... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO)... more ... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO) and N,N-dimethyl-acetamide C3H9NO ... Pharmacie de l'Université Paris Descartes, 4, avenue de l'observatoire, 75006 Paris, France e-mail: beatrice.nicolai@parisdescartes ...
ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have ... more ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have been measured and assigned to separate CH3 groups on the basis of the low-temperature crystal structure. Ab initio and molecular-mechanics calculations have been applied to account for the anti-parallel orientation of the two CH3 groups in the crystal. For the isolated molecule the rotational potential of one group depends on the orientation of the other.
Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the t... more Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the tunnelling splittings to the two crystallographically-inequivalent methyl groups in 2,6-dimethylpyrazine (C6N2H8) at 2 K. Their antiparallel conformation found by crystallography and their respective rotational barriers are reproduced by a combination of ab-initio and molecular mechanics calculations. These results are used for a better understanding of the methyl groups dynamics.
the room-temperature crystal structure of LiAc и 2H 2 O Neutron powder diffraction is used to det... more the room-temperature crystal structure of LiAc и 2H 2 O Neutron powder diffraction is used to determine the crystal persists down to liquid-helium temperatures. Even the structure of LiCD 3 COO ؒ 2D 2 O at 293 and 1.5 K. Lithium crystal structure of this phase has been questioned, and acetate dihydrate crystallizes in the Cmmm space group in the the most recent study was made with X-rays more than 25 room-temperature phase with a ؍ 6.82082(9) Å , b ؍ years ago (9). In the present paper we present the crystal 10.88842(12) Å , c ؍ 6.59911(7) Å , and Z ؍ 4. The CH 3 groups structures of the room-temperature and low-temperature are dynamically disordered, and there are short H bonds bemodifications of LiAc и 2H 2 O as determined by neutron tween the water molecules and the acetate oxygen atoms. There powder diffraction, and relate this to the low-temperature is a phase transition to a low-temperature modification which motions of the hydrogen atoms. The use of neutron diffrachas the space group Pman with a ؍ 6.70246(7) Å , b ؍ tion allows us to locate the deuterium atoms. 10.87932(11) Å , c ؍ 6.56999(7) Å , and Z ؍ 4. The CH 3 groups are ordered in this phase, but have large thermal ellipsoids even at 1.5 K. The H atoms of the water molecules also have EXPERIMENTAL large thermal ellipsoids even at 1.5 K, but the CH 3 group tunneling spectrum shows no evidence for coupling with the motions Samples of LiCD 3 COO и 2D 2 O were prepared via the of the water molecules.
Biclotymol, 2,2¢-methylenebis(4-chloro-3-methyl-6isopropylphenol), C21H26Cl2O2, is used in human ... more Biclotymol, 2,2¢-methylenebis(4-chloro-3-methyl-6isopropylphenol), C21H26Cl2O2, is used in human therapeutics as a pulmonary antiseptic (Fig. 1), and the crystal structure of the usual raw material (Phase I) was solved by Rantsordas et al. 1 A new phase of biclotymol, Phase II, was recently found 2 to recrystallize upon heating the glass. To try and grow single crystals of this new phase, biclotymol solutions in solvents with different polarities were slowly evaporated. 3 The present paper describes the structure of the colorless, prismatic single crystals of biclotymol-DMF (1:1) obtained by slowly evaporating solutions of biclotymol powder of medicinal grade (from Bouchara-Recordati, France) in N,N¢dimethylformamide (DMF). Intensities from a single-crystal sealed in a glass capillary were collected over a hemisphere with an Enraf-Nonius CAD4 diffractometer at 293(2)K, using the CAD4 Express Enraf-Nonius programs package and XCAD4 for data collection and reduction. The structure was solved by direct methods using the program SHELXS86, 4 and refined by full-matrix least-squares procedures on F 2 , using the program SHELXL97. 5 All programs used in the structure refinement were incorporated in the WINGX package. 