Molecular antiprism

Fig. 12. (Left) Molecular structure of the mixed-valent cluster 10 and 11 in the crystal. (Right) Representation of the E10-dicapped-Archimedean antiprism as anionic partial structure in 10 and 11 (E = P, As). For clarity the organic groups of the silyl groups have been omitted.

Complex [Fe6(L8)6] (23) can be described as having idealized D3-molecular symmetry. The iron centers define the apices of a distorted trigonal antiprism in which six tripodal, tris(bidentate) ligands (L8)3 make up the equatorial faces, leaving the top and bottom triangles unoccupied. All six iron(III) ions are... 

In these complexes anion coordination must be present with the exception of perchlorate. Lanthanide contraction may also be an influencing factor. The molecular structure [ 189] of Eu(TMU)3(N03)3 shows the presence of bidentate nitrates with a coordination number of nine. The coordination polyhedron is neither the tricapped trigonal prism nor the monocapped square antiprism which may be due to the small bite of nitrate ligand. The dimethyl acetamide (DMA) complexes behave similarly as those of tetramethyl urea (TMU) with less steric requirements as evidenced by the synthesis of [180-182] La(DMA)8(C104)3, La = La-Nd La(DMA)7(C104)3, La=Sm-Er La(DMA)6(C104)3, La = Tm-Lu. 

Many other linked polyhedra similar to molecular boranes are found for B-rich solid compounds of alkali and alkaline-earth metals. There are octahedra in Li2B6, octahedra and pentagonal bipyramids in Na3B2o, dodecahedra and bicapped square antiprisms in U3B14 and icosahedra in Na2B29. The cluster connection is particularly clear for compounds of this type. 

The iodide complexes are somewhat less stable, and well-characterized examples exist only for thorium, protactinium, and uranium. The thorium and uranium derivatives can be coveniently prepared by the reaction of iodine and metal, while protactinium tetraiodide is generated by reduction of Pals. The molecular structure of Thl4 has been examined the metal lies within a distorted square antiprism of iodide ions. 

Symmetry co-ordinates of molecular vibrations for trigonal prism (fljd and antiprism (Dj ) models of sandwich compounds... 

The crystal and molecular structure of tetrachlorobis(triphenylphosphine oxide) uranium(vi) has been determined from three-dimensional AT-ray diffraction data. The complex was found to adopt a distorted octahedral configuration with the neutral ligands co-ordinated in the cis positions. The single-crystal study of chlorohexakis-(trimethylphosphine oxide)uranium(iv) trichloride showed the uranium atom to be co-ordinated to one chlorine and six oxygen atoms. The co-ordination polyhedron was described in terms of a distorted monocapped trigonal antiprism or a distorted monocapped octahedron. 

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