The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP-PCP) and its deuterated analogue (MP-PCP-d) were determined at 80 K by X-ray diffraction. The MP-PCP complex crystallizes in the space group P with a = 7.267(7), b = 8.966(9), c = 13.110(14)Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP-PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12)Å, β = 101.38(9)° and Z = 4. The O… H … N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D … N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP---PCP) and its deuterated analogue (MP---PCP-d) were determined at 80 K by X-ray diffraction. The MP---PCP complex crystallizes in the space group with a = 7.267(7), b = 8.966(9), c = 13.110(14) Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP---PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12) Å, β = 101.38(9)° and Z = 4. The O…H…N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D…N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

Effects of wave function modifications on calculated carbon–hydrogen bond lengths

The two-level factorial design (FD) and principal component analysis (PCA) chemometric techniques were used to investigate the carbon–hydrogen bond lengths dependence on the basis set size and quantum chemistry method, for H–C≡CH, H–C≡CF, H–C≡CCH₃, H–C≡CCN, H–C≡CCl and H–C≡CCCH molecular systems. The calculations were performed by using Hartree-Fock (HF), Møller-Plesset 2 (MP2) and Density Functional Theory (DFT) with B3LYP exchange-correlation functional methods. The effects concerning basis set size include the number of valence and polarization functions as well as the cooperative effect between them, at all computational levels. The increase in the number of valence functions decreases the calculated C–H bond lengths by approximately 0.0022 Å, while the inclusion of polarization functions at HF and B3LYP levels increases the C–H bond length, in contrast to the behavior obtained at MP2 level. The effect of the inclusion of diffuse functions is non-significant, at all three computational levels. Moreover, the valence–polarization interaction effects are not significant, except at the MP2 calculational level, in which such effects lead to an increase in the calculated C–H bond lengths. When the computational level changes from HF→B3LYP and B3LYP→MP2 the calculated C–H bond length values increase (on average) by +0.0100 and +0.0027 Å, respectively. Algebraic models (one for each level of calculation) successfully employed to reproduce the calculated values for H–C≡N bond length, a system not included in the training set. The HF/6-31G(d,p) and HF/6-31++G(d,p) results yield the lowest standard errors (0.0015 and 0.0014 Å, respectively) and correspond to the calculated points in closest proximity to the experimental one.     

Reduction pathway of end-on terminally coordinated dinitrogen. IV. Geometric, electronic, and vibrational structure of a W(IV) dialkylhydrazido complex and its two-electron-reduced derivative undergoing N-N cleavage upon protonation

The molybdenum and tungsten dialkylhydrazido complexes [M(dppe)2 (NNC5H10)]2+ (M = Mo, W; compounds A(Mo) and A(W)) and their two-electron-reduced counterparts [M(dppe)2 (NNC5H10)] (compounds B(Mo) and B(W)) are characterized structurally and spectroscopically. The crystal structure of B(W) indicates a geometry between square pyramidal and trigonal bipyramidal with the NNC5H10 group in the apical position and in the trigonal plane of the complex, respectively. Temperature-dependent 31P NMR spectra of B(Mo) show that this geometry is present in solution as well. At room temperature, rapid Berry pseudorotation between the "axial" and "equatorial" ligand positions gives rise to a singlet in the 31P NMR spectrum. This exchange process is slowed at low temperature, leading to a doublet. The N-N distance of B(W) is 1.388 A, and the W-N distance is 1.781 A. Infrared and Raman spectroscopy applied to A(W), B(W), and their 15N isotopomers reveals extensive mixing between the N-N and W-N vibrations of the metal-N-N core with the modes of the piperidine ring. The N-N force constant of A(W) is determined to be 6.95 mdyn/A, which is close to the values of the Mo and W NNH2 complexes. In B(W), the N-N force constant decreases to 6.4 mdyn/A, which is between the values found for the Mo/W NNH3 and NNH2 complexes. This allows us to attribute N-N double bond character to A(W) and intermediate character between the double and single bonds for the N-N bond of B(W). These findings are supported by DFT calculations. More importantly, the HOMO of B(W) corresponds to a linear combination of the metal d(sigma) orbital with a ligand orbital having N-N sigma* character, inducing a weakening of the N-N bond. This contributes to the cleavage of the N-N bond taking place upon protonation of B(W) at the Nbeta atom of the NNC5H10 group.     

