Inorganic Chemistry, Vol. 18, No. 12, 1979 3595
Allotropic Transitions of Mg,NiH, of Education of Japan (Grant No. 255315). Registry No. 12597-50-1.
S42+, 12597-09-0; Se42+, 123 10-32-6; Te?+,
References and Notes (1) (a) V. V. Walatka, Jr., M. M. Labes, and J. H. Perlstein, Phys. Reu. Lett., 31, 1139 (1973); (b) C. Hsu and M. M. Labes, J. Chem. Phys., 61, 4640 (1974). (2) R. L. Greene, G. B. Street, and L. J. Suter, Phys. Reo. Lett., 35, 1799 (1975). (3) For example, see (a) S. R. Ovshinsky, J . Non-Cryst. Solids, 2, 99 (1970); (b) S. R. Ovshinsky and H. Fritzsche, IEEE Trans. Electron Deuices, ed-20, 91 (1973); (c) S . R. Ovshinsky and K. Sapru, Amorphous Liq. Semicond., Proc. In!. Conf., Sth, 447 (1974); (d) S. R. Ovshinsky, Int. Kongr. Reprogr. Znf., 4th, 109 (1975). (4) (a) T. Yamabe, K. Tanaka, A. Imamura, H. Kato, and K. Fukui, Bull. Chem. SOC.Jpn., 50,798 (1977); (b) K. Tanaka, T. Yamabe, K. Fukui, A. Imamura, and H. Kato, Chem. Phys. Lett., 53, 452 (1978), and
references therein. (5) (a) I. Chen, Phys. Rev. B, 8, 1440 (1973); (b) T. Shimizu and N. Ishi, Phys. Status Solidi B, 74, K39 (1976); (c) M. Kastner, D. Adler, and H. Fritzsche, Phys. Reu. Lett., 37, 1504 (1976); (d) A. Tachibana, T. Yamabe, M. Miyake, K. Tanaka, H. Kato, and K. Fukui, J . Phys. Chem., 82, 272 (1978). (6) (a) A. Caron and J. Donohue, Acta Crystallogr., 14, 548 (1961); (b) P. Uneer and P. Cherin in “Physics of Selenium and Tellurium”, W. C. Cooper, Ed., Pergamon, Oxford, 1969, p 223. (7) (a) I. Chen, Phys. Reu. B, 2, 1053, 1060 (1970); 7, 3672 (1973); 11, 3976 (1975); (b) W. R. Salaneck, N. 0. Lipari, A. Paton, R. Zallen, and K. S. Liang, Phys. Reu. B, 12, 1493 (1975); (c) W. R. Salaneck, C. B. Duke, A. Paton, C. Griffiths, and R. C. Keezer, Phys. Reu. B, 15, 1100 (1977). (8) For example, see (a) J. Sharma, D. S. Downs, Z. Iqbal, and F. J. Owens, J . Chem. Phys., 67,3045 (1977); (b) R. D. Smith, Chem. Phys. Lett., 55, 590 (1978); (c) J. Bojes and T. Chivers, Inorg. Chem., 17, 318 (1978). (9) For example, see (a) D. R. Salahub and R. P. Messmer, J . Chem. Phys., 64, 2039 (1976); (b) W. R. Salaneck, J. W-p. Lin, A. Paton, C. B. Duke, and G. P. Ceasar, Phys. Rev. B, 13,4517 (1976); (c) T. Yamabe, K. Tanaka, K. Fukui, and H. Kato, J. Phys. Chem., 81,727 (1977); (d) J. A. Jafri, M. D. Newton, T. A. Pakkanen, and J. L. Whitten, J . Chem. Phys., 66,5167 (1977); ( e ) K. Tanaka, T. Yamabe, A. Tachibana, H. Kato, and K. Fukui, J . Phys. Chem., 82, 2121 (1978). (10) (a) C. F. Bucholz, Gehlen’s Neues J . Chem., 3, 7 (1804); (b) G. Magnus, Ann. Phys. (Leipzig), 10 (2), 491 (1827); 14, 328 (1828); (c) M. H. Klaproth, Philos. Mag., 1, 78 (1798).
