Molecular solids octahedral

The MXg series represents a set of molecular solids and liquids at ambient conditions, owing to the octahedral coordination of the transition metals. Many of the other second and third row metal hexafluorides show the same phenomenon. Mode and WCle have d ions in hep with 1/6 of the octahedral holes occupied. The fluorides are volatile solids with low melting and boiling points, while WCle and WBre melt around 570 K. 

UFe is a molecular solid—its solid state structure contains isolated, octahedral UF molecules held together via relatively weak intermolecular forces. The intermolecular forces are very easy to break and this compound sublimes easily. On the other hand, UF3 and UF4 form network solids in which each U atom is surrounded by nine jmd eight fluorines respectively. As a consequence, UF3 and UF4have high melting points. 

In molecular chemistry, octahedral and tetrahedral molecules can link together to form clusters. One way in which we can visualize solid structures is as semi-infinite lattices built up from unlimited numbers of tetrahedral and octahedral units (atoms or ions). We can consider poly-hedra packing in various ways by sharing edges or vertices to form dense structures. This procedure is covered in many texts,and will not be described in detail here. 

An interesting feature of phosphorus pentachloride is that it is an ionic solid of tetrahedral PC14+ cations and octahedral PC16 anions, but it vaporizes to a gas of trigonal bipyramidal PC15 molecules (see Section 2.10). Phosphorus pentabromide is also molecular in the vapor and ionic as the solid but, in the solid, the anions are simply Br ions, presumably because six bulky Br atoms simply do not fit around a central P atom. 

Fig. 2.3-12. Molecular structures of 59, 60, 60a, and topological relationships of 59 and 60 to the corresponding sections from the solid-state structure of elemental aluminum, and structural similarities of the clusters Ali2R6 and In Rs- In the latter cluster the octahedral sections are highlighted.

X-ray crystallography, 40 20-21 synthetic models, 40 23-48 xanthane oxidase, 40 21-23 chalcogenide halides, 23 370-377, 413 Chevrel phases, 23 376-377 metal-metal bonding, 23 330, 373 structural data, 23 373-376 as superconductors, 23 376 synthesis, 23 371-372 chloride, 46 4-24, 35-44 heterocations of, 9 290, 291 cluster compounds, 44 45-46 octahedral, 44 47-49, 53-63 electronic structure, 44 55-63 molecular structure, 44 53-54 synthesis, 44 47-49 rhomboidal, 44 75-82 solid-state clusters and, 44 66-72, 74-75, 80-82, 85-87 tetrahedral, 44 72-75 triangular, 44 82-87 cofactor, 40 2, 4-12 anaerobic isolation, 40 5 molybdopterin and, 40 4-8 reduced form, 40 12 synthesis, 40 8-12 xanthine oxidase, 45 60-63 complexes... 

In solids where cation-cation interaction is significant, by can be related to R, where R is the cation-cation separation. In cases where cation-anion-cation interaction is important, by is related to the covalent mixing parameter, X, of the cation-anion orbitals. For octahedrally coordinated cations, as in rocksalt and perovskite structures, the relevant mixing parameters are and in the following molecular wave functions... 

The structural relationship between the molecular and solid-state compounds has been a hot issue in inorganic chemistry for some time (25-27). The extrusion (or excision) from preformed solid-state cluster compounds is one of the major synthetic methods of the preparation of cluster complexes (26). Use of cluster complexes as precursors to solid-state cluster compounds is the reverse reaction of excision. Both reactions utilize the structural similarity of the metal cluster units. The basic cluster units of polyhedra (deltahedra) or raft structures are triangles, and both molecular and solid-state clusters with octahedral, tetrahedral, and rhomboidal cores have been reported. Similarity of other properties such as electronic structures based on the cluster units is also important. The present review is concerned with the syntheses and structures of the cluster complexes of the group 6 metals and with their relationships to solid-state chemistry. 

The differences between the cluster skeletons of the three molecules of 2 are very small with the mean values of the Ru-Ru distances being similar and the mean Ru-C(carbide) distances being identical. The most notable differences between the structures arise from the orientation of the tricarbonyl units attached to the apical Ru atoms above and below the molecular equator of the octahedral cluster (the molecular equator is defined as the Ru4 plane in which the bridging carbonyl ligand is present). The two tricarbonyl units are almost exactly staggered in the crystal obtained from benzene, whereas they approach an eclipsed conformation in the other polymorph. Although the 13C-NMR spectrum of 2 has not been recorded in solution (or in the solid state), it is not unreasonable to anticipate that... 

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