Nonbonding Electrons Research Articles

LiMoO 3(IO 3): A new molybdenyl iodate based on WO 3-type sheets with large SHG response

A novel lithium molybdenyl iodate, LiMoO 3(IO 3), has been prepared by hydrothermal reactions at 170 °C. Its crystal structure has been determined from single-crystal X-ray data: space group P2 1, a = 5.4104(4) Å, b = 5.3158(3) Å, c = 9.0025(7) Å, β = 106.863(6)°, Z = 2. LiMoO 3(IO 3) is a new layered material containing [ Mo O 3 ( I O 3 ) ] 1 − anionic layers separated by Li + cations. The anionic layer has an unprecedented configuration consisting of WO 3-type sheets “capped” by IO 3 − groups. The iodate groups have their stereochemically active nonbonded electron pairs align along the b-axis, which creates the polarity in the structure. Second-harmonic-generation measurements on LiMoO 3(IO 3) display a response of about 4 × KH 2PO 4. DTA measurements demonstrate that LiMoO 3(IO 3) is stable up to at least 430 °C. UV–vis diffuse reflectance spectrum of this compound shows a high degree of transparency from 1.1 to 2.8 eV and a band gap of about 2.8 eV.

Lanthanoid(III) oxide chloride oxoselenates(IV): A fascinating class of multinary compounds

Compounds in the systems M 3+–O 2−–Cl −–Se 4+ are more than just quaternaries, for they can offer both oxygen that is bonded to selenium(IV) to form discrete [SeO 3] 2− ψ 1-tetrahedra ([SeO 3 E] 2− with E: non-bonding electron pair as pseudo-ligand) and oxygen that is only bonded to the trivalent lanthanoid (M = Ce–Lu) to form regular [OM 4] 10+ tetrahedra. The latter share edges and vertices in most cases to build up cationic chains ([OM 2] 4+ in Cl −-free Tb 2O[SeO 3] 2: a = 1064.57(7) pm, c = 521.56(4) pm, Z = 4, tetragonal, P4 2/ ncm), double strands ([O 2M 3] 5+ in Tb 3O 2Cl[SeO 3] 2: a = 535.16(4) pm, b = 1530.51(9) pm, c = 1081.72(7) pm, Z = 4, orthorhombic, Pnma; Er 3O 2Cl[SeO 3] 2: a = 1498.23(9) pm, b = 1102.04(7) pm, c = 547.95(4) pm, β = 105.515(6)°, Z = 4, monoclinic, C2/ c) or layers ([O 3M 4] 6+ in Yb 4O 3Cl 2[SeO 3] 2: a = 853.87(6) pm, b = 1145.92(8) pm, c = 1195.46(8) pm, α = 68.132(6)°, β = 78.113(6)°, γ = 85.748(6)°, Z = 2, triclinic, P 1 ¯ , [O 4M 5] 7+ in Tb 5O 4Cl 3[SeO 3] 2: a = 1229.13(8) pm, b = 546.17(4) pm, c = 978.79(6) pm, β = 90.485(6)°, Z = 2, monoclinic, C2/ m; [O 8M 9] 11+ in Gd 9O 8Cl 3[SeO 3] 4: a = 680.17(5) pm, b = 882.86(7) pm, c = 960.18(7) pm, α = 97.241(6)°, β = 95.539(6)°, γ = 96.265(6)°, Z = 1, triclinic, P 1 ¯ ; [O 3M 3] 3+ in CsEu 4O 3Cl 3[SeO 3] 2: a = 545.09(4) pm, b = 879.98(7) pm, c = 1597.45(9) pm, α = 81.036(6)°, β = 89.992(6)°, γ = 71.925(6)°, Z = 2, triclinic, P 1 ¯ ). On the other hand and much like in the pure lanthanoid(III) oxoselenates(IV) M 2[SeO 3] 3 themselves, segregation of the stereochemically active non-bonding electron pairs (one per Se 4+ cation) of the pyramidal [SeO 3] 2− units occurs, such that “lone-pair” channel or layer structures emerge. Sometimes even the “lone-pair” electrons of the chloride anions help to construct these structural features as also observed in the O 2−-free chloride oxoselenates(IV) MCl[SeO 3].

