Trigonal-pyramidal units

Gep2 is formed as a volatile white solid (mp 110°) by the action of Gep4 on powdered Ge at 150-300° it has a unique structure in which trigonal pyramidal [GePsI units share 2 P atoms to form infinite spiral chains (Pig. 10.2). Pale-yellow GeCl2 can be prepared similarly at 300° or by thermal decomposition of GeHCls at 70°. Typical reactions are summarized in the scheme ... 

The HP may then be removed by adding MgO to precipitate MgF2 and the colourless deliquescent solid Xe03 obtained by evaporation. The aqueous solution known as xenic acid is quite stable if all oxidizable material is excluded, but the solid is a most dangerous explosive (reported to be comparable to TNT) which is easily detonated. The X-ray analysis, made even more difficult by the tendency of the crystals to disintegrate in an X-ray beam, shows the solid to consist of trigonal pyramidal Xe03 units, with the xenon atom at the apex (cf. the isoelectronic iodate ion 103 p. 863). 

Figure 3. Plastocyanin orientations. The Cu(N-Imid)2(S-Cys)(S-Met) unit has approximately trigonal pyramidal symmetry, with the S(Met) ligand at the apex of the pyramid. Key top, orientation giving predominantly Cu-S(Met) EXAFS and bottom, orientation giving no Cu-S(Met) EXAFS. (Reproduced from Ref. 30. Copyright 1982, American Chemical Society.)...

Bismuth phosphine complexes represent a substantial component of the established phosphine complexes of heavier p-block elements, and an excellent overview has presented an important bonding model for these systems (7). The observed structures are considered as trigonal-pyramidal BiX3 units with three secondary trans bonds. If the acceptor orbitals are the Bi-X trans arrangement is expected, as the relationship between the trans X-Bi-P bond distances. The shortest Bi-P distance [2.7614(2) vs 2.866(3) A] is trans to the longer Bi-Br distance [3.403(1) vs 2.9916(1) A], as the only arrangement that will allow the phosphine ligands to occupy trans... 

SnBr2 in liquid ammonia. The anionic trigonal pyramidal [Sn(NH2)3] units are linked via interactions with the K+ cations into a strongly distorted hexagonally close-packed array (K-N = 2.907(7) and 2.949(8) A, and Sn is 2.154(7) A). 

Five-Center Four-Electron Bonding Structures. The potential for the existence of 5-center 4-electron (5c-Ae) bonding structures 558 have recently been surveyed by Tantillo and Hoffmann980 [calculations at the B3LYP/6-31G(d) level], A cation with three anthracenyl units joined around the C -H-C -H--C core with two approximately trigonal pyramidal carbon atoms and one five-coordinate trigonal bipyramidal carbon was found to have 5c-Ae bonding. The anticipated existence of... 

In the solid state, GeF2 has a unique structure in which trigonal pyramidal GeF3 units share two F atoms to form an infinite spiral chain. Reaction between GeFi and F gives GeF3, which is a trigonal pyramidal ion. 

The structure of SnCl2 is shown in Fig. 14.5.1(a). In the crystalline state it has a layer structure with chains of corner-shared, trigonal-pyramidal SnCb units. The commercially available solid hydrate SnCl2-2H20 also has a puckered-layer structure. 

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