Cobalt complex compounds, anions structure

As with most complexation and drug solubility situations, pH b a critical variable. Cocaine base b not soluble in water, and if the drug b in thb form rather than a soluble salt, no reaction occurs. Acid b needed to ensure that the cocaine b in the water-soluble ionic form to allow for the formation of a complex. The color b the result of an ion-pair compound formed from the cationic cocaine and the anionic cobalt complex. As with all amine bases, such as ammonia, the base becomes protonated in acidic solution. The pKg of the base determines the ratio of the protonated, ionized form to the neutral form. It is possible to add too much HQ, because cobalt forms a water-soluble pink complex with chloride [CoCy . The pH can also influence the type of complex and ion pair formed. Under acidic conditions, the ion pair favored b [Co(cocaine)2l(SCN)2 (which b pinkbh and soluble in water), while in the neutral-to-basic ranges, the ion pair b assigned the structure [cocaine-H ]2 [Co(SCN)4] (which b a blue solid and soluble in chloroform). The important points of the cobalt thiocyanate reaction with cocaine are summarized in Figures 7.24r-7.26. 

The structure of the active component, manganese pyrophosphate, has been reported in the literature (24). It is layer like with planes of octahedrally coordinated Hn ions being separated by planes of pyrophosphate anions (P20y ). Examination of models of this compound gave calculated Hn-Hn thru space distances of 3.26 and 3.45 angstroms, a metal-metal distance close to that found for binuclear dibridged peroxo- and superoxo- complexes of cobalt ( ). 

We have mentioned that the structural parameters of C2H4 bridged compounds can vary over a wide range. Whereas most examples reported do not have metal-metal bonds, there is one conspicuous exception. Theopold and Bergman succeeded in synthesizing the propane-1,3-d iyl cobalt derivative 125 from the radical anion [(t) ,-C5H5)Co(/z-CO)12 and 1,3-dibromopropane (98, 295) in 40 5 yield. This compound is best described as a dimetallacyclopentane, and its chemistry (thermolysis and reaction with CO and phosphines Scheme 34) supports this view. Formation of cyclopropane (100°C or I2/25°C) is probably the most remarkable feature of this cyclic system. Simple C—C bond formation has never been observed before in ligand-induced or thermal reactions of either mono- or binuclear cyclopentadienylcobalt complexes. The architectural details of... 

The complexation of coordination compounds may make it possible to control their photochemical behaviour via the structure of the supramolecular species formed. For instance, the binding of cobalt(m) hexacyanide by macrocyclic polyammonium receptors markedly affects their photoaquation quantum yield in a structure-dependent manner [8.73-8.77]. It thus appears possible to orient the photosubstitution reactions of transition-metal complexes by using appropriate receptor molecules. Such effects may be general, applying to complex cations as well as to complex anions [2.114]. 

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