Capped octahedron structures

Tlie Re complexes, generally prepared by X2 oxidative addition to the parent Re species (equation 6), are normally seven coordinate and diamagnetic with a capped octahedron structure, but six-coordinate, 16-electron derivatives have been found, especially with isocyanide ligands. see Structure Property Maps for Inorganic Solids). 

Reported rhenium complexes possess one [70-74], two [75], and three [75] dithiocarboxylato ligands coordinated to the one rhenium atom to form a high coordination state, as in the case of the technetium complex [76]. One of these complexes 29 is synthesized from Re(VII)S4 and (PhCSS)2 (Fig. 10) [72]. An internal redox reaction occurs and Re( VII) is reduced to Re(III) in the synthetic process. Addition of sulfur-abstracting reagents, Ph3P or Et4NCN, produces the heptacoordinate complex 30 with the neutral capped octahedron structure or... 

Let US consider the repulsive force model. The repulsive force is proportional to the inverse power n) of the distance (r) force l/r . Based on this consideration alone the pentagonal bipyramidal structure seems to be more stable for small values of n, the capped trigonal prism for intermediate values and the capped octahedron for large values of n, upto the limit of hard-sphere model. It is obvious, however, that such analysis cannot be applied for systems where all the hgands are not equal, i. e. MX Y 7- , and the ligands X and Y are very different from each other. 

TaCl4(PMe3)3] X-Ray structure, capped octahedron (C symmetry) 2... 

The thermolysis of 4 with Ru3(CO)12 3 in bis(2-methoxyethyl)ether under reflux for 3 h affords the decanuclear cluster [RuioC(CO)24]2 218 in 81% yield (Scheme 36).124 The same cluster has also been isolated from the thermolysis of 3 with mesitylene.95 The structure of 218 has been established by single crystal X-ray diffraction, which shows that the metal skeleton consists of a tetra-capped octahedron decorated with terminal carbonyl ligands. Cluster 218 reacts with CO in dichloromethane under ambient conditions to regenerate 4 and 3 in quantitative yield.109 The decanuclear cluster 218 also undergoes a reversible reaction with two equivalents of iodine to afford [RuioC(CO)24I] 219.109 At higher temperatures further reaction occurs with iodine to produce a species tentatively characterized as the hexamer [Ru6C(CO)i6I2] 220. 

When the number of metal atoms in a cluster increases, the geometries of the clusters become more complex, and some are often structurally better described in terms of capped or decapped polyhedra and condensed polyhedra. For example, the first and second clusters listed in Table 19.4.3 are a capped octahedron and a bicapped octahedron, respectively. Consequently, capping or decapping with a transition-metal fragment to a deltapolyhedral cluster leads to an increase or decrease in the cluster valence electron count of 12. When a transition-metal atom caps a triangular face of the cluster, it forms three M-M bonds with the vertex atoms, so according to the 18-electron rule, the cluster needs an additional 18 - 6 = 12 electrons. The parent octahedron of [Os6(CO)is]2- has g = 86, the monocapped octahedron Osy(CO)2i has g = 98, and the bicapped octahedron [Oss(CO)22]2- hasg = 110. 

Such polyhedra are relatively rare. The isoelectronic B - and B5C2H7 species have pentagonal bipyramidal (D5h) structures. The Os7(CO)2i molecule has a capped octahedron of Os atoms with three CO groups on each Os. 

The structures are known for a number of these compounds thus, of the eight-coordinate compounds, Eu(acac)3(phen) is square antiprismatic, Eu(dpm)3(py)2 and Nd(tta)3(Ph3PO)2 are dodecahedral seven-coordinate Lu(dpm)3(3-picoline) is a face-capped trigonal prism and Eu(dpm)3(quinuclidine) a capped octahedron. Nine-coordination is found in Eu(dpm)3(terpy) and also in Pr(facam)3(DME)3(facam = 3-trifluoroacetyl-D-camphorate). 

A theoretical calculation has been made (443) of the structures of mono-adducts of tris-(/i-diketonato) LSR of the type [Ln(bidentate)3 (unidentate)]. Three favoured structures having similar potential energies are suggested. These are a capped octahedron (C3 ), an irregular polyhedron (CJ, and a structure intermediate between a pentagonal bipyramid and a capped trigonal prism. The first two structures have been observed experimentally when the unidentate ligand is water or a carbonyl function. 

Mo, R = Bu", R" = Me. The structure is described as intermediate between a distorted capped trigonal prism and a distorted capped octahedron. Reaction of [MoCl(SnBu"Cl2)(CO)3(NCMe)2] with two equivalents of S2CPR3 (R = Cy, Et, Bu") gives the complexes 2, which are the first examples of complexes whereby S2CPR3 bridges between a transition and main-group metal. The molecular structure for R = Cy has been determined crystallographically. ... 

Fig. 4. Isomeric structures of [BioHio] (a) bicapped square antiprism and (b) tri-capped octahedron.

Amines, hydrazines, and hydroxylamines. Amine complexes are known for tetravalent complexes of the earliest actinides (Th, U), particularly for the halides, nitrates, and oxalates. The complexes are generated either in neat amine, or by addition of amine to the parent compound in a nonaqueous solvent. Some of the known simple amine compounds are presented in Table 6. The molecular structure of ThCl4(NMe3)3 has been determined. The coordination environment about the metal is a chloride capped octahedron. A very limited number of adducts exist in which a tetravalent actinide is coordinated by a hydrazine or hydroxylamine ligand the parent compound is generally a halide or sulfate complex. Cationic metal hydrates coordinated with primary, secondary, or tertiary amines have also been isolated with acetylacetonate, nitrate, or oxalate as counterions. 

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