Related Experiment Video
Updated: Sep 14, 2025

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
CsICl2: A Record-Birefringent Inorganic Crystal with Ultrawide Infrared Transparency Enabled by Linear Interhalogen
Chong-An Chen1, Yang Li1, Congcong Jin1
1Department of Chemistry, Sogang University, Seoul 04107, Republic of Korea.
Abstract:
Birefringent crystals are essential optical materials for polarized light modulation, yet few exhibit both large birefringence and broad transparency in the mid- to far-infrared (MIR-FIR) regions. Here, we report the successful synthesis of an inorganic birefringent crystal, CsICl2 (CIC), by incorporating the highly anisotropic linear ICl2- birefringence-active group (BAG) with a heavy Cs+ cation under hydrothermal conditions. The large polarization anisotropy, perfect alignment, and dense packing of ICl2- endow CIC with record-high birefringence values in both the visible (Δnexp = 0.994 at 546 nm) and infrared (Δncal = 0.719 at 1064 nm) regions among all known inorganic crystals with Eg > 2.0 eV. CIC also exhibits an ultrawide optical transparency window from 0.367 to at least 25 μm and can be grown into centimeter-scale single crystals. This study introduces CIC as a promising IR birefringent material and highlights the potential of linear interhalogen BAGs for the design of next-generation IR optical crystals.
Related Concept Videos
Alkyl Halides
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
Halogens
Chemical Ionization (CI) Mass Spectrometry
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Mass Spectrometry: Alkyl Halide Fragmentation
Infrared (IR) Spectroscopy: Overview
Different compounds display unique properties due to their...

