GA-71 and P-31 MAS NMR Spectroscopic Studies of Cloverite

Ga-71 and P-31 MAS NMR studies have been undertaken of the gallophosphate molecular sieve, cloverite. Two Ga-71 resonances were observed of the as-synthesized cloverite (ambient humidity) at 92 and -24 ppm. The first of these is assigned to five coordinate and the second to six coordinate gallium, where in both cases there is one fluoride ion in the first gallium coordination sphere. Dehydration of the sample decreased the intensity of the six coordinate signal relative to that of the five coordinate one, whereas hydrating had the reverse effect, suggesting that the upfield signal is due to six coordinate gallium sites generated through the adsorption of water. The P-31 MAS NMR spectrum of a dehydrated sample revealed one weak resonance at -0.8 ppm as well as strong signals at -9.7 and -11.2 ppm. The -0.8 ppm resonance is attributed to the T5 [P(OGa)3OH] sites whereas the strong signals are assigned to the T1-T4 sites [P(OGa)4]. Upon humidifying, several new resonances appear between 0 and -6 ppm which have been assigned to phosphorus atoms having nearest neighbour gallium atoms in varying degrees of hydration.