Comparative study of the hydrogen-bonded complexes of phenol and o-cyanophenol with CO Ab initio and DFT approachs

The structures, stability and vibrational spectra of the hydrogen-bonded complexes of carbon monoxide (CO) with phenol and o-cyanophenol (syn and anti) have been studied using ab initio and DFT calculations. Full geometry optimization has been performed for the studied complexes by DFT (BLYP/6-311++G(d,p)) calculations. The calculations show that the hydrogen-bond formation of carbon monoxide (CO) with phenol and o-cyanophenol (syn and anti) leads to the following stable structures: C6H5OH...CO (1A); C6H5OH...OC (1B); (syn) o-CNC6H4OH...CO (2A-syn); (syn) o-CNC6H4OH...OC (2B-syn); (anti) o-CNC6H4 OH...CO (2A-anti) and (anti) o-CNC6H4OH...OC (2B-anti). Having in mind the corrected values of the dissociation energy, the studied hydrogen-bonded complexes can be ordered according their stability as follows: 2A-anti>2A-syn>1A>2B-anti>1B>2B-syn. The predicted red-shifts for the nuOH vibration with the B3LYP/6-311++G(d,p) calculations for the structures 1A (-46 cm-1), 2A-syn (-60 cm-1) and 2A-anti (-73 cm-1) are in very good agreement with the experimentally observed. The magnitudes of the wavenumber shifts are indicative of relatively weak OH...C hydrogen-bonded interactions. The calculations predict an increase of the IR intensity of the nuOH vibration in the complexes 1A, 2A-anti and 2A-syn up to five times.     

Infrared spectroscopy and structure of photochemically protonated biomolecules in the gas phase: a noradrenaline analogue, lysine and alanyl alanine

A novel photochemical technique combined with mass spectrometry and resonant infrared multiphoton dissociation spectroscopy (R-IRMPD) has been used to record infrared vibrational spectra of the free protonated noradrenaline analogue, 2-amino-1-phenylethanol (APE-H(+)), the amino acid, lysine (Lys-H(+)), and the dipeptide, alanyl alanine (Ala-Ala-H(+)) in the gas phase. Coupling their spectra, obtained in the OH, NH and CH stretch regions, with ab initio calculations has allowed assignment of their preferred protonation sites and conformations. This simple technique will have wide applicability in future investigations of protonated biomolecular structure and conformation.     

Fluorescence-dip IR spectra of jet-cooled benzoic acid dimer in its ground and first excited singlet states

The IR spectra of three isotopomers of the benzoic acid dimer have been recorded under jet-cooled conditions using the double resonance method of fluorescence-dip IR spectroscopy. In so doing, the spectra are assuredly due exclusively to dimers in the ground-state zero-point level at a rotational temperature of 3-5 K. Even under these conditions, the three isotopomers have remarkably broad spectra, extending from 2600 to almost 3150 cm-1. The spectra show extensive substructure consisting of some 15-20 transitions where only a single OH stretch fundamental should appear in the harmonic limit. The comparison of the undeuterated d0-d0 dimer with the ring-deuterated d5-d5 dimer tests the effect of mixing with the C-H stretches and overtones of the C-H bends. The mixed OH/OD ring-deuterated d6-d5 dimer shifts the frequency and changes the form of the OH stretch normal mode. The analogous OH stretch IR spectrum of the d0-d0 dimer out of the S1 excited-state zero-point level has also been recorded. In this case, much of the closely-spaced substructure is not apparent. What remains is a set of three bands separated from one another by about 180 cm-1. Preliminary results of model calculations of the anharmonic coupling, responsible for the broadening and substructure, are presented. These calculations indicate that it is OH stretch-OH bend coupling, rather than coupling with the intermolecular stretch, that is responsible for much of the observed structure and breadth.     

