Display omitted
•Spectroscopic determination of deacylation degree of chitosan has been proposed.•Equations for determination of degree of deacetylation have been derived.•The discussions have been ...based on DFT quantum chemical calculations of chitosan.
Application of Raman spectroscopy in determination of the acetylation degree (DA) of chitosan has been developed. The spectra of several chitosan samples characterized by different DD (degree of deacetylation) in the range 50–100% have been measured. The integral intensities of the bands assigned to the vibrations of amine group and glucosidic ring were used to calculate the DA from the intensity ratio. The assignment of the bands to the respective normal modes of chitosan was based on the DFT quantum chemical calculations. This method has a number of advantages over other techniques. It is fast and does not require purification of the sample nor require dissolution of the chitosan in any solvent.
Display omitted
•Raman and IR spectra of multiferroic (CH3)2NH2Ni(HCOO)3 were recorded.•DFT calculations for the model compounds were performed.•Assignment of vibrational modes has been ...proposed.•Modes sensitive to formation of hydrogen bonds have been identified.
Experimental Raman and IR spectra of multiferroic (CH3)2NH2Ni(HCOO)3 were recorded at room temperature. The three-parameter hybrid B3LYP density functional method has been used with the 6-31G(d, p) basis set to derive the equilibrium geometry, atomic spin densities, vibrational wavenumbers, infrared intensities and Raman scattering activities. Based on these calculations, the assignment of the observed bands to the respective internal and lattice modes is proposed. The performed calculations revealed that the ν(NH2) stretching, ρ(NH2) rocking and τ(CH3) torsional modes are very sensitive to formation of the hydrogen bond between the DMA+ cation and Ni-formate framework. Therefore, these modes are suitable probes for strength of hydrogen bonds in this family of metal-formate frameworks and study of their temperature dependence may provide significant information on a role of the hydrogen bonds in mechanism of the ferroelectric phase transition occurring in these compounds at low temperatures.
We report the structural, phonon and luminescence properties of Eu3+-doped Gd3-xEuxNbO7 niobates prepared by conventional solid state reaction. Although a few different crystal structures of pure ...Gd3NbO7 have been reported so far, their properties still remain controversial and the mechanism of their structural phase transition is not well understood. The temperature-dependent IR and Raman spectra show a structural phase transition occurring at 340 K. The detailed analysis of vibrational spectra and correlation diagrams as well as theoretical factor group considerations allowed us to propose the detailed assignment of the observed bands, define the symmetry of low and high-temperature phases and explain the mechanism of their structural transformation from the Pmcn to the Cmcm centrosymmetric orthorhombic space group. Powder X-Ray diffraction patterns confirm our analysis. The temperature-dependent emission, room-temperature excitation spectra and luminescence decay times are reported to achieve more information on structural and optical properties of the studied niobates.
•Gd3Nb2O7 niobates doped with Eu3+ ions were prepared using solid state reaction method.•Factor group analysis was applied to explain Raman and IR spectra.•Low- and high-temperature phases were described and the mechanism of phase transition was proposed.
Display omitted
•The structural and spectroscopic properties of Sc2(MoO4)3: Cr3 + were investigated.•The influence of synthesis conditions on the structural properties was studied.•The emission ...spectra of samples doped with 0.1–2.0 % of Cr3 + were investigated.•The broadband NIR luminescence from Cr3+ ions may be attractive for LED applications.
The structural and spectroscopic properties of Sc2(MoO4)3 molybdate containing various concentrations of Cr3+ ions were investigated in a temperature range of 80–300 K. The samples were prepared using hydrothermal as well as solid-state reaction methods. The influence of synthesis conditions and the molybdenum source on the structural properties was studied by X-ray diffraction (XRD), IR (infrared), and Raman methods. The optical properties of Sc2(MoO4)3 samples doped with 0.1, 0.5, 1.0, and 2.0 % of Cr3+ ions were investigated. The broadband near-infrared (NIR) luminescence spectra generated from the 4T2 and 2E levels of Cr3+ ions may be attractive for NIR light-emitting diode (LED) applications. Emission decay profiles and the crystal field parameters of Cr3+ ions are discussed. In particular, the mechanism of photoluminescence generation and the thermal quenching path are described in detail.
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.
•Raman spectra of horse, beef meats and their mixtures were measured.•Vibrational assignment of observed bands to respective amino acids was proposed.•The analytical relations between the integral ...band intensities were studied.•New spectroscopic method for determination of the horse meat content in its mixture with beef is proposed.
A new method based on FT-Raman measurements that allows to determine the content of horse meat in its mixture with beef has been proposed. In the analysis of the Raman spectra of the meat mixtures, the integral intensity ratios of the 937/1003, 879/1003, 856/1003, 829/1003, and 480/1003cm−1 pairs of bands have been determined the intensities of which were related to the reference intensity of the band at 1003cm−1. The reasonable results that show good fitting between the spectroscopic parameters and chemical content of the studied samples have been obtained. The analytical equations between these parameters have been proposed.
