Solid-state versus solution preparation of two crystal forms of [HN(CH2CH2)3NH][OOC(CH2)COOH]2. Polymorphs or hydrogen bond isomers?
The reaction of [N(CH2CH2)3N] with malonic acid [HOOC(CH2)COOH] in the molar 1:2 ratio yields two different crystal forms of the salt [HN(CH2CH2)3NH][OOC(CH2)COOH]2 depending on the preparation technique and crystallization speed: form I, containing malonate anions with intramolecular hydrogen bonds, is obtained by solid-state co-grinding or by rapid crystallization, whereas form II containing intermolecular hydrogen bonds is obtained by slow crystallization. Form I and II do not interconvert, and form I undergoes an order-disorder phase transition on cooling.
Braga
Dario
D
Dipartimento di Chimica G. Ciamician, Via Selmi 2, 40126 Bologna, Italy. dario.braga@unibo.it
Maini
Lucia
L