Title:
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Characterisation of non-metal cation polyborate salts and silicate solutions
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The preparation and characterisation of 17 previously unreported non-metal
cation (NM,C) 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 (IH, lIB and
¹³C) NMR spectroscopy. Many compounds were characterised by single-crystal XRD
methods (EPSRC service, Southampton University): benzylammonium pentaborate, 1;
cyclopropylammonium pentaborate, 2; cyclopentylammonium pentaborate, 3;
bis(cyclohexylammonium) heptaborate .B(OH)3 .3H20, 7; bis(cycloheptylammonium)
heptaborate .2B(OH)3 .2H20, 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
.H20, 24; 1,2,3-trimethylimidazolium pentaborate, 25; 2-isopropylimidazolium
pentaborate,
2-ethyl-4-methylimidazolium
pentaborate,
26;
29;
tetraphenylphosphonium pentaborate .1.5H20, 34; methyltriphenylphosphonium
pentaborate .B(OH)3 .O.5H20, 36; isopropyltriphenylphosphonium pentaborate
.3.5H20, 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.
I
B203 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.
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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.
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