Covalent hydration—continued

The nature of the [Ir(bipy)3(OH2)] cation continues to be probed. Neither recent paper favors covalent hydration. An X-ray study was interpreted in terms of the structure shown as 17, on which two comments must... 

The anomalous behavior of quinazoline was first discovered by Albert et who made the surprising observation that 4-methyl-quinazoline 2.5) was a weaker base than quinazoline (pA 3.5). Mason then observed that the ultraviolet spectrum of the quinazoline cation was abnormal but that the spectrum of 4-methylquin-azoline was normal (see Fig. 2). These anomalies led to the suggestion that water adds covalently to the cation of quinazoline to give 12 (R = H). The occurrence and position of hydration were confirmed by a detailed study of the ultraviolet and infrared spectra of the anhydrous and hydrated hydrochlorides and by mild oxidation of the cation to 4(3 )-quinazolinone. Using the rapid-reaction technique (the continuous-flow method), the spectrum of the unstable... 

Despite the fact that clathrate hydrate science can be considered to be a mature field, numerous challenges remain. In part, this is because hydrates exist in nature and hence exhibit the complexity of mineral phases, where the structure and composition reflect not only the conditions of synthesis but also subsequent exposure to changing conditions after synthesis. Another part is that the principal component of these materials is water, likely the most important material on earth, and the clathrates offer a possibility to study the diverse ways in which water interacts with other materials. In this respect, it is interesting to note that new structures continue to be found. Structurally related families of materials such as the sUica-based zeosils and clathrasils tend to show a far greater structural diversity. In part, this is because of the covalent nature of the silica lattices that give far more robust frameworks than the water-based ones however, each structure in these classes of materials could be considered as a candidate for clathrate synthesis. 

The transitions in the partly filled 4f shell of lanthanide compounds are sufficiently similar to spectral lines of monatomic entities that the overall, small shift toward lower wave numbers is a rather direct indicator of partly covalent bonding. Hofmann and Kirmreuther (1910) suggested that the electronic orbits had slightly larger radii in Er203 than in hydrated erbium (III) salts, and Ephraim et al. (1926, 1928, 1929) made an extensive systematic study of band shifts in Pr(III), Nd(III) and Sm(III). Such work was continued by Boulanger (1952) and... 

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