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

Abstract

Multinuclear solid-state NMR and powder X-ray diffraction data collected for phosphonate materials Zr(O PC H PO ) · 3.6H O and Sn(O PC H PO ) (O POH) · 3.09H O have resulted in the layered structure, where the phosphonic acids cross-link the layers. The main structural motif (the 111 connectivity in the PO group) has been established by determination of chemical shift anisotropy parameters for phosphorus nuclei in the phosphonate groups. An analysis of the variable-temperature P T measurements and the shapes of the phosphorus resonances in the 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 P T 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 H T times for protons of the phenylene rings.

Benzene‐d6 and toluene‐d8 as guest molecules in micropores of a layered zirconium phosphonate: 2H, 13C{1H}, and 31P{1H} solid‐state NMR, deuterium NMR relaxation, and molecular motions

“…The X‐ray powder diffraction patterns obtained for compounds ZrPhos‐Ben10 , ZrPhos‐Ben1.5 , ZrPhos‐Ben0.3 , and ZrPhos‐Tol0.6 are practically identical to that of initial phosphonate 1 , published earlier . They show the peak corresponding to the interlayer distance of 9.5 Å in the layered structure.…”

“…The treatments of phosphonate 1 with benzene‐ d 6 and toluene‐ d 8 and the following high‐temperature manipulations may lead to changes in its host structure due to intercalation shown in Figure . However, the 5 kHz 31 P{ 1 H} MAS NMR spectra recorded for 1 , ZrPhos‐Ben10 , ZrPhos‐Ben1.5 , ZrPhos‐Ben0.3 , and ZrPhos‐Tol0.6 remain identical: showing a single phosphorus site at a δ of −6.0 ppm . The shape of the signal in the 31 P{ 1 H} static NMR spectra of 1 corresponds to a 111 connectivity in the PO 3 groups (when each oxygen atom is binding to a single metal atom), and this does not change in the presence of guest molecules (Figure S1).…”

“…However, the 5 kHz 31 P{ 1 H} MAS NMR spectra recorded for 1 , ZrPhos‐Ben10 , ZrPhos‐Ben1.5 , ZrPhos‐Ben0.3 , and ZrPhos‐Tol0.6 remain identical: showing a single phosphorus site at a δ of −6.0 ppm . The shape of the signal in the 31 P{ 1 H} static NMR spectra of 1 corresponds to a 111 connectivity in the PO 3 groups (when each oxygen atom is binding to a single metal atom), and this does not change in the presence of guest molecules (Figure S1). Furthermore, the CP 31 P{ 1 H} NMR spectra of static samples 1 and ZrPhos‐Ben0.3 (obtained with a 1 H spin‐lock pulse applied prior to the CP section) are practically identical (Figure S1).…”

“…Finally, the phosphorus relaxation could demonstrate the possible structural changes caused by the appearance of guest molecules in the interlayer space of 1 affecting the phenylene ring dynamics. However, the 31 P T 1 relaxation time in static sample ZrPhos‐Ben0.3 was found to be 11.4 s within error equal to 11.8 s obtained for initial phosphonate 1 . Thus, the guest molecules occupying pore spaces of 1 (Figure ) do not affect the host structure in accordance with the elimination of the guests from pores by simple heating (see Section 2).…”

“…In general, these systems are synthesized by the hydrothermal method, which leads to the layered structures shown schematically for the zirconium phosphonate material ( 1 ) in Figure . Recently, the structure of 1 has been characterized in detail by both solid‐state 1 H, 13 C{ 1 H}, and 31 P{ 1 H} MAS/static NMR spectra and powder X‐ray diffraction . It has been found that the phosphonic acids crosslink the layers, and the phenylene rings experience a low‐energy rotation ( E a = 12.5 kJ/mol), providing the phosphorus relaxation mechanism.…”