V. Agafonov - Academia.edu (original) (raw)
Papers by V. Agafonov
Parametrization of Semiempirical Models against ab Initio Crystal Data: Evaluation of Lattice Energies of Nitrate Salts
The Journal of Physical Chemistry B, 2005
A method to estimate the lattice energies E(latt) of nitrate salts is put forward. First, E(latt)... more A method to estimate the lattice energies E(latt) of nitrate salts is put forward. First, E(latt) is approximated by its electrostatic component E(elec). Then, E(elec) is correlated with Mulliken atomic charges calculated on the species that make up the crystal, using a simple equation involving two empirical parameters. The latter are fitted against point charge estimates of E(elec) computed on available X-ray structures of nitrate crystals. The correlation thus obtained yields lattice energies within 0.5 kJ/g from point charge values. A further assessment of the method against experimental data suggests that the main source of error arises from the point charge approximation.
A method to predict crystal structures of crystaline drugs by systematic searching for minimum-en... more A method to predict crystal structures of crystaline drugs by systematic searching for minimum-energy packings is outlined. It bases on the use of the observed space-group occurrence factors to postulate crystal symmetry. The search region is chosen within the fundamental unit of multi-dimensional crystal-structure parameter space, including the cell parameters and rigidbody mlecular parameters. A version of the accelerated convergence method for lattice energy, and a multi-step structure optimization technique realized in the PM: (Packing of Molecules in Crystal) program are used in practical calculations. The calculated packings are tested for their similarity and occurrence of implicit symmetry with the CRYCOA4(CRYstal COMparison) program. As a numerical example, the computational study of crystalstructure polymorphism in piracetam, aimed at the structure prediction of its metastable form, is reported.
Journal de Physique I, 1992
ChemInform Abstract: Fullerene C60 Under the Influence of High Pressure Together with High Shear Stresses: How to Scratch Diamond
ChemInform, 2010
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Thermodynamic Study of Sulfanilamide Polymorphism: (I) Monotropy of the α-Variety
ABSTRACT
Study of Strain-Induced Martensites Obtained in the β-Cu-Zn-Al System
Materials Science Forum, 1990
A Theoretical Study of the Pressure-Induced Dimerization of C60 Fullerene
The Journal of Physical Chemistry A, 1999
We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs und... more We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+ 2] cycloaddition of double bonds. The possible crystal packings of (C60) 2 molecules are calculated by minimization of the lattice energy with a bond ...
Determination of the reaction rate constant and activation energy for pressure-induced 2+2 cycloaddition of the C60 fullerene
Physics of the Solid State, 2002
ABSTRACT
EPR study of the crystalline polymerized phases of C60
physica status solidi (a), 2010
Comparative electron paramagnetic resonance (EPR) study of the monomer and 1D (orthorhombic) and ... more Comparative electron paramagnetic resonance (EPR) study of the monomer and 1D (orthorhombic) and 2D (tetragonal and rhombohedral) polymerized phases of C 60 has been carried out. It was shown that the concentration of paramagnetic centers (PC) depends on ...
Pressure-induced dimerization kinetics of fullerene C60
Journal of Experimental and Theoretical Physics Letters, 2000
ABSTRACT
Formation of a New Phase of C 60 under the Combined Action of High‐Pressure and X‐Ray Radiation
Fullerenes, Nanotubes and Carbon Nanostructures, 2008
... Only the O‐phase will be dealt with in what follows. Additional published key results must be... more ... Only the O‐phase will be dealt with in what follows. Additional published key results must be mentioned: (i) the more accurate crystal symmetry Pmnn (instead of Immm) of the O‐phase 66. Moret, R., Launois, P., Persson, P.‐A. and Sundquist, B. 1997. ...
Chemistry of Materials, 2002
Triclinic C 60 ‚2ferrocene, which melts peritectically at 495 K (∆ π H) +50 J g-1), can form by d... more Triclinic C 60 ‚2ferrocene, which melts peritectically at 495 K (∆ π H) +50 J g-1), can form by direct union of its components with a negative excess volume of-68 Å 3 per formula unit, although the enthalpy of deferrocenation into fcc C 60 and ferrocene vapor is virtually the same as for the sublimation of pure ferrocene. C 60 solubility in molten ferrocene is about 0.5 mol % at 495 K. The strong anisotropy of the thermal expansion tensor illustrates the anisotropy of intermolecular interactions inferred from the crystal structure in the 90-300 K range. The existence of nonnegligible interactions is corroborated by the persistence of the crystalline local order in the amorphous phase obtained by grinding, which reverts to the initial crystalline phase upon heating. Thus, from the thermodynamic and structural points of view, C 60 ‚2ferrocene behaves as the C 60 ‚2S 8 solvate.
