A Rearrangement Reaction to Yield a NH4+ Ion Driven by Polyoxometalate Formation

Triethylamine is a volatile liquid and exists in the atmosphere in the gas phase. It is a hazardous air pollutant and identified as a toxic air contaminant. Thus, producing ammonia (a vital chemical for fertilizer production) from the vapor state of this toxic substance is a challenging task. Diffusion of the vapor of triethylamine, (C2H5)3N, into an acidified aqueous solution of sodium molybdate results in the formation of single crystals of compound [(C2H5)3NH]2[(C2H5)4N]­[NaMo8O26] (1). Notably, compound 1 includes a [(C2H5)4N]+ cation, even though the concerned reaction mixture was not treated with any tetraethylammonium salt. The formation of the [(C2H5)4N]+ cation from (C2H5)3N in an acidic aqueous medium is logically possible only when an ammonium cation (NH4+) is formed in the overall reaction: 4­(C2H5)3N + 4H+ = 3­[(C2H5)4N]+ + [NH4]+. Although the resulting NH4+ cation (identified by Nessler’s reagent test) is not included in the crystals of compound 1 as a cation, it can be made associated with a crown ether in the isolation of single crystals of compound [NH4⊂B15C5]3[PMo12O40]·B15C5 (2), (B15C5 = benzo-15-crown-5). Crystal structure analysis and 1H NMR studies of compound 2 have established the presence of an H-bonded NH4+ ion in compound 2, thereby established the rearrangement reaction.