Synthesis, Crystal Structure, and Electrochemical and Magnetic Study of New Iron (III) Hydroxyl-Phosphates, Isostructural with Lipscombite Yanning Song, Peter Y. Zavalij, Natasha A. Chernova, and M. Stanley Whittingham* Department of Chemistry and Institute for Materials Research, State UniVersity of New York at Binghamton, Binghamton, New York 13902-6000 ReceiVed April 9, 2004. ReVised Manuscript ReceiVed December 20, 2004 Two novel iron (III) hydroxyl phosphates, of general formula Fe 2-y 0 y (PO 4 )(OH) 3-3y (H 2 O) 3y-2 (y ) 2 / 3 or 0.82; 0 represents vacancy), have been synthesized by the solvothermal method. The Rietveld refinement of the crystal structure from the X-ray powder diffraction was performed in a tetragonal cell with space group I4 1 /amd. The structure is isotypic with the mineral caminite Mg 1.33 [SO 4 (OH) 0.66 (H 2 O) 0.33 ] and is closely related to the mixed-valence lipscombite Fe 2-y PO 4 (OH) (0e y e 2 / 3 ). The interconnection of the chains of face-sharing iron octahedra forms the “rod-packing” structure. In Fe 1.18 (PO 4 )(OH) 0.57 (H 2 O) 0.43 (y ) 0.82), about 60% of the chain sites are occupied, whereas about 2 / 3 of the chain sites are occupied in Fe 1.33 (PO 4 )(OH) (y ) 2 / 3 ). The partial occupancy of the Fe 3+ sites allows the incorporation of other cations into the structure. When ZnCl 2 and NiCl 2 were added into the hydrothermal mix, iron was partially substituted by these metal ions, giving Fe 4/3-z M z 0 2/3 (PO 4 )(OH) 1-z (H 2 O) z (M ) Ni, Zn; z ) 0.28 and 0.26 for Ni and Zn, respectively), and increasing the cation occupation of the chains to about 2 / 3 . The protons of the hydroxyl groups in these compounds can be replaced by lithium ions with structure retention. Lithium can also be incorporated electrochemically into the lattice, and the disordered compounds are good candidates for the cathode for secondary lithium batteries. The compounds exhibit magnetic phase transitions in the temperature range 60 to 90 K; the transition temperature increases with the number of magnetic ions in the chains. Introduction Iron hydroxyl phosphates are well-known minerals and important catalysts. The natural minerals include barbosalite Fe 3 (PO 4 ) 2 (OH) 2 , 1-3 rockbridgeite Fe 5 (PO 4 ) 3 (OH) 5 , 4-5 be- raunite Fe 6 (PO 4 ) 4 (OH) 5 ‚6H 2 O, 6-7 and whitmoreite Fe 3 (PO 4 ) 2 - (OH) 2 ‚4H 2 O. 8 The structure of some of the minerals is not well determined yet, such as giniite Fe 5 (PO 4 ) 4 (OH) 2 ‚2H 2 O. 9 Some of them have varying compositions with the same structure, such as the synthetic ferric giniite with the composition from Fe 4.52 (PO 4 ) 4 (OH) 1.56 (H 2 O) 2.75 to Fe 5 (PO 4 ) 4 - (OH) 3 (H 2 O) 4.6 . 10 Iron phosphates have been identified as efficient catalysts for the selective dehydrogenation of isobutyric acid (IBA) to methacrylic acid, which can be esterified to produce methyl methacrylate, a very important intermediate in a large number of chemical processes. 11 Since the first patent dealing with the preparation and reaction of an iron phosphate catalyst was published in 1971, 12 many patents and research articles have appeared in the literature; these have been reviewed in ref 11. The iron hydroxyl phosphates were first proposed by Ruszala 13 as catalysts in the production of IBA. Barbosalite and lipscombite were also characterized and tested as catalysts. 14 Gheith 15 applied the name of lipscombite to a series of compounds of general formula Fe 2-y (PO 4 )(OH) with tet- ragonal symmetry. Only the tetragonal compounds with y < 2 / 3 have been studied; 16-19 for example, the structure of Fe 1.475 (PO 4 )(OH) (y ) 0.525) has P4 3 2 1 2 symmetry with a ) 7.310 Å and c ) 13.212 Å. 16 Schmid-Beurmann 20,21 showed the existence of a restricted tetragonal solid solution of general formula Fe III 4/3-z/3 Fe II z (PO 4 )(OH) 1-z O z (0.18 < z < 0.60). The monoclinic dimorphic variety of the ferric end member of this series (y ) 2 / 3 ), Fe 1.33 (PO 4 )(OH), has been synthesized hydrothermally at 400 °C. 22-23 * Corresponding author. Tel/fax +1-607-777-4623. E-mail: stanwhit@ binghamton.edu. (1) Lindberg, M. L.; Pecora, M. Am. Mineral. 1955, 40, 952. (2) Lindberg, M. L.; Christ, C. L. Acta Crystallogr. 1959, 12, 695. (3) Redhammer, G. J.; Tippelt, G.; Roth, G.; Lottermoser, W.; Amthauer, G. Phys. Chem. Miner. 2000, 27, 419. (4) Moore, P. B. Science 1969, 164, 1063. (5) Moore, P. B. Am. Mineral. 1970, 55, 135. (6) Fanfani, L.; Zanazzi, P. F. Acta Crystallogr. 1967, 22, 173. (7) Moore, P. B.; Kampf, A. R. Z. Kristall. 1992, 201, 263. (8) Moore, P. B.; Kampf, A. R.; Irving, A. J. Am. Mineral. 1974, 59, 900. (9) Keller, P. Neues Jahrb. Miner., Monatsh. 1980, 49. (10) Jambor, J. L.; Dutrizac, J. E. Neues Jahrb. Miner., Monatsh. 1988, 159, 51. (11) Millet, J. M. M. Catal. ReV. Sci. Eng. 1998, 40, 1. (12) Hsueh-Yan Tsu, K. BP 1,250,749, 1971. (13) Ruszala, F. U. S. Patent 4,410,727, Ashland Oil Inc., 1983. (14) Millet, J. M. M.; Rouzies, D.; Vedrine, J. C. Appl. Catal. 1995, 124, 205. (15) Gheith, M. A. Am. Mineral. 1953, 38, 612. (16) Vencato, I.; Mattievich, E.; Mascarenhas, Y. P. Am. Miner. 1989, 74, 456. (17) Matvienko, E. N.; Yakubovich, O. V.; Simonov, M. A.; Belov, N. B. Zh. Strukt. Khim. 1981, 22, 121. (18) Vocheten, R.; De Grave, E. Phys. Chem. Miner. 1981, 7, 197. (19) Rouzies, D.; Moral, P.; Millet, J. M. M. J. Phys. Chem. 1995, 99, 12576. (20) Schmid-Beurmann, P. J. Solid State Chem. 2000, 153, 237. (21) Schmid-Beurmann, P. J. Mater. Chem. 2001, 11, 660. 1139 Chem. Mater. 2005, 17, 1139-1147 10.1021/cm049406r CCC: $30.25 © 2005 American Chemical Society Published on Web 02/09/2005