The conjugate base of 19.27 forms the complex [CoL₃] which has mer-and fac-isomers. 

(a) Draw the structures of these isomers, and explain why the labels mer and fac are used. 

(b) What other type of isomerism does [CoL₃] exhibit? 

(c) When a freshly prepared sample of [CoL₃] is chromatographed, two fractions, A and B, are collected. The ¹⁹F NMR spectrum of A exhibits a singlet, while that of B shows three signals with relative integrals of 1 :1 : 1. Rationalize these data.

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H₂C. 0 0 HL (19.27) CF3