We report on temperature-dependent infrared (IR) and Raman studies of (CH3)2NH2M(HCOO)3 metal–organic frameworks (MOFs) with M=Zn, Fe. Based on Raman and IR data, an assignment of the observed modes ...to respective vibrations of atoms is proposed. Temperature-dependent studies revealed abrupt changes below 160K that are attributed to the onset of first-order structural phase transition. The most pronounced changes are observed for the modes corresponding to the dimethylammonium cation, especially those involving motion of hydrogen atoms. This behavior proves that the phase transition has an order–disorder character and is associated with the ordering of protons. The abrupt splitting of some modes related to the formate ion indicates that this transition is also associated with significant distortion of the metal-formate framework.
In the present work we report detailed structural, magnetic and phonon properties of NiCr2O4 powders synthesized via a simple coprecipitation method. Temperature-dependent XRD as well as ...temperature-dependent IR studies reveal that cubic to tetragonal phase transition is lowered due to size effects. Observed changes in the IR spectra indicate that the paramagnetic–ferrimagnetic phase transition taking place at 74K is related to further lowering of symmetry to orthorhombic system. Assignment of modes was proposed and factor group analyses in three possible symmetries were carried out. Our results show strong anomalies due to the Jahn–Teller tetragonal distortion and weak due to the orthorhombic distortion and onset of collinear ferrimagnetic order. Shifts of wavenumbers observed below 31K, where the onset of antiferromagnetic ordering occurs, were attributed to spin–phonon interactions.
XRD pattern of NiCr2O4 sample synthesized via a coprecipitation method followed by calcination at 1000oC. Display omitted
•NiCr2O4 starts to crystallize near 750°C.•Coexistence of cubic and tetragonal phases of NiCr2O4 was revealed.•Temperature of the Jahn–Teller distortion is lowered due to the size effects.•Evidences of tetragonal and orthorhombic distortions were found.•Weak spin–phonon interactions were evidenced.
The crystal and molecular structure and physicochemical properties of 2-N-methylamino-3-methylpyridine N-oxide (MA3MPO) have been studied. MA3MPO was synthesized from 2-amino-3-methylpyridine by ...several steps to form colorless crystals suitable for crystallographic analysis. The data reveal that MA3MPO crystallizes in the monoclinic space group P21/n. The studied compound contains a nearly flat triply substituted pyridine skeleton whose structure is stabilized by an intramolecular N–H⋅⋅⋅O hydrogen bond. The N-oxide molecules are connected together by weak C–H⋯O hydrogen bonds, an acceptor of which is the oxygen atom from the N-oxide group. This leads to creation of two-dimensional network of hydrogen bonds. Its IR, Raman, UV–Vis and luminescence spectra have been measured and analyzed on the basis of DFT and NBO quantum chemical calculations in which the B3LYP/6-311++G(d,p) approach was applied. The distribution of the electron levels in the studied compound has been analyzed in terms of the possibility of its participation in the ligand-to-lanthanide ion energy transfer.
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•The 2-N-methylamino-3-methylpyridine N-oxide (MA3MPO) was synthesized and characterized.•The studied compound structure is stabilized by an intramolecular N–H⋯O hydrogen bond.•The molecules are connected together by weak C–H⋯O hydrogen bonds.•The amino group plays the role of effective hydrogen-bond donor but the N-oxide group is a hydrogen-bond acceptor.•X-ray, IR, Raman and DFT methods recognized the existence of the intramolecular N–H⋯O hydrogen bond in the studied compound.
The Pechini and microwave-assisted hydrothermal syntheses of nanocrystalline Er3+ and Tm3+ co-doped MY(WO4)2, where M = Li, Na, K, double tungstates are reported. The obtained samples were ...characterized using standard X-ray powder diffraction (XRD) technique, Rietveld method, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and IR spectroscopy. The smallest crystallites (about 13 nm) could be obtained for the sodium samples synthesized by both the Pechini (for the resin calcined at 550 °C) and hydrothermal methods (synthesis at 230 °C). The average particle size of nanocrystalline powders increases with increasing temperature. It was found that nanocrystals retain the bulk structure with tetragonal and monoclinic symmetry for the sodium and potassium analogues, respectively. In contrast to this behaviour, LiY(WO4)2 undergoes a size-induced structural transformation from monoclinic (space group P2/n) to tetragonal (space group I41/a) symmetry. IR spectra of the synthesized sodium and potassium compounds are very similar to their bulk counterparts. IR spectra of the lithium analogues show, however, abrupt changes when the calcination temperature increases to 850 °C or higher. This behaviour is consistent with the size-induced phase transition in this compound.
