The Raman spectra of the equimolecular mixture HN03.H20 in the liquid and glassy states have been investigated in the range 4000-50 cm-'. At least four species have been characterized: (i) The free molecular association H 2 0 . . . HON02 voH(H2O) = 3550 cm-' (3440 cm-') and voH(HN03) = 2930 cm-' (2915 cm-') respectively in the liquid (and the glass). (ii) The free ionic pair (H20H)'. . . (ON02)-that give a splitting (Av = 170 cm-') of the v,(NO;) vibration. (iii) Free HNOl molecules: vNOH = 940 and 950 cm-' respectively in the liquid and the glass. (iv) The 'nitric acid trihydrate': H,O;NO;voH between 3100 and 3300 cm-'.Dans l'etat cristallise, le monohydrate de I'acide nitrique est en realit6 le nitrate d'oxonium.' Depuis 1951, il a CtC etudie tant par radiocristallographie X2,3 que par spectroscopie de Cependant les Ctudes Raman6" sont anciennes et incomplttes. Par ailleurs les travaux de spectroscopie de vibration IR se rtfbrent i la structure proposke par Luzzati2 oij les longueurs N-0 de la molecule H N 0 3 sont diffkrentes. On recemment, Delaplane, Taesler et Olovsson3 ont montrk qu'on est en presence d'ion NO; (conservant la symktrie ternaire) qui sont en interactions fortes avec les ions oxonium puisqu'il existe des liaisons hydrogbne de 2,60 A. Ces conclusions sont ttaykes par les donnees de RMN en bande large' puisque, dbs la temperature de cristallisation, le second moment du nitrate d'oxonium est de 31 G 2 (reseau rigide) valeur que les autres sels d'oxonium n'atteignent qu'B basse tempkrature.Ce n'est pas lh le seul phenomkne remarquable pour ce sel. En effet, la cristallisation de la solution de composition H N 0 3 . H 2 0 n'est pas instantanee, on est en presence d'un exemple type des processus de vitrification -dCvitrification.8 Les difficultks rencontrees pour obtenir une bonne cristallisation sont certainement dues 2i un changement de structure profond quand on passe des ktats dtsordonnes (liquide ou verre) A l'etat organis6 (cristal). Eff ectivement plusieurs auteurs9-I2 ont montrk qu'a la composition du monohydrate il existait essentiellement, dans 1'Ctat liquide, de l'acide nitrique moleculaire en interaction avec des molecules d'eau et en proportions plus faibles des ions nitrates associes B des hydrates du proton (mono et trihydrate). L'etude Raman de Chedin ef a1.' est limitee B celle de I'ivolution des raies caracteristiques de la molecule HN03 principalement VOH et &OH.+ 11s ont dkduit de + Cette attribution etant ]'attribution actuelle.20.2' cette etude fragmentaire que la molecule H 2 0 est Iiee au groupe NO2 de H N 0 3 ; or ce mode d'association est peu compatible avec les connaissances actuelles des interactions a~i d e -b a s e . '~' '~ I1 a paru interessant de reprendre cette etude par spectroscopie Raman afin d'etudier la composition particulaire du liquide et du verre et de la comparer B l'espkce unique (H30'NO;) dans le cristal. On verra ainsi que dans le verre et dans le liquide I'interaction des deux especes dominantes H N 0 3 -HzO est un exemple d'interaction acide-base sans ...
The infrared and Raman spectra of the mixture HC104 0 2H20 in the glassy and liquid states have been investigated. Two species have been characterized: (a) the dioxonium perchlorate where the H50:, and CIO; ions are linked by hydrogen bonds weaker than in the crystal (vOH(HSO:) = 3430 and 3460 cm-' respectively in the glass and liquid state Raman spectra and 3340 cm-' for the crystal). (b) an ionic association, 0,CIO---* H(OH)HOH;, in which the vibrational motions of the terminal H 2 0 molecules are characterized by SOH = 1530 and 1550 cm-' and wOH = 3480 and 3520 cm-' respectively in the glass and liquid state Raman spectra and in which ul(CIO;) shifts to lower frequencies (Au = -12 cm-').
247Tous nos remerciements vont 5. M P. Eymard, du CREPS, qui nous a fait don des compos6s 6tudi6s ici, et /t M A. Durif du CNRS, pour l'accueil dans son laboratoire lors de l'utilisation du diffractom&re automatique.
Crystals of dichloroantimony(III) tetrachlorogallate(III) are monoclinic, space group P21/c with: a = 9.837(2) Å, b = 7.812(2) Å, c = 12.504(2) Å, β = 101.0(2)°. The structure was refined by three dimensional least‐squares method to R = 5.2% for 1051 independent reflections. The antimony atom has two nearest chlorine neighbours at 2.295(4) Å and 2.299(4) Å giving the expected angular conformation and two other neighbours at 2.713(4) Å and 2.772(4) Å completing with the lone pair a trigonal bipyramid environment around antimony. The GaCl4− groups, highly distorted from regular tetrahedral geometry, strongly interact with SbCl2+ via GaCl···Sb bridges giving an endless polymeric chain.
A quantum chemical scheme adapted to study charge separation processes in crystalline molecular/ionic defects is presented. The scheme derives from a generalized self-consistent reaction field theory of surrounding medium effects. Computational implementation has been done at the CNDO/2-INDO approximate level; lattice sums are performed by direct summation techniques. The sums are essential for building the static dielectric response function of the crystal to the field set up by the defect charge density and the Madelung potential created by the surrounding crystal permanent charge density. The scheme has been applied to study some aspects of the proton conductivity mechanism in crystalline hydronium perchlorate. The theoretical results lend support to an experimentally grounded molecular mechanism. The theoretical scheme can easily be extended to describing chemical processes taking place at crystal surfaces.
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