(11) (a) R. J. Gillespie and J. Passmore, Acc. Chem. Res., 4, 413 (1971); (b) R. J. Gillespie and J. Passmore, Adu. Inorg. Chem. Radiochem., 17, 49 (1975), and references therein. (12) C. G. Davies, R. J. Gillespie, J. J. Park, and J. Passmore, Inorg. Chem., 10, 2781 (1971). (13) I. D. Brown, D. B. Crump, and R. J. Gillespie, Inorg. Chem., 10, 2319 (1971). (14) (a) R. K. McMullan, D. J. Prince, and J. D. Corbett, Chem. Commun., 1438 (1969); (b) R. K. McMullan, D. J. Prince, and J. D. Corbett, Inorg. Chem., 10, 1749 (1971). (15) T. W. Couch, D. A. Lokken, and J. D. Corbett, Inorg. Chem., 11,357 (1972). (16) R. Steudel, 2. Naturforsch., B, 30, 281 (1975). (17) K. Tanaka, T. Yamabe, H. Terama-e, and K. Fukui, Nouu. J . Chim., 3, 379 (1979). (18) A. G. MacDiarmid, C. M. Mikulski, P. J. Russo, M. S. Saran, A. F. Garito, and A. J. Heeger, J . Chem. SOC.,Chem. Commun., 476 (1975). (19) I. D. Brown, D. B. Crump, R. J. Gillespie, and D. P. Santry, Chem. Commun., 853 (1968). (20) (a) A. E. Foti, V. H. Smith, Jr., and D. R. Salahub, Chem. Phys. Lett., 57,33 (1978); (b) D. R. Salahub, A. E. Foti, and V. H . Smith, Jr., J . A m . Chem. SOC.,100, 7847 (1978). (21) (a) T. Yonezawa, H. Konishi, and H. Kato, Bull. Chem. SOC.Jpn., 42, 933 (1969); (b) H. Konishi, H. Kato, and T. Yonezawa, Theor. Chim. Acta, 19,71 (1970); (c) H. Yamabe, H. Kato, and T. Yonezawa, Bull. Chem. SOC.Jpn., 44, 22 (1971); (d) H. Yamabe, H. Kato, and T. Yonezawa, ibid., 44, 611 (1971). (22) The two-center Coulomb repulsion integrals are calculated by the Ohno approximation (K. Ohno, Theor. Chim. Acta, 2,219 (1964)), and the one-center exchange integrals are evaluated by the Slater-Condon pa-
rameters estimated by Hinze and Jaff6.2s (23) E. Clementi, D. L. Raimondi, and W. P. Reinhardt, J. Chem. Phys., 47, 1300 (1967). (24) J. Hinze and H. H. Jaff6, J . A m . Chem. SOC.,84, 540 (1962). (25) J. Hinze and H. H. Jaff6, J . Chem. Phys., 38, 1834 (1963). (26) (a) A. G. Turner and F. S.Mortimer, Inorg. Chem., 5,906 (1966); (b) M. S. Gopinathan and M. A. Whitehead, Can. J . Chem., 53, 1343 (1974); (c) K. H. Johnson, Adu. Quantum Chem., 7, 143 (1973); (d) V. BonaEiE-Koutecky and J. L’Musher, Theor. Chim. Acta, 33, 227 (1974). (27) C. Edmiston and K. Ruedenberg, Rev. Mod. Phys., 35, 457 (1963). (28) J. A. Pople, D. P. Santry, and G. A. Segal, J . Chem. Phys., 43, S129 (1965). (29) For example, see J. N. Murrell, S. F. A. Kettle, and J. M. Tedder, “Valence Theory”, Wiley, London, 1965, p 52. (30) (a) R. C. Paul, J. K. Puri, and K. C. Malhotra, Chem. Commun., 776 (1970); (b) N. J. Bjerrum, Inorg. Chem., 11, 2648 (1972). (31) (a) W. J. Taylor, J. Chem. Phys., 48, 2385 (1968); (b) E. Switkes, W. N. Lipscomb, and M. D. Newton, J . A m . Chem. SOC.,92,3847 (1970).
Contribution from the Nuclear Research Centre, Negev, Beer-Sheva, Israel, and The Ben-Gurion University of the Negev, Beer-Sheva, Israel
Allotropic Transitions of Mg2NiH4 Z. GAVRA, M. H. M I N T Z , G. KIMMEL, and Z. HADARI* Received May 2, 1979 The crystallographic structure and thermal behavior of Mg2NiH4have been studied in the temperature range 25-500 “ C . Two allotropic forms of this hydride were identified. An orthorhombic structure with a = 11.36 A, 6 = 11.16 A, and c = 9.12 A (P222,) containing 16 formula units per cell is stable a t ambient temperature. This structure transforms at 210-245 “ C to a cubic pseudo-CaF2-type structure with a = 6.490 A and 4 formula units per cell. The allotropic transition is not accompanied by a change in hydrogen composition which remains the same for both structures (under about a 700-torr hydrogen atmosphere). The enthalpy change associated with this transition was estimated to be 0.80 0.05 kcal/mol of H 2 (1.60 kcal/mol of Mg2NiH4).
*
Introduction The Mg2Ni reacts with hydrogen at about 300 “C and moderate pressures.’ The product of the reaction is a ternary hydride with the formula Mg2NiH4. The high hydrogen weight capacity of this hydride (about 3.6%), its moderate stability, and its fast absorption-desorption kinetics make Mg2NiH4 an attractive candidate for hydro*To whom correspondence should be addressed at The Ben-Gurion University of the Negev.
0020-1669/79/1318-3595$01.00/0
gen-storage applications. Thus, for example, Mg2NiH4has been utilized recently as a hydrogen-storage unit in fuel tanks of Mercedes-Benz hydrogen-powered vehicles,2,3 It has been reported’ that Mg2NiH4 has a tetragonal structure with a = 6,464 A and = 7,033 A, No information is available concerning the space group and atomic positions of this structure, During some thermal analyses which we performed on this comwund a reversible allotroDic Dhase transition was observed, A’crystallographic study bas thus been carried out on the two allotropic forms of the hydride combined with simulta0 1979 American Chemical Society
3596 Inorganic Chemistry, Vol. 18, No. 12, 1979 Table I. Crystallographic Data for the Low-Temperature Structure of Mg,NiH, Indexed on the Basis of an Orthorhombic Unit Cell dcalcd
dobsd
Iobsd
hkl
5.68 4.56 4.22 3.98 3.96 3.79 3.72 3.65 2.963 2.840 2.819 2.790 2.712 2.670 2.439 2.380 2.305 2.293 2.280 2.247 2.174 2.056 2.050 2.022 2.005 1.978 1.945 1.933 1.867 1.777 1.765 1.744 1.644 1.621 1.604 1.595 1.571 1.544 1.520 1.503 1.499 1.493 1.488 1.464 1.457 1.361 1.330
5.79 4.55 4.19 4.00 3.95 3.81 3.75 3.68 2.969 2.840 2.820 2.790 2.721 2.675 2.429 2.37 9 2.29 8 2.293 2.280 2.248 2.178 2.062 2.047 2.022 2.009 1.983 1.948 1.929 1.869 1.776 1.765 1.741 1.647 1.620 1.603 1.595 1.571 1.542 1.520 1.503 1.500 1.493 1.489 1.465 1.459 1.361 1.330
5 30
