Synthesis and ferroelectric properties of platinum(II) complexes with chiral isoxazoline ligand

Four chiral square-planar (SP-4) alkynylplatinum(II) complexes Pt(L)(CC–Ph) (1), Pt(L)(CC–Ph–Br) (2), Pt(L)(CC–Ph–CH3) (3) and Pt(L)(CC–Ph–OCH3) (4) (L = (1S,5S)-6,6-dimethyl-3′-(pyridin-2-yl)-4′H-spiro[bicyclo[3.1.1]heptane-2,5′-isoxazole]) were prepared by the complexation of ligand L with K2PtCl4 and subsequent treatment with corresponding alkynes. Their structures were characterized by single crystal X-ray diffraction and electronic circular dichroism (CD) spectra. Although there are little differences in the molecular structures, these complexes exhibit significantly different molecular packing modes in their crystal structures. Moreover, complexes 1 and 4 crystallize in the polar space group P21, while complexes 2 and 3 crystallize in the nonpolar space groups (I222 for 2 and P212121 for 3, respectively). Consequently, complexes 1 and 4 show distinct ferroelectric behaviors and nonlinear optical properties. To the best of our knowledge, our study represents the first example of chiral platinum(II) complexes demonstrating ferroelectric properties.