Terahertz Vibrational Dynamics and DFT Calculations for the Quantum Spin Chain Linarite, PbCuSO4(OH)2.

The low-dimensional quantum-magnet, linarite, PbCuS4(OH)2, has been investigated using terahertz (THz) spectroscopy coupled with detailed density functional theory (DFT) calculations in order to explore the effects of the temperature on its lattice vibrations. Linarite is characterized by largely isolated CuO chains propagating along the crystallographic b-axis, which at very low temperatures are responsible for exotic, quasi-1D magnetism in this material. To better understand the synergy between the structural bonds and lattice oscillations that contribute to these chains, polarized THz spectroscopic measurements were performed. Consolidating these results with detailed DFT calculations has revealed that the anisotropic vibrational motion for the THz modes is correlated with extreme motion associated with the crystallographic b-axis. An unexpected feature observed in the infrared spectrum is attributed to subtle lattice distortions which break the centro-symmetry in linarite at high temperatures. This phenomenon has not previously been observed in linarite and likely results from anharmonicity in lattice oscillations.

Effective Suppressing Phase Segregation of Mixed-Halide Perovskite by Glassy Metal-Organic Frameworks.

Lead mixed-halide perovskites offer tunable bandgaps for optoelectronic applications, but illumination-induced phase segregation can quickly lead to changes in their crystal structure, bandgaps, and optoelectronic properties, especially for the Br-I mixed system because CsPbI3 tends to form a non-perovskite phase under ambient conditions. These behaviors can impact their performance in practical applications. By embedding such mixed-halide perovskites in a glassy metal-organic framework, a family of stable nanocomposites with tunable emission is created. Combining cathodoluminescence with elemental mapping under a transmission electron microscope, this research identifies a direct relationship between the halide composition and emission energy at the nanoscale. The composite effectively inhibits halide ion migration, and consequently, phase segregation even under high-energy illumination. The detailed mechanism, studied using a combination of spectroscopic characterizations and theoretical modeling, shows that the interfacial binding, instead of the nanoconfinement effect, is the main contributor to the inhibition of phase segregation. These findings pave the way to suppress the phase segregation in mixed-halide perovskites toward stable and high-performance optoelectronics.

Translocation and fate of nanospheres in pheochromocytoma cells following exposure to synchrotron-sourced terahertz radiation.

The routes by which foreign objects enter cells is well studied; however, their fate following uptake has not been explored extensively. Following exposure to synchrotron-sourced (SS) terahertz (THz) radiation, reversible membrane permeability has been demonstrated in eukaryotic cells by the uptake of nanospheres; nonetheless, cellular localization of the nanospheres remained unclear. This study utilized silica core-shell gold nanospheres (AuSi NS) of diameter 50 ± 5 nm to investigate the fate of nanospheres inside pheochromocytoma (PC 12) cells following SS THz exposure. Fluorescence microscopy was used to confirm nanosphere internalization following 10 min of SS THz exposure in the range 0.5-20 THz. Transmission electron microscopy followed by scanning transmission electron microscopy energy-dispersive spectroscopic (STEM-EDS) analysis was used to confirm the presence of AuSi NS in the cytoplasm or membrane, as single NS or in clusters (22% and 52%, respectively), with the remainder (26%) sequestered in vacuoles. Cellular uptake of NS in response to SS THz radiation could have suitable applications in a vast number of biomedical applications, regenerative medicine, vaccines, cancer therapy, gene and drug delivery.

Water Sorption Controls Extreme Single-Crystal-to-Single-Crystal Molecular Reorganization in Hydrogen Bonded Organic Frameworks.

