Broadband near-infrared luminescence properties of Sc2(MoO4)3:Cr3+ molybdates.

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.

THz, Raman, IR and DFT studies of noncentrosymmetric metal dicyanamide frameworks comprising benzyltrimethylammonium cations.

We report density functional theory (DFT) studies of vibrational modes for benzyltrimethylammonium cations (BeTriMe+) as well as THz, IR and Raman studies of [BeTriMe][M(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.

Crystal structure, vibrational and optic properties of 2-N-methylamino-3-methylpyridine N-oxide - Its X-ray and spectroscopic studies as well as DFT quantum chemical calculations.

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.

Spectroscopic properties and molecular structure of copper phytate complexes: IR, Raman, UV-Vis, EPR studies and DFT calculations.

The copper phytate IP6Cu, IP6Cu2 and IP6Cu3 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.

Spectroscopic investigation and DFT modelling studies of Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone.

Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone in the solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR and FT-Raman spectroscopies, powder X-ray diffraction, electron emission under femtosecond laser excitation. The stoichiometry and the formula of the studied complex have been proposed. Its physicochemical properties have been analyzed in terms of the structure and DFT calculations performed for the ligand. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. Spectral and energetic transformation of femtosecond light impulses has been studied and possibility of the energy transfer between the ligand and the Eu3+ electron levels has been analyzed.

DFT study of electron absorption and emission spectra of pyramidal LnPc(OAc) complexes of some lanthanide ions in the solid state.

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.

Conformation of the azo bond and its influence on the molecular and crystal structures, IR and Raman spectra, and electron properties of 6-methyl-3,5-dinitro-2-[(E)-phenyldiazenyl]pyridine - Quantum chemical DFT calculations.

The crystal and molecular structures of 6-methyl-3,5-dinitro-2-[(E)-phenyldiazenyl]pyridine have been determined by X-ray diffraction and quantum chemical DFT calculations. The crystal is monoclinic, space group Cc (No. 9) with Z=4 with the unit cell parameters: a=12.083(7), b=12.881(6), c=8.134(3) Å and ß=97.09(5)°. The azo-bridge appears in the trans conformation in which C2-N2-N2'-C1' torsion angle takes a value -178.6(3)°, whereas the dihedral angle between the planes of the phenyl and pyridine rings is 3.5(2)°. The IR and Raman spectra measured in the temperature range 80-350K and quantum chemical calculations with the use of B3LYP/6-311G(2d,2p) approach confirmed the trans configuration of the azo-bridge as the most stable energetically and allowed determination of the energy other virtual structures. The observed effects were used in the discussion of vibrational dynamics of the studied compound. The energy gap between cis and trans conformers equals to 1.054eV (0.03873 Hartree). The electron absorption and emission spectra have been measured and analyzed on the basis of DFT calculations. The life time of the excited state is 12µs and the Stokes shift is close to 5470cm-1.

Polarized Raman and IR spectra of oriented Cd(0.9577)Gd(0.0282)□(0.0141)MoO4 and Cd(0.9346)Dy(0.0436)□(0.0218)MoO4 single crystals where □ denotes the cationic vacancies.

Polarized Fourier Transform IR and Raman spectra of Cd0.9577Gd0.0282□0.0141MoO4 and Cd0.9346Dy0.0436□0.0218MoO4 oriented single crystals have been recorded and analyzed using the factor group approach (□ denotes the cationic vacancies). The tetragonal I41/a (C4h(6)) space group with Z=2 has been applied in the discussion. The influence of the structural changes induced by the defects in the CdMoO4 host lattice on the vibrational symmetry rules has been analyzed. The assignment of the observed bands to the internal and external modes has been proposed.

Synthesis and characterization of [(CH3)2NH2][Na0.5Cr0.5(HCOO)3]: a rare example of luminescent metal-organic frameworks based on Cr(III) ions.

A novel formate [(CH3)2NH2][Na0.5Cr0.5(HCOO)3] (DMNaCr) was prepared by a solvothermal method. This compound crystallizes in the perovskite-type metal formate framework (space group R3[combining macron]) with disordered dimethylammonium (DMA(+)) cations. X-ray diffraction, DSC, Raman and IR studies show that in contrast to the isostructural iron analogue [(CH3)2NH2][Na0.5Fe0.5(HCOO)3] (DMNaFe), DMNaCr does not exhibit any structural phase transition at low temperatures. This behavior has been attributed to the smaller flexibility of the perovskite-like framework in DMNaCr when compared with that of DMNaFe. Dielectric permittivity data reveal pronounced dielectric relaxation that is attributed to the dynamical rotation of DMA(+) ions. Electron absorption and photoluminescence studies show that this material exhibits efficient emission at low temperatures. A detailed analysis of the optical properties shows that chromium ions are located at the site of intermediate crystal field strength with Dq/B = 2.29.

