Cobalt complexes with Lewis bases

Of the cyclic olefins, norbornadiene replaces two CO groups from one Co to yield a labile complex 159, 160, 235), cyclooctatetraene replaces the axial CO ligands from all three cobalt atoms 53) and is itself replaced by other Lewis bases 330), and cyclopentadiene forms the unusual complex [95] with Co3(CO)gCMe 159,160). A few catalytic reactions were observed with methinyltricobalt enneacarbonyls including the dimerization of norbornadiene 160, 235) and the polymerization of functional olefins 312) with different Co3(CO)9CX. 

Complexes related to CoHg(SCN)4, the well-known calibrant used in magnetic susceptibility measurements, have recently been prepared containing silver(I).146,147a In the presence of a number of Lewis bases octahedral adducts such as Co[Ag(SCN)2] -2DMF were obtained. Magnetic moments indicated the presence of high-spin cobalt(II). With nickel(II), two types of complex... 

Transition metals have a particular tendency to form complex ions because they have more than one oxidation state. This property allows them to act effectively as Lewis acids in reactions with many molecules or ions that serve as electron donors, or as Lewis bases. For example, a solution of cobalt(II) chloride is pink because of the presence of the Co(H20)6 ions (Figure 16.8). When HCl is added, the solution turns blue as a result of the formation of the complex ion CoCl4 ... 

A test first described by Parri in 1924 in which the barbiturate gives a colored complex with cobalt(II) has been adapted by the pharmacopoeia. The test parameters of the determination have been modified several times through the years, but the presence of a number of elements constitutes the essence of the procedure a ion, normally cobalt(II) or copper(II) an organic solvent, preferably one with a Lewis base character and an alkaline reaction and the absence of water in the test solution. Furthermore ammonia, or an organic amine, is sometimes added. 

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