Experimental and theoretical studies of the products of laser-ablated thorium atom reactions with H2O in excess argon

Reactions of laser-ablated Th atoms with H2O during condensation in excess argon have formed a variety of intriguing new Th, H, O species. Infrared absorptions at 1406.0 and 842.6 cm-1 are assigned to the H-Th and Th=O stretching vibrations of HThO. Absorptions at 1397.2, 1352.4, and 822.8 cm-1 are assigned to symmetric H-Th-H, antisymmetric H-Th-H, and Th=O stretching vibrations of the major primary reaction product H2ThO. Thorium monoxide (ThO) produced in the reaction inserts into H2O to form HThO(OH), which absorbs at 1341.0, 804.0, and 542.6 cm-1. Both HThO(OH) and ThO2 add another H2O molecule to give HTh(OH)3 and OTh(OH)2, respectively. Weaker thorium hydride (ThH1(-4)) absorptions were also observed. Relativistic DFT and ab initio calculations were performed on all proposed molecules and other possible isomers. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides support for these first identifications of Th, H, O molecular species.     

Synthesis, structure, and magnetic properties of the low-symmetry tetranuclear cubane-like nickel complex [Ni4(pypentO)(pym)(mu 3-OH)2(mu- Oac)2(NCS)2(OH2)

The tetranuclear [Ni4(pypentO)(pym)(mu 3-OH)2(mu-Oac)2(NCS)2(OH2)] cubane-like complex has been prepared, and its structure and magnetic properties have been studied (pypentO and pym are the deprotonated forms of 1,5-bis[(2-pyridylmethyl)amino]pentane-3-ol and 2-pyridylmethanol, respectively). The X-ray diffraction analysis of this novel nickel complex (C61H74N14O25.5S4Ni8, monoclinic, P2(1), a = 13.9375(14) A, b = 20.6604(18) A, c = 16.6684(19) A, beta = 110.619(12) degrees, Z = 2) showed a Ni4O4 cubane arrangement of four nickel atoms, four mu 3-O bridging ligands (one pypentO, one pym, and two OH-), two syn-syn bridging acetates, and three terminal monodentate ligands (two NCS- and one OH2). In this low-symmetry elongated cubane, the four Ni-Ni long distances (3.18 A) correspond to the faces of the cube including two mu 3-OR bridges, and the two Ni-Ni short distances (2.94 A) correspond to the faces including two mu 3-OR and one acetate bridges. The temperature dependence of the magnetic susceptibility was fitted with J1 = -3.09 cm-1, J2 = 15.0 cm-1, J3 = 6.72 cm-1, and g = 2.27. The differences in sign among the J1, J2, and J3 superexchange interactions is in good agreement with the different types of faces present in this Ni4O4 cubane core. The two faces of the cube, including two mu 3-OR bridges associated with one acetate bridge, exhibit ferromagnetic interactions, while the four faces which include only mu 3-OR bridges exhibit antiferromagnetic interactions. The very small zero field splitting may be attributed to the fact that the ground state is diamagnetic. The nature of the ground state is confirmed by the good simulation of the magnetization curves at 2 and 5 K (diagonalization of the full matrix taking into account all energy levels obtained with the parameter set resulting from the fit of the susceptibility curve). The large differences in J values resulting from small differences in Ni-O-Ni angles in this Ni4O4 core of very low symmetry reflect a quite strong magnetostructural correlation.     

Self-assembled cationic heterochiral honeycomb-layered metal complexes with the in situ generated pyrimidine-2-carboxylato bisdidentate ligand. Hydrothermal synthesis, crystal structures, magnetic properties, and theoretical study of [M2(micro-pymca)3]OH.H2O (M = FeII, CoII)

