Desolvation and Dehydrogenation of Solvated Magnesium Salts of Dodecahydrododecaborate: Relationship between Structure and Thermal Decomposition
Attempts to synthesize solvent‐free MgB12H12 by heating various solvated forms (H2O, NH3, and CH3OH) of the salt failed because of the competition between desolvation and dehydrogenation. This competition has been studied by thermogravimetric analysis (TGA) and temperature‐programmed desorption (TPD...
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Published in | Chemistry : a European journal Vol. 20; no. 24; pp. 7325 - 7333 |
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Main Authors | , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Weinheim
WILEY-VCH Verlag
10.06.2014
WILEY‐VCH Verlag Wiley Subscription Services, Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Attempts to synthesize solvent‐free MgB12H12 by heating various solvated forms (H2O, NH3, and CH3OH) of the salt failed because of the competition between desolvation and dehydrogenation. This competition has been studied by thermogravimetric analysis (TGA) and temperature‐programmed desorption (TPD). Products were characterized by IR, solution‐ and solid‐state NMR spectroscopy, elemental analysis, and single‐crystal or powder X‐ray diffraction analysis. For hydrated salts, thermal decomposition proceeded in three stages, loss of water to form first hexahydrated then trihydrated, and finally loss of water and hydrogen to form polyhydroxylated complexes. For partially ammoniated salts, two stages of thermal decomposition were observed as ammonia and hydrogen were released with weight loss first of 14 % and then 5.5 %. Thermal decomposition of methanolated salts proceeded through a single step with a total weight loss of 32 % with the release of methanol, methane, and hydrogen. All the gaseous products of thermal decomposition were characterized by using mass spectrometry. Residual solid materials were characterized by solid‐state 11B magic‐angle spinning (MAS) NMR spectroscopy and X‐ray powder diffraction analysis by which the molecular structures of hexahydrated and trihydrated complexes were solved. Both hydrogen and dihydrogen bonds were observed in structures of [Mg(H2O)6B12H12]⋅6 H2O and [Mg(CH3OH)6B12H12]⋅6 CH3OH, which were determined by single‐crystal X‐ray diffraction analysis. The structural factors influencing thermal decomposition behavior are identified and discussed. The dependence of dehydrogenation on the formation of dihydrogen bonds may be an important consideration in the design of solid‐state hydrogen storage materials.
Desolvation versus dehydrogenation: It is proven that MgB12H12, an intermediate in the hydrogen desorption of a potential candidate for hydrogen storage, [Mg(BH4)2], cannot be prepared by heating its various solvated salts. The competition between desolvation and dehydrogenation was studied by using thermogravimetric analysis (TGA), temperature‐programmed desorption (TPD), IR, NMR spectroscopy, and single‐crystal or powder X‐ray diffraction analyses (see figure). |
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Bibliography: | Department of Energy - No. DE-FC3605GO15062 Office of Science - No. DE-FG02-07ER15896 National Natural Science Foundation istex:F26D6ABD199D08C02BB152CB19EEAFC0D0705989 ark:/67375/WNG-N9NMFWQB-1 NSFC - No. 21371051 NSF - No. 9724240 MRSEC - No. DMR-520565 ArticleID:CHEM201303842 National Science Foundation ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0947-6539 1521-3765 |
DOI: | 10.1002/chem.201303842 |