Mechanochemistry of the LiBH4–AlCl3 System: Structural Characterization of the Products by Solid-State NMR
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Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.
For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.
The Department of Chemistry seeks to provide students with a foundation in the fundamentals and application of chemical theories and processes of the lab. Thus prepared they me pursue careers as teachers, industry supervisors, or research chemists in a variety of domains (governmental, academic, etc).
History
The Department of Chemistry was founded in 1880.
Dates of Existence
1880-present
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- College of Liberal Arts and Sciences (parent college)
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Abstract
The double-cation metal borohydride, Li4Al3(BH4)(13), mechanochemically produced from a 13:3 mixture of lithium borohydride (LiBH4) and aluminum chloride (AlCl3), has a low hydrogen desorption temperature; however, the material's decomposition is accompanied by a large emission of toxic diborane (B2H6). We found that a decrease of the LiBH4:AICl(3) ratio in the starting mixture yields increased amounts of partially chlorinated products that also dehydrogenate at low temperature, but release negligibly small amounts of diborane. Extensive characterization by solid-state NMR spectroscopy (SSNMR) and powder X-ray diffraction (XRD) found that the 11:3 ratio product maintains the Li(4)A(13)(BH4)(13)-like structure, with additional anions substituting for [BH4](-) compared to the 13:3 mixture. Further decrease of relative LiBH4 concentration in the starting mixture to 9:3 results in a different product composed of tetrahedral [Al(BH4)(4)](-) and [Al(BH4)(2)Cl-2](-) complexes, in which two hydrogen atoms of each borohydride group are bridged to aluminum sites. Additionally, SSNMR revealed the covalent character of the Al-H bonds, which is not observed in Li(4)A(13)(BH4)(13). These findings suggest that the Al-Cl bonding present in the chlorinated complexes prevents the formation of Al(BH4)(3), which is a known intermediate leading to the formation of diborane during thermal dehydrogenation of the nearly chlorine-free Li(4)A(13)(BH4)(13).