Chemical Physics Letters, 2007
Pressure dependence of the orthorhombic polymeric phase of C 60 has been studied by angle-dispers... more Pressure dependence of the orthorhombic polymeric phase of C 60 has been studied by angle-dispersive, X-ray powder diffraction in a diamond anvil cell. Transformation to a new phase through the simultaneous action of pressure and X-rays was observed between 0.2 and 1.66 GPa. A possible structure of this new phase of C 60 is discussed. Further increase in pressure leads gradually to the irreversible formation of a disordered phase.
‘Low-pressure’ orthorhombic phase formed from pressure-treated C60
Chemical Physics Letters, 1997
... c Laboratoire de Chimie Appliquée de l'Etat Solide, URA 1466, CNRS, ENSCP, 11 rue Pierre... more ... c Laboratoire de Chimie Appliquée de l'Etat Solide, URA 1466, CNRS, ENSCP, 11 rue Pierre et Marie Curie, 75231, Paris Cidex 05, France. d Laboratoire de Chimie Physique des Matériaux Amorphes, URA D 1104, CNRS, Bâtiment 490, Université Paris Sud. ...
Pressure-induced dimerization of fullerene C60: a kinetic study
Chemical Physics Letters, 2001
The kinetics of pressure-induced dimerization of fullerite C60 at 1.5 GPa in the 373–473 K temper... more The kinetics of pressure-induced dimerization of fullerite C60 at 1.5 GPa in the 373–473 K temperature interval was studied by X-ray diffraction, infrared and Raman spectroscopy. Kinetic curves of the dimerization reaction in the fcc and sc phases of C60 were obtained by monitoring the dimeric (C60)2 IR line at 796 cm−1. The value of the dimerization activation energy was
Study of the Orthorhombic Polymeric Phase of C60Under High Pressure Using Synchrotron X-Ray Powder Diffraction
Fullerenes, Nanotubes and Carbon Nanostructures, 2010
ABSTRACT As an extension of our previously published work (2007) on the orthorhombic phase of pol... more ABSTRACT As an extension of our previously published work (2007) on the orthorhombic phase of polymeric C60, high-resolution powder diffraction experiments under high pressure were recently carried out at the ESRF/SNBL/BM01A beamline. The acquisition times were very short, of the order of 10 minutes. In contrast to our first laboratory experiment, which involved much longer exposures (50–150 hours), no photo-induced transition to a crystalline state of lower symmetry could be observed up to 6 GPa. The obtained powder diffractograms are all consistent with an orthorhombic unit cell. A Birch-Murnaghan equation of state is fitted to the resulting pressure-volume data for the orthorhombic phase.
The European Physical Journal B - Condensed Matter, 2003
We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 singlecr... more We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 singlecrystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.
Acta Crystallographica Section C Crystal Structure Communications, 1993
The molecule of the title compound is made of two asymmetric units related by a centre of symmetr... more The molecule of the title compound is made of two asymmetric units related by a centre of symmetry and exhibits a trans conformation. The aromatic ring is elongated along the C(8)-C(8 i) [(i) 1-x, 1-y, 1-z] direction owing to steric hindrance and substituents on two contiguous C atoms are pushed apart from one another. The distance from an N atom to the aromatic ring plane is 0.105 (1)A and that
Fullerenes, Nanotubes and Carbon Nanostructures, 2006
Le Journal de Physique IV, 2001
Using differential scanning calorimetry (DSc) and X-ray diffraction (XRD) at low temperatures we ... more Using differential scanning calorimetry (DSc) and X-ray diffraction (XRD) at low temperatures we have determined a phase relation between y-butyrolactone and dimethyl carbonate. Two polymorphs of ybutyrolactone with a monotropic transformation and two polymorphs of dimethyl carbonate with an enantiotropic transformation induced by BL were observed. The diagram is characterised by an eutectic point for xDMC=O. 12 and T=-.57.5OC.
