Carbon Doping of Defect Sites in Stone–Wales Defective Boron-nitride Nanotubes: A Density Functional Theory Study

We have performed a density functional theory study to investigate the effect of carbon doping on Stone–Wales (SW) defective sites in the armchair (4, 4), (5, 5) and (6, 6) BNNTs, in order to remove structural instability induced by homonuclear N–N and B–B bonds. Two different orientations of SW defect are considered, parallel and diagonal, and then C atoms are doped at different positions of the defect sites. In general, it seems that among the considered arrangements, C atoms prefer to be substituted for the homonuclear B–B bond. The larger HOMO–LUMO band gaps for the most stable configurations indicate that C doping at B–B sites is kinetically more favorable than the other ones. According to calculated nuclear quadrupole resonance (NQR) parameters as a result of C-doping on SW defective sites, the quadrupole coupling constants (C _Q ) of boron nuclei at defective sites decrease by about 0.508–1.406 MHz while ¹⁴N C _Q of the defective sites, except for N₈, increases. Interestingly, C _Q of the N sites directly connected to dopant sites has maximum increment (0.612–2.596 MHz) while C _Q of the N sites belonging to the B₂N₃ pentagon is undergone to some minor changes.     

Reaction of [η 5:σ-Me2C(C5H4)(C2B10H10)]Ru(NCCH3)2 with internal alkynes: Synthesis and structural characterization of ruthenium-cyclobutadiene and ruthenacyclopentatriene complexes

Reaction of [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NCCH₃)₂ (1) with R¹C≡CR¹(R¹ = Et, Ph) in toluene at 80°C yielded organoruthenium cyclobutadiene complexes [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(η ⁴-C₄R ₄ ¹ ) in >80% yield. Treatment of 1 with diynes R₂C≡C(CH₂)₃C≡CR² (R² = Me, Et) in toluene at room temperature yielded ruthenacyclopentatrienes [η ⁵:σ-Me₂C (C₅H₄)(C₂B₁₀H₁₀)]Ru[=C₂(R²)₂C₂(CH₂)₃] in >85% yield. These new complexes were fully characterized by various spectroscopic techniques, elemental analyses and single-crystal X-ray diffraction studies. The possible reaction mechanism was proposed.     

Reactions of [η:σ-Me2C(C5H4)(C2B10H10)]Ru(COD) with Lewis bases: Synthesis, structure, and electrochemistry of ruthenium amine, nitrile, carbene, phosphite and phosphine complexes

Treatment of [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(COD) (1) with phosphites, phosphines, amines or N-heterocyclic carbene in THF afforded the COD displacement complexes [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[P(OEt)₃]₂ (2), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[PPh₂(OEt)]₂ (3), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[NH₂CH₂CH₂Prⁱ]₂ (4), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)₂ (5), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru (η²-NH₂CH₂CH₂NH₂) (6), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[η²-NH(CH₃)CH₂CH₂NH(CH₃)] (7) or [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[NHC]₂ (8, NHC = 1,3,4,5-tetramethylimidazol-2-yilidene), respectively. Ruthenium-amine complexes were much more labile than 1. Upon exposure to moisture, 5 was converted into [{η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)}Ru(μ-H₂O)]₂ (9). Reactions of 5 with PR₃ (R = PPh₃, Cy), TMEDA (TMEDA = N,N,N′,N′-tetramethylethylenediamine) and CH₃CN afforded the corresponding amine replacement products[η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)(PPh₃) (10), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)(PCy₃) (11), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(TMEDA) (12) and [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NCCH₃)₂ (13). These results indicated that the steric factor dominated these substitution reactions. The electrochemical studies showed that the electron richness of the Ru atom decreased in the order L₂Ru(NHC)₂ > L₂Ru(amine)₂ > L₂Ru(NCMe)₂ > L₂Ru(P)₂. All of these complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 2, 3, 5-10, 12 and 13 were further confirmed by single-crystal X-ray analyses.     

