Copper(II) complexes of 7-amino-2-methylchromone and 7-aminoflavone: Magneto-structural, spectroscopic and DFT characterization

Abstract

Four new complexes of copper(II) consisting of two different chromone derivatives with carbonyl and amine donor atoms: 7-aminoflavone (L1) and 7-amino-2-methylchromone (L2), were synthesized and characterized by X-ray diffraction, UV–Vis, FT-IR, EPR spectroscopy, MS and elemental analysis. The complexes were synthesized using 2:1 ligand-to-metal ratio, but while three products [Cu(L2)2Cl2]2 (1b), Cu(L1)2(ClO4)2(H2O)2 (2a), Cu(L2)2(ClO4)2(H2O)2 (2b) maintained the applied stoichiometry, the fourth compound showed an unexpected 1:1 ratio and was identified as [Cu(L1)Cl2]n (1a). In all four compounds, the chromone derivatives were found to act as monodentate O- or N-ligands. Interestingly, in a doubly chloro-bridged dinuclear complex 1b each Cu(II) cation interacts with one L2 ligand through the carbonyl O-donor, and with another L2 molecule through the amine N-donor, so the complex adopts a square pyramid geometry. According to a single-crystal X-ray diffraction analysis the complex 2b is a distorted mononuclear octahedron with the central Cu(II) cation interacting only with oxygen donors (two perchlorate anions, two L2 ligands, and two water molecules). The structural characteristics of 1a and 2a complexes were elucidated from EPR measurements, where their g-tensor components were compared to those observed for 1b and 2b, the structures of which were determined by X-ray diffraction method. DFT calculations were performed to estimate the most favored mode of coordination, whereas comparative Hirshfeld surface studies were used to characterize intermolecular interactions in the studied complexes. Magnetic interactions of 1a and 2a were also analyzed.