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The switching behavior of the novel hybrid material (FA)Na[Fe(CN)5(NO)].H2O (1) in response to temperature (T), light irradiation and electric field (E) is studied using in situ X-ray diffraction (XRD). Crystals of 1 display piezoelectricity, pyroelectricity, second and third harmonic generation. XRD shows that the FA+ are disordered at room-temperature, but stepwise cooling from 273-100â K induces gradual ordering, while cooling under an applied field (E=+40â kVcm-1) induces a sudden phase change at 140â K. Structural-dynamics calculations suggest the field pushes the system into a region of the structural potential-energy surface that is otherwise inaccessible, demonstrating that application of T and E offers an effective route to manipulating the crystal chemistry of these materials. Photocrystallography also reveals photoinduced linkage isomerism, which coexists with but is not correlated to other switching behaviors. These experiments highlight a new approach to in situ studies of hybrid materials, providing insight into the structure-property relationships that underpin their functionality.
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We present a charge density study of two linkage isomer photoswitches, [Pd(Bu4dien)(NO2)]BPh4·THF (1) and [Ni(Et4dien)(NO2)2] (2) using Hirshfeld Atom Refinement (HAR) methods implemented via the NoSpherA2 interface in Olex2. HAR is used to explore the electron density distribution in the photoswitchable molecules of 1 and 2, to gain an in-depth understanding of key bonding features and their influence on the single-crystal-to-single-crystal reaction. HAR analysis is also combined with ab initio calculations to explore the non-covalent interactions that influence physical properties of the photoswitches, such as the stability of the excited state nitrito-(η1-ONO) isomer. This insight can be fed back into the crystal engineering process to develop new and improved photoswitches that can be optimised towards specific applications.
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There is a need to develop rapidly responsive chemical sensors for the detection of low concentrations of volatile organic solvents (VOCs). Platinum pincer complexes have shown promise as sensors because of their colours and vapochromic and solvatochromic properties, that may be related to the non-covalent interactions between the pincer complexes and the guest VOCs. Here we report an investigation into a series of Pt(II) complexes based on the 1,3-di(pyridine)benzene tridentate (NâCâN) skeleton with the formula [Pt(NâC(R)âN)(CN)] (R = C(O)Me 2, C(O)OEt 3, C(O)OPh 4) with the fourth coordination site occupied by a cyanide ligand. Solid-state samples of the complexes have been tested with a range of volatiles including methanol, ethanol, acetone, dichloromethane and water, and while 2 displays thermochromism, 3 and 4 display rapidly reversible vapochromism and solvatochromism. These results are correlated with X-ray powder and single crystal X-ray structural data including an assessment of the crystal packing and the void space in the crystalline space. The cyanide ligand and the R substituents are involved in hydrogen bonding that creates the voids within the structures and interact with the solvent molecules that influence the Ptâ¯Pt separation in the crystalline state.
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The design of solid-state materials whose properties and functions can be manipulated in a controlled manner by the application of light is an important objective in modern materials chemistry. When the material changes property or function, it is helpful if a simple measurable response, such as a change in color, can be detected. Potential applications for such materials are wide ranging, from data storage to smart windows. With the growing emphasis on solid-state materials that have two or more accessible energy states and which exhibit bistability, attention has turned to transition metal complexes that contain ambidentate ligands that can switch between linkage isomeric forms when activated by light. Suitable ligands that show promise in this area include nitrosyls, nitro groups, and coordinated sulfur dioxide molecules, each of which can coordinate to a metal center in more than one bonding mode. A nitrosyl normally coordinates through its N atom (η1-NO) but when photoactivated can undergo isomerism and coordinate through its O atom (η1-ON). At a molecular level, converting between these two configurations can act as an "on/off" switch. The analysis of such materials has been aided by the development of photocrystallographic techniques, which allow the full three-dimensional structure of a single crystal of a complex, under photoactivation, to be determined, when it is in either a metastable or short-lived excited state. The technique effectively brings the dimension of "time" to the crystallographic experiment and brings us closer to being able to watch solid-state processes occur in real time. In this Account, we highlight the advances made in photocrystallography for studying solid-state, photoactivated linkage isomerism and describe the factors that favor the switching process and which allow complete switching between isomers. We demonstrate that control of temperature is key to achieving either a metastable state or an excited state with a specific lifetime. We draw our conclusions from published work on the formation of photoactivated metastable states for nitrosyl and sulfur dioxide complexes and from our own work on photoactivated switching between nitro and nitrito groups. We show that efficient switching between isomers is dependent on the wavelength of light used, on the temperature at which the experiment is carried out, on the flexibility of the crystal lattice, and on both the electronic and steric environment of the ambidentate ligand undergoing isomerism. We have designed and prepared a number of nitro/nitrito isomeric metal complexes that undergo reversible 100% conversion between the two forms at temperatures close to room temperature. Through our fine control over the generation of the metastable states, it should be possible to effectively "dial up" a suitable temperature to give a metastable or an excited state with a desired lifetime.