The molecular structure of benzene sulphonyl chloride

An electron diffraction structure analysis was carried out on benzene sulphonyl chloride, C₆H₅SO₂Cl, utilizing data from concurrent vibrational spectroscopie calculations. The following bond lengths (r_a parameters): C-H 1.14 ± 0.03 Å, C-C 1.403 ± 0.010 Å, S-O 1.417 ± 0.012 Å, C-S 1.764 ± 0.009 Å and S-Cl 2.047 ± 0.008 Å and bond angles (r parameters): C-S-C1 100.9 ± 2.0°, C-S-O 110.0 ± 2.5°, O-S-O 122.5 ± 3.6° and O-S-Cl 105.5 ± 1.8° were determined for an asymmetric model in which the benzene ring is rotated by 75.3 ± 5.0° relative to the plane containing the sulphur-chlorine bond and bisecting the O-S-O angle. The experimental data could equally well be approximated by a symmetric model with the benzene ring perpendicular to the reference plane described previously, if a particularly large amplitude of vibration was associated with the shortest rotation-dependent carbon-chlorine distance. The bond configuration around the sulphur atom in benzene sulphonyl chloride is consistent with the structural variations observed for a series of sulphone molecules.     

Relativistic DFT calculations of the NMR properties and reactivity of transition metal methane σ-complexes: insights on C-H bond activation

Relativistic ZORA DFT methods have been employed to predict the NMR properties of methane and methyl hydride complexes of rhodium and iridium. Two of these compounds, the rhodium methane and the iridium methyl hydride complexes, have been recently characterized by NMR spectroscopy. Calculations reveal that relativistic effects are largely responsible of the high shielding observed for the proton and carbon resonances of the methane moiety. The key steps for the reaction mechanism of C-H cleavage catalyzed by both compounds have been investigated at the relativistic level. Although the structure of the intermediates and TSs for the Rh and Ir complexes is rather similar, subtle differences in the energetics are responsible of the different catalytic activity of the two complexes.     

Syntheses and structures of dimesitylbismuth(III) bromide, Mes2BiBr, and bis(diphenyldithiophosphinato)mesitylbismuth(III), MesBi(S2PPh2)2

Addition of BiBr₃ to Mes₃Bi (Mes = 2, 4, 6-Me₃C₆H₂) in Et₂O gives 86% of Mes₂BiBr (1) as yellow crystals. Reaction of 1 with Ph₂PS₂NH₄ in a 1 : 1 molar ratio gives a quantitative yield of MesBi(S₂PPh₂)₂ (2) rather than the expected dimesitylbismuth compound. The crystal and molecular structures of 1 and 2 were determined at 153 K and 173 K, respectively. They contain Mes₂BiBr molecules with trigonal pyramidal coordination around Bi. The mean Bi---C bond distance is 2.27 Å and the Bi---Br bond distance is 2.690(2) Å. The angles around Bi vary between 89.4 and 106.4°. Intermolecular Bi…Br contacts of 3.795 Å, indicating weak secondary bonding, give rise to zig-zag shaped (Bi---Br)_x chains. In the polymeric chain the coordination geometry around bismuth atoms can be described as pseudo-trigonal bipyramidal. The crystals of 2 consist of discrete monomeric MesBi(S₂PPh₂)₂ molecules with a symmetry plane containing the metal atom and the aromatic ring of the attached mesityl group. The dithiophosphinato ligands exhibit an anisobidentate coordination pattern with long and short phosphorus—sulfur bonds, i.e. P(1)---S(1) 2.051(31) Å and P(1)---S(2) 1.980(3) Å, related to short and long bismuth—sulfur distances, respectively, i.e. Bi---S(1) 2.662(2) Å and Bi---S(2) 3.123(3) Å. This leads to a square-pyramidal geometry around the bismuth atom, with the metal lying 0.33 Å above the basal plane formed by the four sulfur atoms.     

Molecular structure of benzene

The molecular structure of benzene has been determined by combining the average distances obtained by the present electron diffraction study and the moments of inertia reported by Cabana et al. The following thermal average bond distances have been determined: r_g(C-C) = 1.399 ± 0.001 Å and r_g (C-H) = 1.101 ± 0.005 Å. The uncertainties represent the estimated limits of error. The C-H distance of this molecule is similar to vinyl C-H distances.     

