Synthesis, Crystal Structure and Charge Transfer Spectra of Dinuclear Copper(I) Complexes bearing 1,2-Bis(arylimino)acenaphthene Acceptor Ligands

A series of dinuclear halide bridged copper(I) complexes with a central [Cu2(μ-X)2] diamond core (X = Cl, Br and I) and substituted bis(imino)acenaphthene (BIAN) ligands acting as strong π-acceptor subunits was prepared and characterized by elemental analysis, X-ray crystallography and various spectroscopic techniques. In the visible spectral range, the electronic spectra of these deeply colored air-stable compounds are dominated by low-lying charge transfer (CT) transitions. The corresponding broad absorption bands display a bathochromic shift and a decreasing amount of negative solvatochromism in the series X = Cl, Br and I. At the same time, the distance between the two metals becomes shorter and reaches the range of cuprophilic interactions. These systematic trends are interpreted as a decreasing amount of charge transfer character and a more pronounced delocalization between the two copper centers within in the same series.