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The uptake of gaseous iodine into the crystalline sponge material [(ZnI2)3(tpt)2]·0.7triphenylene·0.3PhNO2·0.7C6H12 1 (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) has been monitored by dynamic X-ray diffraction and thermogravimetric analysis. The X-ray analyses have enabled the location, quantity, uptake rate, and subsequent chemistry of the iodine upon inclusion into the pores to be determined. An uptake of 6.0 wt % (0.43 I2 per formula unit) was observed crystallographically over a period of 90 min before crystal degradation occurred. The included iodine molecules interact with the iodine atoms of the ZnI2 nodes at three different sites, forming coordinated I3- ions. The results contrast to recent observations on [(ZnI2)3(tpt)2] without the triphenylene guests which show the presence of I42- ions with low quantities of absorbed iodine.
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We present a detailed kinetic study of photo-induced solid state linkage isomerism in the compound [Pd(Bu4dien)NO2]BPh4 (Bu4dien = N,N,N',N'-tetrabutyldiethylenetriamine) using in situ photocrystallographic techniques. We explore the key variables that influence the photoconversion and develop a detailed kinetic model for the excitation and decay processes and the temperature dependence of the conversion rates. We show that by varying the temperature the lifetime of the excited state can be varied over orders of magnitude, making these systems ideal test cases for the development of new time-resolved X-ray diffraction methods. The kinetic model is used to build a numerical-simulation tool, which we use to explore the practicalities of pump-probe single-crystal diffraction experiments with minute and second time-resolution.
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The formation and chemistry of flavin-indole charge transfer (CT) complexes has been studied using a model cationic flavin. The ability to form a CT complex is sensitive to indole structure as gauged by spectroscopic, kinetics and crystallographic studies. Single crystals of sufficient quality of a flavin-indole CT complex, suitable for X-ray diffraction, have been grown, allowing solid-state structural analysis. When CT complex formation is conducted in d4-methanol, an efficient and synthetically useful C-3 indole deuteration is observed.
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Flavinas/química , Indóis/química , Catálise , Cristalografia por Raios X , Deutério/química , Transporte de Elétrons , FMN Redutase/química , Modelos Moleculares , Streptomyces/enzimologiaRESUMO
The design of ligands that mediate through-bond long range super-exchange in metal-organic hybrid materials would expand chemical space beyond the commonly observed short range, low temperature magnetic ordering. Here we examine acetylene dicarboxylate as a potential ligand that could install long range magnetic ordering due to its spatially continuous frontier orbitals. Using a known Mn(ii)-containing coordination polymer we compute and measure the electronic structure and magnetic ordering. In this case, the latter is weak owing to the sub-optimal ligand coordination geometry, with a critical temperature of 2.5 K.
