Hydrogen bonds and proton location in 1:1 and 2:1 complexes of N-methylmorpholine betaine with picric acid

Add time:07/18/2019    Source:sciencedirect.com

The 1:1 and 2:1 complexes of N-methylmorpholine betaine (MMB) with picric acid (TNPH) have been prepared and their structures determined by X-ray diffraction. In the 1:1 complex, MMBH·TNP, betaine is protonated and carboxylate group forms a hydrogen bond with the picrate anion, the O⋯O distance is 2.588(4) Å. The 2:1 complex, (MMB)2H·TNP·(1/2)H2O, crystallises as semihydrate with partly disordered water molecule. The carboxylate groups of a pair of MMB molecules are bridged by a proton to form a dimeric cation with a short and asymmetric hydrogen bonds with O⋯O distance equals 2.458(5) Å. The FTIR spectrum of the 1:1 complex shows a strong absorption at ca. 2500 cm−1 due to the νOH vibration. A broad and intense absorption in the 1500–400 cm−1 region in the spectrum of the 2:1 complex is typical for a very short hydrogen bonds. NMR spectra of investigated complexes are discussed. (MMB)2H·TNP·(1/2)H2O complex is the first example of betaine homoconjugated cation with phenolate counter anion.

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