Measurements of Rayleigh scattering and relativistic calculations of incoherent scattering functions

Recent measurements of Rayleigh scattering employing neutron capture γ-rays are presented. Experimental conditions are achieved such that the Rayleigh contribution is dominant and much larger than the other competing coherent processes. A detailed comparison with the modified relativistic form factor (MRFF) approximation is made and it is concluded that the latter overestimates the cross-section by 3–4%. New calculations of S, the incoherent scattering function, are presented in the relativistic treatment of Ribberfors and Berggren, using multiconfiguration Dirac–Fock relativistic wavefunctions. Tables of S, for Z=1–110, are shown on a momentum transfer mesh identical to previous non-relativistic calculations. S has been calculated at a representative angle θ=60° and energies compatible with the presentation mesh. For other scattering angles, the values presented in the tables are accurate to within 1–2% for momentum transfers larger than 0.1 Å⁻¹. In the region below 0.1 Å⁻¹ the accuracy worsens with decreasing momentum transfer, reaching 6% at 0.01 Å⁻¹ and 10% at 0.005 Å⁻¹. The same multiconfiguration wave functions were used to evaluate new MRFFs. The new elastic scattering cross sections differ by 3–6% compared with calculations based on single configuration wave functions.     

Dirac-Fock one-centre calculations. The molecules CuH,AgH and AuH including p-type symmetry functions

Relativistic and non-relativistic Hartree-Fock one-centre expansion calculations including valence s and p orbitals are reported for CuH, AgH and AuH molecules. Relativistic effects diminish the bond length by 0.86, 2.0 and 4.9%, respectively. Without p functions this relativistic contraction is 6.0% for AuH. Relativistic effects strengthen the chemical bond by 0.002, 0.013 and 0.053 au, respectively. The calculated force constants are in reasonable agreement with experiment. The non-relativistic valence orbital energies of AgH and AuH are quite similar while the relativistic ones are not.     

The molecular structure and conformation of dichlorotetramethyldisiloxane as determined by gas phase electron diffraction

Dichlorotetramethyldisiloxane is studied by gas-phase electron diffraction at room temperature. The least-squares values of the bond distances (r_g) and bond angles () are: r(C---H)=1.084(5) Å, r(Si---O) = 1.624(2) Å, r(Si---C) = 1.852(2) Å, r(Si---Cl) = 2.067(2) Å, SiOSi = 154.0° (1.5), ClSiO = 110.2° (0.8), ClSiC = 109.6°(0.7), HCSi = 111.7°(1.5), OSiC = 110.0°(0.8), τ₁ (zero corresponds to the Si---Cl bond trans to the Si---O---Si linkage) = 78°(6) and τ₂ = 141°(19). A two-conformer model cannot be ruled out.     

The crystal and molecular structure of (---)436-(η-C5H5)Fe(CO)(CH3CO)[Ph2PNHCH(Me)(Ph)]

The X-ray crystal structure and absolute configuration of (−)₄₃₆-(η⁵-C₅H₅)Fe(CO)(CH₃CO)[Ph₂PNHCH(Me)(Ph)] have been determined from single crystal diffraction data. The compound crystallizes in the monoclinic space group P2₁ with two molecules in a unit cell of dimensions a = 10.676(4), b = 8.913(7), c = 13.275(9) Å, and β = 91.36°. The structure was solved by the Patterson method and refined to a final R value of 4.7% using 2299 independent data. The iron atom has distorted octahedral coordination, and the configuration at the iron is found to be (S) for the (−)₄₃₆ diastereoisomer. The Fe---Cp distances average 2.131 Å, with an Fe-(ring centroid)distance of 1.76 Å. The Fe-acetyl distance is virtually identical to that found in another iron/acetyl complex, but shows substantial variation from other compounds where the nature of the C(=O)R group is changed. Comparison to the Mo-alkyl/Mo-acetyl series is made, and the argument for back-donation in transition metal acyls is strengthened.

The orientation of the acetyl group is determined by a strong NHO intra-molecular hydrogen bond having an NO separation of only 2.86 ». The phosphine ligand has a very short Fe---P bond which could be in part caused by the role of the adjacent nitrogen in hydrogen bonding. The remaining ligand geometry is the same as that found in a recently reported ruthenium structure, although the absolute configurations at the chiral carbons are reversed, with the current compound being designated (S) at this site.     

The quasi-symmetric OHN and ODN bridges in the adducts of 3,5-dimethylpyridine with 3,5-dinitrobenzoic acid

The crystal structure of the adduct of 3,5-dimethylpyridine and 3,5-dinitrobenzoic acid (DMP-DNB) has been determined at room temperature and 80 K for both undeuterated and deuterated compounds. The monoclinic crystals are isomorphous, space group P2₁/c and Z = 4. Very strong OHN hydrogen bonds are almost linear with fully disordered (1:1) bridge hydrogen atoms between oxygen and nitrogen atoms. This is well reflected in the difference in electron density maps the contours of which depend both on cooling and deuteration. The intramolecular hydrogen bond lengths are 2.550(2) Å for the (OHN) and 2.563(2) Å for (ODN) at room temperature and 2.529(2) Å for (OHN) and 2.531(2) Å for (ODN) at 80 K. Therefore, there is a small but meaningful isotope effect upon the O…N hydrogen bridge length at room temperature and no Ubbelohde isotope effect is observed at 80 K. The infra-red spectra show very broad stretching protonic bands in the 200–1600 cm⁻¹ range. The isotopic ratio v(H)/v(D) at room temperature is about 1.1.     

