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(-1)nica)(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. [GRAPHICS] .