6 Complete data collection parameters and details of the structure solution and refinement are given in Table 1. Hydrogen atoms, except for H231, H232 and H233, were located from the difference Fourier maps. H231, H232 and H233 were positioned geometrically, and a riding-model with Uiso(H) = 1.5Ueq(Cmethyl) was used during the refinement process (C-H distances 0.95, 0.99, 0.98 Å for CH, CH2 and CH3 groups, respectively). The same isotropic thermal parameters were used for all H-atoms. Final coordinates and equivalent thermal parameters are listed in Table 2. Selected bond lengths and hydrogen bonds are compiled in Table 3. The structure of biclotymol-DMF 1:1 solvate is shown in Fig. 2. The two aromatics rings of the biclotymol molecule are linked by a methylene group. Angle C6-C7-C8 (117.7(3)˚) is close to that found in the biclotymol Phase I (118.55˚). 1 The two phenyl rings (formed by C1 to C6 and by C8 to C13) make a dihedral angle of 72.42(9)˚, comparable to that found in the structure of biclotymol Phase I. Torsion angles of the Phase-I biclotymol molecule compare well with those found in the structure of the DMF solvate. For example, torsion angle C13-C8-C7-C6 is worth 115.03˚ and X-ray Structure Analysis Online
European Physical Journal-special Topics, Apr 1, 2017
The specific volume of vitamin C has been investigated by X-ray powder diffraction as a function ... more The specific volume of vitamin C has been investigated by X-ray powder diffraction as a function of temperature from 110 K up to complete degradation around 440K. Its thermal expansion is relatively small in comparison with other organic compounds with an expansivity v of 1.2(3) ×10-4 K-1. The structure consists of strongly bound molecules in the ac plane through a dense network of hydrogen bonds. The thermal expansion is anisotropic. Along the b axis, the expansion has most leeway and is about 10 times larger than in the other directions.
The crystal structure of the methyl-deuterated lithium acetate dihydrate, 7 LiCD 3 COO, 2H 2 O, h... more The crystal structure of the methyl-deuterated lithium acetate dihydrate, 7 LiCD 3 COO, 2H 2 O, has been determined at 300, 40 and 14 K with the single crystal neutron diffraction technique. The probability density distributions of deuterium atoms were obtained by Fourier difference in the plane of the D atoms. At 14 K, the crystal symmetry is Pman. Methyl-groups are totally ordered and the angular probability density has three sharp peaks. A phase transition to the Cmmm symmetry occurs at (17.5 ± 0.5) K. This structure is analogous to that of the fully hydrogenated derivative at any temperature. However, the Fourier difference at 40 K reveals six maxima of probability for the D atoms, due to centrosymmetric pairs of face-to-face methyl groups, on the top of a continuous ring due to delocalised or disordered atoms. At 300 K, only the continuous and nearly isotropic distribution survives. In order to analyse the tunnelling spectra obtained with the inelastic neutron scattering technique we introduce symmetry-adapted angular coordinates for the strongly coupled pairs of methyl rotors. The dynamics are represented with in-phase and anti-phase rotation of the two partners. The effective moment of inertia is twice that of a single methyl group. The effective potential barrier with the threefold symmetry for in-phase rotation is %2 meV for the CH 3 pairs and %4.5 meV for the CD 3 analogues. These effective potentials are tentatively decomposed into two contributions that favour opposite orientations: the onsite potential and the interaction with next nearest neighbours, respectively. Both temperature and mass effects are rationalised with the mean angular amplitude of the rotors. We can thus account for the crystal phase transition upon methyl deuteration. The potential barrier with the sixfold symmetry for anti-phase rotation is %32 meV. It does not play any role in the ordering/disordering mechanism.
Proton transfer in the chelated form of malonaldehyde is commonly supposed to occur between two t... more Proton transfer in the chelated form of malonaldehyde is commonly supposed to occur between two tautomers, across a transition state involving changes of the chemical bonding. We show that this view is in conflict with rotational spectra. The molecule is better thought of as a superposition of indistinguishable and non-separable C s tautomers and proton tunneling is totally decoupled from the other degrees of freedom. Double minimum potential functions are determined from experiments and ab initio calculations.
