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Polymorphism, Weak Interactions and Phase Transitions in Chalcogen-Phosphorus Heterocycles.
Paula Sanz Camacho1, Martin W Stanford1, David McKay1
1School of Chemistry and EaStCHEM and Centre of Magnetic Resonance, University of St Andrews, St Andrews, Fife, KY16 9ST, UK.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|May 24, 2018
Summary
This study synthesized phosphorus-element heterocycles, revealing distinct solid-state and solution NMR differences due to conformational changes. Polymorphism was observed, with solid-state NMR often showing a single major form.
Area of Science:
- Organophosphorus chemistry
- Solid-state NMR spectroscopy
- Crystallography
Background:
- Phosphorus-element (P-E) heterocycles with aromatic backbones are important in materials science.
- Understanding their solid-state properties is crucial for applications.
- Conformational flexibility can significantly impact molecular properties.
Purpose of the Study:
- To synthesize and characterize novel P-E heterocycles.
- To investigate the differences in NMR parameters between solution and solid states.
- To explore the phenomenon of polymorphism in these compounds.
Main Methods:
- Synthesis of P-E heterocycles
- Single-crystal and powder X-ray diffraction (XRD)
- Microanalysis and mass spectrometry
- Solution-state and solid-state Phosphorus-31 (31P) and Selenium-77 (77Se) Nuclear Magnetic Resonance (NMR) spectroscopy
- Density Functional Theory (DFT) calculations
Main Results:
- Successful synthesis and characterization of various P-E heterocycles.
- Significant discrepancies observed between solution-state and solid-state NMR parameters, attributed to conformational transitions.
- Identification of multiple polymorphic forms for several compounds via single-crystal XRD.
- Solid-state NMR predominantly indicated a single major polymorph in bulk samples.
- DFT calculations explored weak intermolecular J couplings in unoxidised heterocycles.
Conclusions:
- Conformational changes significantly influence NMR spectroscopic properties of P-E heterocycles in different phases.
- Polymorphism is a common feature in these systems, impacting bulk material characterization.
- Solid-state NMR is a valuable tool for probing molecular conformations and polymorphism in solid-state P-E heterocycles.
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