Lone pair effects in trihalo-stannate and -plumbate anions in the crystal structures of Sr(MX 3) 2 · 5H 2O (M = Sn, X = Cl, Br; M = Pb, X = Br): A joint crystallographic and electronic structure calculation approach

The crystal structures of Sr(SnCl 3) 2 · 5H 2O, Sr(SnBr 3) 2 · 5H 2O and Sr(PbBr 3) 2 · 5H 2O are presented along with the predicted structure of Sr(PbCl 3) 2 · 5H 2O. The compounds are essentially isostructural with Sn/Pb in a trigonal pyramidal environment with Cl/Br. Stereochemical activity of the non-bonding valence electrons on Sn/Pb is evident in the crystal structures, with the degree of distortion less pronounced in the two lead containing structures. Valence electron pair distributions have been examined using a combination of density functional theory and localised Wannier functions. The valence electron distribution around M in the [MX 3] − anion (M = Sn, Pb, X = Cl, Br) is compared in the gas phase and solid state. Electronic structure calculations reveal a contraction towards the metal centre of the orbital associated with the non-bonding valence electrons, on substitution of Sn by Pb. Relatively large deviations of the calculated charge centre maxima from the bond centre in the M–X bonds are an indication of the polarity of the M–X bonds and lead to the conclusion that while the [SnX 3] − anion appears to be a discrete entity within the system Sr(SnX 3) 2 · 5H 2O, there is less evidence for the existence of a corresponding discrete [PbX 3] − anion in lead analogues.

Gallium Tris(iodate), Ga(IO3)3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Study of fragmentation pattern and adsorption of 9‐O‐(triphenylsilyl)‐10,11‐dihydrocinchonidine on platinum by hydrogen/deuterium exchange using electrospray ionization ion‐trap tandem mass spectrometry

We have studied the adsorption on a platinum (Pt) catalyst of two compounds utilizable as a chiral basic catalyst and a chiral modifier, dihydrocinchonidine (DHCD), and a new cinchona alkaloid derivative containing a bulky group, the Ph3SiO-DHCD molecule. The method of choice was the detection by electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS) of hydrogen/deuterium (H/D) exchange at room temperature, in tetrahydrofuran, at a D2 pressure of 1 bar. Based on the ESI-MS/MS spectrum of the new compound, we propose a mechanism for the formation of the silatropylium cation containing a Si-O bond. From the fragmentation pattern of Ph3SiO-DHCD it was confirmed that ESI-ion-trap MS/MS can be used to study the adsorption processes of complicated carbon compounds by investigating their H/D exchange reactions. In the case of Ph3SiO-DHCD, the results demonstrate that H/D exchange takes place mainly on the quinoline skeleton. However, the strong pi-bonded adsorption of the quinoline skeleton parallel with the imaginary plane of Pt is not preferred because the bulky Ph3Si group inhibits the multiple pi-bonded adsorption of the Ph3SiO-DHCD. Because of this hindrance the molecule was adsorbed tilted via the nonbonding electron pair of the N atom and C2' atom of the quinoline skeleton; consequently, mainly alkaloid-d1 and alkaloid-d2 are formed.

An overview of organic molecule soft ionization using vacuum ultraviolet laser radiation

The utility of coherent vacuum ultraviolet (VUV) single-photon ionization (SPI) combined with time-of-flight mass spectrometry (TOF-MS) for organic molecule detection by parent mass is explored in this short review. Nonresonant tripling in phase-matched Xe–Ar gas mixtures was used to generate photons at a fixed energy of 10.5 eV. Representative organic molecules with different functional groups were examined, including aliphatic and aromatic alkanes, alkenes, alkynes, alkanols, ethers, amines, aldehydes, ketones, carboxylic acids, and esters. In almost every case, the intensity of the resultant parent molecular ion peak detected by TOF-MS was found to be superior to that obtained using 70 eV electron impact (EI), and comparable to that obtained with 12 eV EI. In those instances when fragmentation reactions did occur, the resultant ions were similar to those found using EI but with significantly reduced mass spectral intensities. It was still possible to establish one dominant fragmentation pathway that could be used for molecular identification even if the parent molecular ion was not the strongest feature in the spectrum, for example, in the case of alcohols, alcohol clusters, and alcohol–ether adducts. Several of the fragment ions were metastably broadened. Not surprisingly, their known appearance energies or estimated reaction enthalpies were very similar to the fixed photon energy used. The success of using VUV for organic molecule soft ionization is attributed to the low photon energy that removes predominantly a π- or non-bonding electron from the functionalized species. As most organic compounds have ionization potentials in the 10.5 eV region, this approach is expected to be near universal.Key words: vacuum ultraviolet laser, single photon ionization, organic molecule detection, soft-ionization, mass spectrometry.