As hydrogen bonded frameworks are held together by relatively weak interactions, they often form several different frameworks under slightly different synthesis conditions and respond dynamically to stimuli such as heat and vacuum. However, these dynamic restructuring processes are often poorly understood. In this work, three isoreticular hydrogen bonded organic frameworks assembled through charge-assisted amidinium⋅⋅⋅carboxylate hydrogen bonds (1C/C , 1Si/C and 1Si/Si ) are studied. Three distinct phases for 1C/C and four for 1Si/C and 1Si/Si are fully structurally characterized. The transitions between these phases involve extreme yet recoverable molecular-level framework reorganization. It is demonstrated that these transformations are related to water content and can be controlled by humidity, and that the non-porous anhydrous phase of 1C/C shows reversible water sorption through single crystal to crystal restructuring. This mechanistic insight opens the way for the future use of the inherent dynamism present in hydrogen bonded frameworks.

Monitoring the chemical changes in fingermark residue over time using synchrotron infrared spectroscopy.

Degradation of fingermark residue has a major impact on the successful forensic detection of latent fingermarks. The time course of degradation has been previously explored with bulk chemical analyses, but little is known about chemical alterations within specific regions of the fingermark, which is difficult to study with bulk measurement. Here we report the use of synchrotron-sourced attenuated total reflection-Fourier transform infrared (ATR-FTIR) microspectroscopy to provide spatio-temporal resolution of chemical changes within fingermark droplets, as a function of time since deposition, under ambient temperature conditions. Eccrine and sebaceous material within natural fingermark droplets were imaged on the micron scales at hourly intervals from the time of deposition until the first 7-13 hours after deposition, revealing that substantial dehydration occurred within the first 8 hours. Changes to lipid material were more varied, with samples exhibiting an increase or decrease in lipid concentration due to the degradation and redistribution of this material. Across 12 donors, it was noticeable that the initial chemical composition and morphology of the droplet varied greatly, which appeared to influence the rate of change of the droplet over time. Further, this study attempted to quantify the total water content within fingermark samples. The wide-spread nature and strength of the absorption of Terahertz/Far-infrared (THz/Far-IR) radiation by water vapour molecules were exploited for this purpose, using THz/Far-IR gas-phase spectroscopy. Upon heating, water confined in natural fingermarks was evaporated and expanded in a vacuum chamber equipped with multipass optics. The amount of water vapour was then quantified by high-spectral resolution analysis, and fingermarks were observed to lose approximately 14-20 µg of water. The combination of both ATR-FTIR and Far-IR gas-phase techniques highlight important implications for experimental design in fingermark research, and operational practices used by law enforcement agencies.

Vibrational mode analysis of hydrogen-bonded organic frameworks (HOFs): synchrotron infrared studies.

Hydrogen-bonded organic frameworks (HOFs) are a promising class of porous crystalline materials for gas sorption and gas separation technologies that can be constructed under mild synthetic conditions. In forming three-dimensional networks of flexible hydrogen bonds between donor/acceptor subunits, these materials have displayed high stability at elevated temperature and under vacuum. Although the structural properties of HOFs are commonly characterized by diffraction techniques, new complimentary methods to elucidate phase behaviour and host-guest interactions at the molecular level are sought, particularly those that can be applied under changing physical conditions or solvent environment. To this end, this study has applied synchrotron far-IR and mid-IR spectroscopy to probe the properties of two known and one new HOF system assembled from tetrahedral amidinium and carboxylate building blocks. All three frameworks produce feature-rich and resolved infrared profiles from 30 to 4000 cm-1 that provide information on hydrogen-bonded water solvent networks and the HOF channel topography via lattice and torsional bands. Comparison of experimental peaks to frequencies and atomic displacements (eigenvectors) predicted by high-level periodic DFT calculations have allowed for the assignment of vibrational modes associated with the aforementioned physicochemical properties. Now compiled, the specific vibrational modes identified as common to charge-assisted hydrogen-bonding motifs, as well as low frequency lattice and torsional bands attributed to HOF pore morphology and water-of-hydration networks, can act as diagnostic features in future spectroscopic investigations of HOF properties, such as those toward the design and tuning of host-guest properties for targeted applications.

Tissue Characterization Using Synchrotron Radiation at 0.7 THz to 10.0 THz with Extended ATR Apparatus Techniques.

