Clusters trigonal bipyramidal geometry

The cluster Sng 4 has a monocapped square antiprismatic geometry. On the other hand, the cluster SM5 ]2, 68b, has a trigonal bipyramidal geometry, as shown by X-ray crystallography107. 

Clearly, the third and fourth molecules cannot be bound to the (Me-Mg-Cl)2(Me20)2 cluster, 9a. Therefore, 9a is a saturated shell. Since the double trigonal-bipyramidal geometry of 9b (n = 4) in Figure 12 does not involve significant steric congestion, expulsion... 

The Ni3S2 fragments in the two complexes (263) and (265) have a trigonal bipyramidal geometry with the two S atoms in the apical positions and the three nickel atoms in the equatorial plane, as found in other organometaUic compounds which contain the same Ni unit.1939 The formation of the enneanuclear complex (264), on the contrary, is exceptional and no other complex of this stoichiometry was isolated with analogous tertiary phosphines, with selenium, or with metals other than nickel. It is not possible to assign any definite oxidation number to nickel in complex (264). The lack of two electrons with respect to the situation of nine nickel(II) ions was reported to be essential for the existence of complex (264) because the oxidation is spontaneous and its reduction invariably leads to the decomposition of the cluster compound.19 ... 

The cluster [Os5C(CO)i4(C>2CMe)I] has 78 valence electrons, which is not shown in Table 19.4.1, and its bond valence is equal to 6 [b = (5x18—78) = 6], This cluster has a deformed trigonal bipyramidal geometry with no bonding in the equatorial plane of the bipyramid. 

The capped trigonal bipyramid geometry has been observed in another rather unusual kind of clusters, as the hydroxo or oxo compounds of Sn, Pb, Al, etc. . which show weak metal-metal interactions. X-ray studies on the two forms of [Pb60(0H)6] [CIO4] H2O have confirmed a structure consistent with an arrange-... 

Perhaps the most fruitful of these studies was the radiolysis of HCo(C0)4 in a Kr matrix (61,62). Free radicals detected in the irradiated material corresponded to processes of H-Co fission, electron capture, H-atom additions and clustering. Initial examination at 77 K or lower temperatures revealed the presence of two radicals, Co(C0)4 and HCo(C0)4 , having similar geometries (IV and V) and electronic structures. Both have practically all of the unpaired spin-density confined to nuclei located on the three-fold axis, in Co 3dz2, C 2s or H Is orbitals. Under certain conditions, a radical product of hydrogen-atom addition, H2Co(C0)3, was observed this species is believed to have a distorted trigonal bipyramidal structure in which the H-atoms occupy apical positions. 

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