Estimation of coordination bond energies of NH3, H2O and Et2NH ligands in the Ni(II) and Cu(II) complexes

Tridentate ligands 2-hydroxyphenylsalicylaldimine (SAPH₂), 2-hydroxyphenyl-2-hydroxy-1-naphtalaldimine (NAPH₂) and Ni(II) complexes with multidentate ligand Bis-N·N′-(salicylidene)-1,3-propanediamine (LH₂) as well as mononuclear complex of Cu(II) were prepared using the same multidentate ligand. Diethylamine (Et₂NH), NH₃ and H₂O monodentate ligands were bound to these complexes coordinatively. The heat absorbed at the temperatures where these ligands thermally dissociated from the complexes were measured using the TG and DSC methods. It is assumed that the states both of the complexes with and without the monodentate ligands are solid and coordination bond energy for the monodentate ligand is calculated. It is seen that these calculated coordination bond energies are comparable with hydrogen bond energies.     

A kinetic study of the reactions of Fe+ with N2O, N2, O2, CO2 and H2O, and the ligand-switching reactions Fe+.X + Y --> Fe+.Y + X (X = N2, O2, CO2; Y = O2, H2O)

A series of reactions involving Fe(+) ions were studied by the pulsed laser ablation of an iron target, with detection of ions by quadrupole mass spectrometry at the downstream end of a fast flow tube. The reactions of Fe(+) with N(2)O, N(2) and O(2) were studied in order to benchmark this new technique. Extending measurements of the rate coefficient for Fe(+) + N(2)O from 773 K to 185 K shows that the reaction exhibits marked non-Arrhenius behaviour, which appears to be explained by excitation of the N(2)O bending vibrational modes. The recombination of Fe(+) with CO(2) and H(2)O in He was then studied over a range of pressure and temperature. The data were fitted by RRKM theory combined with ab initio quantum calculations on Fe(+).CO(2) and Fe(+).H(2)O, yielding the following results (120-400 K and 0-10(3) Torr). For Fe(+) + CO(2): k(rec,0) = 1.0 x 10(-29) (T/300 K)(-2.31) cm(6) molecule(-2) s(-1); k(rec,infinity) = 8.1 x 10(-10) cm(3) molecule(-1) s(-1). For Fe(+) + H(2)O: k(rec,0) = 5.3 x 10(-29) (T/300 K)(-2.02) cm(6) molecule(-2) s(-1); k(rec,infinity) = 2.1 x 10(-9) (T/300 K)(-0.41) cm(3) molecule(-1) s(-1). The uncertainty in these rate coefficients is determined using a Monte Carlo procedure. A series of exothermic ligand-switching reactions were also studied at 294 K: k(Fe(+).N(2) + O(2)) = (3.17 +/- 0.41) x 10(-10), k(Fe(+).CO(2) + O(2)) = (2.16 +/- 0.35) x 10(-10), k(Fe(+).N(2) + H(2)O) = (1.25 +/- 0.14) x 10(-9) and k(Fe(+).O(2) + H(2)O) = (8.79 +/- 1.30) x 10(-10) cm(3) molecule(-1) s(-1), which are all between 36 and 52% of their theoretical upper limits calculated from long-range capture theory. Finally, the role of these reactions in the chemistry of meteor-ablated iron in the upper atmosphere is discussed. The removal rates of Fe(+) by N(2), O(2), CO(2) and H(2)O at 90 km altitude are approximately 0.1, 0.07, 3 x 10(-4) and 1 x 10(-6) s(-1), respectively. The initially formed Fe(+).N(2) and Fe(+).O(2) are converted into the H(2)O complex at approximately 0.05 s(-1). Fe(+).H(2)O should therefore be the most abundant single-ligand Fe(+) complex in the mesosphere below 90 km.     

Zum System H2O2, Fe2+-, Fe3+-Ion

Ohne Zusammenfassung     

Many-body decomposition of the binding energies for OH.(H2O)2 and OH.(H2O)3 complexes

We use ab initio electronic structure methods to calculate the many-body decomposition of the binding energies of the OH.(H2O)n (n=2,3) complexes. We employ MP2 and CCSD(T) levels of theory with aug-cc-pVDZ and aug-cc-pVTZ basis sets and analyze the significance of the nonpairwise interactions between OH radical and the surrounding water molecules. We also evaluate the accuracy of our newly developed potential function, the modified Thole-type model, for predicting the many-body terms in these complexes. Our analysis of the many-body contributions to the OH.(H2O)n binding energies clearly shows that they are just as important in the OH interactions with water as they are for interactions in pure water systems.     

Fundamental excitations of the shared proton in the H3O2- and H5O2+ complexes

We exploit recent advances in argon predissociation spectroscopy to record the spectroscopic signature of the shared proton oscillations in the H3O2- system and compare the resulting spectrum with that of the H5O2+ ion taken under similar conditions. Very intense 1 <-- 0 transitions are observed below 1100 cm(-1) in both cases and are surprisingly sharp, with the 697 cm(-1) transition in H3O2- being among the lowest in energy of any shared proton system measured to date. The assignments of the three fundamental transitions associated with the three-dimensional confinement of the shared proton in H3O2- are carried out with full-dimensional (DMC) calculations to treat this strongly anharmonic vibrational problem.     

