X-ray and B3LYP structures and vibrational spectra of pyridine betaine perchlorate monohydrate and conformation of ≥N+CH2COO moiety in crystalline betaines

Add time:08/20/2019    Source:sciencedirect.com

Pyridine betaine (PB) perchlorate monohydrate, PBH·OH2·ClO4, has been synthesized and characterized by X-ray diffraction, B3LYP calculation, FTIR and Raman spectroscopy. The complex crystallizes in space group P212121, with a=7.677(2), b=9.804(2), c=14.474(3)Å, and Z=4. PB is protonated and the resulting COOH group participates in a moderate hydrogen bond to water molecule (O(1)⋯O(w)=2.632(4) Å). The water molecule is further connected by hydrogen bonds to two neighbouring disordered ClO4− anions. Both geometry and conformation predicted by B3LYP calculations agree well with the X-ray data, while the COOH⋯OH2 hydrogen bond is ca. 0.1 Å shorter. The FTIR and Raman spectra of the complex have been analyzed and vibration assignments are proposed. In betaines and their complexes, two diastereoisomeric-eclipsed conformers can be distinguished. The close proximity of O(2) to N(1) (2.840(96) Å) indicates that the conformation of betaines is principally controlled by the electrostatic interaction between the positively charged nitrogen atom with the negatively charged oxygen atom of COO− or COOH groups.

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