Cl-O Bond Research Articles

Unusual Mechanisms Can Dominate Reactions at Hyperthermal Energies: An Example from O(3P) + HCl → ClO + H

An unusual mechanism in the reaction, O(3P) + HCl --> ClO + H, dominates at hyperthermal collision energies. This mechanism applies to collision geometries in which the H atom in the HCl molecule is oriented toward the reagent O atom. As the Cl-O bond forms, the H atom experiences a strong repulsive force from both the O and Cl atoms. The ClO product scatters forward with respect to the initial velocity of the O atom, and the H atom scatters backward. This mechanism accounts for more than half the reactive trajectories at energies >110 kcal mol-1, but it does not involve motion near the minimum energy path, which favors an SN2-like reaction mechanism where the H atom is oriented away from the reagent O atom during the collision.

Pulse shaping for optimal control of molecular processes

In this paper, a new method is proposed to design optimized control fields with desired temporal and/or spectral properties. The method is based on penalizing the difference between an optimized field obtained from an iterative scheme and a reference field with desired temporal and/or spectral properties. Compared with the standard optimal control theory, the current method allows a simple, experimentally accessible field be found on the fly; while compared with parameter space searching optimization, the iterative nature of this method allows automatic exploration of the intrinsic mechanism of the population transfer. The method is illustrated by examing the optimal control of vibrational excitation of the Cl-O bond with both temporally and spectrally restricted pulses.

Thiaminium chloride perchlorate

In the title compound, C12H18N4OS2+center dot Cl-center dot ClO4-, the thiaminium cations form `head-to-tail' N-H center dot center dot center dot O hydrogen-bonded dimers about inversion centres. N-H center dot center dot center dot Cl and O-H center dot center dot center dot Cl hydrogen bonds further stabilize the structure, forming a one-dimensional chain running along the diagonal of the ac plane. Both anions are located adjacent to `anion holes' in the thiaminium cation. The perchlorate anions show rotational disorder about a Cl-O bond.

Photodissociation Dynamics of Chlorine Peroxide Adsorbed on Ice

Chlorine peroxide plays an important role in the chlorine-ozone chemistry in the antarctic stratosphere. Adsorption by ice crystals may alter its photochemistry in different ways. We have simulated the photodissociation of a ClOOCl molecule adsorbed on ice by means of a semiclassical representation of the excited state dynamics. Electronic energies and wave functions of ClOOCl are computed by an ad hoc reparametrized semiempirical method, and the interaction with ice is taken into account by a QM/MM strategy. The reaction mechanism is similar to what was previously found for the isolated molecule: sequential or almost simultaneous breaking of both Cl-O bonds leads to the 2Cl + O2 reaction products in most cases. The Cl atoms remain temporarily adsorbed on the ice surface, whereas O2 is ejected. The main effect for the overall chlorine chemistry is probably an increase of the photodissociation rates at long wavelengths, due to the change of adsorption cross sections induced by the interaction with ice.

An experimental (120 K) and theoretical electron-density study of KMnO4 and KClO4.

The experimental electron density rho(r) of the two isomorphic salts KMnO(4) and KClO(4) was determined by a multipole analysis of accurate X-ray diffraction data at 120 K. The quantum theory of atoms in molecules was applied to rho(r) and to its Laplacian nabla(2)rho(r). The bonds were characterized using the topological parameters at the bond critical points of the density rho(r), nabla(2)rho(r), G(r) (kinetic energy density), V(r) (potential energy density) and H(r) (total energy density). According to the classification recently proposed by Espinosa, Alkorta, Elguero & Molins [J. Chem. Phys. (2002), 117, 5529-5542], the K-O and Cl-O bonds have a pure ionic and covalent character, respectively, while the Mn-O bonds show an intermediate behaviour. The results of the topological analysis of the experimental and theoretical (fully periodic Hartree-Fock and density functional calculations) electron density are in good agreement, even on a quantitative level. The atomic charges, determined by performing an integration over the topological basins, are about +2 e for Mn and Cl atoms. The ionic radius, estimated with the distance of the bond critical point from the nucleus, is in agreement with a charge of +2 e for the Mn atom.