Gallium tris(iodate), Ga(IO3)3

Ga(IO(3))(3) crystallizes in the space group P6(3), with the Ga atom at a site with imposed threefold symmetry. The crystal structure consists of slightly distorted GaO(6) octahedra that are bridged by I atoms of IO(3)(-) groups, giving rise to a three-dimensional polar network. The framework contains unoccupied hexagonal channels running parallel to the hexagonal [001] direction. The iodate groups have their stereochemically active non-bonded electron pairs pointing in the same direction along [001], which creates the polarity in the structure. The I-O bond distances and O-I-O angles are normal, being in the ranges 1.783 (3)-1.847 (2) A and 94.68 (11)-99.61 (12) degrees , respectively.

Electronic and Infrared Spectroscopy of [Benzene−(Methanol)n]+ (n = 1−6)

The microsolvation structure of the [benzene-(methanol)(n)](+) (n = 1-6) clusters was analyzed by electronic and infrared spectroscopy. For the n = 1 and 2 clusters, further spectroscopic investigation was carried out by Ar atom attachment, which has been know as a useful technique for discriminating isomers of the clusters. The coexistence of multiple isomers was confirmed for the n = 1 and 2 clusters, and remarkably, preferential production of the specific isomers occurred in the Ar attachment. The most stable isomer of the n = 1 cluster was suggested to be of the "on-ring" structure where the nonbonding electrons of the methanol moiety directly interact with the pi orbital of the benzene cation moiety. This is a sharp contrast to [benzene-(H(2)O)(1)](+), exhibiting the "side" structure, where the water moiety is bound to the C-H sites of the benzene cation moiety. The structure of the n = 2 cluster was discussed with the help of density functional theory calculations. Spectral signatures of the intracluster proton-transfer reaction were found for n > or = 5. The intracluster electron-transfer reaction leading to the (methanol)(m)()(+) fragment was also seen upon vibrational and electronic excitation of n > or = 4.

The conformation of the hydrogen bonded complex cyclohexene oxide⋯HCl: A rotational study

Cyclohexene oxide and its hydrogen bonded complex cyclohexene oxide⋯HCl have been investigated using a molecular beam Fourier Transform microwave spectrometer. The spectra of the parent species of cyclohexene oxide and its 13C and 18O isotopomers have been measured in their natural abundances. This has allowed obtaining the substitution and effective structures of the monomer heavy atom skeleton. A fast mixing nozzle has been designed to generate the complex preventing the reaction between the components. Only the equatorial conformer of the complex has been detected and its 35Cl and 37Cl isotopic species have been measured in their natural abundances. From the spectroscopic data the hydrogen bond structural parameters were obtained assuming that the structures of the monomers do not change upon complexation. HCl lies in the COC bisecting plane forming a non-linear hydrogen bond to the equatorial non-bonding electron pair at oxygen. The geometries of the axial and equatorial conformers have been optimized at MP2/6-311++G(d,p) level of theory predicting the equatorial conformer as the most stable one. The non-observation of the axial form is discussed.

Mixed‐Metal Tellurites: Synthesis, Structure, and Characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electronic and structural effects in muscular relaxants: Riparin I and Riparin III

Two muscular relaxants (MR), methyl ethers of N-benzoyl tyramine (Riparin I) and N-(1,6-dihydroxybenzoyl) tyramine (Riparin III) were studied with X-ray diffraction (XRD), optical spectroscopy and semi-empirical calculations. The XRD data show that the C O group in Riparin I is 34° out of plane from the closest benzene ring. The abinitio calculations using RHF/6-31G* suggest that the dihydroxybenzoyl (DHB) group in Riparin III forms intramolecular hydrogen bond between the H of the O–H group and the O of the C O group, and gives a relatively planar structure between DHB group and C O group. The spectral analysis together with the excitation energy calculations using the ZINDO program showed that the absorption band at 309 nm in Riparin III, absence in Riparin I, is assigned to the π→π* transition associated mainly from the DHB. A long range charge-transfer (CT) transition, as the low-lying excited electronic state, S 1 has been calculated for both relaxants involving the non-bonding electron on carbonyl and/or amine group and the antibonding orbitals of aromatic ring. The planar structure of Riparin III and its extensive electron delocalization may have an important role on the pharmacological action mode and on the potency this MR as compared to those of Riparin I.

UV photofragmentation of gas phase M and M2 complexes with ketones, where M = Cu and Ag

Results are reported of an experimental study of the UV photofragmentation patterns of singly and doubly charged complexes consisting of either copper or silver in association with a series of ketones. Considerable variation is seen in response to photoexcitation, ranging from extensive chemical reactivity in the case of Cu+ through to no evidence of photoabsorption on the part of Ag2+ complexes. It is concluded that the close proximity of a charge has a considerable influence on energy of the non-bonding electrons of the carbonyl group in the ketones, and that this, in turn, influences the π* ← n electronic transition promoted at UV wavelengths.

