Cubane tetramer

The compounds for n - 1 or 0.5 undoubtedly have polymeric (layer) structures, of which (13) is an example. There is also an example of a cubane tetramer like (18) in this class, MnF(BF4) (2,6-diMepyO) MeOH, which resulted239 from the reaction of 2,6-dimethylpyridine JV-oxide with Mn(BF4)2. 

Thiolate exchange reactions of the dimeric iron(III) and the iron(II)/iron(III) cubane tetramers, [Fe2S2(SR)4]2 and [Fe4S4(SR)4]2, have been studied750,759 in some detail and provide routes to several related complexes. Exchange takes place with other thiols (R SH) as in equation (64). 

Magnesium ethoxide undergoes redistribution with (h -CjH5)2Mg to give h -CjHjMgOEt in THF the product is a monomeric THF adduct, but in toluene an unsolvated cubane tetramer is formed. 

Cul)2(bpds)] oc [bpds = i5(4-pyridyr)disulfide] in which CU4I4 cubane tetramers are linked via bridging bipyridyl ligands. 

The other tetrahalides can all readily be made by direct reactions of the elements. Crystalline SeCU, TeCU and -SeBr4 are isotypic and the structural unit is a cubane-like tetramer of the same general type as [Me3Pt(/Z3-Cl)]4 (p. 1168). This is illustrated schematically for TeCU in Fig. 16.13d each Te is displaced outwards along a threefold axis and thus has a distorted octahedral environment. This can be visualized as resulting from repulsions due to the Te lone-pairs directed towards the cube centre and, in the limit, would result in the separation into... 

Fig. 13.6 Shown are (a) a dimer of cubanes (bonded via indium vertices) found in CsT3Nb2ln6AsTo (b) a tetramer of two cubanes and two semicubanes found in Cs24Nb2lni2Asi8.

The colorless tetramer Ccu(py)l] is fairly stable only in non- or weakly coordination solvents such as benzene, CH Cl, or acetone. At room temperature in solution this copper complex shows an intense red photoluminescence ( 0.04 a f nax = nm (54). The emitting state is a metal-centered 3d 4s excited state which is strongly modified by Cu(I)-Cu(I) interaction in the tetramer. This consists of a (Cul) cubane core. 

The electrochemical results described above indicate that unlike in the cases of other cobalt-catalyzed oxidation processes where the Co /Co redox couple is invariably involved [19b,38], in the present case where cubane clusters of the general formula Co4(p3-0)4( J,-02-CR)4(L)4 are to be employed as catalysts for the air/02 or TBHP oxidation of alkylaromatics, alcohols, etc., we have a catalytic system wherein the oxidation states of cobalt cycle between +3 and +4. The kinetic inertness of Co(lll) coupled with the inadequately explored reactivity of Co(lV) thus make the catalysts based on C04O4 cubanes quite interesting [36]. We shall now discuss the resulting materials prepared by supporting the cubane-like cobalt(lll)-oxo clusters discussed above in this section by following the chemical route in which the carboxylate anion derived from CMS-CH2CH2CO2H binds the in situ or preformed cobalt(III)-oxo tetramers at elevated temperatures. 

The strong preference for oxygen over carbon as a donor atom is shown by the rapid decomposition in water of most compounds with a covalent M—C bond or an ionic M+. .. C- interaction. The effect of the differences in electronegativity is shown in the structures of methyl lithium and methyl potassium. The methyl lithium tetramer, (39), has a cubane ... 

FIGURE 5. Cubane structure of the tetrameric compounds RMgOR. The tetramers are thermodynamically favoured when the alkyl groups are small and the solvent is only weakly co-ordinating... 

With less bulky groups on the nitrogen atoms, the most common oligomer formed by the hypothetical monomeric group 14 imides, M=NR (M = Ge, Sn, Pb), is the cubic tetramer, e.g. [M()i3-N Bu)]4. This is especially true for the heavier (larger) elements tin and lead for which, in contrast to germanium, cubanes are observed even when R = 2,6- Pr2C6H3. " ... 

In addition, crystal structures of several halomethylzinc alkoxides and an acy-loxymethylzinc reagent have been reported (Figure 2, 7-9). lodo- and chloromethylzinc alkoxides exist as tetramers in cubane or bis(cubane)-like structures. However, these... 

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