Polyborate Anions Partnered with Large Nonmetal Cations: Triborate(1–), Pentaborate(1–) and Heptaborate(2–) Salts

Pentaborate(1-) Salts and a Tetraborate(2-) Salt Derived from C2- or C3-Linked Bis(alkylammonium) Dications: Synthesis, Characterization, and Structural (XRD) Studies

“…[28]. The B-O bond lengths, OBO and BOB angles observed for the [B 4 O 5 (OH) 4 ] 2− and B(OH) 3 motifs are in accord with previous tetraborate(2-)[47][48][49][50][51][52][53][54][55][56] and polyborates with co-crystallized B(OH)3 [32,33,39,55,57,58]; for full details see the Supplementary Information.…”

“…Using Etter nomenclature [46] There is some disorder present in the cation and/or cocrystallized molecules all pentaborate(1-) anion structures except 3. Bond lengths and bond angles found for C, N atoms within the organic cations [19,28,37,40,41] are as expected as are the B-O bond lengths, OBO and BOB angles observed for the [B5O6(OH)4] − anion [19,21,28,29,[31][32][33][34][35]; for full details see the Supplementary Information. H-bonding interactions within polyborate salts are extremely common and anion-anion interactions between pentaborate(1-) units, forming giant lattices, are well documented and are signaled as a strong driving force [5,29,34] in templating the crystallization of these anions from the Dynamic Combinatorial Library [42][43][44][45] arising from B(OH)3 under basic conditions [35,36].…”

“…1 H-, 13 C-and 11 B-NMR spectra were recorded on compounds 1-9 (D 2 O solvent) and 1 H-and 13 C-spectra were in accord with the cations present. Exchangeable NH and B-OH protons were absent as specific signals and it is assumed were observed in the HOD signal present at +4.79 ppm as has been observed previously in related non-metal cation systems [31][32][33]. The pentaborate(1-) anion, although very stable in the solid-state and is readily templated by many organic cations [34], decomposes in aqueous solution as various equilibrium determined borate species are rapidly obtained and influenced by the boron concentration, the temperature and the pH of the aqueous solution [35,36].…”

“…However, there are no direct anion-anion interactions within the lattice and the B(OH)3 units serve to bridge tetraborate(2-) anions by acting as ′spacers′ to expand the lattice so that it can accommodate the relatively large cation, [Me3N(CH2)2NMe3]. This spacer role for B(OH)3 has been observed before [32,33,39,[55][56][57][58]. With reference to Figure 6 it can be seen that the H-bond structure can be envisaged as ′horizontal′ chains of alternating [B4O5(OH)4] 2-/B(OH)3 units held together by R2 2 (8) interaction, crosslinked by ′vertical′ C2 2 (8) chains (involving O8,H8 … O12,H12 … O5,B1,O2,B3) in a regular 2D arrangement.…”

“…The pentaborate(1-) anion, although very stable in the solid-state and is readily templated by many organic cations [34], decomposes in aqueous solution as various equilibrium determined borate species are rapidly obtained and influenced by the boron concentration, the temperature and the pH of the aqueous solution [35,36]. However, 11 B spectra of 1-8 were obtained and these samples all showed three peaks centred at 1 (~5) 13 (~35%) and 18 (~60%) ppm in a pattern typical of solutions arising from pentaborate(1-) salts [31][32][33][34]37]. The 11 B spectra of 9, originating from a tetraborate(2-) salt, was significantly different with three peaks now at 1.3 (5%), 7.4 (43%) and 11.7 (52%).The upfield shift of the 'average' 11 B chemical shift on going from a pentaborate (1-) anion (1-8) to a tetraborate(2-) anion (9) is in accord with the average B/charge ratio changing from 5:1 to 2:1 [34].…”