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At temperatures below 150â K, the photoactivated metastable endo-nitrito linkage isomer [Ni(Et4 dien)(η(2)-O,ON)(η(1)-ONO)] (Et4 dien=N,N,N',N'-tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro-(η(1)-NO2) isomer on irradiation with 500â nm light, in the single crystal by steady-state photocrystallographic techniques. Kinetic studies show the system is no longer metastable above 150â K, decaying back to the ground state nitro-(η(1)-NO2) arrangement over several hours at 150â K. Variable-temperature kinetic measurements in the range of 150-160â K show that the rate of endo-nitrito decay is highly dependent on temperature, and an activation energy of Eact =+48.6(4)â kJ mol(-1) is calculated for the decay process. Pseudo-steady-state experiments, where the crystal is continually pumped by the light source for the duration of the X-ray experiment, show the production of a previously unobserved, exo-nitrito-(η(1)-ONO) linkage isomer only at temperatures close to the metastable limit (ca. 140-190â K). This exo isomer is considered to be a transient excited-state species, as it is only observed in data collected by pseudo-steady-state methods.
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A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Auâ â â Au interactions in a series of pyrazolate-based gold(I) trimers; tris(µ2 -pyrazolato-N,N')-tri-gold(I) (1), tris(µ2 -3,4,5- trimethylpyrazolato-N,N')-tri-gold(I) (2), tris(µ2 -3-methyl-5-phenylpyrazolato-N,N')-tri-gold(I) (3) and tris(µ2 -3,5-diphenylpyrazolato-N,N')-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Auâ â â Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100â K is accompanied by a reduction in the shortest intermolecular Auâ â â Au contacts of between 0.04 and 0.08â Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Auâ â â Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630â cm(-1) per GPa between ambient and 3.80â GPa. The shifts in all the complexes can be correlated with changes in Auâ â â Au distance observed by diffraction.
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Over the last 30 years, the single-crystal photocrystallographic technique has been developed to determine the three-dimensional crystal and molecular structures of metastable species which have been generated in the crystal photochemically. Transition-metal complexes that have been investigated using this methodology include complexes that contain nitrosyl, dinitrogen, sulfur dioxide and nitrite ligands, all of which form new linkage isomers in the solid state when photoactivated by light of the appropriate wavelength. Both steric and electronic factors determine the level of the conversion from the ground-state structure to the metastable isomeric structure, and both the `reaction cavity' size and the nature of the intermolecular interactions are shown to be among the key factors that influence the percentage conversion.
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The visualization of chemical processes that occur in the solid-state is key to the design of new functional materials. One of the challenges in these studies is to monitor the processes across a range of timescales in real-time. Here, we present a pump-multiprobe single-crystal X-ray diffraction (SCXRD) technique for studying photoexcited solid-state species with millisecond-to-minute lifetimes. We excite using pulsed LEDs and synchronise to a gated X-ray detector to collect 3D structures with sub-second time resolution while maximising photo-conversion and minimising beam damage. Our implementation provides complete control of the pump-multiprobe sequencing and can access a range of timescales using the same setup. Using LEDs allows variation of the intensity and pulse width and ensures uniform illumination of the crystal, spreading the energy load in time and space. We demonstrate our method by studying the variable-temperature kinetics of photo-activated linkage isomerism in [Pd(Bu4dien)(NO2)][BPh4] single-crystals. We further show that our method extends to following indicative Bragg reflections with a continuous readout Timepix3 detector chip. Our approach is applicable to a range of physical and biological processes that occur on millisecond and slower timescales, which cannot be studied using existing techniques.
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A simple yet efficient instrument-model refinement method for X-ray diffraction data is presented and discussed. The method is based on least-squares minimization of differences between respective normalized (i.e. unit length) reciprocal vectors computed for adjacent frames. The approach was primarily designed to work with synchrotron X-ray Laue diffraction data collected for small-molecule single-crystal samples. The method has been shown to work well on both simulated and experimental data. Tests performed on simulated data sets for small-molecule and protein crystals confirmed the validity of the proposed instrument-model refinement approach. Finally, examination of data sets collected at both BioCARS 14-ID-B (Advanced Photon Source) and ID09 (European Synchrotron Radiation Facility) beamlines indicated that the approach is capable of retrieving goniometer parameters (e.g. detector distance or primary X-ray beam centre) reliably, even when their initial estimates are rather inaccurate.