Oxotellurate(IV) der Lanthanide: II. Die isotype Reihe M2Te5O13 (M = Dy – Lu) / Oxotellurates(IV) of Lanthanides: II. The Isotypic Series M2Te5O13 (M = Dy – Lu)

For the shortly discovered formula type M2Te5O13 (triclinic, P1̄), the establishment of an isostructural series in the last third of the lanthanide family (M = Dy - Lu) was possible. The excessive formula unit TeO2 additional to the well-known composition M2Te4O11 (monoclinic, C2/c) leads to the slicing of the [M2O10]14− layers which are typical for the tellurium-oxide poorer compounds. By coupling together the bicapped trigonal prismatic (M1, CN = 8) and the pentagonal bipyramidal (M2, CN = 7) lanthanide-oxygen polyhedra via edges, [M4O20]28− bands are formed stretching along the a axis and piling up to a primitive rod-packing. The linkage of these bands occurs parallel to the (010) plane via Te3 as well as via Te4 parallel to (100). Besides the usual 3+1 coordination, two of the five crystallographically independent tellurium sites are coordinated regularly fourfold (d(Te−O) ≈ 186−213 pm) and even 3+2-fold by oxygen atoms. The tellurium-oxygen polyhedra form corrugated layers running parallel to (101) which follow so close to each other that the tellurium-oxygen partial structure appears to be almost three-dimensional at a passing glance. As in M2Te4O11-type representatives, the non-bonding electron pair (lone pair) of each Te4+ cation shows stereochemical activity which always appears to flock together in large tellurium neighboured positions.

Mixed-Metal Tellurites: Synthesis, Structure, and Characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16

Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data: Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) A, b = 7.4541(11) A, c = 6.5649(9) A, beta = 95.636(5) degrees, V = 1576.7(4) A3, and Z = 4; NaNb3Te4O16, monoclinic, space group P2(1)/m (No. 11), with a = 6.6126(13) A, b = 7.4738(15) A, c = 14.034(3) A, beta = 102.98(3) degrees, V = 675.9(3) A3, and Z = 2.

Investigating the Mechanism for the Formation of Nitrous Oxide [N2O(X1Σ+)] in Extraterrestrial Ices

The formation of nitrous oxide, N2O(X 1Σ+), in interstellar space and in ices on Pluto and Triton has been experimentally investigated. A molecular nitrogen (N2) and carbon dioxide (CO2) ice mixture was irradiated at 10 K with 5 keV electrons to simulate the electronic interaction effects of Galactic cosmic-ray bombardment of extraterrestrial ice samples over a time of 5 × 106 yr. By monitoring the experiment with a Fourier transform infrared spectrometer on line and in situ, the temporal evolution of the 2235 cm-1 absorption band of nitrous oxide was found to follow pseudo-first-order kinetics. This indicates that the mechanism of formation is most likely a reaction between ground-state molecular nitrogen, N2(X 1Σ), and an oxygen atom, either in the ground state (3P) or in the first electronically excited state (1D), within the matrix cage through an addition of the oxygen atom to a nonbonding electron pair on the nitrogen molecule. The observation of nitrous oxide together with the kinetics and dynamics studies investigated in this paper underline the role of nonequilibrium processes in low-temperature ice matrices, aid in the understanding of chemical reaction pathways that exist in extraterrestrial ices, and assist a prospective identification of nitrous oxide on the surfaces of Pluto and Triton.

Understanding the Conformational Dependence of Spin-Spin Coupling Constants: Through-Bond and Through-SpaceJ(31P,31P) Coupling in Tetraphosphane-1,4-diides [M(L)x]2[P4R4

The characteristic dependence of J(31P,31P) spin-spin coupling constants of alkali metal tetraphosphane-1,4-diides on structure and composition has been analyzed by density functional methods. The computations confirm that the structure of the contact ion pairs is conserved in solution. Calculations on model systems M2P4H4, on naked P4H4(2-) anions, and on models including point charges, show that the role of the cations is mainly structural and to a smaller extent electrostatic. Three of the four J(P,P) coupling constants depend characteristically on the conformation of the anion, which in turn is determined by the substituents R and by cation-anion interactions. Several couplings exhibit a large through-space component and are thus strongly dependent on the relative orientation of nonbonding electron pairs on the phosphorus atoms involved. This is shown by visualization of coupling pathways using the recently introduced coupling energy density (CED), in combination with the electron localization function (ELF).