The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delt... more The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delta(fus)H(I) = 36.6 +/- 0.9 kJ mol(-1)) recrystallizes into another phase, Phase II, that melts at T(fusII) = 373.8 +/- 0.2 K (Delta(fus)H(II) = 28.8 +/- 1.0 kJ mol(-1)). The transformation of Phase II into Phase I is found to be exothermic upon heating either as a direct process at 363 K or through a melting-recrystallization process (II --> liquid --> I). The melting curves, obtained from differential thermal analyses at various pressures ranging from 0 to 85 MPa, diverge as the pressure increases ((dP/dT)(fusI) = 2.54 +/- 0.07 MPa K(-1), (dP/dT)(fusII) = 5.14 +/- 0.85 MPa K(-1)). A topological P-T diagram with no stable phase region for Phase II, and similar to the 4th case of the P-T state diagrams formerly published by Bakhuis Roozeboom, is drawn, thus illustrating the overall monotropic behavior of Phase II.
La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupemen... more La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupements methyles donnent des informations tres precises sur le potentiel rotationnel local. La presence de plusieurs transitions d'effet tunnel pour le meme systeme reste un phenomene rare qui peut etre interprete en termes de rotateurs inequivalents ou de couplages. Il apparait que l'interpretation de ces donnees experimentales necessite la connaissance precise de la structure cristalline a tres basse temperature et si possible la distribution des protons. L'objectif de cette these est d'interpreter ces mesures experimentales en attribuant les transitions observees. Une fois ce travail experimental acheve, il reste a comprendre les relations entre structure et dynamique. Les modelisations utilisant diverses methodes de calcul ont permis de relier les dynamiques observees a des parametres physico-chimiques. Ces differentes methodes de calcul du potentiel rotationnel sont comparees et leurs fiabilites et limites sont discutees.
ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKa... more ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKay, M P Zorzano, (World Scientific, Publishing Co., Inc) p68 (2003) ISBN 981-283-296-8
1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensat... more 1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensation of propane-1,3-diamine with a mixture of (1H-1,2,4-triazol-1-yl)methanol and formaldehyde. The 1H- and 13C-NMR spectroscopic data of this ligand have been fully assigned and are consistent with the molecular structure. The crystalline structure of the compound was fully determined by single crystal X-ray diffraction at 150K and at room temperature, together with the isobaric thermal expansion. Finally, during the first heating, DSC measurements showed no phase transition up to the melting temperature at 385.1 K (111.9°C).
Carbamazepine (CBZ) and aspirin (ASP) drug molecules in their 1:1 co-crystal interact by relative... more Carbamazepine (CBZ) and aspirin (ASP) drug molecules in their 1:1 co-crystal interact by relatively strong hydrogen bonds and aromatic-aromatic contacts. The crystal structure and the experimental electron density in the CBZ:ASP co-crystal were derived from a high resolution X-ray diffraction experiment at K and the results are compared to those previously obtained for the CBZ form III. The isobaric thermal expansion tensor appears to be much more anisotropic for the co-crystal than for CBZ form III. The thermal expansion coefficients V are found equal to 1.3 for CBZ III and 1.5×10-4 K-1 for CBZ:ASP co-crystal. The interactions in the CBZ:ASP co-crystal have also been analyzed through the electrostatic properties derived from both experimental and theoretical electron densities: topological features, atomic charges and electrostatic potential. A very good agreement was found for the values of the electron density at the critical points (r CP) obtained from both experiment and theory. This is not, however, true for the Laplacian values which are systematically weaker in the theoretical approach. In contrast, the integrated atomic charges have higher magnitudes for the theoretical density. Additionally, it is shown here that the total molecular energies can be obtained from the electrostatic potential at the nuclei (EPN) within the Thomas-Fermi approximation. The best agreement with the conventional quantum calculations (Restricted Hartree-Fock RHF or Density Functional Theory DFT) was surprisingly obtained for the promolecule (superposition of Independent Atomic Model, IAM) density and not from the multipole model which overestimates or underestimates the energies.
... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO)... more ... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO) and N,N-dimethyl-acetamide C3H9NO ... Pharmacie de l'Université Paris Descartes, 4, avenue de l'observatoire, 75006 Paris, France e-mail: beatrice.nicolai@parisdescartes ...
ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have ... more ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have been measured and assigned to separate CH3 groups on the basis of the low-temperature crystal structure. Ab initio and molecular-mechanics calculations have been applied to account for the anti-parallel orientation of the two CH3 groups in the crystal. For the isolated molecule the rotational potential of one group depends on the orientation of the other.
Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the t... more Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the tunnelling splittings to the two crystallographically-inequivalent methyl groups in 2,6-dimethylpyrazine (C6N2H8) at 2 K. Their antiparallel conformation found by crystallography and their respective rotational barriers are reproduced by a combination of ab-initio and molecular mechanics calculations. These results are used for a better understanding of the methyl groups dynamics.
the room-temperature crystal structure of LiAc и 2H 2 O Neutron powder diffraction is used to det... more the room-temperature crystal structure of LiAc и 2H 2 O Neutron powder diffraction is used to determine the crystal persists down to liquid-helium temperatures. Even the structure of LiCD 3 COO ؒ 2D 2 O at 293 and 1.5 K. Lithium crystal structure of this phase has been questioned, and acetate dihydrate crystallizes in the Cmmm space group in the the most recent study was made with X-rays more than 25 room-temperature phase with a ؍ 6.82082(9) Å , b ؍ years ago (9). In the present paper we present the crystal 10.88842(12) Å , c ؍ 6.59911(7) Å , and Z ؍ 4. The CH 3 groups structures of the room-temperature and low-temperature are dynamically disordered, and there are short H bonds bemodifications of LiAc и 2H 2 O as determined by neutron tween the water molecules and the acetate oxygen atoms. There powder diffraction, and relate this to the low-temperature is a phase transition to a low-temperature modification which motions of the hydrogen atoms. The use of neutron diffrachas the space group Pman with a ؍ 6.70246(7) Å , b ؍ tion allows us to locate the deuterium atoms. 10.87932(11) Å , c ؍ 6.56999(7) Å , and Z ؍ 4. The CH 3 groups are ordered in this phase, but have large thermal ellipsoids even at 1.5 K. The H atoms of the water molecules also have EXPERIMENTAL large thermal ellipsoids even at 1.5 K, but the CH 3 group tunneling spectrum shows no evidence for coupling with the motions Samples of LiCD 3 COO и 2D 2 O were prepared via the of the water molecules.
Biclotymol, 2,2¢-methylenebis(4-chloro-3-methyl-6isopropylphenol), C21H26Cl2O2, is used in human ... more Biclotymol, 2,2¢-methylenebis(4-chloro-3-methyl-6isopropylphenol), C21H26Cl2O2, is used in human therapeutics as a pulmonary antiseptic (Fig. 1), and the crystal structure of the usual raw material (Phase I) was solved by Rantsordas et al. 1 A new phase of biclotymol, Phase II, was recently found 2 to recrystallize upon heating the glass. To try and grow single crystals of this new phase, biclotymol solutions in solvents with different polarities were slowly evaporated. 3 The present paper describes the structure of the colorless, prismatic single crystals of biclotymol-DMF (1:1) obtained by slowly evaporating solutions of biclotymol powder of medicinal grade (from Bouchara-Recordati, France) in N,N¢dimethylformamide (DMF). Intensities from a single-crystal sealed in a glass capillary were collected over a hemisphere with an Enraf-Nonius CAD4 diffractometer at 293(2)K, using the CAD4 Express Enraf-Nonius programs package and XCAD4 for data collection and reduction. The structure was solved by direct methods using the program SHELXS86, 4 and refined by full-matrix least-squares procedures on F 2 , using the program SHELXL97. 5 All programs used in the structure refinement were incorporated in the WINGX package. 