Crystal structure and thermal behavior of three potential high-energy compounds of hydro-closo-borates with guanidinium

Abstract

The novel guanidinium hydro-closo-borates featuring [BnHn]2– (n = 10 and 12) anions were successfully synthesized via the direct reaction of the corresponding free acids, (H3O)2[BnHn], with guanidinium carbonate, (CN3H6)2[CO3], in aqueous media. The resulting compounds crystallize in different monoclinic space groups such as C2/c, P2/c and P21/n for (CN3H6)2[B10H10], (CN3H6)2[B12H12] ⋅ 2 H2O and Cs(CN3H6)[B12H12], respectively. An intriguing aspect of these crystal structures was the observation of dihydrogen bonding interactions involving the negatively polarized hydrogen atoms of the boron clusters and the positively polarized hydrogen atoms in the guanidinium cations (Bδ+–Hδ–⋅⋅⋅Hδ+–Nδ–). Furthermore, a classical hydrogen bonding system is evident in (CN3H6)2[B12H12] ⋅ 2 H2O. The presence of negatively charged hydrogen (Hδ–) in hydroborate anions and positively charged hydrogen atoms (Hδ+) in guanidinium cations in these structures suggests their potential for facilitating H2 generation upon thermal decomposition. Furthermore, theoretical analysis predicts that under an oxygen atmosphere, diguanidinium dodecahydro-closo-hydroborate has the capacity to yield energy up to 11 MJ/mol.