly bound HF-C(6)H(5)(+) ion-dipole complexes. The dissociation energy of F-C(6)H(6)F(+) with respect to dehydrofluorination is calculated as D(0) = 4521 cm(-1) (approximately 54 kJ/mol). Analysis of the charge distribution in F-C(6)H(6)F(+) supports the notation of a HF-C(6)H(5)(+) ion-dipole complex, with nearly the whole positive charge of the added proton distributed over the C(6)H(5)(+) ring. As a result, protonation at the F atom strongly destabilizes the C-F bond in C(6)H(5)F.     

Imaging studies of the photodissociation of H2S+ cations. I. Illustrations of the role of nuclear spin

Ion imaging methods have been used to study the dynamics of H(2)(D(2)) molecular elimination from H(2)S(+)(D(2)S(+)) cations following photoexcitation to the A(2)A(1) state in the wavelength range 300相似文献   

Multiconfigurational second-order perturbation study of the decomposition of the radical anion of nitromethane

The doublet potential energy surfaces involved in the decomposition of the nitromethane radical anion (CH(3)NO(2) (-)) have been studied by using the multistate extension of the multiconfigurational second-order perturbation method (MS-CASPT2) in conjunction with large atomic natural orbital-type basis sets. A very low energy barrier is found for the decomposition reaction: CH(3)NO(2) (-)-->[CH(3)NO(2)](-)-->CH(3)+NO(2) (-). No evidence has been obtained on the existence of an isomerization channel leading to the initial formation of the methylnitrite anion (CH(3)ONO(-)) which, in a subsequent reaction, would yield nitric oxide (NO). In contrast, it is suggested that NO is formed through the bimolecular reaction: CH(3)+NO(2) (-)-->[CH(3)O-N-O](-)-->CH(3)O(-)+NO. In particular, the CASSCF/MS-CASPT2 results indicate that the methylnitrite radical anion CH(3)ONO(-) does not represent a minimum energy structure, as concluded by using density functional theory (DFT) methodologies. The inverse symmetry breaking effect present in DFT is demonstrated to be responsible for such erroneous prediction.     

Synthetic models of the reduced active site of superoxide reductase

We report the synthesis, structural and spectroscopic characterization, and magnetic and electrochemical studies of a series of iron(II) complexes of the pyridyl-appended diazacyclooctane ligand L(8)py(2), including several that model the square-pyramidal [Fe(II)(N(his))(4)(S(cys))] structure of the reduced active site of the non-heme iron enzyme superoxide reductase. Combination of L(8)py(2) with FeCl(2) provides [L(8)py(2)FeCl(2)] (1), which contains a trigonal-prismatic hexacoordinate iron(II) center, whereas a parallel reaction using [Fe(H(2)O)(6)](BF(4))(2) provides [L(8)py(2)Fe(FBF(3))]BF(4) (2), a novel BF(4)(-)-ligated square-pyramidal iron(II) complex. Substitution of the BF(4)(-) ligand in 2 with formate or acetate ions affords distorted pentacoordinate [L(8)py(2)Fe(O(2)CH)]BF(4) (3) and [L(8)py(2)Fe(O(2)CCH(3))]BF(4) (4), respectively. Models of the superoxide reductase active site are prepared upon reaction of 2 with sodium salts of aromatic and aliphatic thiolates. These model complexes include [L(8)py(2)Fe(SC(6)H(4)-p-CH(3))]BF(4) (5), [L(8)py(2)Fe(SC(6)H(4)-m-CH(3))]BF(4) (6), and [L(8)py(2)Fe(SC(6)H(11))]BF(4) (7). X-ray crystallographic studies confirm that the iron(II)-thiolate complexes model the square-pyramidal geometry and N(4)S donor set of the reduced active site of superoxide reductase. The iron(II)-thiolate complexes are high spin (S = 2), and their solutions are yellow in color because of multiple charge-transfer transitions that occur between 300 and 425 nm. The ambient temperature cyclic voltammograms of the iron(II)-thiolate complexes contain irreversible oxidation waves with anodic peak potentials that correlate with the relative electron donating abilities of the thiolate ligands. This electrochemical irreversibility is attributed to the bimolecular generation of disulfides from the electrochemically generated iron(III)-thiolate species.     

