³¹P NMR as a Tool for Studying Incorporation of Ni, Co, Fe, and Mn into Aluminophosphate Zeotypes

Abstract

The incorporation of moderate amounts of Ni(II), Co(II), Fe(II/III), and Mn(II/III) into aluminophosphate zeotype AlPO4-34 and Fe(II/III) into aluminophosphate zeotype AlPO4-36 was studied by broadline 31P NMR. The technique provided direct evidence on isomorphous substitution of framework aluminum by transition metals and allowed us to determine the extent of the substitution. 31P NMR proved to be complementary to other spectroscopic techniques such as X-ray absorption spectroscopy (XAS), Mössbauer, electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR) spectroscopies. The position of the NMR signal belonging to phosphorus in the P(OAl)3(OMe) environment depended mostly on the magnitude of the hyperfine interaction between a phosphorus nucleus and an unpaired electron, which was delocalized from the transition metal atom Me by covalent bonding. The width of the NMR signal was dominated by dipolar coupling among phosphorus nuclei and nearest paramagnetic centers. In addition, broadline NMR of ethylenediamine-templated manganese phosphate (C2H10N2)[Mn2(HPO4)3(H2O)], which was used as a model compound, showed that on the basis of line positions and line widths different 31P signals could easily be assigned to different phosphorus crystallographic sites. The technique could thus be applied to extract valuable structural information about metal phosphates as well.

Ionothermal synthesis and characterization of CoAPO-34 molecular sieve

“…The 31 P lineshape of CoAPOs changes upon calcination, although, while Canesson and Tuel suggested that the intensity in the region between 500 and 1500 ppm typically increases relative to that above 2500 ppm, [30] Mali et al showed that, for CoAPO-34, the signal actually broadens and a greater proportion of the intensity is observed at higher shifts. [31] This is observed here for the 31 P spectrum of the calcined CoAPO-34 shown in Fig. 6(f).…”

“…The interaction of unpaired electrons from the paramagnetic Co 2+ or Co 3+ with 31 P nuclei in P(OAl) 4-n (OCo) n environments can lead to both very large isotropic shifts and very broad resonances (owing to paramagnetic shift anisotropy and relaxation effects). [31] Thus, the resulting 31 resonance at δ ≈ 0 ppm in Fig. 6(e) is the overlap of the static lineshapes of the three inequivalent P species observed in the 31 P MAS NMR spectrum in Fig.…”

Solid‐state NMR spectra of paramagnetic silica‐based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions

“…Unfortunately, the 29 Si isotropic paramagnetic shifts in manganese-containing silica solids have not been reported, to our knowledge. Taking into account the 31 P and 13 C NMR data collected for solids with P-O-M or C-O-M bonds (M D Mn, Co, Fe and Ni), 9,11,12 this 29 Si shift does not look large. Nevertheless it is remarkably larger than paramagnetic shifts of 29 Si nuclei in zeolites, containing paramagnetic lanthanide ions.…”

“…This effect has been reported for the solid-state 31 P NMR spectra of aluminophosphates, doped with paramagnetic ions of Ni, Co, Fe and Mn. 11 The second part in Eqn (1) corresponds to the dipole field caused by dipolar electron-nucleus interaction. Such dipole fields appear even in the absence of chemical bonding between paramagnetic centers and atoms, whose nuclei are observed in the solid-state NMR spectra (through-space effects).…”

Synthesis and characterization of hypoxia-mimicking bioactive glasses for skeletal regeneration

“…The effect of paramagnetic cations is very difficult to analyse using the same approach as for alkali earth or alkali cations. The paramagnetic cations have many unpaired electrons that can interact with the nuclei and produce a number of different effects on the NMR spectrum [45][46] , including a reduction in spin-lattice relaxation, T 1 , times and broadening of the resonance line. Whereas some reduction in spin-lattice relaxation, T 1 , time is beneficial, for obtaining improved signalto-noise ratios, line broadening is detrimental, especially in MAS-NMR spectra of BGs where the peaks are already broad due to the variation in bond angles and distances in a disordered glass structure.…”