B3N3 Borazine Substitution in Hexa‐peri‐Hexabenzocoronene: Computational Analysis and Scholl Reaction of Hexaphenylborazine

The doping of graphene molecules by borazine (B₃N₃) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa‐peri‐hexabenzocoronene (HBC, C₄₂H₁₈) by an isoelectronic B₃N₃ ring resulting in C₃₆B₃N₃H₁₈ (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all‐B/N molecule B₂₁N₂₁H₁₈ (termed BN) and its carbon derivative C₆B₁₈N₁₈H₁₈ (C6BN), obtained by substitution of a central B₃N₃ by a C₆ ring, are also studied. The substitution of C₆ in the HBC molecule by a B₃N₃ unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm^?1 due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B₃N₃ ring by C₆ changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl₂/AlCl₃ in CS₂) is investigated. Rather than the desired B3N3HBC an insoluble and X‐ray amorphous polymer P is obtained. Its analysis by IR and ¹¹B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the ¹¹B quadrupolar coupling constant C_Q, asymmetry parameter η, and isotropic chemical shift δ_iso(¹¹B) with respect to HPB are in agreement with a structural model that includes B3N3HBC‐derived monomeric units in polymer P. This indicates that both intra‐ and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.     

Hydration Structure Around the Carboxyl Group Studied by Neutron Diffraction with 12C/13C and H/D Isotopic Substitution Methods

Time-of-Flight (TOF) neutron diffraction measurements have been carried out on aqueous 8 mol% sodium acetate solutions in D₂O. Scattering cross sections that were observed for sample solutions involving ¹²C/¹³C and H/D isotopically substituted acetate ions were used to derive the first-order difference functions, Δ_H(Q) and Δ_C(Q), and corresponding distribution functions, G _H(r;r) and G _C(r;r), which describe the environmental structure around the methyl and the carboxyl groups within the acetate ion, respectively. Structural parameters concerning the first hydration shell of the carboxyl group within the acetate ion were obtained through the least squares fit to the observed intermolecular difference function, Δ_C ^inter(Q). The nearest neighbor C _O...D _W1 (C_O: carboxyl carbon atom, D_W1: water deuterium atom) distance, r(C _O...D _W1 ), and the angle, ∠ C _O ...D _W1 -O _W (O _W : water oxygen atom), were determined to be 2.63(1) Å and 120(1)°, respectively. The coordination number, n(C _O ...D _W1 ), was obtained to be 4.0(1). These results are consistent with the hydration structure in which water molecules in the first hydration shell of the carboxyl group are hydrogen-bonded with oxygen atoms of the carboxyl group.     

Molecular structure of the boron(III) oxide molecule in the SCF approximation

The potential surface for the boron(III) oxide (B₂O₃) ground state has been calculated in restricted HF approximation with a minimal STO—3G basis set. The equilibrium geometry has C_2v symmetry; the corresponding structural parameters are as follows: r(O_i—B₁)= 1.241 Å; r(B_i—O)= 1.341 Å ; ∠B₁QB₂ = 142° and ǒO₁B₁O = 177°. Calculations were also carried out using the SCF-Xα approach for two configurations of B₂O₃ with C_2v and D_∞h symmetry.     

Solid state NMR spectroscopy as a probe of structure and bonding in the carbides Sc3TC4 (T = Co,Ni, Ru,Rh, Os,Ir)

Scandium transition metal carbides having the formula Sc₃TC₄ (T = Co, Ni, Ru, Rh, Os, Ir) have been structurally characterized by solid state ¹³C and ⁴⁵Sc nuclear magnetic resonance spectroscopy. In all the compounds investigated, well-resolved signals are observed for crystallographically distinct carbon and scandium sites, confirming the formation of superstructures in the Rh and Ir compounds at ambient temperature. ⁴⁵Sc NMR spectra are dominated by anisotropic broadening due to second-order quadrupolar perturbations. The nuclear electric quadrupolar coupling parameters (the coupling constant C_Q and the asymmetry parameter η) are generally found in good agreement with values calculated theoretically from the crystal structure using the WIEN2k program. Furthermore, the spectra reveal large isotropic resonance shift differences between inequivalent Sc sites in a given compound and between sites of the same type for different compounds. Altogether the results illustrate that ⁴⁵Sc NMR is a sensitive method for detecting isotropic and anisotropic local electron density variations in the Sc₃TC₄ family.     

