Histidinium‐Driven Chirality Control of Self‐Assembled Hybrid Molybdenum Oxyfluorides

Abstract

Exploring macroscopic chiral materials with extended structures has become an important and fundamental topic in chemistry. To systematically control the chirality of novel organic–inorganic frameworks, histidinium‐based cationic structure‐directing agents containing specific chiral information are introduced. In this way, two chiral compounds, [(l‐hisH2)MoO2F4]3⋅H2O (L) and [(d‐hisH2)MoO2F4]3⋅H2O (D), and an achiral oxyfluoride, (l/d‐hisH2)MoO2F4 (LD) (his=histidine, C6H9N3O2) have been successfully self‐assembled by a slow evaporation method. The structures of these compounds are composed of histidinium cations and distorted [MoO2F4]2− octahedra. Surprisingly, the histidinium cations not only control macroscopic chirality, but also induce O/F ordering in MoO2F4 octahedra through hydrogen‐bonding interactions. Compounds L and D crystallize in the extremely rare polar space group P1, and exhibit positive second harmonic generation (SHG) signals attributable to a net moment originating from the MoO2F4 groups. Solid‐state circular dichroism (CD) spectra indicate that the MoO2F4 units templated by histidinium cations are chirally aligned through ionic interactions. Crystallization processes influenced by the chirality of the reported materials are also discussed herein.

Dimensionality–Band Gap–Third-Harmonic Generation Property Relationship in Novel Main-Group Metal Iodates

“…Solid-state compounds with macroscopic noncentrosymmetric (NCS) crystal structures have drawn enormous academic attention owing to their second-order nonlinear optical (NLO) applications in photonic technologies, such as cascaded frequency conversions, optical parameter oscillators (OPO), and optical communications. − Especially, second-harmonic generation (SHG), the most straightforward second-order NLO process, has been extensively researched for several decades as it can efficiently produce a new coherent light ray by frequency doubling of an input coherent light ray. − Therefore, it is of utmost importance to ensure an NCS structure when targeting a novel material for SHG and the second-order applications mentioned above. Although several effective strategies toward the macroscopic NCS structures have been suggested, major solid-state compounds reported to date have still exhibited centrosymmetric (CS) structures perhaps attributable to the facile alignment of the asymmetric units in an antiparallel manner. − In contrast, third-order NLO effects have been much less explored although most solid-state compounds even including glassy materials possess third-order nonlinearity .…”

Role of Fluorooxo-Functional Units in Symmetry Breaking and Second Harmonic Generation Response Contribution in Fluorooxoborate Nonlinear Optical Crystals

“…Non-centrosymmetric (NCS) materials that do not have crystallographic inversion centers have aroused technical interest in ferroelectric, pyroelectric, piezoelectric, and nonlinear optics. − For a second-order nonlinear optical (NLO) material, the non-centrosymmetry is one necessary condition. The borate crystals, for example, have a flexible B–O coordination environment; the B atom can be sp 2 or sp 3 hybridized with the O atom to form a tricoordinated BO 3 triangle or a tetra-coordinated BO 4 tetrahedron, and further form borates of various degrees of polymerization by corner-sharing or edge-sharing .…”

Order and Disorder: Toward the Thermodynamically Stable α-BaMoO2F4 from the Metastable Polymorph

“…966–897 and 579–400 cm –1 , respectively (Figure S6). ,− Although the IR spectra of α- and β-BaMoO 2 F 4 are very similar, two bands occurring at ca. 500–600 cm –1 due to Mo–F vibrations of α-BaMoO 2 F 4 merged to form a broad single band for β-BaMoO 2 F 4 attributable to the O/F disorder.…”