The hydrothermal reaction of 2-cyanopyrimidine and either CoCl2.6H2O or FeCl2.4H2O affords 2D isostructural coordination polymers [M2(micro-pymca)3]OH.H2O ((M = CoII (1) and FeII (2) pymca = pyrimidine-2-carboxylato). The bisdidentate ligand (pymca) that can be considered an intermediate between bipyrimidine and oxalato is generated in situ from the hydrolysis of 2-cyanopyrimidine. The structure of 1 and 2 consists of heterochiral (6,3) honeycomb layers, crystal water molecules, and OH- anions, the latter playing a template and balancing charge role in the structure. Both compounds exhibit antiferromagnetic interactions between metal ions through the pyrimidine-2-carboxylate bridging ligand. Compound 1 is a spin-canted antiferromagnet leading to weak ferromagnetism at Tc < 10 K with a coercitive field of 580 Oe, whereas compound 2 is an antiferromagnet with TN = 21 K. Fit of the variable-temperature magnetic susceptibility data of 2 to the empirical equation for a regular honeycomb with S = 1 derived from Monte Carlo simulations leads to the following parameters: J = -4.57(2) cm-1 and g = 2.300(4). Density functional calculations have been used to explain the magnetic coupling in 2.     

Theoretical studies of the hydroxide-catalyzed P-O cleavage reactions of neutral phosphate triesters and diesters in aqueous solution: examination of the changes induced by H/Me substitution

DFT calculations and dielectric continuum methods have been employed to map out the lowest activation free-energy profiles for the alkaline hydrolysis of representative phosphate triesters and diesters, including trimethyl phosphate (TMP), dimethyl 4-nitrophenyl phosphate (DMNPP), dimethyl hydrogen phosphate (DMHP), and the dimethyl phosphate anion (DMP-). The reliability of the calculations is supported by the excellent agreement observed between the calculated and the experimentally determined activation enthalpies for phosphate triesters with poor (TMP) and good (DMNPP) leaving groups. The results obtained for the OH- + DMHP and OH- + DMP- reactions are also consistent with all the available experimental information concerning the hydrolysis reaction of dimethyl phosphate anion at pH > 5. By performing geometry optimizations in the dielectric field (epsilon = 78.39), we found that OH- can attack the phosphorus atom of DMHP without capturing its proton only if the O-H bond of DMHP is oriented opposite the attacking OH- group. In these conditions, the rate for OH- attack on DMHP was found to be approximately 10(3)-fold faster than that for OH- attack on TMP. The calculated rate acceleration induced by the phosphoryl proton corresponds to the maximum rate effect expected from kinetic studies. Overall, our calculations performed on the dimethyl phosphate ester predict that, contrary to what is generally observed for RNA and aryl phosphodiesters, the water-promoted P-O cleavage reaction of DNA should dominate the base-catalyzed reaction at pH 7. These results are suggestive that nucleases may be less proficient as catalysts than has recently been suspected.     

Synthesis of uniform anatase TiO2 nanoparticles by the gel-sol method 2. Adsorption of OH- Ions to Ti(OH)4 gel and TiO2 particles

The pH value in the gel-sol system for the preparation of uniform anatase TiO2 nanoparticles, as a decisive factor for controlling the size and shape of the final product, was found to be significantly changed during the formation process of the anatase TiO2 particles from a condensed Ti(OH)4 gel. The dramatic evolution of pH with the progress of the synthetic process has clearly been explained in terms of the adsorption and desorption of a hydroxide ion (OH-) ora proton (H+) on the solids transforming with time. The adsorption and desorption of OH- or H+ were enhanced by the presence of an inert electrolyte such as NaClO4, as explained by its shielding effect on the electrical interactions between the electrically charged precipitates and free OH- and H+ ions. The electrolyte also hampered the phase transformation of Ti(OH)4 precipitate to anatase TiO2. This effect of electrolytes was explained in terms of the inhibited nucleation of anatase TiO2 by enhanced adsorption of OH- ions toTiO2 embryos. The points of zero charge (PZC) of the amorphous Ti(OH)4 precipitate and the anatase TiO2 particles at 25 degrees C were obtained from the change in pH associated with the adsorption and desorption of OH- or H+, i.e., 4.6 for Ti(OH)4 precipitate and 6.0 for anatase TiO2 in the presence of 0.1 mol dm(-3) NaClO4. The PZCof the Ti(OH)4 precipitate measured at 25 degrees C after additional aging at 100 degrees C for 30 min was shifted to 4.1, owing to the promoted adsorption of OH-.     

