Complex compounds are defined as compounds that are constructed of a metal center and an inner and outer sphere filled with ligands. They differ in geometric shapes, colors, and magnetic properties as explained by crystal field theory. Binding of ligands to metal cations leads to energy cleavage of d orbitals, which causes the formation of high- and low-spin complex compounds. Furthermore, the geometric shapes most often formed by complex compounds are square planar, tetrahedral, and octahedral shapes. Nitrogen heterocyclic compounds are a type of compound that contains one or more attached nitrogen atoms in a cyclic structure instead of carbon atoms. The main representatives are pyridine, pyrimidine and quinoline, and equally important are piperidine, pyrrole, indole and quinazoline. Due to the presence of nitrogen in the structure and its inductive action on electrons, their reactivity in electrophilic aromatic substitution is reduced, and it increases in nucleophilic aromatic substitution. In complex compounds they are bound by electronic nitrogen pairs. Synthesized complex compounds with ligand (4-oxoquinazoline-3(4H)-yl)-acetic acid with metal cations of silver, cadmium, copper and zinc were analyzed by FT-IR and TGA methods. Using the obtained results, it is assumed that the ligand binds to metal cations using a carboxyl group and via nitrogen from the quinazoline ring.