Dimagnesium cobalt(I) pentahydride, Mg2CoH5, containing square-pyramidal pentahydrocobaltate(4-) (CoH54-) anions

Abstract

87191-41-1; TeF5N(I)CF3, 98720-72-0; TeF5N(CF3)C(0)CH3, 98720-73-1; (TeF,),NCF,, 87191-42-2; TeFSN(SF5)CF3, 98720-74-2; TeF5N-(CF,)CH,CH,Br, 98720-75-3; TeF,N=C(CI)OCH,, 98720-76-4; Te-24, Mg2CoHS and its deuteride have been prepared as black crystalline solids by a sintering technique at temperatures between 620 and 770 K and hydrogen (deuterium) pressures between 40 and 60 bar. X-ray and neutron powder diffraction data recorded at room temperature suggest a tetragonally distorted CaF,-type metal atom structure (for the deuteride a = 4.463 (4) A, c = 6.593 (6) A, space group P 4 / n m m , and 2 = 2). The D atoms surround the Co atoms in an ordered square-pyramidal configuration (d[Co-D] = 1.590 (17) A (apical) and 1.515 (3) A (basal)). The structure transforms at 488 (5) K into a disordered cubic modification ( a = 6.453 (6) A, at 498 K). The heat of dissociation of the hydride as measured from pressure-composition isotherms is 86 (5) kJ/mol of H,. The electrical resistivity suggests nonmetallic behavior.

Drastic changes in electronic, magnetic, mechanical and bonding properties from Zr2CoH5 to Mg2CoH5

“…The latter show some differences with respect to experiment especially for the H2 coordinate which was obtained for the deuteride in both compounds [5,6]. Nevertheless the agreement is such that it can allow establishing trends between the two compounds as for the energies, the mechanical properties as well as for the relative charge transfers.…”

“…In as far as fairly good agreements between experimental and calculated crystal parameters are found (Table 1), the electronic density of states and the chemical bonding were analyzed for the two compounds based on experimental data [5,6] and assuming firstly spin degenerate total spin (NSP) configuration. At self consistent convergence the charge transfer follows the trends observed above with additional charge residues of ~ 0.15 electrons from the atomic spheres to IS.…”

“…One initial impetus for such extended research is the non usability of archetype MgH 2 , characterized by a large hydrogen capacity (7.6 wt.-%), owing to the elevated desorption temperature (~350°C) caused by highly ionic Mg-H bond. Other Mg based compounds were then studied as candidates for hydrogen storage such as Mg 2 CoH 5 [5] synthesized starting from a mixture of the constituents because Mg 2 Co intermetallic does not exist. On the contrary Zr 2 CoH 5 with similar formulation is an insertion compound obtained by hydrogenation of Zr 2 Co intermetallic [6].…”

Mixed metal films with switchable optical properties

“…3 In all of these systems, a thin Pd overlayer (generally > 5 nm) is applied to catalyze absorption and desorption of hydrogen and to protect the readily oxidized rare earth and/or Mg from oxidation. Infrared internal reflectance spectroscopy was used to characterize the transparent Ni-Mg hydride films as a mixture of Mg 2 8 and Mg 2 FeH 6 (E g = 1.8 eV) 9 support experimental evidence 4,6 for semiconductor behavior in these materials. Mg 3 MnH 7 (calculated Eg = 2.56 eV) 10 is orange in color, 7 and is also presumably semiconducting.…”

Mg-Based Hydrogen Absorbing Materials for Thermal Energy Storage—A Review

“…Yvon et al [64] reported a value of 86 kJ/mol H2 upon the hydrogen dissociation and 60 kJ/mol H2 for the hydrogen absorption for the Mg2CoH5 phase. Lower values were published by Konstanchuk's group.…”