Determination of N-acetylation degree in chitosan using Raman spectroscopy.

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.

Vibrational properties and DFT calculations of the perovskite metal formate framework of [(CH3)2NH2][Ni(HCOO3)] system.

Experimental Raman and IR spectra of multiferroic [(CH3)2NH2][Ni(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.

The hydrazo-bond in 4,4'-dimethyl-3,3'-dinitro-2,2'-hydrazobipyridine - crystal structure, conformation and vibrational characteristics.

The crystal and molecular structure of 4,4'-dimethyl-3,3'-dinitro-2,2'-hydrazobipyridine have been determined by X-ray diffraction and quantum chemical DFT analysis. The title compound crystallizes in P1¯ space group, with one-half molecule in the asymmetric unit. The molecular structure is stabilized by intramolecular NH···O hydrogen bonds. The molecules are linked by a combination of weak intermolecular CH⋯O interactions and also aromatic π-π stacking. The molecular structure of the studied compound has been determined using the DFT B3LYP/6-311G(2d,2p) approach and compared to that derived from X-ray studies. The IR and Raman wavenumbers have been calculated for the optimized geometry of a possible monomer structural model. The structural and vibrational properties of the intramolecular NH···O interaction are described.

Raman spectroscopy in determination of horse meat content in the mixture with other meats.

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.

Conformation of azo-bridge in 3,3'-dinitro-2,2'-azobipyridine and its 4,4'(or 5,5' or 6,6')-dimethyl-derivatives: vibrational studies and DFT quantum chemical calculations.

Syntheses of 3,3'-dinitro-2,2'-azobipyridine and 4,4' (or 5,5' or 6,6')-dimethyl-3,3'-dinitro-2,2'-azobipyridine have been described. Molecular structures of these compounds have been determined and compared, to the basic compound, azobipyridine, reported by us earlier. The conformation of the azo-bond and other structural data are discussed in terms of substitution place of methyl chromophore. Fourier transform IR and Raman spectra of these compounds have been measured and analysed. The 6-311G (2d,2p) basis set with the B3LYP functional have been used to discuss the space conformation and dynamics of the studied compounds.

The role of the Ca vacancy in the determination of the europium position in the energy gap, its valence state and spectroscopic properties in KCa(PO3)3.

A new very promising red phosphor KCa1-xEux(PO3)3 (x = 1-5%) has been grown by the solid state method. Its luminescent quantum efficiency is close to 100% and the emission is stable over a wide temperature range i.e. 90% and 60% of the room temperature emission intensity remains at 200 °C and at 600 °C, respectively. The chromaticity coordinates were calculated as being x = 0.63, y = 0.37. The IR and Raman spectra were measured, and the maximum phonon energy of KCa1-xEux(PO3)3 is 1276 cm(-1). In the measured emission and excitation spectra of all samples only Eu(3+) ion emission was observed, emission of Eu(2+) is not present. Quantum mechanical calculations showed that in a perfect crystal the 5d levels of Eu(2+) are embedded in the conduction band. Consequently, neither absorption nor emission assigned to the Eu(2+) ions could be observed. The presence of a calcium vacancy is crucial for the explanation of the observed spectrum. The existence of a Ca(2+) vacancy compensates for the charge of Eu(3+) and results in the creation of the magnetic moment which moves the 4f levels to the valence band. Thus, transitions to the Eu(3+) excited levels located in the energy band gap are observed.

The role of hydrogen bonds in the crystals of 2-amino-4-methyl-5-nitropyridinium trifluoroacetate monohydrate and 4-hydroxybenzenesulfonate - X-ray and spectroscopic studies.

Two new organic-organic salts, 2-amino-4-methyl-5-nitropyridinium trifluoroacetate monohydrate (AMNP-TFA), and 2-amino-4-methyl-5-nitropyridinium 4-hydroxybenzenesulfonate (AMNP-HBS), were obtained and characterized by means of FT-IR, FT-Raman and single crystal X-ray crystallography. In the former crystal, the cations, anions and water molecules are linked into layers by three types of hydrogen bonds, NPH⋯O, NAH⋯O and OH⋯O. These layers are connected by weaker CH⋯O hydrogen bonds. In the latter crystal, the cations and anions form one-dimensional structure through a number of hydrogen-bonding interactions involving the OH, NH(+) and NH2 groups as donors. In this case the NPH⋯O and NAH⋯O hydrogen bonds are formed. The combination of interactions between cations and anions results in the formation of columns. Additionally, there are π-π stacking interactions between the columns. The obtained X-ray structural data are related to the vibrational spectra of the studied crystals.

