Synthesis, Crystal Structure, and DFT Study of Two New Dinuclear Copper(I) Complexes Bearing Ar-BIAN Ligands Functionalized with NO₂ Groups

Two new bis(aryl-imino)-acenaphthene, Ar-BIAN (Ar = 2,4,6-trimethylphenyl = mes) ligands, bearing the NO₂ group in the naphthalene moiety of the iminoacenaphthene at para- (5-NO₂) and meta- (4-NO₂) position, of formulations 1,2-bis(mes-imino)-5-nitroacenaphthene, 1, and 1,2-bis(mes-imino)-4-nitroacenaphthene, 2, were synthesized. Their respective dinuclear iodide bridged copper(I) complexes [Cu₂(µ-I)₂(mes-BIAN-5-NO₂)₂], 3 and [Cu₂(µ-I)₂(mes-BIAN-4-NO₂)₂]_, 4, were obtained in good yields by treatment with an equimolar amount of CuI. All compounds were characterized by elemental analysis, single-crystal X-ray diffraction, ¹H-NMR,¹³C-NMR, FTIR, UV/Vis spectroscopy. DFT calculations helped to understand the different molecular structure observed in the crystals of 3 and 4 and the determining role of packing forces. TDDFT revealed that the absorption bands in the visible were essentially MLCT (Metal to Ligand Charge Transfer), with some n→π* character (intra ligand). The shift to the red compared to the spectrum of the Cu(I) complex analogue without the NO₂ group, [Cu₂(µ-I)₂](mes-BIAN)₂], 6, could be explained by the stabilization of the ligand unoccupied π* orbitals in the presence of NO₂.