Dioxygen reactivity of a copper(I) complex with a N3S thioether chelate; peroxo-dicopper(II) formation including sulfur-ligation

Employing a tetradentate N3S(thioether) ligand, LN3S, dioxygen reactivity of a copper(I) complex, [(LN3S)CuI]+ (1) was examined. In CH2Cl2, acetone (at -80 degrees C), or 2-methyltetrahydrofuran (at -128 degrees C), 1 reacts with O2 producing the end-on bound peroxodicopper(II) complex [{(LN3S)CuII}2(mu-1,2-O2(2-))]2+ (2), the first reported copper-dioxygen adduct with sulfur (thioether) ligation. Its absorption spectrum contains an additional low-energy feature (but not a Cu-S CT band) compared to the previously well-characterized N4 ligand complex, [{(TMPA)CuII}2(mu-1,2-O2(2-))]2+ (3) (TMPA = tris(2-pyridylmethyl)amine). Resonance Raman spectroscopy confirms the peroxo formulation {nu(O-O) = 817 cm-1 (16-18O2 Delta = 46 cm-1) and nu(Cu-O) = 545 cm-1 (16-18O2 Delta = 26 cm-1), in close analogy to that known for 3 {nu(O-O) = 827 cm-1 and nu(Cu-O) = 561 cm-1}. Direct evidence for thioether ligation comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 A}.     

Spectroscopic and density functional theory studies of the blue-copper site in M121SeM and C112SeC azurin: Cu-Se versus Cu-S bonding

S K-edge X-ray absorption, UV-vis absorption, magnetic circular dichroism (MCD), and resonance Raman spectroscopies are used to investigate the electronic structure differences among WT, M121SeM, and C112SeC Pseudomonas aeruginosa (P.a) azurin. A comparison of S K-edge XAS of WT and M121SeM azurin and a CuII-thioether model complex shows that the 38% S character in the ground state wave function of the blue-copper (BC) sites solely reflects the Cu-SCys bond. Resonance Raman (rR) data on WT and C112SeC azurin give direct evidence for the kinematic coupling between the Cu-SCys stretch and the cysteine deformation modes in WT azurin, which leads to multiple features in the rR spectrum of the BC site. The UV-vis absorption and MCD data on WT, M121SeM, and C112SeC give very similar C0/D0 ratios, indicating that the C-term MCD intensity mechanism involves Cu-centered spin-orbit coupling (SOC). The spectroscopic data combined with density functional theory (DFT) calculations indicate that SCys and SeCys have similar covalent interactions with Cu at their respective bond lengths of 2.1 and 2.3 A. This reflects the similar electronegativites of S and Se in the thiolate/selenolate ligand fragment and explains the strong spectroscopic similarities between WT and C112SeC azurin.     

Synthesis,Characterization, and Reaction Studies of Pd(II) Tripeptide Complexes

The aqueous synthesis of Pd(II) complexes with alkylated tripeptides led to the hydrolysis of the peptides at low pH values and mixtures of complexed peptides were formed. A non-aqueous synthetic route allowed the formation and isolation of single products and their characterization. Pd(II) complexes with α-Asp(OR)AlaGly(OR), β-Asp(OR)AlaGly(OR), and TrpAlaGly(OR) (R = H or alkyl) as tri and tetradentate chelates were characterized. The tridentate coordination mode was accompanied by a fourth monodentate ligand that was shown to participate in both ligand exchange reactions and a direct removal to form the tetradentate coordination mode. The tetradentate coordination revealed a rare a hemi labile carbonyl goup coordination mode to Pd(II). Reactivity with small molecules such as ethylene, acids, formate, and episulfide was investigated. Under acidic conditions and in the presence of ethylene; acetaldehyde was formed. The Pd(II) is a soft Lewis acid and thiophilic and the complexes abstract sulfur from episulfide at apparent modest catalytic rates. The complexes adopt a square planar geometry according to a spectroscopic analysis and DFT calculations that were employed to evaluate the most energetically favorable coordination geometry and compared with the observed infrared and NMR data.     

