Krystyna Hołderna-Natkaniec

Dynamical disorder in 2-methyl-4-nitroaniline and its deuterated analogue crystals studied by Fourier transform infrared and nuclear magnetic resonance.

The Fourier transform infrared spectra of the thin layers of 2-methyl-4-nitroaniline (MNA) and its deuterated analog were recorded in the 500-4000 cm(-1) region in the 10-300 K temperature range. Activation energies of the -CH(3), -NH(2), and -NO(2) groups reorientations were estimated. The (1)H-NMR spin-lattice relaxation time, T(1), and the second moment of (1)H-NMR resonance line, M(2), measured in the 80-298 K temperature range, were used to determine the parameters of the -CH(3) group motion. The experimental potential barriers for the amine, nitro, and methyl group reorientations are considered in the context of strengths of the N-H([ellipsis (horizontal)])O, C-H([ellipsis (horizontal)])O intermolecular hydrogen bonds, and other short contacts, recognized recently [U. Okwieka et al., J. Raman Spectrosc. 39, 849 (2008)], and they agree with the barriers calculated by quantum chemical methods. The dynamical disorder found in the MNA crystal in the large temperature range seems to be important from the point of view of its nonlinear optical and other properties.

Structure, molecular motion, and phase transition of a highly disordered crystal [Co(NH3)6](ClO4)3

Four crystalline phases of the coordination compound [Co(NH3)6](ClO4)3 are identified by adiabatic calorimetry. An order–disorder phase transition (II→I) occurs at TC1 = 334.2 K with an entropy change of 6.4 J K−1 mol−1. The X-ray single-crystal diffraction at 340 K demonstrates that phase I is cubic (Z = 4) and that two types of anions exist with different types of disorder. In phase II at 200 K, five anions (out of twelve) become ordered and three cations (out of four) are deformed to give a lower symmetry, still in a cubic system (Z = 32). This is attributed to orientational ordering of the anions triggered by NH⋯O hydrogen-bonding interactions. The 1H-NMR study suggests that some NH3 ligands are oriented because of hydrogen bonding, whereas some cations reorient isotropically like in phase I. The energy required to reorient an ordered anion in the crystal lattice of phase II is estimated from the excess heat capacity below TC1 to be 40 kJ mol−1, which corresponds to the energy needed to break the hydrogen bond, 8 kJ mol−1. While the transitions at 111.7 K (III→II) and 97.6 K (IV→II), with an entropy change of 5.7 J K−1 mol−1, do not substantially affect the dynamics, they are attributed to further orientational ordering of the anions still disordered in phase II.

Neutron scattering study of reduced graphene oxide of natural origin

This paper presents a direct confirmation of graphene-like configuration and first suggests the chemical composition of basic structural elements of shungite attributing the latter to reduced graphene oxide nanosheets with an average 11:1:3 (C:O:H) atomic content ratio.

Effect of fullerene derivates on thermal and crystallization behavior of PBT/decylamine-C 60 and PBT/TCNEO-C 60 nanocomposites

The paper describes the process of the preparation of new nanocomposites based on poly(butylene terephthalate) and C60 nanoparticles modified by decylamine (DA) and tetracyanoethylene oxide (TCNEO), respectively. Thermal and crystallization properties of new synthesized nanocomposites were investigated by means of thermal differential scanning calorimetry (DSC). The experimental results demonstrate the effect of fullerene derivates, DA-C60 and TCNEO-C60, on the melting and crystallinity processes of nanocomposites. The morphology of new nanocomposites was investigated by SEM.

Optical nonlinearity and electric conductivity origin study on sucrose crystal by using IR, Raman, INS, NMR, and EPR spectroscopies.

