TY - JOUR
T1 - Synthesis and Characterization of Ether Adducts of Thorium Tetrahydroborate Th(BH4)4 and Chemical Vapor Deposition of Thorium Boride Thin Films
AU - Dunbar, Andrew C.
AU - Gozum, John E.
AU - Lin, Wenbin
AU - Flores, Vincent J.
AU - Girolami, Gregory S.
N1 - This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Separation Science program under Award DE-SC0019021. We thank Dr. James A. Jensen for assistance in the early stages of this project and Joseph C. Wright for helpful advice. We thank Drs. Danielle Gray and Amy Fuller of the George L. Clark X-ray Facility at the University of Illinois at Urbana-Champaign for collecting the X-ray diffraction data. Ex situ materials characterization was carried out in the Center for Microanalysis of Materials at the Frederick Seitz Materials Research Laboratory.
PY - 2023/3/13
Y1 - 2023/3/13
N2 - Treating ThCl4 with LiBH4 in various ethereal solvents affords the adducts Th(BH4)4(Et2O)2, Th(BH4)4(thf)2, and Th(BH4)4(dme) (thf = tetrahydrofuran and dme = 1,2-dimethoxyethane). The structures of these three compounds have been established by single-crystal X-ray diffraction: if the tetrahydroborate groups are considered as occupying one coordination site, the Et2O and thf complexes adopt trans-octahedral coordination geometries, whereas the dme complex exhibits a cis-octahedral structure. All four BH4- ligands in each compound are tridentate, rendering each thorium center 14-coordinate. The Th···B distances range from 2.64 to 2.67 Å, and the Th-O bond lengths are 2.47-2.52 Å. We propose that crystals of Th(BH4)4(thf)2 are isomorphous with those of U(BH4)4(thf)2, but owing to pseudosymmetry the latter was reported in a unit cell that was too small by a factor of 2. IR spectra and 1H and 11B NMR data are reported as well. All three adducts are volatile, subliming readily at 60 °C and 10-4 Torr, making them potentially useful as precursors for the chemical vapor deposition (CVD) of thin films of thorium boride. Passage of Th(BH4)4(Et2O)2 over glass, Si(100), and aluminum substrates heated to 350 °C yields amorphous films of approximate stoichiometry ThB2; films deposited from Th(BH4)4(thf)2 have stoichiometries closer to ThB2.5 and contain some oxygen. Auger, XPS, XRD, and SEM studies of these films are reported.
AB - Treating ThCl4 with LiBH4 in various ethereal solvents affords the adducts Th(BH4)4(Et2O)2, Th(BH4)4(thf)2, and Th(BH4)4(dme) (thf = tetrahydrofuran and dme = 1,2-dimethoxyethane). The structures of these three compounds have been established by single-crystal X-ray diffraction: if the tetrahydroborate groups are considered as occupying one coordination site, the Et2O and thf complexes adopt trans-octahedral coordination geometries, whereas the dme complex exhibits a cis-octahedral structure. All four BH4- ligands in each compound are tridentate, rendering each thorium center 14-coordinate. The Th···B distances range from 2.64 to 2.67 Å, and the Th-O bond lengths are 2.47-2.52 Å. We propose that crystals of Th(BH4)4(thf)2 are isomorphous with those of U(BH4)4(thf)2, but owing to pseudosymmetry the latter was reported in a unit cell that was too small by a factor of 2. IR spectra and 1H and 11B NMR data are reported as well. All three adducts are volatile, subliming readily at 60 °C and 10-4 Torr, making them potentially useful as precursors for the chemical vapor deposition (CVD) of thin films of thorium boride. Passage of Th(BH4)4(Et2O)2 over glass, Si(100), and aluminum substrates heated to 350 °C yields amorphous films of approximate stoichiometry ThB2; films deposited from Th(BH4)4(thf)2 have stoichiometries closer to ThB2.5 and contain some oxygen. Auger, XPS, XRD, and SEM studies of these films are reported.
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U2 - 10.1021/acs.inorgchem.2c03960
DO - 10.1021/acs.inorgchem.2c03960
M3 - Article
C2 - 36848600
AN - SCOPUS:85149139250
SN - 0020-1669
VL - 62
SP - 4106
EP - 4115
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 10
ER -