Hydrolysis, Solvation, and Reduction of SO3, S2O6, ClO3(OH), Cl2O7, and ArO4Relating Chemical Properties to the Instability of SO, ClO, and ArO Groups

Successive water addition to the mononuclear species SO3(g) and ClO3(OH)(g) and ArO4(g), as well as the binuclear clusters S2O6(g) and Cl2O7(g), is studied by means of quantum chemistry. A large basis set effect is observed for the S−O, Cl−O, and Ar−O bond distances, as well as for redox energetics. While the 6-311+G(d,p) basis set is enough for O and H atoms, S, Cl, and Ar require the 6-311+G(3df) set for an accurate description. Given this combination of basis sets, B3LYP is found to give very good results of equal quality to high-level methods. The dominating chemical feature that is monitored is the instability of the SO, ClO, and ArO bonds. This instability causes the acidity displayed by water solutions of SO2(OH)2 and ClO3(OH) and makes the Cl and Ar systems prone to O2(g) evolution. The latter system is also reduced directly by water, while the reduction of SO2(OH)2 to H2S requires a reducing agent of equivalent power to H2. Three water ligands are necessary to produce nanoscale deprotonation of SO2(OH)2 and ClO3(OH). The hydrolytic cleavage of the S−O−S and Cl−O−Cl bridges is exothermic by 23−30 kJ/mol, which explains the sensitivity to excess of water displayed by these polymers.

Static SIMS Studies of Reactions on Mimics of Polar Stratospheric Clouds III: Mechanism of Chlorine Nitrate Decomposition and Reaction

Static secondary ion mass spectrometry (SSIMS) was used to probe the interactions of chlorine nitrate (ClONO{sub 2}) or of chlorine nitrate plus HCl with condensed water ice films to probe the molecular interactions that may occur on polar stratospheric clouds. The experiments were carried out in an ultrahigh vacuum chamber on ice films at temperatures between 90 and 170 K and at pressures up to 5 x 10{sup {minus}7} mbar. A reference set of SSIMS spectra obtained at <100 K on gold and on ice were used as the basis set from which to probe molecular transformations and surface reactions. at 90--100 K chlorine nitrate adsorbs on gold or ice as a molecular species. Depth profiling experiments through chlorine nitrate multilayers laid down on an ice film indicated a change in the degree of polarization of the Cl-O bond in the chlorine nitrate molecules as proximity to water molecules increased (i.e., as the chlorine nitrate/ice interface was approached). Upon warming, the chlorine nitrate began to desorb from the ice film at 120 K. Despite the polarizing influence of the water molecules, no hydrolysis products were observed under these conditions. In contrast, the ClONO{sub 2} reacted readily above 120 K whenmore » HCl was present. Formation of nitrate ions, implying the formation of surface-adsorbed nitric acid was indicated by the appearance of an NO{sub 3}{sup {minus}} signal in the negative ion SSIMS spectrum. This was accomplished by a simultaneous increase in the partial pressure of chlorine species in the gas phase. It was thus concluded that chlorine nitrate can react directly in the presence of the strong solvated Cl{sup {minus}} nucleophile to form molecular chlorine (which desorbs) and solvated or condensed nitric acid.« less

The ultraviolet photodissociation of Cl2O at 235 nm and of HOCl at 235 and 266 nm

The primary photochemistry of gas phase dichlorine monoxide (Cl2O) and of hypochlorous acid (HOCl) following excitation at 235 nm has been investigated using photofragment ion imaging to obtain the recoil velocity and angular distributions of the ground (2P3/2) and spin-orbit excited (2P1/2) atomic chlorine products. In the case of Cl2O, both Cl spin-orbit products exhibit angular distributions characterized by an anisotropy parameter, β=1.2±0.2, consistent with previous interpretations of the ultraviolet (UV) absorption spectrum of Cl2O which associate the broad intense absorption feature peaking at λ∼255 nm with excitation to a (bent) dissociative state of B21(C2v) symmetry. The recoil velocity distributions of the two Cl spin-orbit products are markedly different. The ground state atoms (which constitute &amp;gt;90% of the total Cl atom yield) are partnered by ClO fragments carrying significantly higher average levels of internal excitation. The slowest Cl atoms are most readily understood in terms of three body fragmentation of Cl2O to its constituent atoms. These findings are rationalized in terms of a model potential energy surface for the 1 1B2 state, which correlates diabatically with ClO(X) radicals together with a spin-orbit excited Cl atom, with efficient radiationless transfer to one (or more) lower energy surfaces at extended Cl-O bond lengths accounting for the dominance of ground state Cl atom fragments. The image of the ground state Cl atoms resulting from photolysis of HOCl at 235 nm is consistent with parent excitation via a transition for which the dipole moment is closely aligned with the Cl-O bond, followed by prompt dissociation (β=1.7±0.2) with the bulk of the excess energy partitioned into product recoil. Such conclusions are consistent with the results of laser induced fluorescence measurements of the OH(X) products resulting from 266 nm photodissociation of HOCl which reveal OH(X) products in both spin-orbit states, exclusively in their zero-point vibrational level, and carrying only modest levels of rotational excitation (well described by a Boltzmann distribution with Trot∼750±50 K).

