Nonlinear Optical and Magnetic Properties of FeII-SCN-HgII Isomers: Centrosymmetric Layers and Chiral Networks

Research on isomers is highly desirable due to their prospective role in better understanding of physicochemical properties of similar systems and further development of multifunctional molecular materials. Iron(II) and tetra(thiocyanato)mercury(II) ions self-assembled in the presence of 2-acetylpyridine (2-acpy) excess to form two {[Fe(2-acpy)][Hg(mu- SCN)4]}n isomers: two-dimensional (2D) centrosymmetric layers with folded ring structural motifs (1) and three-dimensional (3D) chiral networks with right-or left-handed {center dot center dot center dot Fe-NCS-Hg-SCN center dot center dot center dot}infinity helixes (2). New methods of designing and synthesizing functional thiocyanate-bridged materials have been proposed. In addition, the similarity between 1 and 2 allowed for the description of subtle changes in IR and UV-visible spectra. Moreover, 2 shows spontaneous resolution, and it crystallizes in the noncentrosymmetric space group P21, leading to the occurrence of nonlinear optical activity in circular dichroism studies and second harmonic generation (SHG). At room temperature, the SH susceptibility for powder sample 2 reached 6.0 x 10-11 esu. Ab initio calculations indicated the electric polarization vector and the crystallographic twofold screw axis pass through the aromatic ring. Magnetic studies for 1 and 2 revealed high-spin iron(II) with zero-field splitting at low temperatures. Analysis of magnetic data gave |D| = 37.45 cm-1, |E/D| = 5.59 cm-1, and (g) = 2.15 for 1, |D| = 36.78 cm-1, |E/D| = 4.92 cm-1, and (g) = 2.18 for 2, and information about the orientation of magnetic anisotropy vectors for both compounds.

Automated summary

This research successfully synthesized two self-assembled complexes composed of iron(II) and tetra(thiocyanato)mercury(II) ions. These complexes showed similar physicochemical properties with subtle differences. Additionally, one of the complexes exhibited nonlinear optical activity. Magnetic studies revealed the presence of high-spin iron(II) ions and provided information about the orientation of their magnetic anisotropy vectors.