Nicotinamide complex of silver(III) with expanded coordination number
In strongly alkaline media ([OH−] ≥ 0.12 M), nicotinamide (nica) forms a complex with square-planar Ag(OH)4 − [nica] ≥ 0.05 M. The complex decomposes in seconds to nicotinamide N-oxide. The correlation of maximum absorbance of the complex with concentrations of nicotinamide and hydroxide requires that the complex is either the five-coordinate Ag(OH)4(H-1nica)2− or the six-coordinate Ag(OH)5(nica)2−. Comparison with the reactions of Ag(OH)4 − with nicotinate ion (nic −) and acetamide under similar conditions indicates that nicotinamide coordinates with Ag(OH)4 − by the amido group rather than the nitrogen on the pyridine ring or the amido oxygen. Kinetics of the Ag(III)-nica redox reaction are consistent with direct reaction between nicotinamide and uncoordinated Ag(OH4)−. Oxidation takes place at the pyridine ring, yielding nicotinamide N-oxide. Silver(III) is reduced to monovalent silver.
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