The attenuated total reflection (ATR) apparatus, with an added partial reflection/partial transmission mode, was used to demonstrate a novel way of characterizing water-based substances at 0.7 to 10.0 THz at the Australian Synchrotron THz-far infrared beamline. The technique utilized a diamond-crystal-equipped ATR to track temperature-dependent changes in reflectance. A "crossover flare" feature in the spectral scan was noted, which appeared to be a characteristic of water and water-dominated compounds. A "quiet zone" feature was also seen, where no temperature-dependent variation in reflectance exists. The variation in these spectral features can be used as a signature for the presence of bound and bulk water. The method can also potentially identify the presence of fats and oils in a biological specimen. The technique requires minimal sample preparation and is non-destructive. The presented method has the promise to provide a novel, real-time, low-preparation, analytical method for investigating biological material, which offers avenues for rapid medical diagnosis and industrial analysis.

Mechanochemically Synthesised Flexible Electrodes Based on Bimetallic Metal-Organic Framework Glasses for the Oxygen Evolution Reaction.

The melting behaviour of metal-organic frameworks (MOFs) has aroused significant research interest in the areas of materials science, condensed matter physics and chemical engineering. This work first introduces a novel method to fabricate a bimetallic MOF glass, through melt-quenching of the cobalt-based zeolitic imidazolate framework (ZIF) [ZIF-62(Co)] with an adsorbed ferric coordination complex. The high-temperature chemically reactive ZIF-62(Co) liquid facilitates the formation of coordinative bonds between Fe and imidazolate ligands, incorporating Fe nodes into the framework after quenching. The resultant Co-Fe bimetallic MOF glass therefore shows a significantly enhanced oxygen evolution reaction performance. The novel bimetallic MOF glass, when combined with the facile and scalable mechanochemical synthesis technique for both discrete powders and surface coatings on flexible substrates, enables significant opportunities for catalytic device assembly.

THz/Far infrared synchrotron observations of superlattice frequencies in MgB2.

THz/Far Infrared synchrotron absorption experiments on pure and doped MgB2 samples show that the absorption spectral weight at low wavenumber (i.e., <110 cm-1) evolves as the temperature is reduced to 10 K. Distinct spectral peak intensities increase as the temperature of MgB2 and doped MgB2 approaches, and then crosses, the superconducting transition temperature. These experimental data suggest a strong link to superconductivity induced by subtle shifts in structural symmetry. Significant increases in absorption are observed at frequencies that correspond to the superconducting gaps for doped and pure MgB2, and at fractions of these frequency (or energy) values. This low wavenumber spectral transition is consistent with the notion that superlattice frequencies contribute to the optic modes of the MgB2 phonon dispersion and are critical to the superconducting transition for this structure. Key integer ratios are identified in real and reciprocal spaces that link bonding character, Fermi vectors and Fermi surfaces as well as phonon properties with geometric parameters and specific superlattice symmetries for MgB2. Similarly consistent spectral data at low wavenumber are also obtained for carbon doped Mg11B2. Density Functional Theory calculations of superlattice phonon dispersions result in folded mode frequencies that match these observed low wavenumber experiments. These results show that symmetry reductions, largely electronic in character although coupled to vibrations, occur with change in temperature and imply strong links to superconductivity mechanisms.

Torsion-vibration interactions determined from (far) infrared spectra.