Defect Engineering on Boron Nitride for O2 Activation and Subsequent Oxidative Desulfurization

The rational design of highly active hexagonal boron nitride (h-BN) catalysts at the atomic level is urgent for aerobic reactions. Herein, a doping impurity atom strategy is adopted to increase its catalytic activities. A series of doping systems involving O, C impurities and B, N antisites are constructed and their catalytic activities for molecular O₂ have been studied by density functional theory (DFT) calculations. It is demonstrated that O₂ is highly activated on O_N and B_N defects, and moderately activated on C_B and C_N defects, however, it is not stable on N_B and O_B defects. The subsequent application in oxidative desulfurization (ODS) reactions proves the O_N and C-doped (C_B, C_N) systems to be good choice for sulfocompounds oxidization, especially for dibenzothiophene (DBT). While the B_N antisite is not suitable for such aerobic reaction due to the extremely stable B−O^*−B species formed during the oxidation process.     

Exploring the electronic and magnetic properties of zigzag and armchair BC2N nanotubes: a DFT study

A density functional study is performed to investigate the electronic and magnetic properties of zigzag and armchair BC₂N nanotubes based on the ¹³C, ¹⁵N, and ¹¹B NMR parameters and natural charge analysis. We considered three types of zigzag nanotubes, ZZ-1, ZZ-2, and ZZ-3 (n, 0) with n = 3, 4, and 5, as well as two types of armchair nanotubes: AC-1 and AC-2 (n, n) with n = 3 and 4. The obtained results indicate the divisions of the electrostatic environments around C nuclei into a few layers, consistent with the calculated natural charges on C atoms. A good correlation is seen between the layers of chemical shielding isotropy as well as anisotropy, σ _iso, and Δσ, and the five local structures around carbon atoms. Successive BN units lead to larger ¹⁵N σ _iso values (96.5–105.5 ppm) in comparison with the individual BN units (74.3–92.0 ppm in the ZZ-2(n, 0) and 47.4–61.7 ppm in the ZZ-3(n, 0)). Slight differences in the values of ¹¹B σ _iso clarify diminutive diversity in the electron densities of boron nuclei, while Δσ values indicate the more apparent range of changes.     

The crystal structure of Sc2Ru5B4

The crystal structure of Sc₂Ru₅B₄ has been determined by single-crystal X-ray analysis. Sc₂Ru₅B₄ crystallizes in the primitive monoclinic space group $\text{P2}\text{m}$ with a = 9.983(6), b = 8.486(4), c = 3.0001(3)Å, γ = 90.01(7)°, Z = 2. Deviations from the orthorhombic space group Pbam-D⁹_2h are small but significant. Intensity measurements were obtained from a four-circle diffractometer. The structure was solved by Patterson methods and refined by full matrix least-squares calculation. $\text{R =}\text{∑|ΔF|}\text{∑|F}{}_0\text{|}\text{= 0.036}$ for an asymmetric set of 863 independent reflections (|F₀|>2σ(F₀)). The crystal structure is characterized by two different types of boron atoms: (a) isolated borons B(1) and B(3) in distorted trigonal Ru-prisms with tetrakaidekahedral metal coordination: 6Ru + 3Sc, and (b) boron atoms B(2) and B(4) with a pronounced tendency to form boron pairs (B(2)-B(2) = 1.86 Å, B(4)-B(4) = 1.89 Å); the metal coordination of these boron atoms is 6Ru + 2Sc. Sc atoms have a coordination number of 17 consisting of 10Ru + 2Sc + 5B. The crystal structure of Sc₂Ru₅B₄ is a pentagon layer structure (Ru, B atoms) with a 4.3.4.3²-secondary layer of Sc atoms. The structure is furthermore related to the structure types of Ti₃Co₅B₂ and CeCo₃B₂. From powder photographs Sc₂Os₅B₄ is isotypic. No superconductivity was observed for Sc₂(Ru, Os)₅B₄ down to 1.5 K.     

