Abstract. Microcrystalline opal-CT and opal-C were investigated by 298i MAS NMR and 298i {1H} cross polarisation MAS NMR spectroscopy, X-ray small angle scattering, X-ray powder diffraction and infrared absorption spectroscopy. The results are compared with those for non-crystalline precious opal (opal-AG), non-crystalline hyalite (opal-AN), moderately disordered cristobalite and with well ordered low-cristobalite and low-tridymite.Opal-C is confirmed to be strongly stacking disordered low-cristobalite with about 20 to 30% probability for tridymitic stacking. More extensively stacking disordered opal-CT does not contain detectable domains of low-cristobalite or low-tridymite. The stacking sequence is close to 50% cristobalite and 50% tridymitic. The local order decreases with increasing stacking disorder, so that the structural state of microcrystalline opals lies between cristobalite, tridymite and non-crystalline opals.

No abstract

The structure of the (1,3-butadiene)M(R2PC2H4PR2) compounds (M = Ni, Pd, Pt; R = Pri, Bu′, Cy) in the solid-state have been investigated by 13C and 31P CP/MAS NMR spectroscopy. The bonding mode adopted by the diene is dependent upon the nature of the metal: the palladium compounds contain an η2-diene molecule, the nickel compound where R is cyclohexyl contains an η4-diene molecule whereas the Pr2iPC2H4PPr2i-stabilized platinum compound con- tains a platinacyclopentene ring. The crystal structures of (η2-1,3-C4H6)Pd(Cy2PC2H4PCy2) and (η4-1,3-C4H6)Ni(Cy2PC2H4PCy2) have been confirmed by X-ray diffraction.

No abstract

No abstract