Thermal Stability, Polymorphism, and Spectroscopic Properties of [Mn(DMSO)₆](ReO₄)₂.

Area of Science:

• Solid-state chemistry
• Materials science
• Coordination chemistry

Background:

• Hexadimethylsulfoxidemanganese(II) rhenate(VII), [Mn(DMSO)6](ReO4)2, is a coordination compound with potential applications in materials science.
• Understanding its thermal and structural properties is crucial for predicting its behavior under various conditions.

Purpose of the Study:

• To comprehensively investigate the structural, thermal, and vibrational properties of [Mn(DMSO)6](ReO4)2.
• To elucidate the mechanisms and nature of solid-state phase transitions in this compound.
• To correlate spectroscopic and computational findings with observed thermal events.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Thermogravimetric analysis coupled with mass spectrometry (TG-QMS) for thermal stability and decomposition analysis.
• Differential scanning calorimetry (DSC) for identifying phase transitions.
• Optical microscopy, infrared (IR), and Raman spectroscopy for vibrational analysis.
• Density functional theory (DFT) calculations for theoretical support.

Main Results:

• The compound crystallizes in the triclinic system (space group P1¯) with octahedral Mn(II) coordination.
• Two first-order solid-state phase transitions were observed at 338 K and 358 K via DSC.
• Thermal stability was confirmed up to ~405 K, followed by stepwise DMSO ligand loss.
• Phase transitions involve symmetry changes from triclinic P1¯ to monoclinic C2/m and trigonal P3¯m1, associated with significant reorientational disorder.
• Spectroscopic data and DFT calculations confirmed the molecular structure and purity, with FT-IR showing changes indicative of increasing crystal symmetry upon heating.

Conclusions:

• [Mn(DMSO)6](ReO4)2 undergoes distinct solid-state phase transitions upon heating, leading to increased crystal symmetry and rotational disorder.
• The compound exhibits limited thermal stability, decomposing above 405 K after ligand dissociation.
• Combined experimental and theoretical approaches provide a detailed understanding of the structural dynamics and thermal behavior of this coordination compound.