Electronic structure and reactivity of low-spin Fe(III)-hydroperoxo complexes: comparison to activated bleomycin

The spectroscopic properties, electronic structure, and reactivity of the low-spin Fe(III)-hydroperoxo complex [Fe(N4Py)(OOH)](2+) (1, N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) are investigated in comparison to those of activated bleomycin (ABLM). Complex 1 is characterized by Raman features at 632 (Fe-O stretch) and 790 cm(-1) (O-O stretch), corresponding to a strong Fe-O bond (force constant 3.62 mdyn/A) and a weak O-O bond (3.05 mdyn/A). The UV-vis spectrum of 1 shows a broad absorption band around 550 nm that is assigned to a charge-transfer transition from the hydroperoxo to a t(2g) d orbital of Fe(III) using resonance Raman and MCD spectroscopies and density functional (DFT) calculations. Compared to low-spin [Fe(TPA)(OH(x))(OO(t)Bu)](x+)(TPA = tris(2-pyridylmethyl)amine, x = 1 or 2), an overall similar Fe-OOR bonding results for low-spin Fe(III)-alkylperoxo and -hydroperoxo species. Correspondingly, both systems show similar reactivities and undergo homolytic cleavage of the O-O bond. From the DFT calculations, this reaction is more endothermic for 1 due to the reduced stabilization of the .OH radical compared to .O(t)Bu and the absence of the hydroxo ligand that helps to stabilize the resulting Fe(IV)=O species. In contrast, ABLM has a somewhat different electronic structure where no pi donor bond between the hydroperoxo ligand and iron(III) is present [Neese, F.; Zaleski, J. M.; Loeb-Zaleski, K.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122, 11703]. Possible reaction pathways for ABLM are discussed in relation to known experimental results.     

Comprehensive analysis of the hydrogen bond network morphology and OH stretching vibrations in protonated methanol-water mixed clusters, H(+)(MeOH)1(H2O)n (n = 1-8)

Density functional theory (DFT) calculations of protonated methanol-water mixed clusters, H (+)(MeOH) 1(H 2O) n ( n = 1-8), were extensively carried out to analyze the hydrogen bond structures of the clusters. Various structural isomers were energy optimized, and their relative energies with zero point energy corrections and temperature dependence of the free energies were examined. Coexistence of different morphological isomers was suggested. Infrared spectra were simulated on the basis of the optimized structures. The infrared spectra were also experimentally measured for n = 3-9 in the OH stretching vibrational region. The observed broad bands in the hydrogen-bonded OH stretch region were assigned in comparison with the simulations. From the DFT calculations, the preferential proton location was also investigated. Clear correlations between the excess proton location and the cluster morphology were found.     

Reactions of mu3-alkenyl triruthenium carbonyl clusters with alkynes: synthesis of trinuclear mu-//-alkyne, mu-vinylidene, and mu-dienoyl derivatives

