Cubic cluster condensation

The reduction of the ligand-to-metal ratio leads to either spherical or non-spherical clusters with metal atoms shared between clusters. As examples of non-spherical 

Such examples of empty or metal-centered condensed cubic clusters suggest that larger clusters with additional layers could be prepared, leading ultimately to an 

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The scheme of cluster condensation or cluster fragment condensation leads eventually to structures observed in bulk metals. Particularly through extensive condensation of tetrahedral and octahedral clusters, arrangements closely related to the hexagonal and cubic close-packed structures can be obtained. Condensation also of icosahedral five-fold symmetrical clusters may be related to crystalline and quasicrystalline metallic structures. 

Answer. The metal count is 59 (9 x 9 (Co) — 11x2 ([Se]2—) = 59). This is 25 more than for [Mo9Sen]2 Indeed a large gamut of electron counts is possible for these condensed octahedral clusters, either molecular or part of extended solids. They are nice examples of compounds which can display variable electron count with constant shape. This situation is somewhat reminiscent of the transition-metal elements which exhibit a metallic d band which is gradually filled as we go from the left to the right of the periodic table without substantial change in their structure. Also review the discussion of cubic clusters in Section 5.2.5. 

R. 0. Holmes, R. R., unpublished work). The cube may be viewed as a condensation product of the dimeric cluster according to the expression in Equation 6. Hence, the dimeric cluster may serve as a precursor on the way to the cubic form. 

Another contribution is represented by an investigation of a cubic thallium cluster phase of the Bergmann type Na13(TlA.Cdi A.)27 (0.24 < x <0.33) (Li and Corbett 2004). For this phase too the body centred cubic structure (space group Im 3, a = 1587-1599 pm) may be described in terms of multiple endo-hedral concentric shells of atoms around the cell positions 0, 0, 0, and 14,14,14. The subsequent shells in every unit are an icosahedron (formed by mixed Cd-Tl atoms), a pentagonal dodecahedron (20 Na atoms), a larger icosahedron (12 Cd atoms) these are surrounded by a truncated icosahedron (60 mixed Cd-Tl atoms) and then by a 24 vertices Na polyhedron. Every atom in the last two shells is shared with those of like shells in adjacent units. A view of the unit cell is shown in Fig. 4.38. According to Li and Corbett (2004), it may be described as an electron-poor Zintl phase. A systematic description of condensed metal clusters was reported by Simon (1981). 

Co-condensed EtOH-water mixtures reveal the formation of distinct EtOH hydrate phases in different temperature domains. A hydrate 1 appears in the 130 K - 163 K range depending on the EtOH content. It is proposed to have a cubic lattice similar to that of the clathrate type I. Hydrate 2 is found to crystallize at 158 K or 188 K-193 K in correlation with the absence or the presence of ice Ic and EtOH content. Its composition seems to correspond to the monohydrate. The deposited solids undergo crystallization 10 K lower in comparison to frozen aqueous solutions. This reflects the remarkable ease with which water molecules initiate molecular rearrangement at low temperature. This seems most likely due to EtOH generating defects that facilitate the water reorientation . This may also reflect the generation of clusters (in the vapour phase before deposition) having a different nature relative to those encountered in the liquid solutions. These unusual structures may have implications in atmospheric chemistry or astrophysics. 

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