Structures of trimethyloxosulfonium salts. VIII. New refinement of the perchlorate (CH3)3SO+.ClO4−

The trimethyloxosulfonium cations, (CH 3 ) 3 SO + , have the same geometry as in the other salts reported previously. The ClO 4 - anions occupy two differentsites of tetrahedral geometry. The first type is regular [Cl-O bonds 1.402 (2) A], while the second has an irregular form [Cl-O bonds from 1.379 (5) to 1.417 (3) A]; two kinds of tetrahedra are located at the site having m symmetry with occupation factors of 0.5. The structure of this compound has been solved previously [Coulder, Gantzel & McCullough, (1963). Acra Cryst. 16, 676-681] but the old data required refinement

Bonding electrons in orthorhombic potassium perchlorate

The crystal structure of KClO 4 has been refined with single-crystal Mo K α X-ray diffraction intensity data. Difference Fourier maps show four positive residuals due to bonding electrons 0.7Å from Cl directed towards oxygen, approximately 0.2Å closer to the cation compared to cases previously reported on silicates, reflecting the more covalent nature of the Cl-O bond. The K-O 1 2 coordination shows a characteristic comparable to that of isostructural BaSO 4 at temperatures higher than 670°C. [Crystal data: KClO 4; Formula weight 138.55; Orthorhombic ( Pnma); a = 8.8606 (8), b = 5.6676 (5), c = 7.2590 (8) A ̊ ; V = 364.54 (6) A ̊ 3 ; Z = 4; D x = 2.52g/cm 3; F 000 = 272; μ (Mo K α) = 20.40cm −1; T = 301K]

Structure and thermochemistry of ClO2 radicals

The structure of ClO2 has been calculated for the X 2A″ ground state using unrestricted Hartree–Fock (UHF), unrestricted second-order Mo/ller–Plesset perturbation (UMP2), configuration interaction using single and double excitation (CISD), and quadratic configuration interaction (QCI) ab initio molecular orbital methods. Calculations using UMP2 and CISD wave functions predict a ClO bond length of 1.728±0.01 Å. The single-configuration based QCI in the singles and doubles space with perturbation inclusion of triple substitutions, denoted QCISD(T), yield a ClO bond length of 2.205 Å. The QCI results are consistent with results of Jensen who showed that the ClO bond length is 2.181 Å using annihilated self-consistent methods (AUMP2). The thermochemistry of ClO2 radical has been calculated using MP2 and QCI methods using an isodesmic scheme. Our scheme predicts the heat of formation for ClO2 at 0 K to be 24.6±2 kcal mol−1.

Investigations on solid chlorine dioxide: temperature-dependent crystal structure, IR spectrum, and magnetic susceptibility

Single crystals of chlorine dioxide were grown in situ on a four-circle diffractometer, and the crystal structures were solved at five different temperatures (-75, -90, -110, -130, and -150 o C). At -150 o C, the crystal system, space group, unit cell parameters, and R factor are as follows: orthorhombic, Pbca, a=10.767 (12) A, b=6.654 (3) A, c=5.518 (1) A, V=395.29 (48) A 3 , Z=8, R=0.024. In the solid state, the ClO 2 molecules associate to form weakly bonded dimers which are «head to tail» with respect to one Cl-O bond

Structure of tetraaquacopper(II) chlorate at 296 and 223 K

[Cu(H2O)4](ClO3)2, Mr = 302.51, orthorhombic, Pbca, lambda (Mo K alpha) = 0.71069 A, Z = 4, F(000) = 604; T = 296 K, a = 12.924 (3), b = 9.502 (2), c = 7.233 (1) A, V = 888.3 (3) A3, D chi = 2.26 g cm-3, mu = 31.04 cm-1, R = 0.041 for 1174 unique reflections with I greater than sigma (I); T = 223 K, a = 12.853 (2), b = 9.492 (2), c = 7.216 (2) A, V = 880.4 (3) A3, D chi = 2.28 g cm-3, mu = 31.28 cm-1, R = 0.033 for 1279 unique reflections with I greater than sigma (I). The single type of copper ion is octahedrally coordinated by four water oxygens and two chlorate ion oxygens; the complex is characterized by three distinct pairs of Cu-O distances (which we have previously described as '2 + 2 + 2' coordination), one of which is substantially larger than the remaining two. The nominal 90 degrees O-Cu-O angles of the complex differ from that value by at most +/- 1.8 degrees. The observed structure of the complex is typical for copper(II) and is consistent with the Jahn-Teller effect. The single type of chlorate ion shows the expected trigonal pyramidal geometry, with average Cl-O bond lengths 1.485 (13) and 1.490 (11) A and average O-Cl-O bond angles 106.8 (13) and 106.8 (13) degrees for 296 and 223 K, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of barium perchlorate trihydrate.