The reactions of doubly face-capped triruthenium cluster complexes of the type [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-CO)(2)(CO)(6)] (HNNMe(2) = 1,1-dimethylhydrazide; R(2)CCHR(1) = alkenyl ligand) with terminal and internal alkynes have been studied in refluxing toluene. The following derivatives have been isolated from these reactions: [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-kappa(2)-//-HCCH)(CO)(7)] (R(1) = R(2) = H, 5; R(1) = Ph, R(2) = H, 6; R(1) = CH(2)OMe, R(2) = H, 7 a; R(1) = H, R(2) = CH(2)OMe, 7 b) from acetylene, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCPh)(CO)(7)] (11) from diphenylacetylene, and three isomers of [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCH)(CO)(7)] (14, 15 a, and 15 b) from phenylacetylene. These products result from substitution of a CO ligand by the alkyne and contain an Ru--Ru edge bridged by the alkyne ligand in a parallel manner. DFT calculations on selected isomeric products have helped to establish that the type of Ru--Ru edge bridged by the alkyne depends more on kinetic factors related to the size of the alkyne substituents than on the thermodynamic stability of the final products. The preparation of triruthenium cluster complexes with mu-//-alkyne ligands is unprecedented and seems to relate to the fact that the starting trinuclear complexes have their two triangular faces protected by capping ligands. The clusters bearing mu-//-acetylene (5-7) are thermodynamically unstable with respect to their transformation into edge-bridging vinylidene derivatives, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCHR)(mu-kappa(1)-CCH(2))(CO)(7)] (R = H, 8; Ph, 9; CH(2)OMe, 10). DFT calculations have shown that complex 8 is 11.2 kcal mol(-1) more stable than its precursor 5. The thermolysis of compound 11 leads to [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu-kappa(4)-H(2)CCHCPhCPhCO)(mu-CO)(2)(CO)(5)] (12), which contains a novel edge-bridging dienoyl ligand that arises from an unusual coupling of diphenylacetylene, carbon monoxide, and the ethenyl ligand of complex 11. A chloro-bridged dimer of trinuclear clusters, [Ru(6)(mu-Cl)(2)(mu(3)-kappa(2)-HNNMe(2))(2)(mu(3)-kappa(2)-HCCH(2))(2)(mu-kappa(2)-PhCCHPh)(2)(mu-CO)(2)(CO)(10)] (13), has been prepared by treating compound 11 with hydrogen chloride. Therefore, edge-bridging parallel alkynes are susceptible to protonation to give edge-bridging alkenyl ligands. Compound 13 is the first complex to contain two alkenyl ligands on a trinuclear cluster, one face-capping and the other edge-bridging.     

Syntheses, structures, and properties of copper(II) complexes of bis(2-pyridylmethyl) derivatives of o-, m-, and p-phenylenediamine and aniline

Copper(II) complexes of the ligand 1,n-bis[bis(2-pyridylmethyl)amino]benzene with n = 2-4 (1,n-tpbd) and its mononuclear derivative bis(2-pyridylmethyl)aniline (phbpa) were synthesized and structurally characterized. Magnetic measurements and DFT calculations were performed on [CuCl2(phbpa)], [Cu2Cl4(1,3-tpbd)], [(Cu2Cl2(ClO4)(1,3-tpbd))Cl(Cu2Cl2(OH2)(1,3-tpbd))](ClO4)2, and [Cu2(OH2)2(S2O6)(1,3-tpbd)]S2O6, and the exchange-polarization mechanism was successfully demonstrated.     

Synthesis, characterization, and solution properties of a novel cross-bridged cyclam manganese(IV) complex having two terminal hydroxo ligands

A novel monomeric tetravalent manganese complex with the cross-bridged cyclam ligand 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (Me2EBC), [Mn(IV)(Me2EBC)(OH)2](PF6)2, was synthesized by oxidation of Mn(II)(Me2EBC)Cl2 with H2O2 in the presence of NH4PF6)in aqueous solution. The X-ray crystal structure determination of this manganese(IV) compound revealed that it contains two rare terminal hydroxo ligands. EPR studies in dry acetonitrile at 77 K show two broad resonances at g = 1.96 and 3.41, indicating that the manganese(IV) exists as a high-spin d3 species. Resonance Raman (rR) spectra of this manganese(IV) species reveal that the dihydroxy moiety, Mn(IV)(OH)2, is also the dominant species in aqueous solution (pH < 7). pH titration provides two pK(a) values, 6.86(4) and 10.0(1), associated with stepwise removal of the last two oxygen-bound protons from [Mn(IV)(Me2EBC)(OH)2](2+). The cyclic voltammetry of this manganese(IV) complex in dry acetonitrile at 298 K demonstrates two reversible redox processes at +0.756 and -0.696 V (versus SHE) for the Mn4+/Mn3+ and Mn3+/Mn2+ couples, respectively. This manganese(IV) complex is relatively stable in weak acidic aqueous solution but easily degrades in basic solution to manganese(III) derivatives with an 88 +/- 1% yield.     

