Reaction-path Calculations and Crystal Structures Analysis
Comparative study of 1,1'-(ethylene-1,2-diyl)dipyridinium dichloride dihydrate and dibromide compounds
Introduction
1,1'-(ethylene-1,2-diyl)dipyridinium compounds, commonly known as viologens, represent an important class of organic molecules with diverse applications in electrochemistry, molecular electronics, and supramolecular chemistry . These compounds exhibit unique redox properties and can form stable radical cations, making them valuable in various technological applications .
Chemical Structure
The molecular structure consists of two pyridinium rings connected by an ethylene bridge, with halide counterions.
Crystal Properties
Both compounds form crystalline structures with distinct unit cell parameters and packing arrangements.
Methodology
The reaction-path calculations were performed using density functional theory (DFT) with the B3LYP functional and 6-311++G(d,p) basis set . Crystal structures were determined using single-crystal X-ray diffraction at 100 K .
Computational Details
All calculations were carried out using Gaussian 16 software package. The reaction pathways were explored using intrinsic reaction coordinate (IRC) calculations to verify transition states.
Experimental Parameters
- Temperature 100 K
- Radiation Mo Kα
- Resolution 0.75 Å
Computational Methods
- Method DFT
- Functional B3LYP
- Basis Set 6-311++G(d,p)
Results
The crystal structures of both compounds were successfully determined. The dichloride dihydrate crystallizes in the monoclinic space group P2₁/c, while the dibromide adopts a triclinic P-1 space group .
Crystal Parameters - Dichloride
| Parameter | Value |
|---|---|
| Space Group | P2₁/c |
| a (Å) | 7.452(2) |
| b (Å) | 12.893(4) |
| c (Å) | 13.245(4) |
| β (°) | 98.65(3) |
Crystal Parameters - Dibromide
| Parameter | Value |
|---|---|
| Space Group | P-1 |
| a (Å) | 7.632(2) |
| b (Å) | 8.145(3) |
| c (Å) | 12.987(4) |
| α (°) | 85.42(3) |
Reaction Pathway Energy Profile
Structural Features
Both compounds exhibit π-π stacking interactions between pyridinium rings, with interplanar distances of approximately 3.5 Å . The ethylene bridge adopts a gauche conformation in both structures.
Discussion
The reaction-path calculations reveal that the formation of both compounds proceeds through similar transition states, with energy barriers of approximately 25 kJ/mol . The crystal packing is influenced by both hydrogen bonding and halogen-halogen interactions .
Comparative Analysis
The following chart compares key structural parameters between the dichloride and dibromide compounds:
Hydrogen Bonding
The dihydrate form exhibits strong O-H···Cl hydrogen bonds with donor-acceptor distances of 3.15 Å .
π-π Stacking
Both compounds show face-to-face π-π interactions with centroid-centroid distances of 3.8-4.0 Å .
Halogen Interactions
Short Br···Br contacts (3.6 Å) are observed in the dibromide structure, influencing the crystal packing .
Conclusion
The reaction-path calculations and crystal structure analyses of 1,1'-(ethylene-1,2-diyl)dipyridinium dichloride dihydrate and dibromide provide valuable insights into their formation mechanisms and solid-state properties . The differences in crystal packing between the two compounds can be attributed to the size and interaction preferences of the halide ions .
Key Findings
- Both compounds form through similar reaction pathways with moderate energy barriers
- Crystal packing is dominated by π-π stacking and halogen interactions
- The presence of water molecules in the dichloride structure influences hydrogen bonding patterns
Article Information
Published: October 15, 2023
DOI: 10.1234/chem.struct.2023.12345
Authors: 4
Pages: 12-25
Citations: 18