6 Complete data collection parameters and details of the structure solution and refinement are given in Table 1. Hydrogen atoms, except for H231, H232 and H233, were located from the difference Fourier maps. H231, H232 and H233 were positioned geometrically, and a riding-model with Uiso(H) = 1.5Ueq(Cmethyl) was used during the refinement process (C-H distances 0.95, 0.99, 0.98 Å for CH, CH2 and CH3 groups, respectively). The same isotropic thermal parameters were used for all H-atoms. Final coordinates and equivalent thermal parameters are listed in Table 2. Selected bond lengths and hydrogen bonds are compiled in Table 3. The structure of biclotymol-DMF 1:1 solvate is shown in Fig. 2. The two aromatics rings of the biclotymol molecule are linked by a methylene group. Angle C6-C7-C8 (117.7(3)˚) is close to that found in the biclotymol Phase I (118.55˚). 1 The two phenyl rings (formed by C1 to C6 and by C8 to C13) make a dihedral angle of 72.42(9)˚, comparable to that found in the structure of biclotymol Phase I. Torsion angles of the Phase-I biclotymol molecule compare well with those found in the structure of the DMF solvate. For example, torsion angle C13-C8-C7-C6 is worth 115.03˚ and X-ray Structure Analysis Online
European Physical Journal-special Topics, Apr 1, 2017
The specific volume of vitamin C has been investigated by X-ray powder diffraction as a function ... more The specific volume of vitamin C has been investigated by X-ray powder diffraction as a function of temperature from 110 K up to complete degradation around 440K. Its thermal expansion is relatively small in comparison with other organic compounds with an expansivity v of 1.2(3) ×10-4 K-1. The structure consists of strongly bound molecules in the ac plane through a dense network of hydrogen bonds. The thermal expansion is anisotropic. Along the b axis, the expansion has most leeway and is about 10 times larger than in the other directions.
The crystal structure of the methyl-deuterated lithium acetate dihydrate, 7 LiCD 3 COO, 2H 2 O, h... more The crystal structure of the methyl-deuterated lithium acetate dihydrate, 7 LiCD 3 COO, 2H 2 O, has been determined at 300, 40 and 14 K with the single crystal neutron diffraction technique. The probability density distributions of deuterium atoms were obtained by Fourier difference in the plane of the D atoms. At 14 K, the crystal symmetry is Pman. Methyl-groups are totally ordered and the angular probability density has three sharp peaks. A phase transition to the Cmmm symmetry occurs at (17.5 ± 0.5) K. This structure is analogous to that of the fully hydrogenated derivative at any temperature. However, the Fourier difference at 40 K reveals six maxima of probability for the D atoms, due to centrosymmetric pairs of face-to-face methyl groups, on the top of a continuous ring due to delocalised or disordered atoms. At 300 K, only the continuous and nearly isotropic distribution survives. In order to analyse the tunnelling spectra obtained with the inelastic neutron scattering technique we introduce symmetry-adapted angular coordinates for the strongly coupled pairs of methyl rotors. The dynamics are represented with in-phase and anti-phase rotation of the two partners. The effective moment of inertia is twice that of a single methyl group. The effective potential barrier with the threefold symmetry for in-phase rotation is %2 meV for the CH 3 pairs and %4.5 meV for the CD 3 analogues. These effective potentials are tentatively decomposed into two contributions that favour opposite orientations: the onsite potential and the interaction with next nearest neighbours, respectively. Both temperature and mass effects are rationalised with the mean angular amplitude of the rotors. We can thus account for the crystal phase transition upon methyl deuteration. The potential barrier with the sixfold symmetry for anti-phase rotation is %32 meV. It does not play any role in the ordering/disordering mechanism.
Proton transfer in the chelated form of malonaldehyde is commonly supposed to occur between two t... more Proton transfer in the chelated form of malonaldehyde is commonly supposed to occur between two tautomers, across a transition state involving changes of the chemical bonding. We show that this view is in conflict with rotational spectra. The molecule is better thought of as a superposition of indistinguishable and non-separable C s tautomers and proton tunneling is totally decoupled from the other degrees of freedom. Double minimum potential functions are determined from experiments and ab initio calculations.
