J. P/y. Chem. Solids Vol. 47, No. II, pp. 1045-1048, 1986 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Printed in Great Britain. 0022-3697/86 S3.W + 0.00 Pergamon Journals Ltd. zyxwvutsrqp DEUTERIUM NMR OF PYRIDINE INTERCALATED CADMIUM CHALCOGENOPHOSPHATE E. LIFSIIITZ, S. VEGA, Z. Luz The Weizmann Institute of Science, Rehovot 76100, Israel A. H. FRANCIS The University of Michigan, Ann Arbor, Michigan 48109, U.S.A. and H. ZIMMERMANN Max-Planck-Institut fur Medizinische Forschung, D-6900 Heidelberg, West Germany (Received 31 March 1986; accepted 1 May 1986) Abstract-Deuterium NMR spectra of the intercalation complexes of lamellar Cd,P,S, with various deuterated pyridine molecules are reported. The measurements indicate that the pyridine molecules lie within the chalcogen van der Waals gaps with their molecular planes parallel to the chalcogen layers. Between room temperature and -60°C the pyridine molecules reorient rapidly (on the NMR time scale) about an axis perpendicular to their molecular plane. Keywords: Deuterium NMR, layered compound, intercalation compound, transition-metal chal- cogenophosphates, pyridine intercalated lamellar semiconductor. INTRODUCTION Transition-metal chalcogenophosphates form a series of lamellar broad-band semiconductors with the gen- eral chemical formula M,P,X, (M = Mn, Fe, Cd, Ni, Mg and X = S, Se). The basic structural unit of these compounds is a sandwich of three covalently bonded atomic layers in which the middle one contains the metal atoms and P, pairs (in a ratio 2: 1) while the chalcogen atoms occupy the outer layers (see Fig. 1). In the crystals these units are stacked on top of each zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA @Cd 15 OS Fig. 1. The layered structure of Cd,P, S, viewed parallel to the chalcogen layer with a pyridine molecule in the VDW gap. other and held together via weak van der Waals (VDW) bonds. At ambient temperatures the transi- tion metal sulfides are reported to be either mono- clinic or rhombohedral and the selenides to be rhombohedral [l-5]. Under appropriate conditions, guest molecules or atoms can intercalate the VDW regions resulting in dramatic changes in the physical properties of the materials [6-lo]. The most common intercalates are alkali metals, organometallic complexes and amines, suggesting that the driving force for intercalation may involve redox reactions. Several techniques have been used to study structural and dynamic character- istics of these intercalation compounds, including X-ray diffraction [6,7], dielectric relaxation [l zyxwvutsrqponml 11, elec- trical conductivity [9], IR [12], ESR [l l] and NMR (particularly ‘H) [13-191. The various techniques have their specific advantages and limitations. To this list we now add deuterium NMR which proved to be a powerful tool in the study of ordered systems [2&23] such as molecular crystals, inclusion com- pounds, polymers and liquid crystals, but has appar- ently not been used so far for chalcogenophosphate complexes of the type described above. The system chosen for our study consists of monoclinic Cd,P,S, (space group C2jm) intercalated with several isotopic species of deuterated pyridine. The results show that the pyridine molecules are oriented parallel to the chalcogen layers and undergo fast rotational motion about an axis perpendicular to the molecular plane. These conclusions are derived from the magnitude and orientation dependence of the quadrupole inter- action of the pyridine deuterons: a specific deuteron 1045