3d and e, form III showed a stronger type B hydrogen bonding than form II since the CϭO stretching mode was 1651 cmϪ1 for form III but 1660cmϪ1 for form II. On the other hand, the type A hy- drogen bonding in form II was stronger than in form III since the N–H stretch mode of Form II (3334cmϪ1) was less fre- quent than form III (3338cmϪ1).