Study of host-guest interactions in benzodiazacoronands by means of solid state NMR spectroscopy, X-ray diffraction and quantum mechanical computations

In this work we present solid state data for five host-guest complexes formed by N-(4,19-dioxo-2,8,15,21-tetraoxa-5,18-diazatricyclohexacosa-1(25),9(14),10,12,22(26),23-hexaen-26-yl)-benzamide (1) belonging to the group of benzodiazacoronands, achiral compounds for which chiral crystals were found (J. Kalisiak and J. Jurczak, Cryst. Growth Des., 2006, 6, 20). The X-ray structure was resolved for four of them. It was found that 1 crystallizes in P2(1)/c, P1 and P2(1)/n achiral space groups. Differentiation of molecular packing and the presence of guest molecules within the crystal lattice were analyzed with solid state NMR. An attempt was made to correlate changes in (13)C δ(ii) and (15)N δ(ii) chemical shift tensor values, obtained from analysis of spinning sidebands of 1D and 2D (2D PASS) NMR spectra, with changes in the strength of hydrogen bonding. Quantum mechanical DFT GIAO calculations of NMR shielding parameters carried out on structures with coordinates taken from XRD were employed for signals assignment and verification of structural constraints.     

Geometrical and electronic structure of LaI3 molecule from the gas electron diffraction data and quantum chemical calculations

The saturated vapor over LaI₃ has been studied using the electron diffraction method with mass-spectral monitoring. It was determined that at a temperature 1142(10) K, along with monomer molecules, dimers are present in the vapor in the quantity of 0.7 mol.%. Effective configuration parameters of LaI₃ molecule were obtained: r _g(La-I) 2.961(6) Å, ∠_g(I-La-I) 116.5(9)°, l(La-I) 0.106(1) Å and l(I…I) 0.412(7) Å. A small deviation of the valence angle ∠_g(I-L-I) from 120° can be totally caused by a contraction effect of the distance r _g(I…I) of LaI₃ molecule with planar equilibrium configuration. The electronic structure of LaI₃ molecule was examined by the B3LYP/SDD method. In terms of the NBO-analysis, the participation of lanthanum 4f-AO in bonding orbitals La-I is noted. It is shown that the NBO-analysis describes the bond La-I in LaI₃ molecule as predominantly ionic one with a noticeable covalence component. The energy of the heterolytic bond breakage E(La-I)_het = 1216 kJ/mole was calculated.     

Electric field gradients from single-crystal X-ray diffraction data

Deuterium quadrupole coupling tensors have been calculated from diffraction determined charge distributions in crystalline LiOH · H₂O, LiNO₃ · 3H₂O and NaHC₂O₄ · H₂O. The sign, orientation, asymmetry and magnitude of these coupling tensors show good agreement with spectroscopic results.     

Molecular structure of noradrenaline according to gas-phase electron diffraction data and quantum chemical calculations

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Dipole moment enhancement in molecular crystals from X-ray diffraction data.

Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled in their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50 % or more), or because the experimental determinations suggest enhancements of 100 % or more--much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated.     

X-ray diffraction and chemical analyses of magnesium aluminium fluoride

The preparation of magnesium aluminium fluoride by addition of hydrofluoric acid to a mixture of aluminium and magnesium nitrates is described. The x-ray diffraction pattern of the complex, identified by chemical and thermogravimetric analyses as MgAlF₅ · 2.2 H₂O, is reported.     

Stereoelectronic interactions and the one-bond C-F coupling constant in sevoflurane

The conformational preference of the widely utilized anesthetic fluoromethyl-1,1,1,3,3,3-hexafluoro-2-propyl ether (sevoflurane) has been investigated computationally and by NMR spectroscopy. Three conformational minima were located at the B3LYP/aug-cc-pVDZ level, but one is significantly more stable (by ca. 4 kcal/mol) than the other two. This is the case both for gas phase calculations and for solution NMR data. Although the main conformer is stabilized by electron delocalization (n(O) → σ*(C-F)), this type of hyperconjugation was not found to be the main driver for the conformer stabilization in the gas phase and, consequently, for the apparent anomeric effect in sevoflurane. Instead, more classical steric and electrostatic interactions appear to be responsible for the conformational energies. Also the (1)J(CF) coupling constants do not appear to be dominated by hyperconjugation; again, dipolar interactions are invoked instead.     

The structure of azomethine block copolymers from X-ray powder diffraction data

The crystal structure of a block copolymer, constituted by the periodic alternation of three thienyl- and two phenyl fragments separated by azomethine residues, has been determined and refined on powder X-ray diffraction data. Polymers of this kind are particularly interesting because of some evidences of electronic confinement, i. e. possible realization of multiple-quantum-dot sequences have been detected. Although the quality of the measured profile was poor, a molecular model is proposed giving a satisfactory agreement with the observed data.     

Crystal structure determination of AlVMoO7 from X-ray powder diffraction data

The structure of AlVMoO₇ was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)Å, b=8.1644(3)Å and c=12.7312Å. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO₅ pyramids are edge linked to infinite (VO₂⁺)_∞ chains. Therefore, AlVMoO₇ can be classified as a polyvanadate.     

The crystal structure of 3-methyluracil from X-ray powder diffraction data

The crystal structure of 3-methyluracil has been determined ab initio by conventional monochromatic X-ray powder diffraction data. The crystal data are: orthorombic, a=6.6294(1), b=13.1816(3), c=6.53938(9) (Å), V=571.45(3) (ų), space group Pbnm, Z=8. The structure was solved by direct methods and the final Rietveld refinement converged to R_p=0.0398, R_wp=0.0528, R_Bragg=0.0294. The crystal structure exhibits endless chains of planar molecules, connected via head-to-tail N-H?O hydrogen bonds.     

X-ray diffraction investigation of nonbonding interactions and coordination in organometallic compounds

Journal of Structural Chemistry -