NO2, OH和OH-对环四甲撑四硝胺初始热解的影响

在密度泛函理论的(DFT)B3LYP/6-31g(d)水平上, 优化得到了环四甲撑四硝胺(β-HMX)及其与高氯酸铵(AP)裂解产物NO2、OH及OH-分别形成复合物的各种稳定构型, 计算了β-HMX及各复合物中最弱的N—NO2键解离能. 结果发现: β-HMX与NO2、OH结合后构型变化不是很大, 但对称性降低; β-HMX与OH-结合后, HMX构型发生较大变化, 原有的对称性明显遭到破坏. 计算表明: NO2易与HMX骨架环上亚甲基(—CH2—)中的H作用,“置换”出H而引发HMX的热解, 从而改变了HMX的初始分解通道; OH对HMX的N—NO2键解离影响不大, 而OH-与β-HMX结合后其N—NO2键解离能比β-HMX降低近200 kJ·mol-1, 表明OH-对其裂解有明显的促进作用. NO2、OH-的存在可使HMX的分解温度大大降低.     

Reduced and excited states of the intermediates (alpha-diimine)(C5R5)Rh in hydride transfer catalysis schemes: EPR and resonance Raman spectroscopy, and comparative DFT calculations of Co, Rh and Ir analogues

The electronic structures of the highly air-sensitive intermediates (N[caret]N) (C(5)Me(5))Rh, (N[caret]N = 2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpym), 2,2'-bipyrazine (bpz) and 3,3'-bipyridazine (bpdz)) of hydride transfer catalysis schemes were studied through resonance Raman (rR) spectroscopy and through EPR of the reduced forms [(N[caret]N) (C(5)Me(5))Rh](.-). The rR results are compatible with a predominant MLCT character of the lowest excited states [ (N[caret]N) (C(5)Me(5))Rh]*, and the EPR spectra of the reduced states reveal the presence of anion radical ligands, (N[caret]N) (.-), coordinated by unusually electron rich rhodium(i) centres. The experimental results, including the assignments of electronic transitions, are supported by DFT calculations for the model compounds [(N[caret]N)(C(5)H(5))Rh](o)/(.-), (N[caret]N) = bpy or bpym. The calculations confirm a significant but not complete mixing of metal and ligand orbitals in the lowest unoccupied MO which still retains about 3/4 pi* (N[caret]N) character. DFT calculations on (bpy)(C(5)H(5))M and [(bpy)(C(5)H(5))ClM](+), M = Co, Rh, Ir, agree with the experimental results such as the differences between the homologues, especially the different LUMO characters of the precursor cations in the case of Co-->d(M)) and Rh or Ir (-->pi*(bpy)).     

Infrared measurements and calculations on H2O.HO

We have measured the infrared spectrum of H2O.HO in argon matrices at 11.5 +/- 0.5 K. We have also calculated the vibrational frequencies and intensities of the H2O.HO complex. As a result of these measurements and calculations, we have assigned a previously unassigned absorption band at 3442.1 cm-1 to the OH stretch in the radical complexed to the water molecule. This absorption originates from a complex that is situated in a different site within the argon matrix to those absorptions already assigned to this vibration at 3452.2 and 3428.0 cm-1. We observe a decrease in intensity of the OH radical stretching vibration of the H2O.HO complex upon isotopic substitution of D for H that agrees well with our calculations.