The supposed importance of hydrogen bonds toward the origin of second harmonic generation (SHG) and electric conductivity in crystalline sucrose was investigated by IR (4000-10cm(-1)), INS (2000-10cm(-1), at 35K), polarized Raman (3600-50cm(-1)) spectra, and (1)H NMR second moment line records in the temperature range 450-80K. The temperature dependence of NIR (7000-5500cm(-1)) polarized spectra gave information about -CH2 motions complementary to NMR results concerning -CH2OH group rearrangements. The EPR spectra were applied to study the generation of radical ions by exposure to NIR radiation. Density functional theory quantum chemical calculations were performed to reproduce the vibrational spectra in order to complete as far as possible the assignments of bands observed by us and in the literature in sucrose crystals, and to throw more light on the possible reasons of sucrose electric conductivity and optical nonlinearity by the knowledge of theoretical values of dipole moments, polarizabilities, first order hyperpolarizabilities of sucrose molecule and clusters as well as ionization energy and electron affinity. The proton transfer in one specific hydrogen bond parallel to the helical axis b is proposed to be the most important in SHG and conductivity origin.

Phase transitions and molecular reorientations in [Mn(OS(CH3)2)6](ClO4)2 studied by proton magnetic resonance and Raman spectroscopy

The temperature dependence of full width at half maximum of bands associated with δ d(OClO)F2, δ(CSC), and ρ(CH3) vibrational modes in the FT-RS spectra of [Mn(OS(CH3)2)6](ClO4)2 have shown that the dynamic of reorientational motions of and CH3 groups (from (CH3)2SO) undergoes distinct changes at the phase transitions at T  ≈ 365 K and T  ≈ 322 K. These are the phase transitions from stable crystal to stable rotational phase and from metastable crystal to metastable rotational phase, respectively. Moreover, characteristic changes of the Raman spectra at these phase transitions, connected with both the shift of the band positions and the scattered light intensity of the bands associated with ν s(SO), ν s(MnO), δ(CSC), and δ(OMnO) modes, suggest that these phase transitions are associated with crystal structure changes, too. Analysis of temperature dependence of the second moment (M2) of 1H NMR showed that on first heating (from room temperature) of the compound the reorientations of the CH3 groups were set in motion in the phase transition at T  ≈ 365 K. On subsequent heating (after cooling the compound to 100 K) molecular reorientation starts just above 150 K, and above the temperature of 223 K all molecular groups containing protons perform nearly free rotation with frequencies of a few kHz, including an isotropic reorientation of the whole [Mn(OS(CH3)2)6]2+.

1H NMR study of molecular dynamics of acetylcholine chloride

The longitudinal relaxation timeT1 and the second momentM2 of1H nuclear magnetic resonance line in a wide temperature range have been measured for acetylcholine chloride. Two different types of the methyl groups reorientation occurred. The first type was the hindered rotation of the methyl group denoted as C(1)H3 about the threefold symmetry axis. The second type was the reorientation of the trimethyl group-N(CH3)3 around the pseudo C3′ axis of C(6)-N(7) bond, which accompanied the standard C3 motion of the methyl group. The Dunn-McDowell model was applied to analyze the dynamics observed.

The relationship between reorientational molecular motions and phase transitions in [Mg(H2O)6](BF4)2, studied with the use of 1H and 19F NMR and FT-MIR

