Catheter-less Cohen transtrigonal ureteric reimplantation.

UNLABELLED: Formamide, the simplest amide, forms an ambient-pressure crystal structure consisting of stacks of NH⋯O hydrogen-bonded layers. Here we report the effect of pressure extending to a maximum of 3.6 GPa on the crystal structures of formamide-h 3 and formamide-d 3 using single-crystal X-ray diffraction and neutron powder diffraction, revealing previously unrecognised but extensive phase diversity between ambient pressure and 1.81 GPa. The crystal structures of five distinct crystalline phases, designated Iα (the known ambient pressure phase), II, III, IVβ (also known from previous work) and V, have been determined. The pressures and isotopologues of the determinations were 0.20 GPa (for h 3 phase Iα), 0.20 and 0.36 GPa (for the d 3 and h 3 forms of phase II), 0.35 GPa (d 3 form of phase III), 0.43 and 0.78 GPa (for the h 3 and d 3 forms of IVβ) and 1.81 GPa (d 3 form of phase V). All phases contain NH⋯O hydrogen-bonded chain motifs, with phases III and IVβ being layered structures similar to Iα, but phases II and V forming 3-dimensional networks. The architectures are determined by whether a hydrogen-bonded chain utilises the oxygen lone pair cis or trans to the amide nitrogen and the orientations of the molecules. The phases conform to well-known topological types, Iα, II and IVβ being based on cubic close packing while phase V is a distorted form of the same topology, reflecting denser packing at elevated pressure. Phase III can be considered to have a body centred cubic topology. Pixel packing energy calculations show that competing H-bonding arrangements are energetically comparable even when they deviate from an ideal H-bonding geometry, while non-H-bonding contacts, including antiparallel stacking and aldehyde-aldehyde interactions, contribute additional stabilisation, also with notable geometric flexibility.

GRAPHICAL ABSTRACT: The simplest amide, formamide, forms no less than five different phases between ambient pressure and about 2 GPa.

SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11224-026-02744-2.