*2.3. Synthesis of Schi*ff *Bases 1–4*

Schiff bases **1–4** were synthesized using a reported procedure by the condensation of melamine and 3 molar equivalents of aromatic aldehydes; 4-nitrobenzaldehyde, 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, and 4-hydroxybenzaldehyde, in boiling dimethylformamide containing acetic acid as a catalyst under reflux for6h[47].

### **3. Results**
