Guest Molecules in a Layered Microporous Tin(IV) Phosphonate-Phosphate Material: Solid State NMR Studies

Area of Science:

• Materials Science
• Solid-State Chemistry
• Supramolecular Chemistry

Background:

• Layered microporous metal(IV) phosphate-phosphonate materials possess poorly understood pore surfaces and guest molecule interactions.
• Systematic understanding of guest molecule mobility within these materials is lacking.

Purpose of the Study:

• To investigate and characterize the mobility and interactions of guest molecules (benzene and pyridine) within layered microporous metal(IV) phosphate-phosphonate materials.
• To utilize multinuclear solid-state Nuclear Magnetic Resonance (NMR) and relaxation time measurements for probing guest molecule dynamics.

Main Methods:

• Multinuclear solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Relaxation time measurements to probe molecular dynamics.
• Thermodynamic analysis of guest molecule adsorption (enthalpy and entropy).

Main Results:

• Benzene-d6 molecules adsorbed on Sn(O3PC6H4PO3)0.85(O3POH)0.33 (1) exhibit fast in-plane C6 rotation, attributed to Sn···π interactions with pore walls, with an adsorption enthalpy of -5.9 kcal/mol.
• Pyridine molecules show specific interactions with pore walls, leading to immobile adsorption, particularly at low temperatures.
• Thermodynamic parameters for pyridine adsorption (-ΔH = 5.0 kcal/mol, ΔS = -11.0 e.u.) suggest N···H-OP hydrogen bonding as the driving force for immobilization.

Conclusions:

• Solid-state NMR and relaxation measurements effectively probe guest molecule mobility in poorly crystalline microporous materials.
• Metal-π interactions significantly influence benzene mobility, while hydrogen bonding dictates pyridine adsorption behavior in these materials.
• The findings provide insights into host-guest interactions within layered metal phosphate-phosphonates, relevant for material design and application.