The preparation and characterisation of 17 previously unreported non-metal
cation (NMC) salts of isolated polyborate anions is reported. Many of the products were pentaborates, but a triborate and two heptaborate salts were also isolated. All compounds were characterised by elemental analysis, IR and multinuclear (¹H, ¹¹B and ¹³C) NMR spectroscopy. Many compounds were characterised by single-crystal XRD methods (EPSRC service, Southampton University): benzylamrnonium pentaborate, 1; cyclopropylammonium pentaborate, 2; cyclopentylamrnonium pentaborate, 3; bis(cyclohexylammonium) heptaborate .B(OH)₃ .3H₂O, 7; bis(cycloheptylammonium) heptaborate .2B(OH)₃ .2H₂O, 8; N,N,N-trimethylcyclohexylammonium pentaborate, 11; piperazinium bis(triborate), 14; N,N-dimethylpiperazinium pentaborate, 17; N,N.N:N'-tetramethylpiperazinium
bis(pentaborate ), 19; 1,2-dimethylimidazolium pentaborate .H₂O, 24; 1,2,3-trimethylimidazolium pentaborate, 25; 2-isopropylimidazolium pentaborate, 26; 2-ethyl-4-methylimidazolium pentaborate, 29; tetraphenylphosphonium pentaborate .1.5H₂O, 34; methyltriphenylphosphonium pentaborate .B(OH)₃ .0.5H₂O, 36; isopropyltriphenylphosphonium pentaborate .3.5H₂O, 37; and bis(triphenylphosphoranylidene)ammonium iodide, 39.
The thermal decomposition (in air) of these polyborates was studied by
DSC/TGA methods. Generally, thermal decomposition occurs as a two stage process with a low temperature ( <250°C) endothermic dehydration step (to an anhydrous NMC polyborate salt) preceding a high temperature (300-800°C) exothermic oxidation step. B₂O₃ is the eventual product. BET analysis was also undertaken on materials arising from the NMC polyborate thermal decompositions, and all are essentially non-porous materials.
The drying of an aqueous sodium silicate solution has been investigated. A
combination of liquid-state and solid-state 29Si NMR techniques demonstrated that dehydration of the solution led to an increase in the extent of cross-linking between Qn silicate units. Two solutions were investigated; one was a commercial sodium silicate solution and the other containing a commercial sodium silicate solution and a polyhydroxyl alcohol.