Das Dreistoffsystem Nickel-Bor-Silicium

The ternary system Nickel-Boron-Silicon was established at 850°C by means of X-ray diffraction, metallographic and micro-hardness examinations. The well known binary nickel borides and silicides resp. were confirmed. In the boron-silicon system two binary phases, SiB_4-x withx≈0.7 and SiB₆ were found the latter in equilibrium with the β-rhombohedral boron. Confirming the two ternary silicon borides a greater homogeneity range was found for Ni₆Si₂B, the phase Ni_4,6Si₂B published byUraz andRundqvist can better be described by the formula Ni_4.29Si₂B_1.43. In relation to further investigations we measured melting temperatures in ternary Ni-10 B?Si alloys by differential thermoanalysis.     

Overhauser shift in single crystals of FA2PF6

The shift ΔB_ov of the ESR line due to the saturation of the NMR of hyperfine-coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA₂)^±PF₆^?. ΔB_ov is proportional to AP, where A is the average hyperfine interaction between the conduction electrons and the nuclei in resonance and P is the dynamic nuclear polarization. The proton spin relaxation times were measured from the time dependence of the Overhauser shift, ΔB_ov(t), after rf pulses.     

New examples of ternary rare-earth metal boride carbides containing finite boron-carbon chains: The crystal and electronic structure of RE15B6C20 (RE=Pr, Nd)

The ternary rare-earth metal boride carbides RE₁₅B₆C₂₀ (RE=Pr, Nd) were synthesized by co-melting the elements. They exist above 1270 K. Their crystal structures were determined from single-crystal X-ray diffraction data. Both crystallize in the space group P1¯, Z=1, a=8.3431(8) Å, b=9.2492(9) Å, c=8.3581(8) Å, α=84.72(1)°, β=89.68(1)°, γ =84.23(1)° (R1=0.041 (wR2=0.10) for 3291 reflections with I_o>2σ(I_o)) for Pr₁₅B₆C₂₀, and a=8.284(1) Å, b=9.228(1) Å, c=8.309(1) Å, α=84.74(1)°, β=89.68(1)°, γ=84.17(2)° (R1=0.033 (wR2=0.049) for 2970 reflections with I_o>2σ(I_o)) for Nd₁₅B₆C₂₀. Their structure consists of a three-dimensional framework of rare-earth metal atoms resulting from the stacking of slightly corrugated and distorted square nets, leading to cavities filled with unprecedented B₂C₄ finite chains, disordered C₃ entities and isolated carbon atoms, respectively. Structural and theoretical analyses suggest the ionic formulation (RE³⁺)₁₅([B₂C₄]⁶⁻)₃([C₃]⁴⁻)₂(C⁴⁻)₂·11ē. Accordingly, density functional theory calculations indicate that the compounds are metallic. Both structural arguments as well as energy calculations on different boron vs. carbon distributions in the B₂C₄ chains support the presence of a CBCCBC unit. Pr₁₅B₆C₁₈ exhibits antiferromagnetic order at T_N=7.9 K, followed by a meta-magnetic transition above a critical external field B>0.03 T. On the other hand, Nd₁₅B₆C₁₈ is a ferromagnet below T_C≈40 K.     

The microwave spectrum of the unsymmetrical conformation of 1-chloro-2-methyl propane

The microwave spectrum of 1-chloro-2-methyl propane has been recorded and lines assigned to ³⁵Cl and ³⁷Cl species in the unsymmetrical conformation. The rotational and distortion constants in MHz are: C₄H₉³⁵Cl, A = 7527.05, B = 2146.21, C = 1793.59, Δ_JK = 4.15 × 10^?3, δ_j = ?8.0 × 10^?5; C₄H₉³⁷Cl, A = 7524.40. B = 2091.73, C = 1755.54, Δ_JK = 2.5 × 10^?3, δ_j = 2.0 × 10^?4.     

