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Stereoisomerism

Stereoisomerism

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...

Stereoisomerism of Cyclic Compounds

Stereoisomerism of Cyclic Compounds

In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...

Isomerism in Alkenes

Isomerism in Alkenes

Alkenes like 1-butene and 2-butene exhibit constitutional isomerism, as they differ in the position of the double bond. Further, 2-butene exhibits stereoisomerism and exists as two distinct compounds differing in spatial arrangement.
An isomer is called cis-2-butene when the methyl groups are on the same side of the double bond, and the other stereoisomer, in which methyl groups are on the opposite side of the double bond, is called trans-2-butene. The cis and trans stereoisomers are not...

Disubstituted Cyclohexanes: cis-trans Isomerism

Disubstituted Cyclohexanes: cis-trans Isomerism

Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers....

Radical Halogenation: Stereochemistry

Radical Halogenation: Stereochemistry

Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
Halogenation to form a new chiral center:

Isomerism

Isomerism

Isomers are molecules with the same molecular formula but different structural arrangements. Isomers can be further classified into constitutional isomers and stereoisomers. Constitutional isomers differ in the connectivity of their constituent atoms. For example, 2-butanol and diethyl ether are constitutional isomers, as they have the same chemical formula, C4H10O, but differ in the connectivity of the carbon and oxygen atoms. Constitutional isomers have different physical and chemical...

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Related Experiment Video

Updated: May 1, 2026

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Published on: July 17, 2020

Positional Isomerism Controls Polarity and Nonlinear Optical Properties in One-Dimensional Hybrid Germanium Halides.

Shaohua Xiao¹, Xingxing Jiang², Kaining Duanmu¹

¹China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical Science and Engineering, Tongji University, Shanghai, China.

Angewandte Chemie (International Ed. in English)

|April 30, 2026

Summary

Positional isomers of methylimidazolium cations in one-dimensional germanium-halide perovskites significantly influence nonlinear optical properties. The N1-methyl substitution in (1-Mim)GeI3 enhances second-harmonic generation and birefringence, making them promising lead-free materials.

Keywords:

halide germanium(II) perovskites noncentrosymmetric structures nonlinear optics second‐harmonic generation structure‐property relationships

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Last Updated: May 1, 2026

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Published on: July 17, 2020

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups

Published on: February 11, 2012

Spatial Separation of Molecular Conformers and Clusters

Spatial Separation of Molecular Conformers and Clusters

Published on: January 9, 2014

Area of Science:

Materials Science
Solid-State Chemistry
Optoelectronics

Background:

Organic-inorganic hybrid perovskites (OIHPs) are versatile materials for optoelectronics.
The influence of organic cations on electronic and nonlinear optical (NLO) properties is underappreciated.
Understanding cation structure-property relationships is crucial for material design.

Purpose of the Study:

To investigate the impact of methylimidazolium cation positional isomers on the NLO properties of 1D germanium-halide perovskites.
To explore the potential of these materials as lead-free alternatives for optoelectronic applications.
To elucidate the structural origins of enhanced nonlinear optical responses.

Main Methods:

Synthesis of three 1D germanium-halide perovskites (AGeI3) using methylimidazolium positional isomers (1-Mim, 2-Mim, 4-Mim).
Characterization of structural and optical properties, including powder second-harmonic generation (SHG) and birefringence.
First-principles calculations to analyze electronic structure and correlate it with NLO properties.

Main Results:

The N1-methyl substitution in (1-Mim)GeI3 leads to polar structures with significantly enhanced SHG (13 × KH2PO4 @1200 nm) and birefringence (0.263 @546 nm).
SHG response arises from the synergistic interaction between [GeI6] units and the π-conjugated 1-Mim cation.
Asymmetric electron distribution due to N1-methylation facilitates ordered alignment of the π-conjugated cation, enhancing SHG.

Conclusions:

Cation positional isomerism is a critical factor in tuning the physical properties of 1D hybrid perovskites.
1D germanium-iodide perovskites are promising lead-free candidates for nonlinear optoelectronic devices.
Tailoring organic cation structure offers a viable strategy for optimizing NLO properties in hybrid materials.