Tetrahydroxidohexaoxidopentaborate(1-) Salts of C6-Linked Substituted Diimidazolium and Dipyrrolidinium Cations: Synthesis, Characterization and XRD Studies

Several tetrahydroxidohexaoxidopentaborate(1-) salts of N-substituted diimidazolium cations or N-substituted dipyrrolidinium cations linked through N-C6-N chains have been synthesized and characterized spectroscopically (NMR, IR) and by single-crystal XRD studies: [R(NC3H3N)(CH2)6(NC3H3N)R][B5O6(OH)4]2·xH2O (R = Me, x = 0 (1); R = Et, x = 3 (2); [Me(NC3H3N)(CH2(C6H4)CH2)(NC3H3N)Me][B5O6(OH)4]2 (3), [(C4H8N)(R)(CH2)6(R)(NC4H8)][B5O6(OH)4]2·xB(OH)3 (R = Me, x = 0 (4, two polymorphs); R = Et, x = 0 (5); R = Bu, x = 4 (6); R = allyl, x = 0 (7)). Representative samples (1 and 7) were also characterized by thermal (TGA/DSC) studies; compounds are thermally decomposed to B2O3 in air. Numerous anion-anion H-bonding interactions are present in the solid-state structures of 1–5 and 7 as giant anionic networks. Unusually, in 6 there are no R22(8) anion-anion interactions as the co-crystallized B(OH)3 bridges between all pentaborate anions. H-bonding interactions in 1–7 have been examined using Etter graph set analysis; C(8), C33(18), R22(8), R22(12) and R44(12) motifs have been identified.