Tricapped trigonal prism structure

Potassium nonahydridorhenate(VII) K2[ReH9] was prepared by reduction of potassium perrhenate in aqueous ethylenediamine with potassium or lithium metal. Neutron diffraction analysis established unequivocally the correct composition and molecular structure of this polyhydride complex. The diffraction study was performed within an evacuated cryostat maintained at room temperature, since the crystals are unstable in moist air. The Re atom hes at the center of a trigonal prism of H atoms, with three H atoms beyond the centers of the prism faces. Thus, the structure is a tricapped trigonal prism of symmetry. The average Re—H distance is 1.68(1) A and the average H—Re—H angle between hydrogens in the same vertical mirror plane is 93.6(6)°. 

Another example of the nine-coordinate polyhydride is WHg PPh(i-Pr)2 3 which was prepared by subjecting a hexane solution of hexamethyltungsten and PPh(i-Pr)2 to hydrogen at 300 atm for five days. The molecular structure was also confirmed by neutron diffraction 

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Figure 1-5 The tricapped trigonal prism structure found in many 9-coordinate complexes.

Cages with nine vertices are rare. Representative ones are Bi + (in Bi24Cl26), B9Hi , and B7QH9, all of which have the tricapped trigonal prism structure (Fig. 1-5), and Sn9, which is a square antiprism capped on one square face. 

Ms " clusters have 12 framework bonding electrons as has [BsHs]- (p. 161) the anions are also isoelectronic with the well-known cation [Bis]. Similarly, the alloy NaSn. 2.23 reacts with cryptand in ethylenediamine to give dark-red crystals of [Na(ciypt)]4 [Sng] the anion is the first example of a C41, unicapped Archi-median antiprism (Fig. 10. lOc) and differs from the >3/, structure of the isoelectronic cation [Bis] + which, in the salt Bi+[Bi9] +[HfCl6]5 (p. 591), features a tricapped trigonal prism, as in [BgHg] " (p. 153). The emerald green species [Pb9] , which is stable in liquid NH3 solution, has not so far proved amenable to isolation via ciyptand-complexed cations. 

The influence of electron-count on cluster geometry has been very elegantly shown by a crystallographic study of the deep-red compound [K(ctypt)]g [Ge9]- [Ge9] .2.5en, prepared by the reaction of KGe with cryptand in ethylenediamine. [Ge9] has the C4, unicapped square-antiprismatic structure (10.10c) whereas [Ge9]- , with 2 less electrons, adopts a distorted Dit, structure which clearly derives from the tricapped trigonal prism (p. 153).The field is one of... 

Nine-coordinate (each NOa group is bidentate) structure tricapped trigonal prism... 

Figure 9. A postulated structure of H Re(P-Me< h)% based on the tricapped trigonal prism, with the phosphine ligands assigned to equatorial positions...

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