Parametrization of Semiempirical Models against ab Initio Crystal Data: Evaluation of Lattice Energies of Nitrate Salts
The Journal of Physical Chemistry B, 2005
A method to estimate the lattice energies E(latt) of nitrate salts is put forward. First, E(latt)... more A method to estimate the lattice energies E(latt) of nitrate salts is put forward. First, E(latt) is approximated by its electrostatic component E(elec). Then, E(elec) is correlated with Mulliken atomic charges calculated on the species that make up the crystal, using a simple equation involving two empirical parameters. The latter are fitted against point charge estimates of E(elec) computed on available X-ray structures of nitrate crystals. The correlation thus obtained yields lattice energies within 0.5 kJ/g from point charge values. A further assessment of the method against experimental data suggests that the main source of error arises from the point charge approximation.
A method to predict crystal structures of crystaline drugs by systematic searching for minimum-en... more A method to predict crystal structures of crystaline drugs by systematic searching for minimum-energy packings is outlined. It bases on the use of the observed space-group occurrence factors to postulate crystal symmetry. The search region is chosen within the fundamental unit of multi-dimensional crystal-structure parameter space, including the cell parameters and rigidbody mlecular parameters. A version of the accelerated convergence method for lattice energy, and a multi-step structure optimization technique realized in the PM: (Packing of Molecules in Crystal) program are used in practical calculations. The calculated packings are tested for their similarity and occurrence of implicit symmetry with the CRYCOA4(CRYstal COMparison) program. As a numerical example, the computational study of crystalstructure polymorphism in piracetam, aimed at the structure prediction of its metastable form, is reported.
Journal de Physique I, 1992
ChemInform Abstract: Fullerene C60 Under the Influence of High Pressure Together with High Shear Stresses: How to Scratch Diamond
ChemInform, 2010
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Thermodynamic Study of Sulfanilamide Polymorphism: (I) Monotropy of the α-Variety
ABSTRACT
Study of Strain-Induced Martensites Obtained in the β-Cu-Zn-Al System
Materials Science Forum, 1990
A Theoretical Study of the Pressure-Induced Dimerization of C60 Fullerene
The Journal of Physical Chemistry A, 1999
We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs und... more We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+ 2] cycloaddition of double bonds. The possible crystal packings of (C60) 2 molecules are calculated by minimization of the lattice energy with a bond ...
Determination of the reaction rate constant and activation energy for pressure-induced 2+2 cycloaddition of the C60 fullerene
Physics of the Solid State, 2002
ABSTRACT
EPR study of the crystalline polymerized phases of C60
physica status solidi (a), 2010
Comparative electron paramagnetic resonance (EPR) study of the monomer and 1D (orthorhombic) and ... more Comparative electron paramagnetic resonance (EPR) study of the monomer and 1D (orthorhombic) and 2D (tetragonal and rhombohedral) polymerized phases of C 60 has been carried out. It was shown that the concentration of paramagnetic centers (PC) depends on ...
Pressure-induced dimerization kinetics of fullerene C60
Journal of Experimental and Theoretical Physics Letters, 2000
ABSTRACT
Formation of a New Phase of C 60 under the Combined Action of High‐Pressure and X‐Ray Radiation
Fullerenes, Nanotubes and Carbon Nanostructures, 2008
... Only the O‐phase will be dealt with in what follows. Additional published key results must be... more ... Only the O‐phase will be dealt with in what follows. Additional published key results must be mentioned: (i) the more accurate crystal symmetry Pmnn (instead of Immm) of the O‐phase 66. Moret, R., Launois, P., Persson, P.‐A. and Sundquist, B. 1997. ...
Chemistry of Materials, 2002
Triclinic C 60 ‚2ferrocene, which melts peritectically at 495 K (∆ π H) +50 J g-1), can form by d... more Triclinic C 60 ‚2ferrocene, which melts peritectically at 495 K (∆ π H) +50 J g-1), can form by direct union of its components with a negative excess volume of-68 Å 3 per formula unit, although the enthalpy of deferrocenation into fcc C 60 and ferrocene vapor is virtually the same as for the sublimation of pure ferrocene. C 60 solubility in molten ferrocene is about 0.5 mol % at 495 K. The strong anisotropy of the thermal expansion tensor illustrates the anisotropy of intermolecular interactions inferred from the crystal structure in the 90-300 K range. The existence of nonnegligible interactions is corroborated by the persistence of the crystalline local order in the amorphous phase obtained by grinding, which reverts to the initial crystalline phase upon heating. Thus, from the thermodynamic and structural points of view, C 60 ‚2ferrocene behaves as the C 60 ‚2S 8 solvate.
