Nonlinear Optical and Magnetic Properties of Fe^II-SCN-Hg^II Isomers: Centrosymmetric Layers and Chiral Networks

Abstract

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(μ-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 {···Fe-NCS-Hg-SCN···}∞ 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 × 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.

Thermometric Properties of Thio/Selenocyanato-Bridged Spin-Crossover Networks

“…Nonetheless, the strong field bridging ligands CN – stabilize LS Fe II centers, thus requiring a precise selection of supporting ligands to achieve the SCO phenomenon. As an alternative to this approach, flexible bridging weak-field ligands (SCN – and SeCN – ) are now being taken into account for obtaining diverse multifunctional networks. − Considering the novelty of these materials, they require the development of new adaptations of previously established experimental (structural, spectroscopic, and magnetic) and theoretical methods to obtain broader knowledge about their properties and to set new research paths toward their practical application.…”

Mechanical Exfoliation of Multilayer Pseudohalogen-Bridged Nanosheets

“…Alternatively, the top-down mechanical exfoliation method is one of the most successful techniques for obtaining high-quality single- or few-layer nanocrystals at a low cost. − Notably, the cyano-bridged CP nanosheet has never been obtained by mechanical exfoliation due to the fragility of the starting crystals and relatively strong interlayer interaction. Therefore, seeking other suitable starting CPs for mechanical exfoliation has ignited considerable interest in the research of 2D materials. , Currently, compared with the relatively rigid structures of CPs using the conventional CN – ligand, the application of other pseudohalogens, e.g., flexible thiocyanate ligand (SCN – ), as a bridging ligand is emerging as a promising technique for constructing new CPs with nontrivial multifunctionality. − Nevertheless, to the best of our knowledge, there is no single report available in the literature that describes the exploration of thiocyanato-bridged CP nanosheets, notwithstanding the fact that bulk CPs that have an inherent 2D structure are abundant. − The versatility of such thiocyanato-bridged CPs and their ability to tune their properties will make them attractive additions to the range of 2D materials.…”