Observations of the torsional and low-lying vibrational-torsional states of toluene, p-fluorotoluene, and m-fluorotoluene using the technique of two dimensional laser induced fluorescence (2D-LIF) have revealed interactions between the methyl torsion and low frequency out-of-plane methyl wagging vibration. These interactions can change the values of constants extracted from the analysis of rotational spectra, which usually assume that the large amplitude torsional motion can be treated independent of the small amplitude vibrations. Since out-of-plane methyl wagging modes will be present whenever a methyl group is attached to a planar frame, this type of torsion-vibration interaction is potentially widespread; it is thus important to establish the extent and strength of this type of interaction. 2D-LIF is limited to molecules that fluoresce from excited electronic states, and to explore interactions between torsion and methyl wagging vibrations in a wide range of molecules necessitates developing alternative experimental approaches. Infrared absorption spectroscopy is one such approach. It is shown that for the low torsional barrier case, the torsional sequence bands accompanying the out-of-plane methyl wagging transition provide a sensitive probe of the interaction. As an illustration, the far infrared absorption spectrum of toluene in the region of the M20 band (∼205 cm-1) is presented and analyzed. The torsional sequence structure provides insight into the higher torsional states (up to m = 7) in the ground vibrational state and M20. An analysis of these bands enables the torsion-vibration coupling and torsional constants to be extracted. A general method to analyze such spectra is presented.

Halogenated Metal-Organic Framework Glasses and Liquids.

The synthesis of four novel crystalline zeolitic imidazolate framework (ZIF) structures using a mixed-ligand approach is reported. The inclusion of both imidazolate and halogenated benzimidazolate-derived linkers leads to glass-forming behavior by all four structures. Melting temperatures are observed to depend on both electronic and steric effects. Solid-state NMR and terahertz (THz)/far-IR demonstrate the presence of a Zn-F bond for fluorinated ZIF glasses. In situ THz/far-IR spectroscopic techniques reveal the dynamic structural properties of crystal, glass, and liquid phases of the halogenated ZIFs, linking the melting behavior of ZIFs to the propensity of the ZnN4 tetrahedra to undergo thermally induced deformation. The inclusion of halogenated ligands within metal-organic framework (MOF) glasses improves their gas-uptake properties.

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene.

Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D5h ) and staggered (D5d ) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7-300 K), and solid (7-300 K) states. In each case the D5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol-1 ) than for the gas-phase species (1-3 kJ mol-1 ). The generality of the approach is demonstrated with application to tricarbonyl(η4 -norbornadiene)iron(0), Fe(NBD)(CO)3 . The temperature-dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)3 is well explained by the RCM without recourse to NMR-like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature-dependence of their vibrational spectra.

Comprehensive Vibrational Spectroscopic Investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) Diazido Anticancer Prodrug Candidate.

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules.

Heavy snow: IR spectroscopy of isotope mixed crystalline water ice.

Mid-infrared spectra have been measured for crystalline water ice aerosols of widely varied H/D isotopic composition. Particles with diameters ranging from 10-200 nm were generated via rapid collisional cooling with a cold buffer gas over a range of temperatures from 7-200 K. In near isotopically pure ices, the νL band position is slightly red-shifted with increasing temperature whilst in the ν2 region apparently anomalous shifts in peak maxima are explained by the contribution of a broad 2νL band of H2O and a 3νL band of D2O together with ν2 intensity that is particularly weak in low temperature crystalline ice. The hydrogen bonded OH (or OD) oscillator bands of near pure H2O (or D2O) ices are blue-shifted with temperature, with a gradient very similar to that of the corresponding band in isotope diluted samples, HOD in D2O (or H2O). It implies that this observed temperature trend is predominantly due to the intrinsic change in local hydride stretch potential energy, rather than to changes in intermolecular coupling. However, it is also observed that the narrow hydride stretch bands of an isotope diluted sample rapidly develop sub-band structure as the oscillator concentration increases, evidence of strong intermolecular coupling and a high degree of delocalisation. Anomalous blue-shifts in the OD stretch profile as D2O concentration grows is attributable to Fermi resonance with 2ν2 of D2O, in much closer proximity than the corresponding H2O levels. Theoretical results from a mixed quantum/classical approach are used to validate these findings in the hydride stretching region. Theory qualitatively reproduces the experimental trends as a function of temperature and isotopic variance.

Double-layered nitrocellulose membrane sample holding technique for THz and FIR spectroscopic measurements.

