Halides empty clusters

Y4CI0 (Mattausch et al., 1980). The structure is a doubly rare example of condensed empty clusters of the M0X3 type in which the exposed (side) triangular faces are capped by halide two rows of chlorine at the top and... 

Ihble 5-3. [MgMg] and [MgXu] halide clusters having interstitial atoms, their interconnection patterns and their corresponding empty cluster structure types. Thken from [6, 10, 13] and additional references in the Ihble. 

Particle irradiation effects in halides and especially in alkali halides have been intensively studied. One reason is that salt mines can be used to store radioactive waste. Alkali halides in thermal equilibrium are Schottky-type disordered materials. Defects in NaCl which form under electron bombardment at low temperature are neutral anion vacancies (Vx) and a corresponding number of anion interstitials (Xf). Even at liquid nitrogen temperature, these primary radiation defects are still somewhat mobile. Thus, they can either recombine (Xf+Vx = Xx) or form clusters. First, clusters will form according to /i-Xf = X j. Also, Xf and Xf j may be trapped at impurities. Later, vacancies will cluster as well. If X is trapped by a vacancy pair [VA Vx] (which is, in other words, an empty site of a lattice molecule, i.e., the smallest possible pore ) we have the smallest possible halogen molecule bubble . Further clustering of these defects may lead to dislocation loops. In contrast, aggregates of only anion vacancies are equivalent to small metal colloid particles. 

These last two cluster types are often referred to as M0X12 and M 0X0 to emphasize the differences in the cores, but it should be remembered that the six exo positions are evidently always occupied by halide or another Lewis base (Smith Corbett, 1985). To do otherwise, leaving a substantial fraction of the bonding sphere about a transition metal empty, would be unusual. 

Both Br and C1 MAS NMR have been used in the investigation of sodium, silver and halo-sodalite semiconductor supralattices. Useful information is available on the environments of the encapsulated clusters within the sodalite lattice. The Na4X (X = Cl, Br) tetrahedra provide a symmetric environment around the halide and give rise to narrow resonances for specific locations. The spectra are sensitive to the distribution of anion empty cavities or to T containing cavities. 

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