Manganese compounds clusters

Compared with cluster complexes of lower nuclearities, the number of mixed chalcogen/carbonyl complexes having more than six metal atoms is small. Besides some complexes containing iron and cobalt, no manganese compound within this class of complexes is known. 

Electron counts for these chain cluster complexes are low, 9-10 CBEs with nonmetal interstitials and only 13 with manganese in MnTb4 l5. This appears to be the lower limit when judging from the chain-like compounds to come, TRslls, where there is also only one manganese compound known with this electron count, MnGd3 l3 (see Table 6). 

This facile approach to the carbene chemistry of rhenium has not yet been investigated with technetium. Further reactions with the technetium cluster 44a have been performed in C6H6/HC1 to yield the compound [( 6H6)Tc(CO)3]+ (66) which previously had only been described for manganese and rhenium [81]. "Tc-NMR of the latter compound exhibits a resonance at -1983 ppm (relative to [Tc04]- ), and it therefore fits very well into the range proposed for Tc(I) complexes. 

Herrmann and coworkers183 reported a series of Cp-manganese carbonyl complexes which bind Ge, Sn and Pb as central atoms linearly coordinated in clusters, to two Mn atoms in one series and trigonal-planar coordinated to three Mn atoms in another series 8 and 9. The group 14 atoms are double-bonded to two Mn atoms in these compounds, or carry one double bond and two single bonds to three Mn atoms. Potentiometric measurements of these compounds show irreversible reductions and oxidation by CV. No products could be isolated from either reduction or oxidation. The exceptionally high oxidation potential of (/i-Pb) r/ -CsHs )Mn(CO)2]2 as compared to the apparently similar Sn compound is noteworthy (Table 15). 

Because of the large number of carbonyl groups required to satisfy the noble gas rule and the relatively small metallic radius, serious steric limitations are present for manganese tetranuclear closed clusters12). The only known tetranuclear compounds are some mixed clusters, MnOs3(CO)16H and MnOs3(CO)13H3 (see later), which have been prepared from Os3(CO)12 and [Mn(CO)s] 161). 

In photosystem II an intermediate tyrosyl radical is formed which then repetitively oxidizes an adjacent manganese cluster leading to a four-electron oxidation of two water molecules to dioxygen. In broad detail, the model compounds" described above were demonstrated to undergo similar reactions on photochemical excitation of the respective ruthenium centers. 

Hiickel method ( Section 4.4). In the hands of Hoffmann, to whom we owe the EHM in its current form [112], extended Hiickel calculations have given powerful insight into the structures of these compounds. Wide-ranging corroboration of this assertion is seen in Hoffmann s Nobel lecture [100]. Some other examples are a polymeric rhenium compound [113], manganese clusters [114], and iridium [115] and nickel [116] coordination compounds. 

It is convenient here to include fluorides with a metal-to-fluorine ratio of 1 2.5. There are three examples. The chromium (53) and manganese (54) compounds, which are not isostructural, can be considered of the type, MF2,MF3, containing di- and trivalent metals. The niobium compound (35) is the only example of a metal cluster fluoride reported as yet. 

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