Dipolar carbonyl–carbonyl contacts generally occur in one of three motifs, and all are exhibited in the X-ray crystal structures of two phases of acetone derived at 15 kBar and at 150 K; a neutron powder-diffraction study at 5 K and an X-ray diffraction study at 110 K reveal strengthened CH···O as well as CO···CO electrostatic contacts which appear to explain the unusual thermodynamic properties of acetone, the nature of which have remained a mystery since 1929.

Herein, we describe the development of a novel dual air-bearing fixed-χ diffractometer for beamline I19 at Diamond Light Source. The diffractometer is designed to facilitate the rapid data collections possible with a Dectris Pilatus 2M pixel-array photon-counting detector, while allowing remote operation in conjunction with a robotic sample changer. The sphere-of-confusion is made as small as practicably possible, through the use of air-bearings for both the ω and φ axes. The design and construction of the new instrument is described in detail and an accompanying paper by Johnson et al. (also in this issue) will provide a user perspective of its operation.

The guest-dependent flexibility of the pillared-layered metal–organic framework (MOF), Zn ₂ bdc ₂ dabco· X (guest), where guest = EtOH, DMF or benzene, has been examined by high-pressure single crystal X-ray diffraction.

Seven multi-component molecular crystals containing O–H⋯O/O⁺–H⋯O⁻ and N⁺–H⋯O⁻ short strong hydrogen bonds (SSHBs) have been engineered by combining substituted organic acids with hydrogen bond acceptor molecules N,N-dimethylurea and isonicotinamide. In these materials, the shortest of the SSHBs are formed in the N,N-dimethylurea set for the ortho/para nitro-substituted organic acids whilst a twisted molecular approach favours the shorter SSHBs N⁺–H⋯O⁻ in the isonicotinamide set. Temperature dependent proton migration behaviour has been explored in these systems using single crystal synchrotron X-ray diffraction (SCSXRD). By using a protocol which considers a combination of structural information when assessing the hydrogen atom (H-atom) behaviour, including refined H-atom positions alongside heavy atom geometry and Fourier difference maps, temperature dependent proton migration is indicated in two complexes (2: N,N-dimethylurea 2,4-dinitrobenzoic acid 1 : 1 and 5: isonicotinamide phthalic acid 2 : 1). We also implement Hirshfeld atom refinement for further confidence in this observation; this highlights the importance of having corroborating trends when applying the SCSXRD technique in these studies. Further insights into the SSHB donor–acceptor distance limit for temperature dependent proton migration are also revealed. For the O–H⋯O/O⁺–H⋯O⁻ SSHBs, the systems here support the previously proposed maximum limit of 2.45 Å whilst for the charge assisted N⁺–H⋯O⁻ SSHBs, a limit in the region of 2.55 Å may be suggested.