Square antiprisms eight-coordinate compounds

Spot tests, 1, 552 Square antiprisms dodecahedra, cubes and, 1, 84 eight-coordinate compounds, 1,83 repulsion energy coefficients, 1, 33, 34 Square planar complexes, 1,191, 204 structure, 1, 37 Square pyramids five-coordinate compounds, 1,39 repulsion energy coefficients. 1,34 Squares... 

The compound Gd(H20)6 Cl3 is eight coordinate with six water molecules and two chloride ions coordinating to the metal ion 331). The third chloride remains ionic. The complex units are held together by hydrogen bonds through both the ionic and coordinated chloride ions. Each noncoordinated Cl" ion forms six Cl... H-0 bonds and each coordinated Cl- ion forms three Cl... H-0 bonds in addition to the Cl—Gd bond. The coordination geometry around Gd(III) has been described as distorted dodecahedron. In [Eu(H20)6 C12]C1, the coordination geometry has been described as distorted square antiprism 332). Similar compounds of Nd(III), Sm(III), Dy(III), Ho(III), and Er(III) are isostructural. 

The two most common geometries for eight-coordinate compounds (a) the trigonal dodecahedron and (b)the square antiprism. 

In the case of eight-coordination, the cube is fairly rare the compounds Na3[MFg] (M = Pa, U, Np) constitute the best-established examples. As for the trigonal prism versus the octahedron, interligand repulsion can be reduced by distortion of the cube to yield the square antiprism or dodecahedron (this is best demonstrated by playing with models). These two are about equally common. For example, in the case of Mo(CN)g-both square antiprismatic and dodecahedral coordination are found in the solid state in solution, the ion is stereochemically nonrigid (or fluxional) and appears to convert rapidly from one geometry to the other. 

V = 1.6874 (4) nm, and Z = 1. The compound is a square antiprism, consisting of the cen-trosymmetric dinuclear [H02(15)4(H2O)4(OH)2]4 cation, uncoordinated 15 molecules, and nitrate anions. The holmium atom is eight-coordinate with four nitrogens from the 15 ligands, two oxygens from H2O molecules, and two oxygens from hydroxo groups. 

Eight coordination frequently occurs in lanthanide and actinide fluoride complexes. The preponderance of these octacoordinate compounds can be assigned to one of two idealized coordination polyhedra, namely the square antiprism, symmetry (D4, ), or the dodecahedron (Dg ) with triangular faces. Of the remaining idealized eight-coordinate polyhedra, some are not represented and others have but few representatives in this class of compounds. 

An uncapped square antiprism of eight metal atoms surrounds the central P atom in Rug(CO),7(ji2 CH2Ph)([t2CO)2(H8-P) and in [Coio(p8P(CO)22] [3-31]. Other less symmetrical schemes for pj pg and Ps P coordination have been established in some compounds. 

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