Effect of hydrocarbon structure of the headgroup on the thermodynamic properties of micellization of cationic gemini surfactants: an electrical conductivity study

A series of cationic gemini surfactants butanediyl-1,4-bis(dodecyldialkylammonium bromide), C(12)H(25)N(+)(C(m)H(2)(m)(+1))(2)C(4)H(8)N(+)(C(m)H(2)(m)(+1))(2)C(12)H(25)·2Br(-), where m=1, 2, 3, 4, referred to as C(12)C(4)C(12)(Me), C(12)C(4)C(12)(Et), C(12)C(4)C(12)(Pr), and C(12)C(4)C(12)(Bu), respectively, were synthesized, and their thermodynamic properties of micellization were studied by electrical conductivity measurements. There existed a minimum critical micelle concentration (cmc) in the curve of cmc versus temperature, and the temperature of the minimum of cmc (T(min)) increased with increasing the headgroup alkyl chain length. The values of log (cmc) depended linearly on carbon number of the alkyl chains, but that was not true for the carbon number of the headgroup substituents. The temperature dependence of cmc and degree of counterion association (β) were used to calculate the Gibbs free energy (Δ(mic)G°), enthalpies (Δ(mic)H°) and entropies (Δ(mic)S°) of micelle formation for these gemini surfactants, and well correlated enthalpy-entropy compensation was observed. The analyses showed C(12)C(4)C(12)(Me) and C(12)C(4)C(12)(Et) behaved similarly in terms of thermodynamics of micellization, but they behaved differently from C(12)C(4)C(12)(Pr) and C(12)C(4)C(12)(Bu), which could be ascribed to the hydrophobicity and the location of the headgroup alkyl chains in the aggregates. These initial results indicate the headgroup alkyl chain plays an important role in influencing the thermodynamic properties of gemini surfactants.     

The aromaticity of pyracylene: an experimental and computational study of the energetics of the hydrogenation of acenaphthylene and pyracylene

In this work, the aromaticity of pyracylene (2) was investigated from an energetic point of view. The standard enthalpy of hydrogenation of acenaphthylene (1) to acenaphthene (3) at 298.15 K was determined to be minus sign(114.5 +/- 4.2) kJ x mol(-1) in toluene solution and minus sign(107.9 +/- 4.2) kJ x mol(-1) in the gas phase, by combining results of combustion and reaction-solution calorimetry. A direct calorimetric measurement of the standard enthalpy of hydrogenation of pyracylene (2) to pyracene (4) in toluene at 298.15 K gave -(249.9 plus minus 4.6) kJ x mol(-1). The corresponding enthalpy of hydrogenation in the gas phase, computed from the Delta(f)H(o)m(cr) and DeltaH(o)m(sub) values obtained in this work for 2 and 4, was -(236.0 +/- 7.0) kJ x mol(-1). Molecular mechanics calculations (MM3) led to Delta(hyd)H(o)m(1,g) = -110.9 kJ x mol(-1) and Delta(hyd)H(o)m(2,g) = -249.3 kJ x mol(-1) at 298.15 K. Density functional theory calculations [B3LYP/6-311+G(3d,2p)//B3LYP/6-31G(d)] provided Delta(hyd)H(o)m(2,g) = -(244.6 +/- 8.9) kJ x mol(-1) at 298.15 K. The results are put in perspective with discussions concerning the "aromaticity" of pyracylene. It is concluded that, on energetic grounds, pyracylene is a borderline case in terms of aromaticity/antiaromaticity character.     