Synthesis and molecular structure of the optically active organoaluminium dimer (S)-(—)-(S)-(—)- [(C6H5)CH(CH3)NHA1(CH3)2]2

Reaction of the optically active primary amine (S)-(—)--methylbenzylamine with trimethylaluminium in heptane affords the crystalline organoaluminium dimer (S)-(—)-(S)-(—)-[(C₆H₅)CH(CH₃)NHA1(CH₃)₂]₂. Isolated as large, colourless, extremely air-sensitive prismatic crystals, the title compound crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters a = 8.406(3), b = 15.505(4), c = 17.547(5) Å, V = 2287 ų and p = 1.03 g cm⁻³ for Z = 4. Least-squares refinement based on 1477 observed reflections converged at R = 0.056, R_w = 0.058. Methane was eliminated during the course of the reaction due to cleavage of A1---C and N---H bonds resulting in an asymmetric A1₂N₂ fragment at the core of the organoaluminium dimer. The mean A1---C bond distance in the dimethylaluminium units is 1.930(8), while the mean A1---N bond distance is 1.950(5) Å. Specific rotation ([]_D²⁵ in CH₂C1₂)of the dimer is determined to be - 20.6°.     

The molecular structure and conformational composition of epichlorohydrin as determined by gas phase electron diffraction

The molecular structure of gaseous epichlorohydrin has been investigated using electron diffraction data obtained at 67°C. The conformational composition at this temperature is such that the molecules exist predominantly in a gauche-2 conformer (where the C---Cl bond is 160° away from the C---O) bond). Refinements showed that 33% (σ = 4) of the molecule exist in the gauche-1 form. The important distances (r_g) and angle () with the associated uncertainties are r(C---H) = 1.095(5) Å, r(C---O) = 1.442(3) Å, r(C---C) = 1.475(8) Å, r(C---C_M) = 1.523(7) Å, r(C---Cl) = 1.788(2) Å, CCO = 114° (1), CCC_M = 119°(1), ClCC = 108.9° (7), and Tau(ClCCO) = −150°(10) (gauche-2) and Tau(ClCCO) = 78° (10) (gauche-1).     

Structural study of Mn2(CO)8[P(NMe2)3]2

An X-ray crystal structure determination for the bimetallic complex Mn₂(CO)₈-[P(NMe₂)₃]₂ reveals that the P(NMe₂)₃ ligands are trans to the Mn---Mn bond and the Mn---Mn bond distance is relatively long, 2.946(1) Å.     

Equilibrium structure of the carbon dioxide-water complex in the gas phase: an ab initio and density functional study

High-level ab initio (MP2/6-311++G(2d,2p) geometry, Gaussian-2, MP4(SDTQ) and QCISD(T) binding energies) and density-functional (Becke3LYP/6-311++G(2df,2pd)) calculations have been performed on the charge-transfer complex between water and carbon dioxide. The complex appears to have two equivalent non-planar minima of C_s symmetry. Minima are separated by transition states with C₁ symmetry, whereas the totally planar structure with C_2v symmetry is a second-order transition state. All the critical points lie at approximately the same energy (less than 0.05 Kj mol⁻¹ difference). Therefore, the experimentally observable structure should be planar. The best equilibrium intermolecular distance for this complex calculated at the MP2/6-311++G(2d,2p) level is 2.800 Å. Our best estimate of the observable intermolecular distance (corrected for anharmonicity) is 2.84 Å, in agreement with the experimentally derived value of 2.836 Å. Our best estimate of the binding energy at the QCISD(T) level, taking into account the variation of the distance owing to anharmonicity and the use of more sophisticated theoretical treatments, is −12.0 ± 0.2 kJ mol⁻¹. Our best estimate of the barrier to internal rotation, also at the MP2/6-311++G(2d,2p) level, is 4.0 kJ mol⁻¹, outside the error limits of the experimental determination (3.64 ± 0.04 kJ mol⁻¹). Density functional theory at the level employed here gives an equilibrium intermolecular distance that is too large (2.857 Å), a binding energy that is too small (8.1 kJ mol⁻¹), attributable neither to geometry nor to the basis set, and also a barrier to internal rotation that is slightly too small (3.39 kJ mol⁻¹). The overall picture is, however, reasonably good.     

