title: A pair of dinuclear Re(I) enantiomers: synthesis, crystal structures, chiroptical and ferroelectric properties.
abstract: The reaction of enantiomeric bis-bidentate bridging ligands (+)/(-)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (L(S)/L(R)) with [Re(CO)5Cl] yielded a pair of dinuclear Re(I) enantiomers formulated as [Re2(L(S)/L(R))(CO)6Cl2]·4CH2Cl2 (R-1 and S-1, the isomers containing the respective L(R) and L(S) ligands). They were characterized by elemental analyses, IR spectra and X-ray crystallography. Circular dichroism spectra verified their chiroptical activities and enantiomeric nature. The measurements of second harmonic generation (SHG) and ferroelectric properties showed that R-1 displays a nonlinear optical (NLO) activity and ferroelectricity with a remnant polarization (P(r)) of 1.6 μC cm(-2) under an applied field of 7.3 kV cm(-1) at room temperature. R-1 and S-1 represent the first example of polynuclear Re(i) complexes with ferroelectric properties. Notably, the P(r) value is much larger than that of the reported mononuclear chiral Re(I) analogue. In particular, unlike mononuclear Re(i) complexes of the type [Re(CO)3(N^N)(X)] (N^N = diimine and X = halide), which usually exhibit an intense emission in the visible range, R-1 and S-1 do not show any detectable emission at any temperature range and the reason for the nonluminescence of R-1 and S-1 was further elucidated in this work. Moreover, our research results also elucidated that Re nuclearity has a great influence on not only the emitting properties but also on ferroelectric behavior.
authors.affiliation: Henan Provincial Key Laboratory of Surface and Interface Science, Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration, Zhengzhou University of Light Industry, Zhengzhou 450002, China. lixl@zzuli.edu.cn smfang@zzuli.edu.cn.
authors.forename: Xi-Li
authors.initials: XL
authors.lastname: Li
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Zhang
authors.forename: Xue-Li
authors.initials: XL
authors.lastname: Zhang
authors.forename: Jia-Long
authors.initials: JL
authors.lastname: Kang
authors.forename: Ai-Ling
authors.initials: AL
authors.lastname: Wang
authors.forename: Liming
authors.initials: L
authors.lastname: Zhou
authors.forename: Shaoming
authors.initials: S
authors.lastname: Fang