A comparative study of the structures and reactivity of cyclometallated platinum compounds of N-benzylidenebenzylamines and cycloplatination of a primary amine

The reaction of cis-[PtCl(2)(dmso)2] with ligands 4-ClC(6)H(4)CHNCH(2)C(6)H(5) (1a) and 4-ClC(6)H(4)CHNCH(2)(4-ClC(6)H(4)) (1b) in the presence of sodium acetate and using either methanol or toluene as solvent produced the corresponding five-membered endo-metallacycles [PtCl{(4-ClC(6)H(3))CHNCH(2)C(6)H(5)}{SOMe(2)}] (2a) and [PtCl{(4-ClC(6)H(3))CHNCH(2)(4'-ClC(6)H(4))}{SOMe(2)}] (2b). An analogous reaction for ligands 2,6-Cl(2)C(6)H(3)CHNCH(2)C(6)H(5) (1c) and 2,6-Cl(2)C(6)H(3)CHNCH(2)(4-ClC(6)H(4)) (1d) produced five-membered exo-metallacycles [PtCl{(2,6-Cl(2)C(6)H(3))CHNCH(2)C(6)H(4)}{SOMe(2)}] (2c) and [PtCl{(2,6-Cl(2)C(6)H(3))CHNCH(2)(4'-ClC(6)H(3))}{SOMe(2)}] (2d) when the reaction was carried out in methanol and seven-membered endo-platinacycles [PtCl{(MeC(6)H(3))ClC(6)H(3)CHNCH(2)C(6)H(4)}{SOMe(2)}] (3c) and [PtCl{(MeC(6)H(3))ClC(6)H(3)CHNCH(2)(4'-ClC(6)H(3))}{SOMe(2)}] (3d) when toluene was used as a solvent. The reaction of 2,4,6-(CH(3))(3)C(6)H(2)CHNCH(2)(4-ClC(6)H(4)) (1e) produced in both solvents an exo-platinacycle [PtCl{(2,4,6-(CH(3))(3)C(6)H(2))CHNCH(2)(4'-ClC(6)H(3))}{SO(CH(3))(2)}] (2e). Cyclometallation of 4-chlorobenzylamine was also achieved to produce compound [PtCl{(4-ClC(6)H(3))CH(2)NH(2)}{SOMe(2)}] (2g). The reactions of endo- and exo-metallacycles with phosphines evidenced the higher lability of the Pt-N bond in exo-metallacycles while a comparative analysis of the crystal structures points out a certain degree of aromaticity in the endo-metallacycle.     

Synthesis and structures of some new types of lithium beta-diketiminates

The tetracyclic dilithio-Si,Si'-oxo-bridged bis(N,N'-methylsilyl-beta-diketiminates) 2 and 3, having an outer LiNCCCNLiNCCCN macrocycle, were prepared from [Li{CH(SiMe(3))SiMe(OMe)(2)}](infinity) and 2 PhCN. They differ in that the substituent at the beta-C atom of each diketiminato ligand is either SiMe(3) (2) or H (3). Each of and has (i) a central Si-O-Si unit, (ii) an Si(Me) fragment N,N'-intramolecularly bridging each beta-diketiminate, and (iii) an Li(thf)(2) moiety N,N'-intermolecularly bridging the two beta-diketiminates (thf = tetrahydrofuran). Treatment of [Li{CH(SiMe(3))(SiMe(2)OMe)}](8) with 2Me(2)C(CN)(2) yielded the amorphous [Li{Si(Me)(2)((NCR)(2)CH)}](n) [R = C(Me)(2)CN] (4). From [Li{N(SiMe(3))C(Bu(t))C(H)SiMe(3)}](2) (A) and 1,3- or 1,4-C(6)H(4)(CN)(2), with no apparent synergy between the two CN groups, the product was the appropriate (mu-C(6)H(4))-bis(lithium beta-diketiminate) 6 or 7. Reaction of [Li{N(SiMe(3))C(Ph)=C(H)SiMe(3)}(tmeda)] and 1,3-C(6)H(4)(CN)(2) afforded 1,3-C(6)H(4)(X)X' (X =CC(Ph)N(SiMe3)Li(tmeda)N(SiMe3)CH; X' = CN(SiMe3)Li(tmeda)NC(Ph)=C(H)SiMe3)(9). Interaction of A and 2[1,2-C(6)H(4)(CN)(2)] gave the bis(lithio-isoindoline) derivative [C6H4C(=NH)N{Li(OEt2)}C=C(SiMe3)C(Bu(t))=N(SiMe3)]2 (5). The X-ray structures of 2, 3, 5 and 9 are presented, and reaction pathways for each reaction are suggested.     