We report synthesis of four novel heterometallic MOFs, (NH4)(H2O)CrIIIMII(HCOO)6 with MII = Zn (NH4CrZn), Co (NH4CrCo), Mn (NH4CrMn) and Ni (NH4CrNi). X-ray diffraction shows that NH4CrZn ...crystallizes in the trigonal structure (space group P3¯1c) with ordered Cr3+ and Zn2+ centers while NH4CrCo, NH4CrMn and NH4CrNi crystallize in the hexagonal system with chiral space group of P6322 and statistical occupation of the same sites by Cr3+ and M2+ ions. Raman and IR data confirm presence of water molecules and different confinement of the ammonium cations in the cavities of chiral and niccolite type metal formate frameworks. Optical studies show that Cr3+ ions in NH4CrZn and NH4CrMn are located at sites of strong crystal field with the Dq/B values of 2.54 and 2.47, respectively. Luminescence studies show that these compounds exhibit efficient Cr3+-based emission with the decay time of 8.1 μs (0.44 ms) at 295 K (10 K) for NH4CrMn and 8.3 μs (0.78 ms) for NH4CrZn.
Display omitted
•Four novel heterometallic formate frameworks were obtained.•X-ray diffraction showed that the obtained compounds crystallize in either niccolite or chiral structure.•Assignment of Raman and IR modes is proposed.•These compounds exhibit efficient chromium(III)-based photoluminescence.
The copper phytate IP6Cu, IP6Cu
2
and IP6Cu
3
complexes were synthesized changing the phytate to metal mole ratio. The obtained products have been characterized by means of chemical and spectroscopic ...studies. Spectroscopic ATR/IR, FT-Raman, UV–Vis, EPR and magnetic measurements were carried out. The structures of these compounds have been proposed on the basis of the group theory and geometry optimization taking into account the shape and number of the bands corresponding to the stretching and bending vibrations of the phosphate group and metal–oxygen polyhedron. The role of the inter- and intra-hydrogen bonds in stabilization of the structure has been discussed. EPR studies showed that a local rhombic symmetry of copper ions appears in the studied phytates. Dominant interactions show antiferromagnetic properties depending on the content of paramagnetic ions.
High pressure has been one of key tools for discovering and accessing new phases and novel properties of materials. Under these extreme conditions, it is possible to obtain information about the ...structural instabilities and to probe the delicate balance between short and long range interactions, which is fundamental for understanding the emergence of many properties. In this paper we reviewed the high-pressure behavior of some molybdate and tungstate materials, which comprises a large class of inorganic compounds that exhibit interesting physical properties (optical, ferroelastic, ferroelectric, negative thermal expansion) and have technological applications in different fields. These materials have a rich polymorphism in high pressures and some of them exhibit pressure-induced amorphization, thus making molybdates and tungstates compounds good prototypes to exploit new concepts about the physics of amorphization processes and about chemical decomposition under high pressure. We discussed how the combination of short and long-range probe techniques (which gives detailed information on the structural changes occurring in these materials) under high-pressures provides significant insight into the origin of lattice instabilities and pressure-induced amorphization in this particular class of inorganic materials. Furthermore, we reviewed in detail, how these structural changes affect their optical and ferroelectric properties. The conclusions derived from the high-pressure studies duly reviewed herewith have important implications for science and applications of these materials.
Display omitted
•Hydrated and anhydrous benzyltrimethylammonium metal-dicyanamides have been studied.•Assignment of vibrational modes is proposed based on DFT studies.•Co analogue shows different ...dehydration mechanism than the Ni and Mn counterparts.•Phase transitions in anhydrous polymorphs are of an order-disorder nature.
We report density functional theory (DFT) studies of vibrational modes for benzyltrimethylammonium cations (BeTriMe+) as well as THz, IR and Raman studies of BeTriMeM(dca)3(H2O) (dca = N(CN)2−, dicyanamide; M = Mn2+, Co2+, Ni2+) and their anhydrous analogues. These studies show that the anhydrous BeTriMeMn and BeTriMeNi have the same or very similar structures and loss of water molecules leads to significant changes in the metal-dicyanamide frameworks. In particular, the number of dca modes decreases, suggesting increase of crystal symmetry, probablly related with decrease in the number of non-equivalent dca bridges from two to one. Although it is possible that dehydration leads to a replacement of the coordinate Mn-O (Ni-O) bonds by Mn-N (Ni-N) bonds, wherein N atoms come from the C≡N groups of previously non-bridged dca units, reversibility of the dehydration process indicates that such new bonds are either not formed or are very weak. The anhydrous Mn and Ni compounds undergo similar reversible phase transitions to lower symmetry phases. The driving force for these transitions is most likely ordering of dca linkers but this process is accompanied by weak distortion of the metal-dicyanamide frameworks. In the case of BeTriMeCo, the loss of water molecules also leads to significant changes in the cobalt-dicyanamide framework. However, the structure of this analogue is different from the structures of the Mn and Ni counterparts, the number of unique dca linkers is preserved and the dehydration process is irreversible, suggesting more drastic rearrangement of the metal-dicynamide framework.
PDF
