Structures tetrahedral clusters

Slovokhotov, Yu.L. and Struchkov, Yu.T (1984) X-ray crystal structure of a distorted tetrahedral cluster in the salt [(Ph P)4Au4N] BF4 . Geometrical indication of stable electronic configurations in post-transition metal complexes and the magic number 18-e in centred gold clusters. Journal of Organometallic Chemistry, 177, 143-146. 

Figure 8.2 Structure (C15) of cubic Laves phases. MgCu2 is the prototype. Top—Mg sub-structure with the pattern of the diamond structure. Bottom—Cu sub-structure with four tetrahedral clusters in the tetroid holes of the diamond structure. The stars indicate the centers of the patterns.

A much more subtle case of stabilisation due to the presence of face-bridging ligands is found in the two tetrahedral clusters Co4Cp4(p3-H)4 (dec. ca. 300 °C)134> and Ni4Cp4(p3-H)3 (dec. ca. 320 °C)133h The structure of the last compound is shown in Fig. 2. 

The crystal structure of the complex between silver iodide and piperidine has been determined.57 The colourless crystals were prepared by warming silver iodide with sufficient piperidine to allow the silver iodide to dissolve and then allowing the resulting solution to cool. The structure consisted of tetrahedral clusters of iodide ions with the silver atoms embedded into the faces of the tetrahedron. The (Agl)4 clusters were separated by the piperidine molecules which were bound to the silver via the N atom. The Ag—N bond lengths were 232.9 pm, while the Ag—I distances were 285.3, 293.6 and 294.2 pm. 

It is interesting to note that the partially substituted derivatives obtained in spite of having the same composition demonstrate quite different molecular structures the fluorosubstituted compound is a tetrahedral cluster, the chloro-derivative a square planar, one and the bromosubstituted a butterfly type cluster [370] (Figs. 4.7 b and 4.5 b, Sections 4.4.2, 4.4.5). 

In the terminology used in Wade s rules1" , the 60-electron tetrahedral cluster [HFeRu3(CO)i3] is considered a closo species (XXIX) and the 62-electron open butterfly structure of [HFe4(CO)13] is considered a nido species (XXX). The structural difference is related to the fact that one of the CO groups is a 2-electron donor in the former and a 4-electron donor in the latter. 

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