STRUCTURE AND ELECTROSTATIC PROPERTIES OF POLYOXOVANADATES.
Virginie Pichon-Pesme1, Hassane Lachekar 1, Claude Lecomte1, Marc Bénard2 & Marie-Madeleine Rohmer2
1LCM3B, Laboratoire de Cristallographie et
Modélisation des Matériaux Minéraux et Biologiques. UPRESA CNRS 7036,Université
Henri Poincaré - Nancy 1, Faculté des Sciences,BP 239, 54506
VANDOEUVRE LES NANCY CEDEX, France. e-mail : pichon@lcm3b.u-nancy.fr
2Laboratoire de
Chimie Quantique, UMR CNRS 7551, Université Louis Pasteur, 4 rue Blaise Pascal,67000
STRASBOURG, France.
Keywords : electron density, electrostatic potential,
theoretical calculation, polyoxovanadates.
The molecular compound Na10[H3V18O44(N3)] is an example in the inorganic chemistry of host-guest species [1]. The closed cluster shell of O=VO4 polyedra square pyramid linked together adopt an oblong shape and encapsulate a linear azide ion (N3-). The attractive and repulsive forces between the electrophilic (Vn+) and nucleophilic (O2-) centers of the negatively charged shell and the enclosed anionic guest shows a dualism of interactions.
This oxovanadate crystallizes in the space group P-1 with the cell parameters a=11.978 A, b=13.084 A, c= 13.428 A, a=114.73°, b=92.99°, g=113.84°. The unit cell contains also 30 water molecules. The X-ray diffraction measurements were performed with AgKa radiation up to sin q /l= 1.26A-1 at room temperature. 72330 reflections were collected yielding 32184 independent reflections. Data were corrected for absorption (m=1.32mm-1). The agreement factors after a conventional refinement are R=0.0398 and RW=0.0548. First results concerning electron density study based on multipole model (Hansen-Coppens [2]) will be displayed.
Ab initio theoretical calculations are performed in the
experimental conformation. From these Hartree-Fock SCF wave
functions, the charge density and the electrostatic potential are
determined and are used to interpret the preferred sites of
proton fixation. A comparison between experimental and
theoretical results will be discussed.