The Pechini and microwave-assisted hydrothermal syntheses of nanocrystalline Er
and Tm
co-doped MY(WO
)
, where M = Li, Na, K, double tungstates are reported. The obtained samples were characterized ...using standard X-ray powder diffraction (XRD) technique, Rietveld method, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and IR spectroscopy. The smallest crystallites (about 13 nm) could be obtained for the sodium samples synthesized by both the Pechini (for the resin calcined at 550 °C) and hydrothermal methods (synthesis at 230 °C). The average particle size of nanocrystalline powders increases with increasing temperature. It was found that nanocrystals retain the bulk structure with tetragonal and monoclinic symmetry for the sodium and potassium analogues, respectively. In contrast to this behaviour, LiY(WO
)
undergoes a size-induced structural transformation from monoclinic (space group
2/
) to tetragonal (space group
4
/
) symmetry. IR spectra of the synthesized sodium and potassium compounds are very similar to their bulk counterparts. IR spectra of the lithium analogues show, however, abrupt changes when the calcination temperature increases to 850 °C or higher. This behaviour is consistent with the size-induced phase transition in this compound.
Experimental Raman and IR spectra of NH2-CH-NH2M(HCOO)3 (M=Co, Fe), containing formamidinium cations NH2-CH-NH2+ (FMD+) were recorded at room temperature. In order to assign the vibrational modes ...corresponding to the FMD+ cation, the three-parameter hybrid B3LYP density functional method has been used with the 6-311G(2d,2p) basis to derive the vibrational wavenumbers (harmonic and anharmonic), infrared intensities and Raman scattering activities of formamidine molecule and FMD+ cation. The performed calculations revealed that protonation should affect most significantly the ν(CH), ρ(NH2), ω(NH2) and τ(NH2) modes, which are expected to shift towards higher wavenumbers after protonation.
•The IR and Raman spectra of studied compounds were recorded.•The IR and Raman wavenumbers were calculated from the optimized geometry of molecule.•IR, Raman and DFT methods confirm the existence of ...an intramolecular HBs.•The vibrational characteristics of OH compounds were analyzed.
Molecular structures of quercitin and quercitin sulfonic acid have been determined by DFT quantum chemical calculations. FT-IR and FT-Raman spectra have been measured in the solid state and discussed in terms of B3LYP/6-311G(2d,2p) approach. The role of the hydrogen bonds in stabilization of their structures has been analyzed. The IR spectra were measured in the temperature range 5–300K and the observed effects were used in the discussion of the hydrogen bond behavior.
•Na3RE(PO4)2, RE=Y or Gd, doped with Yb3+ were synthesised by the hydrothermal method.•As-synthesised samples crystallise in the trigonal modification.•After calcination at 500°C they transform to ...monoclinic (Y) or orthorhombic (Gd) symmetry.•Morphology of the particles for all samples is similar and resembles rice grains.•The decay time of Yb3+ increases when the orthophosphate precursor is calcined at 700°C.
Na3RE(PO4)2 orthophosphates, where RE=Y and Gd, doped with Yb3+ ions were synthesised by hydrothermal method and characterised by X-ray diffraction, microscopic, IR and Raman techniques. The emission, excitation spectra were recorded at room temperature and fluorescence decay time was determined. As-synthesised samples crystallise in a trigonal modification and during calcination at 500°C they transform to a monoclinic or orthorhombic symmetry (for yttrium and gadolinium compounds, respectively). Finally, the samples calcined at 700°C do not reveal the trigonal symmetry. The morphology of particles for all samples is similar and resembles rice grains. All the obtained for the studied orthophosphates data were compared to those previously reported for the same compounds synthesised by Pechini method.
The electron absorption and emission spectra were measured for the pyramidal LnPc(OAc) complexes in the solid state and co-doped in silica glass, where Ln=Er, Eu and Ho. The theoretical electron ...spectra were determined from the quantum chemical DFT calculation using four approximations CAM-B3LYP/LANL2DZ, CAM-B3LYP/CC-PVDZ, B3LYP/LANL2DZ and B3LYP/CC-PVDZ. It was shown that the best agreement between the calculated and experimental structural parameters and spectroscopic data was reached for the CAM-B3LYP/LANL2DZ model. The emission spectra were measured using the excitations both in the ligand and lanthanide absorption ranges. The possibility of energy transfer between the phthalocyanine ligand and excited states of lanthanide ions was discussed. It was shown that the back energy transfer from metal states to phthalocyanine state is responsible for the observed emission of the studied complexes both in the polycrystalline state and silica glass.
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•Lanthanide(III) phthalocyanines of the LnPc(OAc) type were synthesized in the solid state.•Sol-gel glass doped with LnPc(OAc), Ln=Eu, Ho and Er, complexes was obtained.•The quantum chemical DFT calculations using four theoretical models have been done.•Luminescence of ligand is only visible.
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