Exploring Pyroelectricity, Thermal and Photochemical Switching in a Hybrid Organic-Inorganic Crystal by In Situ X-Ray Diffraction.

The switching behavior of the novel hybrid material (FA)Na[Fe(CN)(NO)].HO (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.

Noncovalent bonding assessment by pair distribution function.

Noncovalent interactions are essential in the formation and properties of a diverse range of materials. However, reliably identifying noncovalent interactions remains challenging using conventional methods such as X-ray diffraction, especially in nanocrystalline, poorly crystalline or amorphous materials which lack long-range lattice periodicity. Here, we demonstrate the accurate determination of deviations in the local structure and tilting of aromatic rings during the temperature-induced first order structural transition in the 1 : 1 adduct of 4,4'-bipyridinium squarate (BIPY:SQA) from the low temperature form HAZFAP01 to high temperature HAZFAP07 by X-ray pair distribution function.

Uncovering the role of non-covalent interactions in solid-state photoswitches by non-spherical structure refinements with NoSpherA2.

We present a charge density study of two linkage isomer photoswitches, [Pd(Budien)(NO)]BPh·THF (1) and [Ni(Etdien)(NO)] (2) using Hirshfeld Atom Refinement (HAR) methods implemented 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 calculations to explore the non-covalent interactions that influence physical properties of the photoswitches, such as the stability of the excited state nitrito-(-ONO) isomer.

LED-pump-X-ray-multiprobe crystallography for sub-second timescales.

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.

Determination of H-Atom Positions in Organic Crystal Structures by NEXAFS Combined with Density Functional Theory: a Study of Two-Component Systems Containing Isonicotinamide.

It is important to be able to identify the precise position of H-atoms in hydrogen bonding interactions to fully understand the effects on the structure and properties of organic crystals. Using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory (DFT) quantum chemistry calculations, we demonstrate the sensitivity of core-level X-ray spectroscopy to the precise H-atom position within a donor-proton-acceptor system. Exploiting this sensitivity, we then combine the predictive power of DFT with the experimental NEXAFS, confirming the H-atom position identified using single-crystal X-ray diffraction (XRD) techniques more easily than using other H-atom sensitive techniques, such as neutron diffraction.

An electric field cell for performing single-crystal synchrotron X-ray diffraction.

With the recent increase in research into ferroelectric, anti-ferroelectric and piezoelectric materials, studying the solid-state properties under applied electric fields is vital in understanding the underlying processes. Where this behaviour is the result of atomic displacements, crystallographic insight has an important role. This work presents a sample environment designed to apply an electric field to single-crystal samples on the small-molecule single-crystal diffraction beamline I19, Diamond Light Source (UK).

A quantum crystallographic approach to short hydrogen bonds.

In this work we use high-resolution synchrotron X-ray diffraction for electron density mapping, in conjunction with modelling, to study short O-H⋯O and O-H⋯O hydrogen bonds whose behaviour is known to be tuneable by temperature. The short hydrogen bonds have donor-acceptor distances in the region of 2.45 Å and are formed in substituted urea and organic acid molecular complexes of ,'-dimethylurea oxalic acid 2 : 1 (), ,-dimethylurea 2,4-dinitrobenzoate 1 : 1 () and ,-dimethylurea 3,5-dinitrobenzoic acid 2 : 2 ().

Controlled Light and Temperature Induced Valence Tautomerism in a Cobalt-o-Dioxolene Complex.

The mononuclear cobalt complex of 3,5-di--butylcathecolate and cyan-pyridine (Co()(4-CN-py)) is a very versatile compound that displays valence tautomerism (VT) in the solid state, which is induced by temperature, light, and hard X-rays, and modulated by solvent in the crystal lattice. In our work, we used single crystal X-ray diffraction as a probe for the light-induced VT in solid state and demonstrate the controlled use of hard X-rays via attenuation to avoid X-ray-induced VT interconversion. We report photoinduced VT in benzene solvated crystals of Co()(4-CN-py) illuminated with blue 450 nm light at 30 K with a very high yield (80%) of metastable -Co states, and we also show evidence of the de-excitation of these photoinduced metastable states using red 660 nm light.

Probing the structural and electronic response of Magnus green salt compounds [Pt(NHR)][PtCl] (R = H, CH) to pressure.

Despite possessing the desirable crystal packing and short PtPt stacking distances required for a large piezoresistive response, the conductivity-pressure response of the Magnus green salt [Pt(NH)][PtCl] is extremely sluggish. Through a combination of high-pressure X-ray diffraction and hybrid-DFT solid state calculations this study demonstrates that the poor conductivity-pressure response is due to a low volumetric compression anisotropy, a relatively large ambient pressure band gap and a lack of dispersion in the conduction band. Ligand modification (from NH to NHCH) does not enhance the piezoresistive response, causing even lower anisotropy of the volumetric compression and an unexpected phase transition at above 2 GPa.

Host-guest selectivity in a series of isoreticular metal-organic frameworks: observation of acetylene-to-alkyne and carbon dioxide-to-amide interactions.

In order to develop new porous materials for applications in gas separations such as natural gas upgrading, landfill gas processing and acetylene purification it is vital to gain understanding of host-substrate interactions at a molecular level. Herein we report a series of six isoreticular metal-organic frameworks (MOFs) for selective gas adsorption. These materials do not incorporate open metal sites and thus provide an excellent platform to investigate the effect of the incorporation of ligand functionality amide and alkyne groups on substrate binding.