Ba(ClO4)2.3H2O, Mr = 390.28, hexagonal, P63/m, a = 7.277 (2), c = 9.656 (1) A, V = 442.9 (1) A3, Z = 2, F(000) = 368, D chi = 2.93 g cm3, lambda(Mo K alpha) = 0.71069 A, T = 295 K, mu = 52.60 cm1, 456 unique reflections, R = 0.023. The barium atoms in this structure are coordinated by six water oxygens, O(3), at 2.919 (1) A and by six perchlorate oxygens, O(2), at 3.026 (2) A in a slightly distorted icosahedral arrangement, the average Ba-O separation thus being approximately 2.97 A. The perchlorate ion just fails to have regular tetrahedral geometry within the experimental error, and has an average Cl-O bond length of 1.433 (6) A. Consistent with hydrogen bonding delineated on the basis of least-squares-refined hydrogen-atom positions, each axial [O(1)] perchlorate oxygen is hydrogen bonded to three water molecules and each trigonal [O(2)] perchlorate oxygen is hydrogen bonded to two water molecules; thus each perchlorate ion is hydrogen bonded to nine water molecules. Conversely, each water molecule [O(3)] oxygen is hydrogen bonded to six perchlorate ions to two through axial [O(1)] oxygens and to four through trigonal [O(2)] oxygens.

Crystal and molecular structure of tetrakis-(phenylenethiourea)tellurium(II) perchlorate hexahydrate, C28H24N8O8S4Cl2Te�6H2O

The synthesis and structural characterization of the title compound, C28H24N8O8S4Cl2Te·6H2O are reported. The crystals are triclinic, space group P¯1 (No. 2), withZ=1 in a unit cell of dimensionsa=10.312(7),b=7.144(6),c=14.256(7) A,α=83.04(5),β=92.15(5), andγ=101.25(6)°,V c =1022 A3. The structure was solved by Fourier methods, and refined by full-matrix least squares toR=0.073 andR w =0.077 for 1305 unique reflections. The tellurium atom in the molecule lies at a crystallographic center of symmetry, and is bonded to four phenylenethiourea sulfur atoms in a near square-planar arrangement with Te-S(1)=2.666(5), Te-S(2)=2.675(6) A, and S(1)-Te-S(2)=88.7(3)°. The ligands behave as thiones. The crystal packing is stabilized by the extensive hydrogen bonding involving oxygen and nitrogen atoms. The Cl-O bond lengths are 1.29-1.36 A and the O-Cl-O angles are 90–130° in the ClO4 – moiety, and differ considerably from the normal values of 1.44 A and 109°, respectively.

Ab initio SCF and CI calculations for ground and low-lying valence and Rydberg excited states of HOCl and HClO in linear and bent nuclear conformations

Potential curves are reported for the ground and various valence and Rydberg excited states of HOCl and HClO using abinitio SCF and CI methods. The states of HOCl are found to be generally favored over their counterparts in HClO, but the calculations indicate that small barriers nevertheless exist for angular interconversion between at least some pairs of such states; they also show that dissociation processes involving ClO bond breaking are universally favored for both HOCl and HClO. Additional calculations for the ions have also been carried out, from which the heat of formation of HOCl+ is calculated to be 237 kcal/mol and it is pointed out that a previous estimate for the corresponding HOCl quantity has subsequently been substantiated by experiment; the relative energies of the first four states of HOCl+ are found to be in good agreement with experiment as well.

Disproportionation of some alkali metal chlorites in the solid phase

Thermal behaviours of some alkali metal chlorites were studied under dynamic and isothermal conditions and some physical data of the chlorites were also determined. It was found that these chlorites disproportionate into chlorate and chloride in the solid phase without any measurable evolution of gas. The disproportionations were strongly exothermic. The values of the activation energies for the disproportionation reactions were found to be much smaller than the dissociation energy required for the rupture of the Cl-O bond. It was concluded that the disproportionations of alkali metal chlorites take place by rearrangement inside the lattice, without formation of atomic oxygen.

A nuclear quadrupole resonance study of the chlorate ion

The quadrupole frequencies of the chlorine nuclei in two isomorphous chlorates, RbClO 3 and CsClO 3, were used for the estimation of the corresponding electric field gradients at the chlorine nucleus site in the free chlorate ion. The application of the Townes and Dailey theory led to the calculation of the effective charges on the chlorine and oxygen atoms and the double-bond character of the Cl-O bonds. The results obtained are consistent with all the available theoretical and experimental evidence.

Some properties of cesium perchloratoborate

1. The boron atom is capable of coordinating four perchlorato groups with the formation of the complex anion [B(ClO4)4]−. 2. The properties of cesium perchloratoborate were studied. The low heat stability of Cs[B(ClO4)4] is explained by the substantial deviation in the symmetry of the ClO4 groups from tetrahedral and a weakening of the Cl-O(B) bonds.

Structure of 2 A 2 excited state of chlorine dioxide

The excited 2A2 state of ClO2 has the non-linear, symmetrical structure re(ClO)= 1·619 A, θe= 107° 0′, contrary to earlier suggestions that the ClO bond distances are unequal.