Translational and Rotational Dynamics of Molecules Confined in Zeolite Nanocages by Means of Deuteron NMR

Abstract

The main aim of our approach is to gain a comprehensive view of mobility of small molecules in confinement as reported by 2 H NMR spectroscopy. The spectra and spin−lattice relaxation were measured in a wide range of temperature. A set of molecules, D 2 ,CD 4 ,D 2 O,ND 3 ,CD 3 OD and (CD 3 ) 2 CO, was chosen and introduced into NaX and NaY zeolites. A wide range of loadings provides another dimension in studies of molecular mobility in confinement. Observed features reflect evolution on decreasing temperature of molecular dynamics from gaseous state over liquid-like rotational phase to immobilized molecules. Molecules become immobilized below the temperature T S , which appears to be an important parameter related to the strength of interactions with zeolite framework. For chosen zeolites, NaX and NaY, hydrogen bonding, and electrostatic interaction dominate, respectively. We restrict ourselves in reporting results above T S , as below molecular mobility is reduced to internal rotations when possible. The existence of D 2 O clusters and trimers of CD 3 OD gave particularly significant evidence for importance of their mutual interactions. A transition from translational to rotational mobility on decreasing temperature was a common observation, with transition temperature T TR as a significant parameter. Fast magnetization exchange between these two mobilities was considered as a model in analysis of the relaxation temperature dependence. We point out the effective value of the quadrupole coupling constant as justification for using the exchange model. A wealth of observed features proves particular sensitivity of 2 H NMR spectroscopy in studies of molecular dynamics.

Bridging Structural and Dynamical Models of a Confined Sodium Nitroprusside Complex

“…For each hydration level, we find a common temperature interval for 13 C (probing NP dynamics), 23 Na (counterion), and 1 H (water) nuclei yielding linear evolution of data with a good correlation coefficient R 2 > 0.99. The corresponding activation energies, which are in the expected range for small confined molecules, 36 are summarized in Table 1. For 29% relative humidity storage (sample B), the temperature interval, within which the equality E a NP = E a Na is verified, includes 298 K, that is to say, the experimental condition for which our structural model was previously established by the PDF analysis.…”

Water Interactions in Hybrid Polyacrylate-Silicate Hydrogel Systems

“…Generally, in aqueous silicates, proton ( 1 H) populations (except free water) occur in the form of OH hydroxyl groups or strongly bound molecular water [41,59]. The degree of binding of water molecules depends on the structure and quantity of silica, in synthetic [41,60] and natural systems [61]. This is a phenomenological explanation.…”

2H NMR reveals liquid state-like dynamics of arene guests inside hexameric pyrogallol[4]arene capsules in the solid state

“…Solid-state 2 H NMR is an established method for studying guest and ligand dynamics in metal-organic frameworks and related systems. [31][32][33][34][35][36][37] Here, we applied it to discrete molecular encapsulation complexes in the solid state. 18,38 Using the same procedures for encapsulation complex synthesis by ball milling as discussed above for protio-guests, we prepared encapsulation complexes using fluorene-d 2 , fluoranthene-d 10 , and pyrene-d 10 and recorded their static solid-state 2 H NMR spectra at temperatures from 273-333 K. Control static solid-state 2 H spectra recorded for the pure deuterated fluorene-d 2 and fluoranthened 10 guest molecules showed very weak Pake pattern signals (Figure S10), characteristic of little rotational motion of these molecules, as expected of arenes in the solid state.…”