The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delt... more The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delta(fus)H(I) = 36.6 +/- 0.9 kJ mol(-1)) recrystallizes into another phase, Phase II, that melts at T(fusII) = 373.8 +/- 0.2 K (Delta(fus)H(II) = 28.8 +/- 1.0 kJ mol(-1)). The transformation of Phase II into Phase I is found to be exothermic upon heating either as a direct process at 363 K or through a melting-recrystallization process (II --> liquid --> I). The melting curves, obtained from differential thermal analyses at various pressures ranging from 0 to 85 MPa, diverge as the pressure increases ((dP/dT)(fusI) = 2.54 +/- 0.07 MPa K(-1), (dP/dT)(fusII) = 5.14 +/- 0.85 MPa K(-1)). A topological P-T diagram with no stable phase region for Phase II, and similar to the 4th case of the P-T state diagrams formerly published by Bakhuis Roozeboom, is drawn, thus illustrating the overall monotropic behavior of Phase II.
La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupemen... more La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupements methyles donnent des informations tres precises sur le potentiel rotationnel local. La presence de plusieurs transitions d'effet tunnel pour le meme systeme reste un phenomene rare qui peut etre interprete en termes de rotateurs inequivalents ou de couplages. Il apparait que l'interpretation de ces donnees experimentales necessite la connaissance precise de la structure cristalline a tres basse temperature et si possible la distribution des protons. L'objectif de cette these est d'interpreter ces mesures experimentales en attribuant les transitions observees. Une fois ce travail experimental acheve, il reste a comprendre les relations entre structure et dynamique. Les modelisations utilisant diverses methodes de calcul ont permis de relier les dynamiques observees a des parametres physico-chimiques. Ces differentes methodes de calcul du potentiel rotationnel sont comparees et leurs fiabilites et limites sont discutees.
ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKa... more ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKay, M P Zorzano, (World Scientific, Publishing Co., Inc) p68 (2003) ISBN 981-283-296-8
1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensat... more 1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensation of propane-1,3-diamine with a mixture of (1H-1,2,4-triazol-1-yl)methanol and formaldehyde. The 1H- and 13C-NMR spectroscopic data of this ligand have been fully assigned and are consistent with the molecular structure. The crystalline structure of the compound was fully determined by single crystal X-ray diffraction at 150K and at room temperature, together with the isobaric thermal expansion. Finally, during the first heating, DSC measurements showed no phase transition up to the melting temperature at 385.1 K (111.9°C).
Carbamazepine (CBZ) and aspirin (ASP) drug molecules in their 1:1 co-crystal interact by relative... more Carbamazepine (CBZ) and aspirin (ASP) drug molecules in their 1:1 co-crystal interact by relatively strong hydrogen bonds and aromatic-aromatic contacts. The crystal structure and the experimental electron density in the CBZ:ASP co-crystal were derived from a high resolution X-ray diffraction experiment at K and the results are compared to those previously obtained for the CBZ form III. The isobaric thermal expansion tensor appears to be much more anisotropic for the co-crystal than for CBZ form III. The thermal expansion coefficients V are found equal to 1.3 for CBZ III and 1.5×10-4 K-1 for CBZ:ASP co-crystal. The interactions in the CBZ:ASP co-crystal have also been analyzed through the electrostatic properties derived from both experimental and theoretical electron densities: topological features, atomic charges and electrostatic potential. A very good agreement was found for the values of the electron density at the critical points (r CP) obtained from both experiment and theory. This is not, however, true for the Laplacian values which are systematically weaker in the theoretical approach. In contrast, the integrated atomic charges have higher magnitudes for the theoretical density. Additionally, it is shown here that the total molecular energies can be obtained from the electrostatic potential at the nuclei (EPN) within the Thomas-Fermi approximation. The best agreement with the conventional quantum calculations (Restricted Hartree-Fock RHF or Density Functional Theory DFT) was surprisingly obtained for the promolecule (superposition of Independent Atomic Model, IAM) density and not from the multipole model which overestimates or underestimates the energies.
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Papers by Béatrice Nicolaï