Reactions of palladium germylene complexes: formation of sulfide bridges

Reactivity of three novel Pd germylene species is presented. (Et(3)P)(2)PdGe[N(SiMe(3))(2)](2) (1) and (dppe)PdGe[N(SiMe(3))(2)](2) (6) react with COS to give the sulfide bridged species (Et3P)2Pd(mu S)Ge[N(SiMe3)2]2 (2) and (dppe)Pd(mu S)Ge-[N(SiMe3)2]2 (7) (dppe = (diphenylphosphino)ethane). (Ph(3)P)(2)PdGe[N(SiMe(3))(2)](2) (4) reacts with COS to give the disulfide bridged complex (Ph(3)P)(2)Pd(muS)(2)Ge[N(SiMe(3))(2)](2) (5) resulting in Pd-Ge bond cleavage. This phosphine dependent reactivity is explored. Crystal structures of 2, 5, 7, and the dimeric form of complex 2, (8), are reported. In the presence of excess germylene, complexes 2 and 5 are shown to partially regenerate their parent palladium germylene complexes, 1 and 4, respectively, via photolysis or heating.     

Density functional study of the roles of chemical composition of di-transition-metal-substituted gamma-Keggin polyoxometalate anions

The roles of chemical composition (X, M and M(FW)) of di-transition-metal-substituted gamma-Keggin polytungstates and polymolybdates, [(X(n)(+)O(4))M(2)(OH)(2)(M(FW))(10)O(32)]((8-n)-), on the geometry, electronic structure, and magnetic properties of these species have been investigated at the density functional level. It was shown that the change of the heteroatom X via Al(III)-Si(IV)-P(V)-S(VI) slightly stabilizes the broken-symmetry (BS) state over the high-spin (HS) state, increases the antiferromagnetic coupling constant, J, of these species, and lowers the energies of their highest-occupied molecular orbitals (HOMOs) and lowest-unoccupied molecular orbitals (LUMOs). The change of the redox-active center M from Mn to Fe slightly increases the M-(XO(4)) interaction, J-coupling constant, and energy gap between the HS and BS states. Meanwhile, the LUMOs are stabilized, indicating the stronger oxidant character of [(X(n)(+)O(4))M(2)(OH)(2)W(10)O(32)]((8-n)-) for M = Fe than Mn. It was shown that the change of addenda atom M(FW) from W to Mo makes (a) the geometry of Keggin "cage" slightly smaller, (b) the interaction of redox-active centers (Fe) with the central XO(4)-unit slightly stronger, and (c) the J-coupling constant, as well as the energy gap DeltaE(BS-HS), slightly larger.     

RE(C7H5O3)2(C9H6NO)配合物抗真菌作用的热动力学研究

应用微量热法研究了配合物RE（CTH5O3）2（C9H6NO）（RE代表La，Sm和Nd）对真菌的抗菌作用。在TAM Air热导式等温微量量热仪上，分别测定了桔青霉菌和黑曲霉菌在不同浓度不同稀土配合物及空白条件下生长代谢热谱曲线，并计算得到了真菌在不同条件下的生长代谢速率常数k和传代时间G等热动力学参数。实验表明：3种稀土水杨酸8-羟基喹啉三元配合物对桔青霉菌和黑曲霉菌均有抑制作用，其抑制效果依次为：Sm（Hsal）2（hq）〉La（Hsal）2（hq）〉Nd（Hsal）2（hq）。     

The role of Zn-OR and Zn-OH nucleophiles and the influence of para-substituents in the reactions of binuclear phosphatase mimetics

