New Cu(II) complex with O,N,O-quinazolinone ligand: Spectroscopic characterization, crystal structure and DFT study.

Quinazolinones represent a privileged scaffold in medicinal chemistry due to their wide range of biological activities. They have been reported to exhibit antibacterial, antifungal, antimalarial, anti-inflammatory and anticancer activities [1–2]. Recently, the versatility of transition metal complexes with quinazolinone derivatives, especially those derived from Schiff bases, has been investigated in terms of their coordination geometry, spectroscopic properties, biological activity and therapeutic effects [3]. Many studies have shown that planar quinazolinone ligands play a crucial role in enhancing DNA binding capacity and complexation with metal ions leads to effective interaction with the DNA molecule. Therefore, the study of copper-quinazolinone complexes is of great interest due to their ability to act as potential anticancer agents and diagnostic tools. 

Considering the application of quinazolinone-based compounds in medicine, this work aims to understand the solid-state phase behaviour of the quinazolinone Schiff base ligand 3-[(2‑hydroxy-5-methoxybenzylidene)amino]-2-(2‑hydroxy-5-methoxyphenyl)-2,3-dihydroquinazolin-4-one (L₁) and its Cu(II) complex ([Cu(L₁)Cl(H₂O)]; 1a and [Cu(L₁)Cl]⋅H₂O; 1b) by spectroscopic methods (NMR, FTIR, UV-Vis) and X-ray crystallography complemented by the theoretical study using DFT calculations [4]. The crystal structure of the Cu(II) complex revealed two different coordination of the copper atom in the complex molecules, with 1a being five-coordinated in the shape of a tetragonal pyramid, while the coordination polyhedron around the copper atom in the case of the complex molecule 1b has a square-planar shape. Furthermore, theoretical DFT calculations were performed in order to interpret the experimental data, confirming the presence of two different forms with a detailed description of the geometries of both structures (1a, 1b). This complex is the first case of a solved copper(II) crystal complex with a Schiff base containing a 3-[(2-hydroxyphenyl)methyleneamino]-1,2-dihydroquinazolin-4-one fragment. The combination of different methods provides an important insight into the molecular structure of new compounds, which is crucial for the understanding of the relationships between biological activity and structural features.