Synthesis and Characterization of Cu-Containing Chiral Metal Halides and Role of Halogenation of the Organic Ligand
Andrea Dibenedetto, Clarissa Coccia, Massimo Boiocchi, Marco Moroni, Chiara Milanese, Lorenzo Malavasi
Abstract
We report herein novel chiral copper metal chlorides, namely, ( R / S -ClMBA) 2 CuCl 4 [ClMBA = 4-(chloromethyl)benzylammonium], together with the corresponding racemic compound. The two chiral samples are composed of isolated CuCl 4 tetrahedra crystallizing in the noncentrosymmetric C 2 space group and present a significant absorption in the visible region of the spectrum with a band gap around 2.50 eV. The racemic compound, on the other hand, gives origin to a different structural topology characterized by the presence of a quite unusual five coordination for Cu(II), with Cu 2 Cl 6 – dimers forming infinite chains along the b axis and presents, in addition, a strong reduction of the band gap (around 1.76 eV). The two chiral samples display a circular dichroism response with anisotropy factor values of around 0.02. The actual novel samples are investigated in comparison to the MBA-based (MBA = methylbenzylammonium) system in order to unveil the effect of benzene ring halogenation on the structural and chiroptical properties, indicating that the presence of chlorine leads to a doubling of the anisotropy factor.