Clusters high temperature reactions

Some compounds with network structures are synthesized by high-temperature reactions of metals with elemental sulfur [2, 8]. Rauchfuss et al. exploited the low-temperature synthesis of metal polysulfides by the reaction of metals with elemental sulfur in strong donor solvents. The reaction of copper powder with Ss in pyridine gives a copper polysulfide cluster Cu4(S5)2(-py)4 as orange crystals (Scheme 10) [45]. Furthermore, zinc powder reacts... 

A systematic study of this class of compounds did not start until twenty years later and led to the preparation of a series of M3Q7X4 (M = Mo, W Q = S, Se and X = C1, Br) inorganic polymers by high-temperature reactions (ca. 350 °C) of the elements in a sealed tube [10-14]. The interest on these cluster phases was mainly motivated by their excellent role as synthons for the preparation of molecular M3Q7 and M3Q4 cluster complexes, as will be presented in this section. 

Several compounds with network structures which contain S2 units can be prepared by high-temperature reactions (250-700 °C). An example of a reaction of a metal halide with sulfur and S2C12 is shown in equation (7). The conditions under which these S2 -containing cluster compounds are formed illustrate their high stability. 

One of the stimuli for studying these complexes is their close relationship to the well-known Chevrel phases MMo Yg (Y = S, Se or Te). Accordingly, a noteworthy recent development is the discovery of octahedral rhenium-selenide clusters. The phase Re SegClj has been prepared by the high temperature reaction ( BOOK) of ReQj with mixtures of Re and Se. An X-ray crystal structure has shown the presence of the [RcgScg] core possessing Re—Re distances of 2.6 2.67 A. The presence of two terminal Re—Cl bonds tram to one another) inhibits interlayer linkages. ... 

For polynuclear clusters similar reactions were not obtained These reactions proceed in the forward direction only at high temperatures ( 120 °C) and in the presence of an excess of the bidentate complex-forming agent, whereas the reverse reactions (20-22) also take place at room temperature in the presence of excess HC1 [11,46,49],... 

These reactions are irreversible organic acid ions apparently behave in the reactions as oxidants, being converted into the corresponding alcohols and their esters [11,48], Reactions (23) and (24) take place only at high temperatures (> 150°Q and in the presence of a large excess of organic acid [11,48,58], These reactions are also possible for polynuclear clusters, because redox reactions occur readily and reversibly for them [50],... 

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