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An analysis of the important intermolecular interactions of the active pharmaceutical ingredient lovastatin which contribute to the surface chemistry and attachment energy morphology is presented. The analysis is supported by a recent redetermination of the single-crystal structure (orthorhombic space group P212121) and targets the understanding and potential control of the morphology of lovastatin, which tends to crystallize in a needle-like morphology, where the aspect ratio varies depending on the nature of the solvent. The lattice energy was calculated to be -38.79 kcal mol-1 with a small contribution of -2.73 kcal mol-1 from electrostatic interactions. The lattice structure is significantly stabilized by the hexahydronaphthalene ring of the molecule, which contributes 43.39% of the lattice energy. Synthon analysis shows that the dominant intermolecular interaction within the lattice structure of lovastatin is found to be along the a crystallographic axis, associated with a dispersive stacking interaction due to the close packing of 2 hexahydronaphthalene rings resulting in a total interaction energy of -6.46 kcal mol-1. The attachment energy morphology correlates well with the observed crystal morphology which exhibits a needle-like habit dominated by {0 1 1}, {0 2 0}, {0 0 2}, and {1 0 1} crystal forms. The needle capping faces are found to contain the short stacks of hexahydronaphthalene rings where the strong intermolecular synthon is found to contribute positively to the attachment energy and hence growth at this surface. This dominant intermolecular synthon is concluded to be the major cause of enhanced growth along the crystallographic a axis leading to the formation of a needle-like morphology. A habit modification strategy is discussed which uses recrystallization from apolar solvents to reduce the effective growth rate at the needle-capping surfaces. This is supported through experimental data which shows that crystals obtained from crystallization in hexane and methyl-cyclohexane have significantly reduced aspect ratios in comparison to those grown from the more polar methanol and ethyl acetate solutions. Crystals obtained from nitromethane solutions were also found to have a very large reduction in aspect ratio to a prismatic morphology reflecting this solvent's propensity to interact with hydrophobic surfaces, critically with no polymorph change.
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Lovastatina/química , Preparações Farmacêuticas/química , Solventes/química , Acetatos/química , Cristalografia/métodos , Hexanos/química , Interações Hidrofóbicas e Hidrofílicas , Metanol/química , Soluções/química , Eletricidade EstáticaRESUMO
We report a molecular crystal that exhibits four successive phase transitions under hydro-static pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(µ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5â GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1â GPa, followed by a P21/a phase above 2â GPa and a large-volume C2/c supercell at 2.70â GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040â cm-1 at 2.40â GPa, decreasing steeply to 13550â cm-1 at 3â GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.
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As the spatial and temporal resolution accessible to experiment and theory converge, computational chemistry is an increasingly powerful tool for modelling and interpreting spectroscopic data. However, the study of molecular processes, in particular those related to electronic excitations (e.g. photochemistry), frequently pushes quantum-chemical techniques to their limit. The disparity in the level of theory accessible to periodic and molecular calculations presents a significant challenge when modelling molecular crystals, since accurate calculations require a high level of theory to describe the molecular species, but must also take into account the influence of the crystalline environment on their properties. In this article, we briefly review the different classes of quantum-chemical techniques, and present an overview of methods that account for environmental influences with varying levels of approximation. Using a combination of solid-state and molecular calculations, we quantitatively evaluate the performance of implicit-solvent models for the [Ni(Et4dien)(η2-O,ON)(η1-NO2)] linkage-isomer system as a test case. We focus particularly on the accurate reproduction of the energetics of the isomerisation, and on predicting spectroscopic properties to compare with experimental results. This work illustrates how the synergy between periodic and molecular calculations can be exploited for the study of molecular crystals, and forms a basis for the investigation of more challenging phenomena, such as excited-state dynamics, and for further methodological developments.