In this work, praseodymium(III) borohydride, Pr(BH4)3, and the isotopically enriched analogue, Pr(11BD4)3, are prepared by a new route via a solvate complex, Pr(11BD4)3S(CH3)2. Nd(BH4)3 was synthesized using the same method and the structures, polymorphic transformations, and thermal stabilities of these compounds are investigated in detail. -Pr(BH4)3 and -Nd(BH4)3 are isostructural with cubic unit cells (Pa3 ̅) stable at room temperature (RT) and unit cell volume per formula unit (V/Z) of 180.1 and 175.8 Å3, respectively. Heating -Pr(BH4)3 to T 190 C, p(Ar) = 1 bar, introduces a transition to a rhombohedral polymorph, r-Pr(BH4)3 (R3 ̅c) with smaller unit cell volume and denser structure, V/Z = 156.06 Å3. A similar transition was not observed for Nd(BH4)3. However, heat treatment of -Pr(BH4)3, at T 190 C, p(H2) = 40 bar and -Nd(BH4)3, at T 270 C, p(H2) = 98 bar facilitate reversible formation of another three cubic polymorph, denoted , ’-RE(BH4)3 and ’’-RE(BH4)3 (Fm3 ̅c). Moreover, the transition - to ’- to ’’- is considered a rare example of stepwise negative thermal expansion. For Pr(BH4)3, 2/3 of the sample take this route of transformation whereas in argon only 5 wt%, and the remaining transforms directly from - to r-Pr(BH4)3. The -polymorphs are porous with V/Z = 172.4 and 172.7 Å3 for ’’-RE(BH4)3, RE = Pr or Nd, respectively, and are stabilized by the elevated hydrogen pressures. The polymorphic transitions occur due to rotation of RE(BH4)6 octahedra without breaking or forming chemical bonds. Structural DFT optimization reveals decreasing stability of αPr(BH4)3 > βPr(BH4)3 > rPr(BH4)3.
Synthesis, structure, and polymorphic transitions of praseodymium(iii) and neodymium(iii) borohydride, Pr(BH4)3and Nd(BH4)3
Nervi, Carlo;
2018-01-01
Abstract
In this work, praseodymium(III) borohydride, Pr(BH4)3, and the isotopically enriched analogue, Pr(11BD4)3, are prepared by a new route via a solvate complex, Pr(11BD4)3S(CH3)2. Nd(BH4)3 was synthesized using the same method and the structures, polymorphic transformations, and thermal stabilities of these compounds are investigated in detail. -Pr(BH4)3 and -Nd(BH4)3 are isostructural with cubic unit cells (Pa3 ̅) stable at room temperature (RT) and unit cell volume per formula unit (V/Z) of 180.1 and 175.8 Å3, respectively. Heating -Pr(BH4)3 to T 190 C, p(Ar) = 1 bar, introduces a transition to a rhombohedral polymorph, r-Pr(BH4)3 (R3 ̅c) with smaller unit cell volume and denser structure, V/Z = 156.06 Å3. A similar transition was not observed for Nd(BH4)3. However, heat treatment of -Pr(BH4)3, at T 190 C, p(H2) = 40 bar and -Nd(BH4)3, at T 270 C, p(H2) = 98 bar facilitate reversible formation of another three cubic polymorph, denoted , ’-RE(BH4)3 and ’’-RE(BH4)3 (Fm3 ̅c). Moreover, the transition - to ’- to ’’- is considered a rare example of stepwise negative thermal expansion. For Pr(BH4)3, 2/3 of the sample take this route of transformation whereas in argon only 5 wt%, and the remaining transforms directly from - to r-Pr(BH4)3. The -polymorphs are porous with V/Z = 172.4 and 172.7 Å3 for ’’-RE(BH4)3, RE = Pr or Nd, respectively, and are stabilized by the elevated hydrogen pressures. The polymorphic transitions occur due to rotation of RE(BH4)6 octahedra without breaking or forming chemical bonds. Structural DFT optimization reveals decreasing stability of αPr(BH4)3 > βPr(BH4)3 > rPr(BH4)3.File | Dimensione | Formato | |
---|---|---|---|
Payandeh_Pr(BH4)3_ms_2018_04_22_OA.docx
Accesso riservato
Tipo di file:
POSTPRINT (VERSIONE FINALE DELL’AUTORE)
Dimensione
1.64 MB
Formato
Microsoft Word XML
|
1.64 MB | Microsoft Word XML | Visualizza/Apri Richiedi una copia |
099_Dalton_c8dt00118a.pdf
Accesso riservato
Tipo di file:
PDF EDITORIALE
Dimensione
3.39 MB
Formato
Adobe PDF
|
3.39 MB | Adobe PDF | Visualizza/Apri Richiedi una copia |
Payandeh_Pr(BH4)3_ms_2018_04_22_OA.pdf
Open Access dal 15/05/2019
Tipo di file:
POSTPRINT (VERSIONE FINALE DELL’AUTORE)
Dimensione
2.48 MB
Formato
Adobe PDF
|
2.48 MB | Adobe PDF | Visualizza/Apri |
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.