Synthesis and structural characterization of novel di-substituted pyridine-2,6-dicarboxylic acid hydrazide oxo-quinazoline derivative and Cu (II) pincer complex

Crystal and molecular structures of novel pyridine-2,6-dicarboxylic acid (pdc) hydrazide derivative (H2L) dimethanol solvate (H2L = N,N'-bis(2-methyl-4-oxoquinazolin-3(4H)-yl)pyridine-2,6-dicarboxamide) and its copper(II) complex were determined by the single-crystal X-ray diffraction. In the crystal structure, these nonplanar molecules form specific cavities that are populated by methanol molecules (held by O-H-O and N-H-O hydrogen bonds). Additional stabilization is achieved through a series of offset face-to-face x-x interactions between aromatic moieties. The compound is the first structurally described pdc hydrazide derivative containing quinazoline moieties. The reaction of the H2L with copper(II) chloride in methanol resulted in the formation of a new methanol/water solvate containing discrete CuCl2L molecules. Cu(II) ion is coordinated by three nitrogen atoms (two from hydrazide and one from pyridine moieties) in a chelate fashion. Two chloride ions complete distorted square pyramidal coordination geometry. Unlike in H2L molecules, in CuCl2L the hydrazide N-atoms are deprotonated, and coordinated to Cu(II), while quinazoline N-atoms are protonated. In its crystal structure, CuCl2L molecules form dimeric motifs via O-H-O, N-H-O, O-H-Cl hydrogen bond interactions. The adjacent dimers are stacked along the crystallographic b- and c-axis through N-H-Cl and offset face-to-face x-x interactions. The FT-IR spectra analysis indicates a significant shift of C--O stretching vibrations of uncoordinated carbonyl groups, that can be attributed to the electron-withdrawing effect of Cu(II) ion. The TG analysis indicates that the weakly bounded solvent molecules evaporate at lower temperatures and that the compound is stable up to 300 degrees C.