Nitrilotris(methylenephosphonates) in aqueous solution and solid state – dilatometric, potentiometric and NMR investigations

Proton conducting membranes in fully anhydrous conditions at elevated temperature: Effect of Nitrilotris(methylenephosphonic acid) incorporation into Nafion- and poly(styrenesulfonic acid)

“…The spectrum of PSSA / NTMPA is typical of a phosphorous nuclei in a quite ordered, rigid environment, absolutely compatible with the already observed presence of crystalline domains of NTMPA and the absence of an intimate mixing between NTMPA and PSSA. The chemical shift of about 13 ppm corresponds to that reported for solid NTMPA obtained after dehydration of aqueous solutions[33]. The non observation of three different signals corresponding to the three inequivalent phosphorous nuclei present in pure NTMPA can be explained with a too small difference in their isotropic chemical shifts compared to the experimental linewidth; moreover the interactions with PSSA matrix can modify the structural features of NTMPA with respect to its pure crystal.…”

“…The chemical shift of phosphorous-31 has been found to slightly vary (maximum 1.5 ppm) during the first five steps of deprotonation and complexation, while a strong change, of about 10 ppm, has been observed to occur with the nitrogen deprotonation (in extremely basic conditions) [31][32][33]. The different protonated and complex forms after dehydration have been also investigated by means of 31 P solid-state NMR [33]. Moreover 31 P solid-state NMR, and in particular 31 P isotropic chemical shift, has been exploited for obtaining structural information on possible complexes between NTMPA and tin [34], calcium [35,36] and zirconium-titanate [37] in several organic-inorganic hybrid systems.…”

“…The acidbase dissociation and metal cations complexation equilibria have been extensively studied by means of 31 P NMR in solution. The chemical shift of phosphorous-31 has been found to slightly vary (maximum 1.5 ppm) during the first five steps of deprotonation and complexation, while a strong change, of about 10 ppm, has been observed to occur with the nitrogen deprotonation (in extremely basic conditions) [31][32][33]. The different protonated and complex forms after dehydration have been also investigated by means of 31 P solid-state NMR [33].…”

“…To the best of our knowledge NMR studies on condensation of NTMPA P-OH groups have not been reported yet, while this and other structural and dynamic properties have been investigated in several works, mainly based on 31 P and 1 H solid-state NMR experiments, on polymeric organic phosphonic acids for applications in proton exchange membranes fuel cells [10,11,38,39], layered microporous tin biphosphonates [40] and mesoporous silica functionalized with phosphonic acids [41]. to phosphonic groups interacting through hydrogen-bonding with residual water, which resulted to be present in this sample in larger amount with respect to PSSA / NTMPA and can determine a shielding effect on phosphorous nuclei [33]. Moreover, unlike the resonance at 13 ppm, no spinning sidebands were observed for such lower-chemical-shift signals, suggesting that, as expected, water can determine an increased mobility of phosphonic groups [41].…”

Guidelines for NMR measurements for determination of high and low pKa values (IUPAC Technical Report)

“…Determining extreme values of p[H] requires special attention, since glass electrodes cannot be used reliably [8a,8c,12,13]. Therefore, the traditional single-sample NMR titration is recommended [8c, 13,27,29,30]. A set of individual samples with constant monoprotic acid HL (or ligand L) concentration (e.g., 0.01 mol dm -3 ), constant ionic strength (e.g., 1 mol dm -3 ) and varying p[H] value are prepared one-by-one ("constant volume titration") in such a way that a strong acid or a strong base added for desired p[H] adjustment is taken in a significant excess over HL or L (e.g., 0.1-1.0 mol dm -3 ).…”