Layered metal(IV) phosphonate materials: Solid-state ¹ H, ¹³ C, ³¹ P NMR spectra and NMR relaxation

Multinuclear solid-state NMR and powder X-ray diffraction data collected for phosphonate materials Zr(O₃ PC₆ H₄ PO₃ ) · 3.6H₂ O and Sn(O₃ PC₆ H₄ PO₃ )_0.85 (O₃ POH)_0.30  · 3.09H₂ O have resulted in the layered structure, where the phosphonic acids cross-link the layers. The main structural motif (the 111 connectivity in the PO₃ group) has been established by determination of chemical shift anisotropy parameters for phosphorus nuclei in the phosphonate groups. An analysis of the variable-temperature ³¹ P T₁ measurements and the shapes of the phosphorus resonances in the ³¹ P static NMR spectra have resulted in the dipolar mechanism of the phosphorus spin-lattice relaxation, where the rotating phenylene rings reorient dipolar vectors P^… H as a driving force of the relaxation process. It has been found that water protons do not affect the ³¹ P T₁ times. The activation energy of the phenylene rotation in both compounds has been determined as low as 12.5 kJ/mol. The interpretation of the phosphorus relaxation data has been independently confirmed by the measurements of ¹ H T₁ times for protons of the phenylene rings.