Modulable cooperativity in a valence tautomeric complex functionalized with branched alkyl chains.

Area of Science:

• Coordination chemistry
• Materials science
• Physical chemistry

Background:

• Valence tautomerism (VT) is a spin-crossover phenomenon in transition metal complexes.
• Phase transitions in materials are crucial for their functional properties.
• Controlling the interplay between electronic and structural changes is key in materials design.

Purpose of the Study:

• To investigate the influence of branched alkyl chain functionalization on cobalt/dioxolene complexes.
• To explore the synchronization of valence tautomerism with crystal-to-melt and glass-to-melt phase transitions.
• To understand the role of crystallinity in mediating cooperative and non-cooperative electronic transitions.

Main Methods:

• Synthesis of cobalt/dioxolene complexes with varying branched, asymmetric alkyl chains.
• Differential scanning calorimetry (DSC) to study thermal transitions.
• Variable-temperature UV-Vis spectroscopy to monitor valence tautomerism.
• X-ray diffraction (XRD) to assess the degree of crystallinity.

Main Results:

• Functionalization with branched alkyl chains successfully induced valence tautomerism.
• Non-cooperative VT was observed synchronized with thermodynamically favored crystal-to-melt transitions in crystalline samples.
• Cooperative VT occurred with kinetically generated glass-to-melt transitions in less crystalline or amorphous samples.
• The degree of crystallinity was identified as the critical factor determining the nature of the synchronized transitions.

Conclusions:

• Branched alkyl chains provide a route to control the synchronization of valence tautomerism with phase transitions in cobalt/dioxolene complexes.
• The observed synchronization is dependent on the material's thermal history and degree of crystallinity.
• This study offers insights into designing materials with tunable electronic and structural properties through controlled phase transitions.