A 93Nb Solid‐State NMR and Density Functional Theory Study of Four‐ and Six‐Coordinate Niobate Systems

A variable B₀ field static (broadline) NMR study of a large suite of niobate materials has enabled the elucidation of high‐precision measurement of ⁹³Nb NMR interaction parameters such as the isotropic chemical shift (δ_iso), quadrupole coupling constant and asymmetry parameter (C_Q and η_Q), chemical shift span/anisotropy and skew/asymmetry (Ω/Δδ and κ/η_δ) and Euler angles (α, β, γ) describing the relative orientation of the quadrupolar and chemical shift tensorial frames. These measurements have been augmented with ab initio DFT calculations by using WIEN2k and NMR‐CASTEP codes, which corroborate these reported values. Unlike previous assertions made about the inability to detect CSA (chemical shift anisotropy) contributions from Nb^V in most oxo environments, this study emphasises that a thorough variable B₀ approach coupled with the VOCS (variable offset cumulative spectroscopy) technique for the acquisition of undistorted broad (?1/2?+1/2) central transition resonances facilitates the unambiguous observation of both quadrupolar and CSA contributions within these ⁹³Nb broadline data. These measurements reveal that the ⁹³Nb electric field gradient tensor is a particularly sensitive measure of the immediate and extended environments of the Nb^V positions, with C_Q values in the 0 to >80 MHz range being measured; similarly, the δ_iso (covering an approximately 250 ppm range) and Ω values (covering a 0 to approximately 800 ppm range) characteristic of these niobate systems are also sensitive to structural disposition. However, their systematic rationalisation in terms of the Nb? O bond angles and distances defining the immediate Nb^V oxo environment is complicated by longer‐range influences that usually involve other heavy elements comprising the structure. It has also been established in this study that the best computational method(s) of analysis for the ⁹³Nb NMR interaction parameters generated here are the all‐electron WIEN2k and the gauge included projector augmented wave (GIPAW) NMR‐CASTEP DFT approaches, which account for the short‐ and long‐range symmetries, periodicities and interaction‐potential characteristics for all elements (and particularly the heavy elements) in comparison with Gaussian 03 methods, which focus on terminated portions of the total structure.     

Structure and dynamics of room temperature ionic liquids with bromide anion: results from 81Br NMR spectroscopy

We report the results of a comprehensive ⁸¹Br NMR spectroscopic study of the structure and dynamics of two room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium bromide ([C₄mim]Br) and 1‐butyl‐2,3‐dimethylimidazolium bromide ([C₄C₁mim]Br), in both liquid and crystalline states. NMR parameters in the gas phase are also simulated for stable ion pairs using quantum chemical calculations. The combination of ⁸¹Br spin‐lattice and spin‐spin relaxation measurements in the motionally narrowed region of the stable liquid state provides information on the correlation time of the translational motion of the cation. ⁸¹Br quadrupolar coupling constants (C_Q) of the two RTILs were estimated to be 6.22 and 6.52 MHz in the crystalline state which were reduced by nearly 50% in the liquid state, although in the gas phase, the values are higher and span the range of 7–53 MHz depending on ion pair structure. The C_Q can be correlated with the distance between the cation–anion pairs in all the three states. The ⁸¹Br C_Q values of the bromide anion in the liquid state indicate the presence of some structural order in these RTILs, the degree of which decreases with increasing temperature. On the other hand, the ionicity of these RTILs is estimated from the combined knowledge of the isotropic chemical shift and the appropriate mean energy of the excited state. [C₄C₁mim]Br has higher ionicity than [C₄mim]Br in the gas phase, while the situation is reverse for the liquid and the crystalline states. Copyright © 2015 John Wiley & Sons, Ltd.     

Prediction of ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous acetonitrile

The second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σ_m,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σ_I, resonance, σ^○ _R, and steric, E _s ^B, and Charton υ substituent constants. For ortho derivatives the predicted (log k _X)_calc values were calculated with equation (log k _ortho)_calc = (log k ^H _AN)_exp + 0.059 + 2.19σ_I + 0.304σ^○ _R + 2.79E _s ^B ? 0.0164ΔEσ_I — 0.0854ΔEσ^○ _R, where DE is the solvent electrophilicity, ΔE = E _AN — E _H20 = ?5.84 for aqueous 50.9% acetonitrile. The predicted (log k _X)_calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work. The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in various media with the corresponding log k values for substituted phenyl benzoates, C₆H₅CO₂C₆H₄-X.     

