Natalia Górska

Bistable Multifunctionality and Switchable Strong Ferromagnetic-to-Antiferromagnetic Coupling in a One-Dimensional Rhodium(I)–Semiquinonato Complex

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV-vis-NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium(I)-semiquinonato complex, [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3), where 3,6-DBSQ-4,5-(MeO)2(•-) represents 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound 3 comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh-Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228-207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C-H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound 3 exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature T(N) of 14.2 K. The electrical conductivity of 3 at 300 K is 4.8 × 10(-4) S cm(-1), which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation.

Phase transition and molecular motions in [Co(NH3)6](ClO4)3 studied by differential scanning calorimetry and infrared spectroscopy

Abstract The phase transition in [Co(NH 3 ) 6 ](ClO 4 ) 3 at T c h =103.25 K (on heating) and at T c c =102.68 K (on cooling) was determined by differential scanning calorimetry. Fourier transform far infrared and middle infrared spectra were measured in the temperature range of 25–295 K. The spectra did not show significant changes at the phase transition temperature. However, there were some characteristic changes in the temperature dependence of the full width at half maximum of the ρ r (NH 3 )F 1u mode. It suggests that the discovered phase transition is connected with a sudden change of the orientational dynamics of the NH 3 groups.

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.

Phase Polymorphism, Molecular Motions and Structural Changes in [Cr(NH3)6](ClO4)3

A phase transition in [Cr(NH3)6](ClO4)3 at Thc = 293.5 K (on heating) and Tcc = 293.0 K (on cooling) was determined by differential scanning calorimetry. The temperature dependences of the full width at half maximum of the bands connected with ρr(NH3)F1u and δd(ClO)E modes suggest that the discovered phase transition is not connected with drastic changes in the speed of reorientational motions of the NH3 ligands nor the ClO4 − anions. Temperature dependence of the FT-FIR spectra and the diffraction patterns show that the discovered phase transition is caused by a change in the crystal structure.

A comprehensive study on crystal structure, thermal behavior, and molecular dynamics of [Sr(DMSO)4(NO3)2]

Three solid–solid phase transitions have been detected for [Sr(OS(CH3)2)4(NO3)2] at T = 229.3 K, T = 220.3 K, and T = 171.6 K (on heating) and at T = 226.6 K, T = 219.1 K, and T = 170.9 K (on cooling). The compound melts at Tm ≈ 347 K. Thermal behavior of the deuterated analog is essentially the same, but the phase transitions’ temperatures are shifted slightly towards higher temperature, by ca. 5, 5, and 15 K, respectively. Crystal structure in the lowest temperature of phase III at 93 K consists of completely ordered (CH3)2SO molecules and bidentate nitrate groups, which are coordinated to strontium cation. Infrared (IR) spectra reveal that the phase transition at T is associated with the slowing down of the reorientational motions of (CH3)2SO and NO3– groups and also with the lowering of crystal lattice symmetry of the compound. The extended solid-state vibrational analysis has been performed for both deuterated and protonated species by solid-state density functional theory computations and compared with IR and RS experimental spectra. Thermal decomposition occurs in two stages: in the first stage, in four steps, four (CH3)2SO molecules are liberated and Sr(NO3)2 is formed, and in the second stage, above ca. 800 K, SrO is formed. Graphical Abstract

Surface and liquid-crystalline properties of FmHnFm triblock semifluorinated n-alkanes.

A series of triblock semifluorinated n-alkanes of the general formula: F(CF2)m(CH2)n(CF2)mF, (in short FmHnFm), where m=10, 12, and n=6, 8, and 12 have been synthesized and employed for liquid crystalline studies and Langmuir monolayer characterization. Differential scanning calorimetry (DSC) measurements together with texture observation with polarizing microscope (POM) revealed the presence of liquid crystalline smectic phases for all the investigated homologs. The behavior of the studied molecules spread at the free water surface has also been investigated. Our results show for the first time that these unusual film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are surface active and form insoluble (Langmuir) monolayers at the air/water interface. Due to the fact that these molecules are chemically inert and, similar to the semifluorinated diblocks, are not toxic, they may be destined for biomedical uses as gas carriers and contrast agents, as well as in drug delivery systems.

Structural and calorimetric investigations of a highly disordered crystal [Co(NH3)6](BF4)3

Five crystalline phases of [Co(NH3)6](BF4)3 were identified by adiabatic calorimetry. Two phase transitions at T C1(II → I) = 271.7 K and T C2(III → II) = 152.2 K are accompanied by large entropy changes (8.4 and 6.5 J K1 mol1, respectively), whereas two additional transitions at T C3(IV → III) = 67.4 K and T C4(V → IV) = 48.9 K are accompanied by small entropy changes (0.31 and 0.15 J K−1 mol−1, respectively). X-ray single-crystal diffraction at 293 K demonstrates that phase I is cubic (Z = 4) and that two types of anions exist with different types of orientational disorder. In phase II, at 200 K, which is also a cubic system (Z = 32), five anions (out of 12) become ordered, and three cations (out of four) are deformed to give a lower symmetry. This is attributed to the orientational ordering of the anions triggered by NH F hydrogen-bonding interactions. Further ordering of the anions and the symmetry reduction of the crystal occurred at T C2, but the structure of phase III still remained cubic. The energies required to reorient an ordered anion in the crystal lattice of phases II and III were estimated from the excess heat capacity, demonstrating that the NH F hydrogen-bonding interactions in this compound are considerably weaker than the NH O interactions in an isostructural compound, [Co(NH3)6](ClO4)3.