Analogues of the ligand 2,2'-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)diethanol (CH(3)H(3)L1) are described. Complexation of these analogues, 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (CH(3)HL2), 4-bromo-2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (BrHL2), 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (NO(2)HL2) and 4-methyl-2,6-bis(((2-phenoxyethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (CH(3)HL3) with zinc(II) acetate afforded [Zn(2)(CH(3)L2)(CH(3)COO)(2)](PF(6)), [Zn(2)(NO(2)L2)(CH(3)COO)(2)](PF(6)), [Zn(2)(BrL2)(CH(3)COO)(2)](PF(6)) and [Zn(2)(CH(3)L3)(CH(3)COO)(2)](PF(6)), in addition to [Zn(4)(CH(3)L2)(2)(NO(2)C(6)H(5)OPO(3))(2)(H(2)O)(2)](PF(6))(2) and [Zn(4)(BrL2)(2)(PO(3)F)(2)(H(2)O)(2)](PF(6))(2). The complexes were characterized using (1)H and (13)C NMR spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. The complexes contain either a coordinated methyl- (L2 ligands) or phenyl- (L3 ligand) ether, replacing the potentially nucleophilic coordinated alcohol in the previously reported complex [Zn(2)(CH(3)HL1)(CH(3)COO)(H(2)O)](PF(6)). Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed them to be competent catalysts with, for example, [Zn(2)(CH(3)L2)](+), k(cat) = 5.70 ± 0.04 × 10(-3) s(-1) (K(m) = 20.8 ± 5.0 mM) and [Zn(2)(CH(3)L3)](+), k(cat) = 3.60 ± 0.04 × 10(-3) s(-1) (K(m) = 18.9 ± 3.5 mM). Catalytically relevant pK(a)s of 6.7 and 7.7 were observed for the zinc(II) complexes of CH(3)L2(-) and CH(3)L3(-), respectively. Electron donating para-substituents enhance the rate of hydrolysis of BDNPP such that k(cat)p-CH(3) > p-Br > p-NO(2). Use of a solvent mixture containing H(2)O(18)/H(2)O(16) in the reaction with BDNPP showed that for [Zn(2)(CH(3)L2)(CH(3)COO)(2)](PF(6)) and [Zn(2)(NO(2)L2)(CH(3)COO)(2)](PF(6)), as well as [Zn(2)(CH(3)HL1)(CH(3)COO)(H(2)O)](PF(6)), the (18)O label was incorporated in the product of the hydrolysis suggesting that the nucleophile involved in the hydrolysis reaction was a Zn-OH moiety. The results are discussed with respect to the potential nucleophilic species (coordinated deprotonated alcohol versus coordinated hydroxide).     

Structures of dimeric hydrolysis products of thorium

Three unique thorium dimeric compounds have been crystallized from either direct hydrolysis of Th4+(aq)/HCl or titration of Th(OH)4(am) with Th(NO3)4(aq) and their structures determined using single-crystal X-ray diffraction. The compound [Th2(micro2-OH)2(NO3)6(H2O)6]H2O (1) is identical to that identified previously by Johansson. Two additional unreported compounds have been identified, [Th2(micro2-OH)2(NO3)4(H2O)8](NO3)2 (2) and [Th2(micro2-OH)2Cl2(H2O)12]Cl4.2H2O (3). 1 crystallizes in the monoclinic space group P21/c, with a = 6.792(2) A, b = 11.710(4) A, c = 13.778(5) A, and beta = 102.714(5) degrees and 2 crystallizes in the monoclinic space group P21/n, with a = 6.926(5) A, b = 7.207(1) A, c = 21.502(1) A, and beta = 96.380(1) degrees . The chloride-containing dimer, 3, crystallizes in triclinic P, with a = 8.080(2) A, b = 8.880(2) A, c = 9.013(2) A, alpha = 97.41(3) degrees , beta = 91.00(3), and gamma = 116.54(3) degrees . We also present high-energy X-ray scattering data demonstrating the presence of the hydroxo-bridged moiety in solution and discuss our findings in the context of known solid-state structures. The three structures demonstrate 11-, 10-, and 9-coordinate thorium, respectively, and coupled with the scattering experiments provide additional structural and chemical insight into tetravalent actinide hydrolysis.     

Pseudo Jahn-Teller origin of nonplanarity and rectangular-ring structure of tetrafluorocyclobutadiene

