Experimental and theoretical structural study of (3E,5E)-3,5-bis-(benzylidene)-4-oxopiperidinium mono- and (3E,5E)-3,5-bis-(4-N,N-dialkylammonio)benzylidene)-4-oxopiperidinium trications

(3E,5E)-3,5-Bis(benzylidene)-4-oxopiperidinium tetrafluoroborate [C19H18NO][BF4] (1), (3E,5E)-3,5-bis[4-(dimethylammonio)benzylidene]-4-oxopiperidinium bearing mixed tetrafluoroborate and bis(hexafluoro(μ-hydroxo)diborate) anions [C23H30N3O][B2F6OH]n[BF4]m·xH2O (2), and (3E,5E)-3,5-bis[4-(diethylammonio)benzylidene]-4-oxopiperidinium tris(tetrafluoroborate) monohydrate [C27H38N3O][BF4]3·H2O (3) were obtained via mediated by the boron trifluoride etherate aldol-crotonic condensation of the corresponding aldehyde and piperidin-4-one hydrochloride monohydrate. Their structures were studied by IR and multinuclear NMR spectroscopy, and single crystal X-ray diffraction. The X-ray analysis revealed the presence of monoprotonated piperidinium cation in 1 and triprotonated cations in 2 and 3. The hexafluoro(μ-hydroxo)diborate anion was found in the mixed-anionic salts 2A and 2B which differ by the ratio of the anions. The extended hydrogen-bonded system is registered in all compounds. Static first order hyperpolarizabilities for the neutral (3E,5E)-3,5-bis[4-(dimethylamino)benzylidene]-piperidin-4-one and its positively charged derivatives along with their molecular geometries and binding energy of 1 were calculated using DFT approach.

► Synthesis and structural studies of mono- and tri-cation piperidone derivatives obtained in the form of fluoroborate salts.
► Structural characterization of hexafluoro(μ-hydroxo)diborate anion.
► Correlation was found between bond order alternation (BOA) and hyperpolarizability for neutral and charged species.