1220 Inorg. Chem. 1994, zyxwvut 33, 1220-1226 Topotactic Intercalation of Water and Pyridine into Co(H2POz)ynHzO (0 I z n I 0.69). Crystal Structure of Co(H2P02)~0,53H20 Solved from X-ray Powder Diffraction Data M. Dolores Marcos, Pedro Amor6s,* Daniel Beltrln, and Aurelio Beltrln UIBCM, Departament de Quimica Inorgdnica, Facultat de Quimiques, Universitat de Valbncia, Dr. Moliner No. 50, 46 1 00-Burjassot (Valbncia), Spain Received August 6, 1993" The synthesis of differently hydrated layered cobalt hypophosphites, Co(HzPO2)2.nH20 (0 I n I 0.69), has been possible by carefully controlling the water content in the reaction medium. The crystal structure of Co(H2- P02)y0.53H20 has been refined from X-ray powder diffraction data by the Rietveld method, using as a starting model the structural parameters of the orthorhombicanhydrous zinc hypophosphite Z I I ( H ~ P O ~ ) ~ . The cell is monoclinic (space group P112/a; zyxwvuts 2 zyxwvut = 2) with a = 6.4722(3) A, b = 5.341 l(3) A, c = 7.4900(3) A and zyx y = 90.087(12)O. The final reliability factors were, RI = 5.38%, R, = 7.31%, and R,, = 9.05%. The lamellar structure can be thought of as constructed from corrugated rutile like chains of cationic edge-sharing octahedra running along the u axis and interconnected in the b direction through hypophosphite bridges. Co(H2P02)2.nH20 compounds are suitable hosts lattices for intercalation reactions. Water and pyridine intercalation processes in these matrices have been studied by thermal analysis, variable-temperature X-ray powder diffraction, and spectroscopic techniques. A structural proposal for Co(H2P02)2.1.86(C~H5N)-0.3 1H20 is presented. Introduction The intercalation of guest molecules in layered hosts has received considerable attention in recent years owing to the potential that such materials show for catalysis, molecular sieving, and ion exchange. Intercalation can be considered a reversible topotactic reaction of a solid host (H), which provides an interconnected system of accessible unoccupied lattice sites (O), with ambient mobile guest species (G) that can diffuse into the solid and occupy the empty positions according to the following reaction scheme: xG + o,[H] - GJH]. The term topotactic refers to the idea that the host matrix units retain their integrity with respect to the structure and composition in the course of intercalation and deintercalation. A considerable number of solids with layered structures (clays, graphite, transition metal chal- cogenides, oxide bronzes, zirconium phosphates, vanadium phosphates, etc.) have proved to be suitable host for intercalation, whereas the nature of the guest species (ions or neutral molecules, metal complexes, etc.) is related to the binding modes that these entities may establish with the host lattice (ionicor covalent bonds, van der Waals interaction^,..).'-^ Following our work on oxovanadium phosphate^,^ we explored the idea that the formation of new low dimensional systems (in particular lamellar solids able to act as host lattices) might be further favored by replacing phosphate groups by other related pseudotetrahedral anionic entities having a lower connectivity, such as occurs for hypophosphite groups. The current knowledge on hypophosphites is s c a r ~ e . ~ This is specially the case of transition metal derivatives. The only compounds whose structure has been determined are Ni(H2- P02)y6H20,6 @-Mn(H2POz)2.Hz0,7 Z ~(H~POZ)~.H~O,~ Zn(H2- e Abstract published in Advance ACS Abstracts, February 1, 1994. (1) Whittingham, M. S.; Jacobson, A. J. Intercalation Chemistry; Whit- tingham, M. s., Jacobson, A. J., Eds.; Academic Press, New York, 1982. (2) Murphy, D. W.; Sushine, S. A.; Zahurak, S. M. Chemical Physics of Intercalation; NATO AS1 Series, Series B: Physics; Plenum: New York, 1987; Vol. 172, p 173. (3) Clearfield, A. Chem. Reu. 1988, 88, 125. (4) BeltrBn, D.; BeltrBn, A.; Amorb, P.; Iblilez, R.; Martfnez, E.; Le Bail, A.; Ferey, G.; Villeneuve, G. Eur. J. Solid Stare Inorg. Chem. 1991,28, 131 and references therein. (5) Loub, J.; Kratochvil, B. Chem. Listy 1987, 81. 337. (6) Victor Chemical Works Chem. Weekbl. 1953, 10, 40. 0020-1669 zyxwvutsrq f 9411333- 1220$04.50/0 P02)2,7 MCI(H~PO~).HZO (M = Co, Ni),*v9 a-Mn(H2P02)y H20,10 and VO(H2P02)2.H20.11 In addition, three differently hydrated cobalt hypophosphites have been reported in the literature [Co(H2P02)y6H20,6Co(H2PO2)y2H20,l3 and Co(H2- P02)214 1, but their structures remain unsolved. Our previous work on related systems4 suggests that transition metal layered hypophosphites might be suitable host lattices to support inter- calation reactions, although no successful attempt in this sense has been described in the literature to date. Otherwise, solids with alternating inorganic and organic layers also have been extensively studied due to their useful sorptive and catalytic properties and because they can serve as microcrystalline models for interfacial systems.I5 Such compounds may formally be thought of as resulting from the intercalation of organic species into an inorganic host lattice. In this work, we describe the synthesis and crystal structure of Co(H2P02).nH20 (0 I n I 0.69) solved from X-ray powder diffraction data. Moreover, we present for the first timea detailed study of intercalation processes into a transition metal hypo- phosphite host: the topotactic insertion of water and pyridine into Co(H2POz)z. Experimental Section Synthesis of Co(H$02)2.aH20. An anhydrous variety of cobalt hypophosphite was reported by Brun and Dumail.14 Unfortunately, the synthetic procedure was poorly described in their work (crystallization from aqueous solutions at 60 "C), and all our attempts to isolate it systematically lead to solids showing a variable degree of hydration. Co- (H2P02)~0.53H20 was prepared as follows. A 2.851-g (10.1-mmol) sample of Co(S0&7H20 were dissolved in 10 mL of distilled water. (7) Weakley, T. J. R. Acta Crystallogr.. B 1979, 25,42. (8) Marcos, M. D.; IbBfiez, R.; Amorb, P.; Le Bail, A. Acta Crystallogr., C 1991, 47, 1152. (9) Marcos, M. D.; Amorb, P.; Sapiila, F.; Beltrin, A.; Martfnez-Mafiez, R.; Attfield, J. P. Inorg. Chem. 1993, 32, 5044. (10) Marcos, M. D.; Amorb, P.; Sapifia, F.; BeltrBn, D. J. Alloys Compd. 1992, 188, 133. (1 1) Le Bail, A,; Marcos, M. D.; Amor&, P. Inorg. Chem., submitted for publication. (12) Marcos, M. D.; Amorbs, P.; BeltrBn, A.; BeltrBn, D. Solid State Ionics (13) Gmelin Handbook of Inorganic Chemistry; Springer Verlag: Berlin, (14) Brun, G.; Dumail, M. C. R. Acad. Sci. Paris 1971, 272, 1869. (15) Cao, G.; Hong, H.; Mallouk, T. E. Acc. Chem. Res. 1992, 25, 420. 1993,6345, 96. 1932; Vol. Co (58A). 0 1994 American Chemical Society