In terahertz (THz) and far-infrared (FIR) spectroscopic measurements, weak absorption spectral features due to small quantities of test sample can be masked by undesirable etalon fringe artifacts caused by multiple reflections within a pellet or a rigid sample holder. A double-layered nitrocellulose (NC) membrane structure is proposed in this paper as an alternative holder for small quantities of either dry or wet pure (no added polyethylene powder) samples with significantly reduced etalon artifacts. Utilizing a THz time-domain spectroscopy system and a synchrotron source, we demonstrate the performance of the NC structure across the THz/FIR spectrum, benchmarking against pellets holding similarly small quantities of α-lactose powder either with or without different grades of polyethylene powder. With only pure samples to consider, scattering can be mitigated effectively in NC-derived spectra to reduce their baselines.

The limits of rovibrational analysis: the severely entangled ν1 Polyad vibration of dichlorodifluoromethane in the greenhouse IR window.

Five intense bands of dichlorodifluoromethane (CFC-12, or R12) in the infrared atmospheric window help make it a major greenhouse contributor. These include the ν1 fundamental at 1101.4 cm(-1) and the ν2 + ν3 combination at 1128.6 cm(-1). High-resolution spectra measured using the Australian Synchrotron Far-Infrared beamline were analyzed, and transitions of C(35)Cl2F2 were assigned to ν1, ν2 + ν3, and the ν3 + 2ν5 combination at 1099.7 cm(-1). The (v3 = 1; v5 = 2) state couples indirectly to v1 = 1 via Fermi resonances linking both states with v2 = v3 = 1. The v1 = 1 rotational levels are further riddled with perturbations and avoided crossings due to Coriolis resonance with the upper vibrational states of ν2 + ν9 at 1102.4 cm(-1) and (indirectly) ν2 + ν7 at 1105.8 cm(-1). A global treatment of all these states fits the observed line positions and satisfactorily accounts for the significant intensity of ν2 + ν3. Spectral simulations elucidate resonance perturbations that affect the distribution of IR absorption in the CF stretch region, and consequently the global warming potential of R12. Combination levels derived from rovibrational analysis lead to reassessment of the gas phase wavenumber values for the ν3 (458.6 cm(-1)), ν7 (437.7 cm(-1)) and ν9 (436.9 cm(-1)) fundamentals of C(35)Cl2F2, consistent with a cold, vapor phase far IR spectrum and previously published solid state spectra. B3LYP and MP2 anharmonic frequency calculations provide further support. At the MP2/aug-cc-pVTZ level, the root mean square (r.m.s.) error for unscaled anharmonic fundamentals is 6.2 cm(-1), decreased to 1.7 cm(-1) if only considering the seven lowest wavenumber modes, and integrated band intensities according with experimental literature values. Smaller basis sets produce band strengths that are too high. Low-resolution band assignments are reported for C(35)Cl(37)ClF2, C(37)Cl2F2, and (13)C(35)Cl2F2.

Vibrational anharmonicities and reactivity of tetrafluoroethylene.

Compared to ethylene and its nonfluorinated derivatives, C(2)F(4) is peculiar in many reactions. It very easily adds to radicals and prefers formation of four-membered rings over Diels-Alder reactions. This has been rationalized by the preference of fluorine for carbon sp(3) hybridization, which is possible on opening of the double bond. Another property, the thermal dissociation of the C ═ C bond, has been explained by the stabilization of the product (CF(2)) by back-bonding. Here, it is attempted to correlate such properties with vibrational constants, in particular for C ═ C stretching and twisting and for carbon pyramidalization. The only force constant found to be lowered compared to ethylene is that for trans pyramidalization (ν(8)), and CC bond softening on ν(8) distortion is indicated by the conspicuously large magnitude of anharmonic constant, x(18). Both observations can be rationalized by a valence-bond model that predicts a trans bent structure on weakening the CC bond. Conclusions are drawn about the dissociation path and peculiarities of the potential. Other anharmonicities, both experimental and calculated and some in (12)C(13)CF(4) and (13)C(2)F(4), are also discussed. In particular some strong Fermi resonances are identified and their effects accounted for.

