Capped trigonal prism coordination structures

The three low energy structures available to 7-coordinate compounds are the pentagonal bipyramid, the capped octahedron and the capped trigonal prism. These structures are illustrated in Fig. 24. 

Possible stereochemistries for eight-coordinate [Ln(H20)8]3+ are the dodecahedron, the square antiprism, and the cube, although the last seems less likely (295). The proposed nine-coordinate [Ln(H20)9]3+ tri-capped trigonal prism transition state is similar to the [Ln(H20)9]3+ structures observed in the solid state. Thus, the possible water exchange... 

Treatment of [Mo(CO)3Tp] with X2 (X = Br, I) affords the seven-coordinate complexes [MoX(CO)3Tp], which has been characterized crystallographically for X = Br. The structure can either be viewed as a distorted capped trigonal prism with Br capping a quadrilateral face or as a 3 4 piano stool.73... 

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). 

The H02S3 structure is not a simple c.p. structure but has one-half of the metal atoms 6- and the remainder 7-coordinated, and two-thirds of the S 4-coordinated, and one-third 5-coordinated. The Gd2S3 structure also is complex, with equal numbers of metal atoms 7- and 8-coordinated (mono- and bi-capped trigonal prism), and all S atoms 5-coordinated (two-thirds square pyramidal and one-third trigonal bipyramidal). 

Pentagonal Bipyramid Capped Octahedron Capped Trigonal Prism Fig. 24. Low energy structures of 7-coordinate complexes... 

---