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

The reaction of [N(CH2CH2)3N] with maleic acid [HOOC(HC=CH)COOH] yields the anhyd. salt [HN(CH2CH2)3N][OOC(HC=CH)COOH] which contains chains of (+)N-H-N(+) bonded cations [HN(CH2CH2)3N]+ and isolated [OOC(HC=CH)COOH]- anions. Upon exposure to humidity the anhyd. salt converts within few hours into the hydrated pseudo-polymorphic form [HN(CH2CH2)3N] [OOC(HC=CH)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