Normal halogen dependence of 13C NMR chemical shifts of halogenomethanes revisited at the four‐component relativistic level

The ‘Normal Halogen Dependence’ of ¹³C NMR chemical shifts in the series of halogenomethanes is revisited at the four‐component relativistic level. Calculations of ¹³C NMR chemical shifts of 70 halogenomethanes have been carried out at the density functional theory (DFT) and MP2 levels with taking into account relativistic effects using the four‐component relativistic theory of Dirac‐Coulomb within the different computational methods (4RPA, 4OPW91) and hybrid computational schemes (MP2 + 4RPA, MP2 + 4OPW91). The most efficient computational protocols are derived for practical purposes. Relativistic shielding effect reaches as much as several hundreds of ppm for heavy halogenomethanes, and to account for this effect in comparison with experiment at the qualitative level, relativistic Dyall's basis sets of triple‐zeta quality or higher are to be used within the framework of the four‐component relativistic theory taking into account solvent effects. Relativistic geometrical optimization (as compared with the non‐relativistic level) is essential for the molecules containing at least two iodines at one carbon atom. Copyright © 2016 John Wiley & Sons, Ltd.     

1-Ethylthio-2-[2-thienyltelluro]ethane (L) a new (Te, S) ligand: Synthesis and complexation with Ag(I), Cu(I), Pd(II) and Pt(II) – Single crystal structures of [PdCl2(L)] and bis(thienyl) tellurium(IV) chloride

Lithium 2-thienyltellurolate, generated from 2-thienyl lithium, reacts at −78 °C in THF with chloroethyl ethyl sulfide to give a (Te, S) ligand 1-ethylthio-2-[2-thienyltelluro]ethane (L) as a red oil. The complexes [PdCl₂(L)] (1), [PtCl₂(L)] (2), [Ag(L)₂][ClO₄] (3) and [CuBr(L)]₂ (4) were synthesized. The complex [HgCl₂(L)] on crystallization decomposed giving Th₂TeCl₂ (5) [where Th = 2-thienyl], which was characterized by X-ray diffraction on its single crystals. The ligand L and complexes 1–4 exhibit proton and carbon-13 NMR spectra, which are characteristic. The coordination through Te in 1–4 is indicated by downfield coordination shifts in the position of the TeCH₂ signal of L. Complex 1 was characterized by X-ray diffraction on its single crystals. The geometry around Pd is square planar. The Pd–Te, Pd–S and Pd–Cl bond lengths are 2.5040(4), 2.273(1) and 2.322(1)/2.380(1) Å, respectively. There are intermolecular interactions between Te (coordinated to Pd) and Cl, and sulfur and Cl. The Te–Cl and S–Cl distances, 3.401 and 3.488 Å, respectively, are shorter than the sum of the van der Waal’s radii (3.81 and 3.55 Å, respectively). The Pd–Pd distance between the two molecules is 3.4156(6) Å, greater than the sum of van der Waal’s radii (3.26 Å). The structure of 5 is typical of that of a tellurium(IV) compound (saw-horse type). The two Te–Cl bond lengths are identical, 2.480(1) Å. The geometry around Te in 5 can be best described as pseudo tetrahedral (trigonal bipyramidal with a lone pair on one corner of the triangle).     

Crystal structures of anil of benzoylferrocene and its derivative of mercury: Specific arrangement of the ferrocenyl and phenyl groups around the C=N bond

The crystal structures of [(phenylimino) phenylmethyl]ferrocene (1) and 2-chloromercurio-1-[(phenylimino)phenylmethyl]ferrocene (2) have been determined by X-ray diffraction methods to obtain structural information on the anils of benzoylferrocene and their mercurated derivatives. The most striking feature is the specific arrangements of the phenyl and cyclopentadienyl rings around the C=N bond. It has been found that the N-phenyl ring adopts a trans conformation with the ferrocenyl moiety, and the twist angles of both the N-phenyl and C-phenyl rings out of the plane of C=N bond are much larger than that of the s substituted ferrocenyl ring out of this plane. A comparison between the structures of 1 and 2 is presented. The intramolecular coordination between the Hg and N in compound 2 is confirned, showing an N---Hg distance of 2.870 Å, shorter than the sum of van der Waals radii of N and Hg (3.05–3.15 Å).