It is shown that the pseudo Jahn-Teller effect (PJTE) in combination with ab initio calculations explains the origin of instability of the planar configuration of tetrafluorocyclobutadiene, C(4)F(4), with respect to a puckered structure and square-to-rectangle distortion of the carbon ring, and rationalizes its difference from the planar-rectangular geometry of C(4)H(4) and nonplanar (puckered) structure of Si(4)H(4). The two types of instability and distortion of the high-symmetry D(4h) configuration in these systems emerge from the PJT coupling of the ground B(2g) state with the excited A(1g) term producing instability along the b(2g) coordinate (elongation of the carbon or silicon square ring), and with the excited E(g) term resulting in e(g) (puckering) distortion. A rhombic distortion b(1g) of the ring is also possible due to the coupling between excited A(1g) and B(1g) terms. For C(4)F(4), ab initio calculations of the energy profiles allowed us to evaluate the PJTE constants and to show that the two instabilities, square-to-tetragonal b(2g) and puckering e(g) coexist, thus explaining the origin of the observed geometry of this system in the ground state. The preferred cis-trans (e(g) type) puckering in C(4)F(4) versus trans-trans puckering (b(2u) distortion) in Si(4)H(4) follows from the differences in the energy gaps to their excited electronic E(g) and A(1u) terms causing different PJTE in these two cases.     

Synthesis and characterization of the novel monoamide derivatives of Gd-TTDA

For this study, the N'-monoamide derivatives of TTDA (3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid), N'-methylamide (TTDA-MA), N'-benzylamide (TTDA-BA), and N'-2-methoxybenzylamide (TTDA-MOBA), were synthesized. Their protonation constants and stability constants (log K(ML)'s) formed with Ca(2+), Zn(2+), Cu(2+), and Gd(3+) were determined by potentiometric titration in 0.10 M Me(4)NCl at 25.0 +/- 0.1 degrees C. The relaxivity values of [Gd(TTDA-MA)](-), [Gd(TTDA-BA)](-), and [Gd(TTDA-MOBA)](-) remained constant with respect to pH changes over the range 4.5-12.0. The (17)O NMR chemical shift of H(2)O induced by [Dy(TTDA-MA)(H(2)O)](-) at pH 6.80 showed 0.9 inner-sphere water molecules. Water proton relaxivity values for [Gd(TTDA-MA)(H(2)O)](-), [Gd(TTDA-BA)(H(2)O)](-), and [Gd(TTDA-MOBA)(H(2)O)](-) at 37.0 +/- 0.1 degrees C and 20 MHz are 3.89, 4.21, and 4.25, respectively. The water-exchange lifetime (tau(M)) and rotational correlation time (tau(R)) of [Gd(TTDA-MA)(H(2)O)](-), [Gd(TTDA-BA)(H(2)O)](-), and [Gd(TTDA-MOBA)(H(2)O)](-) are obtained from reduced the (17)O relaxation rate and chemical shifts of H(2)(17)O. The (2)H NMR longitudinal relaxation rates of the deuterated diamagnetic lanthanum complexes for the rotational correlation time were also thoroughly investigated. The water-exchange rates (K(298)(ex) for [Gd(TTDA-MA)(H(2)O)](-), [Gd(TTDA-BA)(H(2)O)](-), and [Gd(TTDA-MOBA)(H(2)O)](-) are lower than that of [Gd(TTDA)(H(2)O)](2)(-) but significantly higher than those of [Gd(DTPA)(H(2)O)](2)(-) and [Gd(DTPA-BMA)(H(2)O)]. The rotational correlation times for [Gd(TTDA-BA)(H(2)O)](-) and [Gd(TTDA-MOBA)(H(2)O)](-) are significantly longer than those of [Gd(TTDA)(H(2)O)](2)(-) and [Gd(DTPA)(H(2)O)](2)(-) complexes. The marked increase of the relaxivity of [Gd(TTDA-BA)(H(2)O)](-) and [Gd(TTDA-MOBA)(H(2)O)](-) results mainly from their longer rotational correlation time. The noncovalent interaction between human serum albumin (HSA) and [Gd(TTDA-BA)(H(2)O)](-) and [Gd(TTDA-MOBA)(H(2)O)](-) complexes containing a hydrophobic substituent was investigated by measuring the water proton relaxation rate of the aqueous solutions. The binding association constant (K(A)) values are 1.0 +/- 0.2 x 10(3) and 1.3 +/- 0.2 x 10(3) M(-1) for [Gd(TTDA-BA)(H(2)O)](-) and [Gd(TTDA-MOBA)(H(2)O)](-), which indicates a stronger interaction of [Gd(TTDA-BA)(H(2)O)](-) and [Gd(TTDA-MOBA)(H(2)O)](-) with HSA.