Electron distribution and molecular motion in crystalline benzene: an accurate experimental study combining CCD X-ray data on C6H6 with multitemperature neutron-diffraction results on C6D6.
The electronic properties of the benzene molecule, for example its quadrupole moment and the electric field gradients (EFG's) at the H nuclei, are of fundamental importance in theoretical and experimental chemistry. With this in mind, single-crystal X-ray diffraction data on C(6)H(6) were collected with a charge-coupled device detector at T approximately 110 K. As accurate modelling of the thermal motion in the crystal was regarded as vital, especially for the hydrogen atoms, anisotropic-displacement parameters (ADP's) for the C and H atoms in C(6)H(6) were derived in a straightforward fashion from analysis of the temperature dependence of ADP's for the C and D atoms in C(6)D(6) at 15 K and 123 K obtained by neutron diffraction. Agreement between C-atom ADP's derived from thermal-motion analysis of neutron data and those obtained from multipole refinement by using the X-ray data is extraordinarily good; this gives confidence in the modelling of vibrational motion for the H atoms. The molecular quadrupole moment derived from the total charge density of the molecule in the crystal is (-29.7+/-2.4)x10(-40) C m(2), in excellent agreement with measurements made in the gas phase and in solution. The average deuterium nuclear quadrupole coupling constant (DQCC) derived from EFG tensors at H atoms is 182+/-17 kHz, also in excellent agreement with independent measurements. The strategy employed in this work may be of more general applicability for future accurate electron density studies.
Bürgi
Hans-Beat
HB
Laboratorium für Kristallographie Universität Bern, Bern, Switzerland.
Capelli
Silvia C
SC
Goeta
Andrés E
AE
Howard
Judith A K
JA
Spackman
Mark A
MA
Yufit
Dmitrii S
DS
D001554:Benzene / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry; D018360:Crystallography, X-Ray; D004583:Electrons; D008958:Models, Molecular; D008968:Molecular Conformation; D015203:Reproducibility of Results; D013816:Thermodynamics
D001555:Benzene Derivatives; D001554:Benzene