A (1)H and (19)F nuclear magnetic resonance study of [Mg(H2O)6](BF4)2 has confirmed the existence of two phase transitions at Tc1 ≈ 257 K and Tc2 ≈ 142 K, detected earlier by the DSC method. These transitions were reflected by changes in the temperature dependences of both proton and fluorine of second moments M2 (H) and M2 (F) and of spin-lattice relaxation times T1 (H) and T1 (F). The study revealed anisotropic reorientations of whole [Mg(H2O)6](2+) cations, reorientations by 180° jumps of H2O ligands, and aniso- and isotropic reorientations of BF4 (-) anions. The activation parameters for these motions were obtained. It was found that the phase transition at Tc1 is associated with the reorientation of the cation as a whole unit around the C3 axis and that at Tc2 with isotropic reorientation of the BF4 (-) anions. The temperature dependence of the full width at half maximum value of the infrared band of ρt(H2O) mode (at ∼596 cm(-1)) indicated that in phases I and II, all H2O ligands in [Mg(H2O)6](2+) perform fast reorientational motions (180° jumps) with a mean value of activation energy equal to ca 10 kJ mole(-1), what is fully consistent with NMR results. The phase transition at Tc1 is associated with a sudden change of speed of fast (τR ≈ 10(-12) s) reorientational motions of H2O ligands. Below Tc2 (in phase III), the reorientations of certain part of the H2O ligands significantly slow down, while others continue their fast reorientation with an activation energy of ca 2 kJ mole(-1). This fast reorientation cannot be evidenced in NMR relaxation experiments. Splitting of certain IR bands connected with H2O ligands at the observed phase transitions suggests a reduction of the symmetry of the octahedral [Mg(H2O)6](2+) complex cation.

Inelastic Neutron Scattering (INS) Study of Low Frequency Vibrations and Hydrogen Bonding of (E)-2-Hydroxyimino-2-Cyanoacetic Acid Ethyl Ester

Abstract The title unsubstituted (normal) (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester (the abbreviated name: (E)-2-cyanoethyl ester-2-oxime or 2-oxime) and its 2-deuterated analogue have been prepared and characterized using infrared, Raman and inelastic, incoherent neutron scattering (IINS) spectroscopy. Molecular structures (molecular conformations) of the compounds are proposed for the vapour state. Four molecular conformers, namely two pairs of the s-cis, s-trans rotational isomers (rotamers) from six lower energetic conformations of E-2-hydroxyimino-2-cyanoacetic ethyl ester, are predominating for the single molecule of the compound. They amount together to almost 100% of the conformational populations of both rotational isomers as it was theoretically calculated using DFT (B3LYP) method with 6-311G++(d,p) basis set. Additionally dimers of 2-oxime were considered using B3LYP/6-31G* method in order to improve the results obtained for single molecule. In both parent (=N–OH) and deuterated (=N–O–D) molecules of the (E)-2-ethylcyano ester-2-oxime respectively, extra bands corresponding primarily to hydrogen (deuterium) bond vibrations (γ–bending out of plane of hydrogen bond, σ–stretching of hydrogen bond bridge, δ–bending in plane of hydrogen bond, λ–bending of hydrogen bond bridge have been identified, namely σ (N–O–H···O) at 132.8, 212.5, 279, 358.7, 424, 448, 523.6, 872, γ (N–O–H···O) at 334, 564, 592, 745, 820, δ (N–OH···O) at 1461, 1600, 1862cm−1 in the low temperature IINS spectrum, whereas the frequency at 365cm−1 has been assigned as the out of plane (o.o.p.) (γO–D···O) vibrational mode. Formation of the O–H···O hydrogen bridge is reflected in shifting of the bands of the stretching and bending vibrations of OH group as well as arising of the bridge vibrations in the low frequency range. Moreover, equilibrium geometries and all harmonic vibrational frequencies of the (E)-2-cyano ethyl ester-2-oxime molecules with potential energy distribution (PED) were also calculated by means of the above mentioned theoretical programs.

Comparative neutron scattering study of molecular ordering in d-camphor and dl-borneole

Abstract Molecules of both studied substances: d-camphor and dl-borneole are nearly globular in shape and show plastic behaviour at room temperature. Neutron scattering investigations have been performed down to a helium temperature under different hydrostatic pressures up to 400 MPa. Neutron diffraction (ND) and incoherent inelastic neutron scattering (IINS) spectra clearly show the existence of phase transition in d-camphor, which has not been observed in dl-borneole. The ND spectra point to a possible cubic structure of dl-borneole crystal down to helium temperatures; temperature dependence of the IINS spectra suggests continuous transition from dynamical to static disorder of molecules in this crystal.