Water-Soluble Cationic Poly(p-phenyleneethynylene)s (PPEs): Effects of Acidity and Ionic Strength on Optical Behavior

Three cationic PPEs P1‘−P3‘ were obtained through quaternization of their neutral polymers, of which all side chains were respectively featured with a tertiary amino group (P1), an alternative tertiary amino and tri(ethylene glycol)methyl ether group (P2), and an alternative tertiary amino and dodecyloxy group (P3). P1‘ showed intrinsic water-solubility although its quaternization degree was only 45%. Slightly blue-shifted UV−vis absorption maxima in an acidic environment (maximal Δλmax ≈ 3 nm) and obvious red-shifted absorption (maximal Δλmax ≈ 30 nm) and emission maxima (maximal Δλmax ≈ 20 nm) in an alkaline environment at pH < 13 are explained in terms of pH-induced planarization of the conjugated backbone. After the pH was increased to 14, a new absorption (λmax ≈ 478 nm) and emission (λmax ≈ 495 nm) peak appeared in the redder region and the fluorescence intensity further dramatically decreased, implying the occurrence of the conformational change from the planarization of conjugated backbone to the interchain aggregation. The fluorescence enhancement of P1‘ in an acidic environment and the fluorescence decrease of P1‘ in an alkaline environment are attributed to the pH-influenced quenching ability of the nonbonding electron pair on the nitrogen atom, which belongs to the unquaternized tertiary amino group on the side chain, and the interchain aggregation. Such pH-influenced fluorescence intensity can be efficiently buffered by adding salts at pH < 10. Although adding salts in a neutral environment only creates the planarization of PPE conjugated backbone, adding salts in an alkaline environment significantly promotes the formation of interchain aggregation. Amplified quenching of P1‘ by anionic quencher Fe(CN)64- was observed and its Ksv increased significantly after adding salts or increasing pH to 14, for example from Ksv = 9.6 × 105 M-1 at pH = 7 to 7.7 × 106 M-1 at pH = 10 when [NaCl] = 0.1 M, due to the formation of elongated π-conjugation.

Synthesis, structure and spectroscopic study of Rh III polypyridine complexes with phenylcyanamide derivative ligands

Several new Rh III complexes, [Rh(tpy)(bpy)L](PF 6) 2 (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, and L=monoanions of phenylcyanamide(pcyd)), 4-methylphenylcyanamide (4-MePcyd), 2,4-dimethylphenylcyanamide (2,4-Me 2pcyd), 4-methoxyphenylcyanamide (4-MeOPcyd), 2-chlorophenylcyanamide (2-Clpcyd) and 2,5-dichlorophenylcyanamide (2,5-Cl 2pcyd) have been synthesized and characterized by elemental analysis, IR, 1H NMR and electronic absorption spectroscopies. ORTEP drawing of [Rh(tpy)(bpy)(2,5-Cl 2pcyd)](PF 6) 2·1/2CH 3CN shows three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The anionic cyanamide group is coordinated end-on by the nitrile nitrogen to the Rh III. The Rh III–NCN bond is bent, having an angle of 125.4°. This bent bond is largely determined by the σ-bonding interaction of a cyanamide non-bonding electron pair in a sp 2 hybrid orbital.

Preliminary Study of the Oxidation of Nitrogen Compounds of Gas Oil from Brazilian Petroleum

This work describes the development of a procedure for the preferential oxidation of nitrogen compounds of a gas oil sample from Brazilian petroleum. The sample was first submitted to an extraction procedure, based on preparative liquid ion-exchange chromatography (IEC), to characterize the main nitrogen compounds. The instrumental analysis was performed by gas chromatography with a mass spectrometer detector (GC/MSD), and the compounds were identified using the GC/MSD library (Wiley). The IEC analysis shows that the nitrogen compounds were concentrated mainly in the acid and neutral fractions of the sample. The hindrance influence of the nonbonded electron pair of the N atom in the IEC process was studied with a standard mixture of three nitrogen compounds. The oxidation reaction used was efficient for the preferential oxidation of nitrogen compounds while keeping the distribution of the other class compounds of the gas oil unchanged. Experiments for the reaction scale reduction were also performed.

The Noncentrosymmetric Chain Compounds, A3M2AsSe11 (A: K, Rb, Cs; M: Nb, Ta).

AbstractFor Abstract see ChemInform Abstract in Full Text.