Structure, vibrational spectra and DFT characterization of the intra- and inter-molecular interactions in 2-hydroxy-5-methylpyridine-3-carboxylic acid--normal modes of the eight-membered HB ring.

Fourier transform IR and Raman spectra, XRD studies and DFT quantum chemical calculations have been used to characterize the structural and vibrational properties of 2-hydroxy-5-methylpyridine-3-carboxylic acid. In the unit-cell of this compound two molecules related by the inversion center interact via OH⋯N hydrogen bonds. The double hydrogen bridge system is spaced parallel to the (102) crystallographic plane forming eight-membered arrangement characteristic for pyridine derivatives. The six-membered ring is the second characteristic unit formed via the intramolecular OH⋯O hydrogen bond. The geometry optimization of the monomer and dimer have been performed applying the Gaussian03 program package. All calculations were performed in the B3LYP/6-31G(d,p) basis set using the XRD data as input parameters. The relation between the molecular and crystal structures has been discussed in terms of the hydrogen bonds formed in the unit cell. The vibrations of the dimer have been discussed in terms of the resonance inside the system built of five rings coupled via hydrogen bonds.

Comprehensive physicochemical studies of a new hybrid material: 2-amino-4-methyl-3-nitropyridinium hydrogen oxalate.

A new organic-organic salt, 2-amino-4-methyl-3-nitropyridinium hydrogen oxalate (AMNPO), and its deuterium analogue have been synthesized and characterized by means of FT-IR, FT-Raman, DSC and single crystal X-ray studies. The DSC measurements and temperature dependence of the IR and Raman spectra in the range 4-295 K show that it undergoes a reversible phase transition at ~240 K. At room temperature it crystallizes in noncentrosymmetric space group P21. The unit-cell is built of the 2-amino-4-methyl-3-nitropyridinium cations and oxalate monoanions which are connected via the N-H···O and O-H···O hydrogen bonds. The geometrical and hydrogen bond parameters are similar for non-deuterated (at 120 and 293 K) and deuterated compounds (at 90K). The phase transition is probably a consequence of order-disorder transition inside of hydrogen network. The 6-311G(2d,2p) basis set with B3LYP functional have been used to discuss the structure and vibrational spectra of the studied compound.

Intra- and inter-molecular hydrogen bonds, conformation and vibrational characteristics of hydrazo-group in 5-nitro-2-(2-phenylhydrazinyl)pyridine and its 3-, 4- or 6-methyl isomers.

Syntheses of 5-nitro-2-(2-phenylhydrazinyl)pyridine (5-nitro-2-phenylhydrazopyridine), 3-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (3-methyl-5-nitro-2-phenylhydrazopyridine), 4-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (4-methyl-5-nitro-2-phenylhydrazopyridine) and 6-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (6-methyl-5-nitro-2-phenylhydrazopyridine) have been described. Their IR and Raman spectra have been measured and analyzed in terms of DFT quantum chemical calculations. The 6-311G(2d,2p) basis set with the B3LYP functional has been used to discuss the optimized structure and vibrational spectra. The vibrational characteristics of the hydrazo-bond have been reported with their relation to the inter- and intra-molecular hydrogen bonds formed in the studied systems. The role and influence of substitution position of the methyl chromophore on the structure and vibrational data have been discussed.

Vibrational spectra, crystal structure, DFT quantum chemical calculations and conformation of the hydrazo-bond in 6-methyl-3-nitro-2-(2-phenylhydrazinyl)pyridine.

The crystal and molecular structures of 6-methyl-3-nitro-2-(2-phenylhydrazinyl)pyridine (6-methyl-3-nitro-2-phenylhydrazopyridine) have been determined by X-ray diffraction and quantum chemical DFT analysis. The crystal is monoclinic, space group C2/c, with Z=8 formula units in the elementary unit cell of dimensions a=16.791(4), b=6.635(2), c=21.704(7)Å, ß=100.54(3)°. The molecule consists of two nearly planar pyridine subunits. A conformation of the linking hydrazo-bridge CNHNHC is bend and the dihedral angle between the planes of the phenyl and pyridine rings is 88.2(5)°. The hydrogen bonding of the type NH···N and possibly also CH···O favors a dimer formation in the crystal structure. The dimers are further linked by a NH···O hydrogen bond, so forming a layer parallel to the ab plane. The molecular structure of the studied compound has been determined using the DFT B3LYP/6-311G(2d,2p) approach and compared to that derived from X-ray studies. The IR and Raman wavenumbers have been calculated for the optimized geometry of a possible monomer structural model but the possibility of the dimer formation through the NH···N hydrogen bond has also been considered. The structural and vibrational properties of the intra-molecular NH···O interaction are described.