2.2.2. DPA\_PA Salt for Single X-ray Crystal Structure Analysis

DPA and PA were each taken in a molar ratio of 1:1, suspended in diethyl ether and stirred at 25 ◦C and 170 rpm (IKA Plate\_RCT 4, IKA, IKA® Japan K.K., Osaka, Japan) for 5 days. After that, the precipitated material was recrystallized in acetone*,* yielding a colorless block-shaped crystal.