A kinetic study of the reactions FeO+ + O, Fe+.N2 + O, Fe+.O2 + O and FeO+ + CO: implications for sporadic E layers in the upper atmosphere

These gas-phase reactions were studied by pulsed laser ablation of an iron target to produce Fe(+) in a fast flow tube, with detection of the ions by quadrupole mass spectrometry. Fe(+).N(2) and Fe(+).O(2) were produced by injecting N(2) and O(2), respectively, into the flow tube. FeO(+) was produced from Fe(+) by addition of N(2)O, or by ligand-switching from Fe(+).N(2) following the addition of atomic O. The following rate coefficients were measured: k(FeO(+) + O --> Fe(+) + O(2), 186-294 K) = (3.2 +/- 1.5) x 10(-11); k(Fe(+).N(2) + O --> FeO(+)+ N(2), 294 K) = (4.6 +/- 2.5) x 10(-10); k(Fe(+).O(2) + O --> FeO(+) + O(2), 294 K) = (6.3 +/- 2.7) x 10(-11); and k(FeO(+) + CO --> Fe(+) + CO(2), 294 K) = (1.59 +/- 0.34) x 10(-10) cm(3) molecule(-1) s(-1), where the quoted uncertainties are a combination of the 1sigma standard errors in the kinetic data and the systematic experimental errors. The surprisingly slow reaction between FeO(+) and O is examined using ab initio quantum calculations of the relevant potential energy surfaces. The importance of this reaction for controlling the lifetime of sporadic E layers is then demonstrated using a model of the upper mesosphere and lower thermosphere.     

Mechanism of phototransfer of hydrogen atom in the model H2CO + H2O system

A system modelling the photochemical abstraction of a hydrogen atom by ketones in alcohols is calculated by the semiempirical INDO and MINDO/3 methods with allowance for the configuration interaction in the singly and doubly excited states. The states participating in the elimination reaction and the electronic rearrangement taking place in the course of the reaction are traced on the basis of an analysis of the wave functions and the electron and spin densities. It is established that the state of the ketone which participates in hydrogen abstraction is a lowest triplet state of the n^* type, which is formed through the avoidance of intersections of several states of different orbital type ^3*, ³n^* and the charge-transfer state.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 476–480, July–August, 1989.     

Toward binary nitrosyls: distinctly bent Fe[bond]N[bond]O linkages in base-stabilized Fe(NO)3+ complexes

Air- and moisture-sensitive Fe(NO)(3)(eta(1)-PF(6)) (1) may be conveniently prepared by treating Fe(NO)(3)Cl with 1 equiv of [Ag][PF(6)] in CH(2)Cl(2) or by reacting [NO][PF(6)] with excess iron filings in MeNO(2). Complex 1 is thermally sensitive both as a solid and in solutions, and is best handled below -20 degrees C. To isolate 1 reproducibly from MeNO(2) solutions it is necessary to remove all traces of propionitrile, which often occurs as an impurity in MeNO(2), because it reacts with Lewis-acidic 1 to form [Fe(NO)(3)(EtCN)][PF(6)] (2). If trace H(2)O is present during the synthesis of 1, some of the PF(6)(-) is converted to PO(2)F(2)(-), which is sufficiently Lewis basic that it captures two Fe(NO)(3)(+) fragments and forms [(ON)(3)Fe(mu-PO(2)F(2))Fe(NO)(3)][PF(6)] (3). Finally, Fe(NO)(3)(eta(1)-BF(4)) (4) can be obtained as a green microcrystalline powder by employing the same synthetic methodologies used to prepare 1. The new complexes 1-4 have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, and 4 and their parent compound, Fe(NO)(3)Cl, have been established by X-ray diffraction methods. The iron centers in the Fe(NO)(3) fragments in all these structures exhibit approximately tetrahedral coordination geometries, and the Fe-N-O linkages are distinctly nonlinear with bond angles in the range of 159 to 169 degrees. DFT calculations on Fe(NO)(3)(eta(1)-BF(4)) (4) confirm that its bent Fe-N-O links have an electronic origin and need not be attributed to other factors, such as packing forces in the crystal. Interestingly, the bending of the NO ligands results in an increase in the energy of the HOMO, relative to the linear case, but at the same time causes a decrease in energy of the HOMO-1 and the HOMO-2 molecular orbitals. This more than compensates for the higher energy of the HOMO, resulting in a lower energy structure.     

·C2H3+O2→HC·O+H2CO 的密度泛函理论研究

应用密度泛函理论研究了@C2H3+O2→HC@O+H2CO的反应机理.在DFT(B3LYP/6-31G*)水平上对反应过程中所有反应物、中间体、过渡态和产物的几何构型进行优化,通过频率振动分析确认中间体和过渡态.计算IRC反应路径的能量,分析了中间体的异构化过程和各主要原子的自旋密度.     

