Crystallography is no longer solely the preserve of the specialist, a situation that has implications for the operation of crystallographic service facilities. This mini-review provides an overview of the challenges in operating a crystallographic facility from the perspective and experience of the UK National Crystallography Service-a modern mid-range facility. Examples of chemical research generating the greatest challenges for the modern crystallography service and the state-of-the-art tools, hardware, facilities and expertise that are required to address them are highlighted. An overview of current research trends in single crystal diffraction research, which will ensure the future development of the technique, is presented. The remit of the service crystallographer is examined, together with proposed examples of best practice.

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The new salts trans‐4′‐(dimethylamino)‐N‐R‐4‐stilbazolium hexafluorophosphate (R = methyl, Me 1, phenyl, Ph 2, 2,4‐dinitrophenyl, DNPh 3, 2‐pyrimidyl, Pym 4, Scheme 1) have been prepared. Their electronic absorption spectra show intense, visible intramolecular charge‐transfer bands, the energy (Emax) of which decreases in the order R = Me > Ph > DNPh > Pym. This trend arises from the steadily increasing electron deficiency of the pyridinium ring, a phenomenon also observed in cyclic voltammetric and 1H nuclear magnetic resonance (NMR) data. Fluorescence‐free first hyperpolarizability β values of [1–4]PF6 were measured by using femtosecond hyper‐Rayleigh scattering (HRS) with acetonitrile solutions and a 1300 nm laser, and static first hyperpolarizabilities β0 were obtained by application of the two‐state model. The HRS results indicate that the N‐aryl chromophores in [2–4]PF6 have considerably larger β0 values than their N‐methyl counterpart in [1]PF6, with a ca. 10‐fold increase in β0 observed in moving from [1]PF6 to [4]PF6 (25 → 230 × 10–30 esu). Stark (electroabsorption) spectroscopic studies in butyronitrile glasses at 77 K allowed the derivation of dipole moment changes Δμ12 (10.9–14.8 D), which have been used to calculate β0 according to the two‐state equation β0 = 3Δμ12(μ12)2/2(Emax)2 (μ12 = transition dipole moment). With the exception of [1]PF6, the Stark‐derived β0 values are in reasonable agreement with those from HRS. However, the increase in β0 in moving from [1]PF6 to [4]PF6 is only 2‐fold for the Stark data (90 → 185 × 10–30 esu). The observed trend of increasing β0 in the order [1]PF6 < [3]PF6 < [2]PF6 < [4]PF6 arises from a combination of decreasing Emax and increasing Δμ12, with only a slight increase in μ12 between [1]PF6 and [4]PF6. It is likely that the β0 values for [3]PF6 are lower than expected due to the steric effect of the ortho‐NO2 group, which causes twisting of the DNPh ring out of the plane of the stilbazolium unit. A single crystal X‐ray structure shows that [2]PF6 crystallizes in the space group Cc, with head‐to‐tail alignment and almost parallel stacking of the pseudo‐planar stilbazolium portions of the cations to form polar sheets within a polar bulk structure. [2]PF6 is essentially isostructural with the related Schiff base salt trans‐4‐[(4‐dimethylaminophenyl)iminomethyl]‐N‐phenylpyridinium hexafluorophosphate ([8]PF6). Second harmonic generation (SHG) studies on [2]PF6 and [8]PF6 using a 1907 nm laser and sieved powdered samples (53–63 μm) afforded efficiencies of 470 and 240 times that of urea, respectively. Under the same conditions, the well‐studied compound [1]p‐MeC6H4SO3 gave an SHG efficiency of 550 times that of urea.

A series of thiophene oligomers bearing core phenylene and fluorinated phenylene units has been synthesized as potential semiconductor materials for organic field-effect transistors (OFETs). Polymerization of these compounds has been achieved using Stille and oxidative coupling methods. Functionalization of the phenylene unit with fluorine atoms has a marked effect on the self-assembly and electronic properties of the parent materials:  the optical band gaps and highest occupied molecular orbital levels are affected with the introduction of fluorine atoms as a result of a combination of inductive effects and rigidification of the main chain. The design of these materials has focused on the self-assembly and solution processability of the materials. All the polymers are readily soluble in common organic solvents. Self-assembly and planarization of the fluorinated materials in the solid state are identified by a combination of X-ray diffraction studies, absorption spectroscopy, and cyclic voltammetry. The organizational behavior of the films is in contrast to the conformational freedom observed in solution (absorption spectroscopy) and in the gas phase (computational studies). Thin-film OFETs have been fabricated for the entire polymer series. Hole mobilities have been measured up to 10-3 cm2/(V·s), with high current modulation (on/off ratios up to 105) and low turn-on voltages (down to 2 V). For the Stille coupled polymers, replacement of the bridging thiophene unit with selenophene generally increases the hole mobility of the polymers.

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In this article, we describe a series of new complex salts in which electron-donating cis-{Ru II (NH3)4} 2+ centers are connected to two electron-accepting N-methyl/aryl-pyridinium groups. These V-shaped complexes contain either monodentate 4,4′-bipyridyl-derived ligands or related chelates based on 2,2′:4,4′′:4′,4′′′-quaterpyridyl and have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses β have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d f π* metal-to-ligand charge-transfer bands. These experiments reveal that these dipolar pseudo-C 2v chromophores exhibit two substantial components of the β tensor, βzzz and βzyy, with the difference between them being most marked for the nonchelated systems. Time-dependent density-functional theory and finite field calculations serve to further illuminate the electronic structures and associated linear and NLO properties of the new chromophoric salts.

The FAIR principles have been widely cited, endorsed and adopted by a broad range of stakeholders since their publication in 2016. By intention, the 15 FAIR guiding principles do not dictate specific technological implementations, but provide guidance for improving Findability, Accessibility, Interoperability and Reusability of digital resources. This has likely contributed to the broad adoption of the FAIR principles, because individual stakeholder communities can implement their own FAIR solutions. However, it has also resulted in inconsistent interpretations that carry the risk of leading to incompatible implementations. Thus, while the FAIR principles are formulated on a high level and may be interpreted and implemented in different ways, for true interoperability we need to support convergence in implementation choices that are widely accessible and (re)-usable. We introduce the concept of FAIR implementation considerations to assist accelerated global participation and convergence towards accessible, robust, widespread and consistent FAIR implementations. Any self-identified stakeholder community may either choose to reuse solutions from existing implementations, or when they spot a gap, accept the challenge to create the needed solution, which, ideally, can be used again by other communities in the future. Here, we provide interpretations and implementation considerations (choices and challenges) for each FAIR principle.