Chemical Physics Letters, 2007
Pressure dependence of the orthorhombic polymeric phase of C 60 has been studied by angle-dispers... more Pressure dependence of the orthorhombic polymeric phase of C 60 has been studied by angle-dispersive, X-ray powder diffraction in a diamond anvil cell. Transformation to a new phase through the simultaneous action of pressure and X-rays was observed between 0.2 and 1.66 GPa. A possible structure of this new phase of C 60 is discussed. Further increase in pressure leads gradually to the irreversible formation of a disordered phase.
‘Low-pressure’ orthorhombic phase formed from pressure-treated C60
Chemical Physics Letters, 1997
... c Laboratoire de Chimie Appliquée de l'Etat Solide, URA 1466, CNRS, ENSCP, 11 rue Pierre... more ... c Laboratoire de Chimie Appliquée de l'Etat Solide, URA 1466, CNRS, ENSCP, 11 rue Pierre et Marie Curie, 75231, Paris Cidex 05, France. d Laboratoire de Chimie Physique des Matériaux Amorphes, URA D 1104, CNRS, Bâtiment 490, Université Paris Sud. ...
Pressure-induced dimerization of fullerene C60: a kinetic study
Chemical Physics Letters, 2001
The kinetics of pressure-induced dimerization of fullerite C60 at 1.5 GPa in the 373–473 K temper... more The kinetics of pressure-induced dimerization of fullerite C60 at 1.5 GPa in the 373–473 K temperature interval was studied by X-ray diffraction, infrared and Raman spectroscopy. Kinetic curves of the dimerization reaction in the fcc and sc phases of C60 were obtained by monitoring the dimeric (C60)2 IR line at 796 cm−1. The value of the dimerization activation energy was
Study of the Orthorhombic Polymeric Phase of C60Under High Pressure Using Synchrotron X-Ray Powder Diffraction
Fullerenes, Nanotubes and Carbon Nanostructures, 2010
ABSTRACT As an extension of our previously published work (2007) on the orthorhombic phase of pol... more ABSTRACT As an extension of our previously published work (2007) on the orthorhombic phase of polymeric C60, high-resolution powder diffraction experiments under high pressure were recently carried out at the ESRF/SNBL/BM01A beamline. The acquisition times were very short, of the order of 10 minutes. In contrast to our first laboratory experiment, which involved much longer exposures (50–150 hours), no photo-induced transition to a crystalline state of lower symmetry could be observed up to 6 GPa. The obtained powder diffractograms are all consistent with an orthorhombic unit cell. A Birch-Murnaghan equation of state is fitted to the resulting pressure-volume data for the orthorhombic phase.
The European Physical Journal B - Condensed Matter, 2003
We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 singlecr... more We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 singlecrystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.
Acta Crystallographica Section C Crystal Structure Communications, 1993
The molecule of the title compound is made of two asymmetric units related by a centre of symmetr... more The molecule of the title compound is made of two asymmetric units related by a centre of symmetry and exhibits a trans conformation. The aromatic ring is elongated along the C(8)-C(8 i) [(i) 1-x, 1-y, 1-z] direction owing to steric hindrance and substituents on two contiguous C atoms are pushed apart from one another. The distance from an N atom to the aromatic ring plane is 0.105 (1)A and that
Fullerenes, Nanotubes and Carbon Nanostructures, 2006
Le Journal de Physique IV, 2001
Using differential scanning calorimetry (DSc) and X-ray diffraction (XRD) at low temperatures we ... more Using differential scanning calorimetry (DSc) and X-ray diffraction (XRD) at low temperatures we have determined a phase relation between y-butyrolactone and dimethyl carbonate. Two polymorphs of ybutyrolactone with a monotropic transformation and two polymorphs of dimethyl carbonate with an enantiotropic transformation induced by BL were observed. The diagram is characterised by an eutectic point for xDMC=O. 12 and T=-.57.5OC.