Full dimensional calculations of vibrational energies of H3O+ and D3O+

We report full dimensional calculations of vibrational energies of H3O+ and D3O+ using two implementations of the code MULTIMODE. In one implementation, the reference geometry is the minimum of the potential (the standard choice for MULTIMODE). This implementation is not able to readily describe splittings in the vibrational energies due to motion through the inversion barrier. A second implementation, in which the reference geometry is the inversion saddle point, is able to describe the splittings. These full dimensional calculations are done using the realistic, though not spectroscopically accurate, potential of Ojamae, Singer and Shavitt, and the results are compared with experiment.     

Reflected shock tube studies of high-temperature rate constants for CH3 + O2, H2CO + O2, and OH + O2

The reflected shock tube technique with multipass absorption spectrometric detection of OH-radicals at 308 nm, corresponding to a total path length of approximately 2.8 m, has been used to study the reaction CH3 + O2 CH2O + OH. Experiments were performed between 1303 and 2272 K, using ppm quantities of CH3I (methyl source) and 5-10% O2, diluted with Kr as the bath gas at test pressures less than 1 atm. We have also reanalyzed our earlier ARAS measurements for the atomic channel (CH3 + O2 --> CH3O + O) and have compared both these results with other earlier studies to derive a rate expression of the Arrhenius form. The derived expressions, in units of cm3 molecule(-1) s(-1), are k = 3.11 x 10(-13) exp(-4953 K/T) over the T-range 1237-2430 K, for the OH-channel, and k = 1.253 x 10(-11) exp(-14241 K/T) over the T-range 1250-2430 K, for the O-atom channel. Since CH2O is a major product in both reactions, reliable rates for the reaction CH2O + O2 --> HCO + HO2 could be derived from [OH]t and [O]t experiments over the T-range 1587-2109 K. The combined linear least-squares fit result, k = 1.34 x 10(-8) exp(-26883 K/T) cm3 molecule(-1) s(-1), and a recent VTST calculation clearly overlap within the uncertainties in both studies. Finally, a high sensitivity for the reaction OH + O2 --> HO2 + O was noted at high temperature in the O-atom data set simulations. The values for this obtained by fitting the O-atom data sets at later times (approximately 1.2 ms) again follow the Arrhenius form, k = 2.56 x 10(-10) exp(-24145 K/T) cm3 molecule(-1) s(-1), over the T-range, 1950-2100 K.     

High-level ab initio versus DFT calculations on (H2O2)2 and H2O2–H2O complexes as prototypes of multiple hydrogen bond systems

The performance of B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91 density functionals to describe multiple hydrogen bond systems was studied. For this purpose we have chosen the dimers of hydrogen peroxide and the hydrogen peroxide–water complexes. The geometries and vibrational frequencies obtained with a 6-311+G(d,p) basis set were compared with those obtained at the MP2 level using the same basis set expansion. The corresponding dimerization energies were obtained using a 6-311+G(3df,2p) basis set and compared with those obtained using the G2(MP2) theory. Red shiftings of the OH donor stretching frequencies were predicted by all approaches investigated; however, in all cases, the DFT values were sizably larger than the MP2 ones. Similarly, the blue shifting of the torsion of the hydrogen peroxide subunit was larger when evaluated at the DFT level. All functionals reproduced the G2(MP2) relative stabilities of the different local minima quite well. With the exception of the B-LYP and B3-PW91 approaches, all functionals yielded binding energies which deviated from the G2(MP2) values by less than 0.5 kcal/mol, provided that G2-type basis sets were used and that the corresponding BSSE corrections were included. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1124–1135     

Hydrolysis of [Pt(dien)H2O]2+ and [Pd(dien)H2O]2+ complexes in water

The hydrolysis of the [Pt(dien)H₂O]²⁺ and [Pd(dien)H₂O]²⁺ complexes has been investigated by potentiometry at 298 K, in 0.1 mol dm^–3 aqueous NaClO₄. Least-squares treatment of the data obtained indicates the formation of mononuclear and -hydroxo-bridged dinuclear complexes with stability constants: log ₁₁ = –6.94 for [Pt(dien)OH]⁺, log ₁₁ = –7.16 for [Pd(dien)OH]⁺, and also log ₂₂ = –9.37 for [Pt₂(dien)₂(OH)₂]²⁺ and log ₂₂ = –10.56 for [Pd₂(dien)₂(OH)₂]²⁺. At pH values > 5.5, formation of the dimer becomes significant for the Pt^II complex, and at pH > 6.5 for the Pd^II complex. These results have been analyzed in relation to the antitumor activity of Pt^II complexes.     

The comparative study of CO2 + Hads reaction on platinum electrode in H2O and D2O

The observed isotopic effect in CO₂ + H_ads reaction showed that at 0.05 V the rate determining step is

formation whereas at 0.2 V the reorientation of adsorbed intermediate:

is probably the slowest step of reaction. The oxidation of adsorbed product is slower in D₂SO₄ than H₂SO₄ solution like the surface oxidation of platinum. The rate determining step of COOH_ads oxidation is a reaction with OH_ads.