Synthesis and Characterization of Cu-containing Chiral Metal Halides and Role of Halogenation of the Organic Ligand

We report herein novel chiral copper metal chlorides, namely (R/S-ClMBA)2CuCl4 (ClMBA = 4-(chloromethyl)benzylammonium), together with the corresponding racemic compound. The two chiral samples are composed of isolated CuCl4 tetrahedra and crystallize in the non-centrosymmetric C2 space group and present a significant absorption in the visible region of the spectrum with 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 Cu2Cl6- dimers forming infinite chains along the b axis and presents, in addition, a strong reduction of band gap (around 1.76 eV). The two chiral samples display a circular dichroism response with anisotropy factors values around 0.02. The actual novel samples are investigated in comparison to the MBA-based (MBA=methylbenzylammonium) system in order to unveil the role of benzene ring halogenation on the structural and chiroptical properties indicating that the presence of chlorine leads to a doubling of the anisotropy factor.