Transition from a charge-opposed(+)N-H–N(+) inter-cation hydrogen bonded form of the salt [HN(CH2CH2)3N][OOC(HCCH) COOH] to the more traditional charge-assisted(+)N-H–O(−)cation-anion hydrogen bonded pseudo-polymorph upon hydration

Abstract

The reaction of [N(CH₂CH₂)₃N] with maleic acid [HOOC(HCCH)COOH] yields the anhydrous salt [HN(CH₂CH₂)₃N][OOC(HCCH)COOH] which contains chains of ⁽⁺⁾N-H–N⁽⁺⁾ bonded cations [HN(CH₂CH₂)₃N]⁺ and isolated [OOC(HCCH)COOH]⁻ anions. Upon exposure to humidity the anhydrous salt converts within few hours into the hydrated pseudo-polymorphic form [HN(CH₂CH₂)₃N] [OOC(HCCH)COOH]·(H₂O)_0.25, which contains more conventional “charge-assisted” ⁽⁺⁾N-H–O⁽⁻⁾ hydrogen bonds between anion and cation. This latter form can also be obtained by co-grinding.