Synthesis and structural elucidation of some new heterocyclic β-diketone derivatives of boron

Some new β-diketone derivatives of boron having the general formula B₂O(OAc)_4?n[OC(R)$\text{C:CON(Ph)N:C}$ CH₃]_n (where n = 1 or 2; R = CH₃, C₂H₅, C₆H₅ and p-ClC₆H₄) have been synthesised by the reactions of oxy-bis(diacetatoborane) and substituted pyrazolones, such as 4-acyl-3-methyl-1-phenyl-2-pyrazolin-5-ones (acyl = acetyl, propionyl, benzoyl and p-chlorobenzoyl) in dry toluene solution in 1:1 and 1:2 molar ratios. These derivatives have been characterised by elemental analysis, molecular weight measurements. Structures have been proposed on the basis of chemical reactions, IR, ¹H and ¹¹B NMR spectral studies.In the derivatives B₂O(OAc)₃[OC(R)$\text{C:CON(Ph)N:C}$ CH₃] two of the three acetate groups are unidentate and the third is bridged between two boron atoms along with BOB linkage. Whereas the derivatives B₂O(OAc)₂[OC(R)$\text{C:CON(Ph)N:C}$ CH₃]₂ are the mixture of geometrical isomers.     

An Investigation of Lanthanum Coordination Compounds by Using Solid‐State 139La NMR Spectroscopy and Relativistic Density Functional Theory

Lanthanum‐139 NMR spectra of stationary samples of several solid La^III coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T. The breadth and shape of the ¹³⁹La NMR spectra of the central transition are dominated by the interaction between the ¹³⁹La nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical‐shift anisotropy on the NMR spectra is non‐negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the ¹³⁹La quadrupolar coupling constants (C_Q) range from 10.0 to 35.6 MHz, the spans of the chemical‐shift tensor (Ω) range from 50 to 260 ppm, and the isotropic chemical shifts (δ_iso) range from ?80 to 178 ppm. In general, there is a correlation between the magnitudes of C_Q and Ω, and δ_iso is shown to depend on the La coordination number. Magnetic‐shielding tensors, calculated by using relativistic zeroth‐order regular approximation density functional theory (ZORA‐DFT) and incorporating scalar only or scalar plus spin–orbit relativistic effects, qualitatively reproduce the experimental chemical‐shift tensors. In general, the inclusion of spin–orbit coupling yields results that are in better agreement with those from the experiment. The magnetic‐shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical‐shift and EFG tensors in the molecular frame. This study demonstrates that solid‐state ¹³⁹La NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.     

Kinetik der Diazotierung der Chloraniline in methanolischer Chlorwasserstofflösung

The kinetics of the diazotization of o-, m-, p-chloroaniline in 0.005n- to 0.4n-methanolic HCl-solution at 25, 15, 0, ?10 ?20, and ?30°C was invertigated. It was found that the nitrosation reaction (the same as in¹) $$C_6 H_4 ClNH_2 + NOCl \mathop \rightleftharpoons \limits^k C_6 H_4 ClNH_2 NO^ + + Cl^ - $$ is a proceeding advance-back-reaction. The decomposition of C₆H₄ClNH₂NO⁺ by splitting off a proton is the rate determining step. The free activation enthalpies ΔG ^* for the nitrosation reaction, the activation entropies ΔS ^*, the activation enthalpies ΔH ^* and the activation energiesE _a at the given temperatures are calculated. The experimentally found and the calculated velocities are given in Tables 1–6. The equilibrium constants of the o-, m-, p-chloroanilinium ions, and nitrosyl-chloride in methanol are indicated in Table 7, diagram 1. TheK _M values (the ionic products of methanol, extrapolated at infinite dilution) together with theK _A values of Table 7 give theK _B values (p. 2) using the table¹⁰. The ΔG _B values can be calculated using equation ΔG _B = ?RTlnK _B Fig 2 shows the linear dependance of the logarithmus of the ΔG ^* values from the logarithmus of theK _B values.