Nitro vs nitrito linkage isomers
Abstract
In this experiment, the nature of linkage isomers will be observed on the example of nitritopentaamminecobalt(III) Chloride and nitropentaamminecobalt(III) Chloride. Their relative stability will be compared on standard conditions and the infrared spectroscopy of both the isomers will be obtained to analyze the characteristic absorption bands for the nitro and nitrito group. Yield for nitritopentamminecobalt(III) Chloride was obtained to be = 1.9221 g(73.24 %) and yield for nitropentamminecobalt(III) Chloride = 0.76 g(76 %)
Introduction
Linkage isomers may arise when one or more of the ligands can coordinate to the metal ion in more than one way. The first reported example of linkage isomerism had the formula [Co(NH3)5(NO2)]Cl2.1 This compound exists in two isomeric forms; one containing Co-NO2 linkage, the other the Co-ONO group.2 In this experiment, the synthesis of both of the isomers will be performed. The figure below illustrates the bonding in nitrito(on the right) and nitro(on the left)
Figure : Nitrito and Nitro linkage isomers.
For the nitrito isomer, the metal(Cobalt in this case) is connected to the oxygen of the ONO group, whereas for nitro isomer, the metal is connected to the nitrogen of the NO2 group. One of the useful techniques identifying linkage isomers is infrared spectroscopy. The characteristic frequencies for both of the isomers are distinguishable in the infrared spectra of these compounds.
There are only minor differences in the procedures for the preparation of the two linkage isomers. In both cases the reaction is represented by
[Co(NH3)5Cl]2+ + NO2- = [Co(NH3)5NO2]2+ + Cl- (eqn 1.1)
The mechanism of reaction will in both cases go through the O-bonded isomer(the nitrito-isomer) which is unstable and gradually converts to the N-bonded isomer in an equilibration process.3 The equilibrium in aqueous acid solution
[Co(NH3)5ONO]2+
In this experiment, the nature of linkage isomers will be observed on the example of nitritopentaamminecobalt(III) Chloride and nitropentaamminecobalt(III) Chloride. Their relative stability will be compared on standard conditions and the infrared spectroscopy of both the isomers will be obtained to analyze the characteristic absorption bands for the nitro and nitrito group. Yield for nitritopentamminecobalt(III) Chloride was obtained to be = 1.9221 g(73.24 %) and yield for nitropentamminecobalt(III) Chloride = 0.76 g(76 %)
Introduction
Linkage isomers may arise when one or more of the ligands can coordinate to the metal ion in more than one way. The first reported example of linkage isomerism had the formula [Co(NH3)5(NO2)]Cl2.1 This compound exists in two isomeric forms; one containing Co-NO2 linkage, the other the Co-ONO group.2 In this experiment, the synthesis of both of the isomers will be performed. The figure below illustrates the bonding in nitrito(on the right) and nitro(on the left)
Figure : Nitrito and Nitro linkage isomers.
For the nitrito isomer, the metal(Cobalt in this case) is connected to the oxygen of the ONO group, whereas for nitro isomer, the metal is connected to the nitrogen of the NO2 group. One of the useful techniques identifying linkage isomers is infrared spectroscopy. The characteristic frequencies for both of the isomers are distinguishable in the infrared spectra of these compounds.
There are only minor differences in the procedures for the preparation of the two linkage isomers. In both cases the reaction is represented by
[Co(NH3)5Cl]2+ + NO2- = [Co(NH3)5NO2]2+ + Cl- (eqn 1.1)
The mechanism of reaction will in both cases go through the O-bonded isomer(the nitrito-isomer) which is unstable and gradually converts to the N-bonded isomer in an equilibration process.3 The equilibrium in aqueous acid solution
[Co(NH3)5ONO]2+
References: 1. Nakomoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds., 4th Edition: Wiley Interscience 2. Housecroft, C.E.; Sharpe, A.G. Inorganic Chemistry, 3rd edition; Prentice Hall: 2008, 725-810. 3. Basolo,F.; Hammaker, G.S. Inorganic Chemistry, 1962,1,1.