IR Band profiling of dichlorodifluoromethane in the greenhouse window: high-resolution FTIR spectroscopy of ν2 and ν8.

The IR spectrum of dichlorodifluoromethane (i.e., R12 or Freon-12) is central to its role as a major greenhouse contributor. In this study, high-resolution (0.000 96 cm(-1)) Fourier transform infrared spectra have been measured for R12 samples either cooled to around 150 K or at ambient temperature using facilities on the infrared beamline of the Australian Synchrotron. Over 14,000 lines of C(35)Cl2F2 and C(35)Cl(37)ClF2 were assigned to the b-type ν2 band centered around 668 cm(-1). For the c-type ν8 band at 1161 cm(-1), over 10,000 lines were assigned to the two isotopologues. Rovibrational fits resulted in upper state constants for all these band systems. Localized avoided crossings in the ν8 system of C(35)Cl2F2, resulting from both a direct b-axis Coriolis interaction with ν3 + ν4 + ν7 and an indirect interaction with ν3 + ν4 + ν9, were treated. An improved set of ground state constants for C(35)Cl(37)ClF2 was obtained by a combined fit of IR ground state combination differences and previously published millimeter wave lines. Together these new sets of constants allow for accurate prediction of these bands and direct comparison with satellite data to enable accurate quantification.

Water ice nanoparticles: size and temperature effects on the mid-infrared spectrum.

Mid-infrared spectra have been measured for cubic ice (I(c)) nanoparticles (3-150 nm diameter) formed by rapid collisional cooling over a wide range of temperatures (5-209 K). Spectral diagnostics, such as the ratio of surface related dangling OH to interior H-bonded OH stretch bands, reveal the manner in which particle size depends on bath gas temperature and density, and on water molecule concentration. For particles smaller than 5 nm strained intermolecular bonds on the surface and subsurface cause the predominant OH stretch peak position to be dramatically blue shifted by up to 40 cm(-1). In the size regime of 8-200 nm the position of the OH stretch absorption band maximum is relatively unaffected by particle size and it is possible to measure the temperature dependence of the peak location without influences from the surface or scattering. The band maximum shifts in a linear fashion from 3218 cm(-1) at 30 K to 3253 cm(-1) at 209 K, which may assist with temperature profiling of ice particles in atmospheric clouds and extraterrestrial systems. Over the same temperature range the librational mode band shifts very little, from 870 to 860 cm(-1). In the water stretching and bending regions discrete spectral features associated with the surface or sub-surface layers have been detected in particles as large as 80 nm.

Stabilizing copper sites in coordination polymers toward efficient electrochemical C-C coupling.

Electroreduction of carbon dioxide with renewable electricity holds promise for achieving net-zero carbon emissions. Single-site catalysts have been reported to catalyze carbon-carbon (C-C) coupling-the indispensable step for more valuable multi-carbon (C2+) products-but were proven to be transformed in situ to metallic agglomerations under working conditions. Here, we report a stable single-site copper coordination polymer (Cu(OH)BTA) with periodic neighboring coppers and it exhibits 1.5 times increase of C2H4 selectivity compared to its metallic counterpart at 500 mA cm-2. In-situ/operando X-ray absorption, Raman, and infrared spectroscopies reveal that the catalyst remains structurally stable and does not undergo a dynamic transformation during reaction. Electrochemical and kinetic isotope effect analyses together with computational calculations show that neighboring Cu in the polymer provides suitably-distanced dual sites that enable the energetically favorable formation of an *OCCHO intermediate post a rate-determining step of CO hydrogenation. Accommodation of this intermediate imposes little changes of conformational energy to the catalyst structure during the C-C coupling. We stably operate full-device CO2 electrolysis at an industry-relevant current of one ampere for 67 h in a membrane electrode assembly. The coordination polymers provide a perspective on designing molecularly stable, single-site catalysts for electrochemical CO2 conversion.