Study of TiO2 in anatase form on selected properties of new aliphatic-aromatic imines with bent shape towards organic electronics

ABSTRACT Two bent-shaped imines (9E)-N-(3-((E)-(4-hexadecylphenylimino)methyl)benzylidene)-4-hexadecylbenzenamine (SL1) and (10E)-N-(3-((E)-(4-(perfluorooctyl)phenylimino)methyl)benzylidene)-4-(perfluorooctyl)benzenamine (SL2) were prepared by condensation reaction in N,N-dimethylacetamide to study their thermal, structural and electrochemical properties, as well as their mixtures with titanium dioxide. Chemical structure, temperature and TiO2 influences on the phase transition temperatures, enthalpy, texture and molecular dynamics of both imines were investigated by differential scanning calorimetry, polarising optical microscopy and Fourier transform middle-infrared absorption spectroscopy during heating and cooling. Changes in the surface morphology of the imines and their mixtures with TiO2 were registered by atomic force microscopy. X-ray study showed the tendency to form lamellas in the case of SL2 as an effect of the presence of two terminal perfluorinated alkyl chains connected to a polar mobile aromatic core, which resulted in microsegregation. Additionally, TiO2 influences the energy gap and HOMO–LUMO levels of imines as was detected by cyclic voltammetry. Finally, devices with two types of architectures, such as ITO/TiO2/SL1(or P3HT)/Au and ITO/TiO2/SL1:P3HT/Au were constructed and investigated under irradiation intensity of 97.7 mW/cm2. GRAPHICAL ABSTRACT

Vibration-reorientation dynamics, structural changes and its interrelation with the phase transition in polycrystalline [Cr(OC(NH₂)₂)₆](BF₄)₃.

Polycrystalline hexakis(urea-O)chromium(III) tetrafluoroborate possesses in the temperature range of 295-105 K one solid-solid phase transition at T(C) ≈ 255 K. Analysis of the band shapes associated with the ν(as)(CN) and δ(as)(NH2) vibrational modes of the Fourier transform infrared absorption (FT-IR) spectra, registered in the temperature range of 295-10 K, indicated existence of fast (τ(R) ≈ 10(-12) s) reorientational motion of the protons from NH2 groups belonging to OC(NH2)2 (urea) ligands, which does not suddenly change at T(C). Moreover, splitting of the IR bands associated with the ν(as)(NH), ν(s)(NH) and ν(as)(BF)F2/ν(s)(CN) modes at T(C) indicated that this phase transition is associated with a change of crystal structure. Similar analysis of the Raman scattering bands (FT-RS), associated with the δ(s)(FBF)E, ν(s)(BF)A and ν(as)(BF)F2/ν(s)(CN) vibrational modes, indicated fast reorientation of the BF4(−) ions, which does not suddenly change at T(C), and additionally confirmed structural character of this phase transition. Results obtained from vibrational spectroscopy measurements are compatible with that obtained by electron paramagnetic resonance spectroscopy (EPR) measurements in function of temperature, where rapid narrowing of the EPR line in the vicinity of the T(C) was observed.

Thermal, structural and electrochemical properties of new aliphatic-aromatic imine with piperazine moieties blended with titanium dioxide

ABSTRACT A new piperazine imine, (7E)-N-((4-((E)-(4-hexadecylphenylimino)methyl)piperazin-1-yl)methylene)-4-dodecylbenzenamine, has been synthesized by the condensation of 1,4-piperazinedicarboxaldehyde with 4-hexadecylaniline. The imine was characterized by cyclic voltammetry, Fourier transform middle-infrared absorption spectroscopy and X-ray diffraction. Thermal properties of imine was analyzed by differential scanning calorimetry method during first and second heating scan at 10 and 20 °C/min. Texture of imine was investigated by polarized optical microscopy and atomic force microscopy. Furthermore, imine was blended with titanium dioxide in anatase form and fully characterized by the same methods. Piperazine imine and its mixture with titanium dioxide exhibited only a transition from crystal to isotropic state. Imine exhibits two-step reduction wave attributed to one-electron transfer in each step as was found by cyclic voltammetry. Both titanium dioxide and poly(3-hexylthiophene) change the electrochemical properties of piperazine imine, however, in different ways. Studied imine blended with titanium dioxide exhibited higher value of energy band gap than pure piperazine imine and lower Eg than pure poly(3-hexylthiophene).