Peripheral metal atoms

The duster 14 contains 121 valence electrons, one electron less than predicted by the 18e rule. An electron counting rule for centered metal clusters, as proposed by Mingos, [30-33] states that the number of valence electrons in dose-packed metal clusters should be (12n, + A), where n, is the number of peripheral metal atoms and is 18 or 24 for centered cubic polyhedra. On this basis, 14 should possess either 114 or 120 valence electrons. 

Au-B bonds are also present in metal clusters with intersticial or peripheral boron atoms. An example is the cluster [Fe4(CO)12BH(AuPPh3)2], which was prepared by reaction of [AuCl(PPh3)] with the carbonyl iron dihydride. With the oxonium salt the reaction proceeds to the trinuclear gold derivative [Fe4(CO)12B(AuPPh3)3] (357).2063-2070 The ruthenium analogues and complexes with other ligands have been also synthesized as, for example, (358).2071-2079... 

The cluster 15, which crystallizes in the rhombohedral space group R3, has a remarkably different structure with respect to the structural features of 3a, 5a, and 10 (see Section II,D). Although a dode-cameric aggregate is present, as is the case for 5a (21), the cluster framework in 15 does not adopt a globular shape (39). The structure is built up of 24 Cu atoms surrounded by 12 triorganosilylphos-phanediyl moieties. The 24-metal-atom cluster consists of three planar Cu6 rings and two peripheral Cu3 cycles that all lie parallel to one another (Fig. 17). 

The pz-diol with M = Ni was peripherally metalated with CpiTiCh, Cp ZrC, and CpjHfC (Cp = r]5-pentamethylcyclopentadienyl) to formporphyrazines 205 (20%), 206 (45%), and 207 (21%) (Scheme 41) (10). The optical spectra of the metalocene appended catecholato pz exhibits a loss of the n-n peak (450 nm), which indicates that the lone pairs of the peripheral oxygen atoms are unavailable for charge transfer into the pz upon peripheral metalation. 

The ring redox potentials for the transition metal complexes are similar to those of the main group with the metal atom at the same oxidation state and of analogous size. The effect of Pc peripheral substitution is small and usually less than 0.1 V unless the substituent is charged. 

The structure of the tetrameric molecule of aluminium isopropoxide containing the metal atoms with 2 types of coordination — octahedral and tetrahedral — has been predicted by Bradley and then confirmed by the NMR data The X-ray single crystal study has shown that the central and the three peripheric aluminium atoms are situated in the same plane perpendicular to the main trigonal axis, which goes through the central atom. The 3 [A1202] 4-member cycles are situated in the mutually perpendicular planes [1642, 574] (Fig. 4.8 b). 

Among the derivatives of halide-substituted alcohols the fluoroalkoxides are of special interest. The presence of peripheral fluorine atoms enables the secondary M...F interaction and filling of the coordination sphere of the metal, which leads to an unusually high volatility. These compounds are described in the review by Willis [1749]. 

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