Chiral anionic layers in tartramide spiroborate salts and variable solvation for (R = Et, Pr or Bu)

• Published in: Acta crystallographica. Section C, Crystal structure communications Vol. 76; no. 7; pp. 695 - 705
• Main Authors: Soecipto, Aristyo, Wong, Lawrence W-Y, Sung, Herman H-Y, Williams, Ian D
• Format: Journal Article
• Language: English
• Published: Chester Wiley Subscription Services, Inc 01.07.2020
• Subjects: Anions; Cations; Ethanol; Hydrogen bonding; Ions; Salts; Solvation
• ISSN: 0108-2701; 1600-5759
• DOI: 10.1107/S2053229620008384

The spiroborate anion, namely, 2,3,7,8‐tetracarboxamido‐1,4,6,9‐tetraoxa‐5λ4‐boraspiro[4.4]nonane, [B(TarNH2)2]−, derived from the diol l‐tartramide TarNH2, [CH(O)(CONH2)]2, shows a novel self‐assembly into two‐dimensional (2D) layer structures in its salts with alkylammonium cations, [NR4]+ (R = Et, Pr and Bu), and sparteinium, [HSpa]+, in which the cations and anions are segregated. The structures of four such salts are reported, namely, the tetrapropylazanium salt, C12H28N+·C8H12BN4O8−, the tetraethylazanium salt hydrate, C8H20N+·C8H12BN4O8−·6.375H2O, the tetrabutylazanium salt as the ethanol monosolvate hemihydrate, C16H36N+·C8H12BN4O8−·C2H5OH·0.5H2O, and the sparteinium (7‐aza‐15‐azoniatetracyclo[7.7.1.02,7.010,15]heptadecane) salt as the ethanol monosolvate, C15H27N2+·C8H12BN4O8−·C2H5OH. The 2D anion layers have preserved intermolecular hydrogen bonding between the amide groups and a typical metric repeat of around 10 × 15 Å. The constraint of matching the interfacial area organizes the cations into quite different solvated arrangements, i.e. the [NEt4] salt is highly hydrated with around 6.5H2O per cation, the [NPr4] salt apparently has a good metric match to the anion layer and is unsolvated, whilst the [NBu4] salt is intermediate and has EtOH and H2O in its cation layer, which is similar to the arrangement for the chiral [HSpa]+ cation. This family of salts shows highly organized chiral space and offers potential for the resolution of both chiral cations and neutral chiral solvent molecules.