N‐Iodosaccharin–pyridine co‐crystal system under pressure: experimental evidence of reversible twinning. Issue 3 (4th May 2022)

• Record Type: Journal Article
• Authors: Vijayakumar-Syamala, Vishnu; Aubert, Emmanuel; Deutsch, Maxime; Wenger, Emmanuel; Dhaka, Arun; Fourmigué, Marc; Nespolo, Massimo; Espinosa, Enrique
• Is Part Of: Acta crystallographica. Volume 78:Issue 3-2(2022)
• Page Start: 436
• Page End: 449
• Publication Date: 2022-05-04
• Subjects: intermolecular interactions -- high‐pressure studies -- single‐crystal X‐ray diffraction -- twinning
• DOI: 10.1107/S2052520622002542
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : Single crystals of the N ‐iodosaccharin–pyridine adduct (NISac·py) undergo reversible mechanical twinning under pressure; the twinned structure is only slightly less stabilized than the untwinned one. Under pressure, the halogen‐bonding interactions taking place within the NISac·py complex evolve as a result of changes in the crystalline environment. Abstract : This work presents a single‐crystal X‐ray diffraction study of an organic co‐crystal composed of N ‐iodosaccharin and pyridine (NISac·py) under hydrostatic pressure ranging from 0.00 (5) GPa to 4.5 (2) GPa. NISac·py crystallizes in the monoclinic system (space group B 21 / e ). The unconventional setting of the space group is adopted (the conventional setting is P 21 / c, No. 14) to emphasise the strongly pseudo‐orthorhombic symmetry of the lattice, with a β angle very close to 90°. The crystal structure contains one molecule each of N ‐iodosaccharin (NISac) and pyridine (py) in the asymmetric unit ( Z ′ = 1), linked via an Nsac …I…N′py halogen‐bonding motif. A gradual modification of this motif is observed under pressure as a result of changes in the crystalline environment. Mechanical twinning is observed under compression and the sample splits into two domains, spanning an unequal volume that is mapped by a twofold rotation about the [100] direction of the B 21 / e unit cell. The twinning is particularly significant at high pressure, being reversible when the pressure is released. The structure of the twinned sample reveals the continuity of a substantial substructure across the composition plane. The presence of this common substructure in the two orientations of the twinned individuals can be interpreted as a structural reason for the formation of the twin and is the first observed example in a molecular crystal. These results indicate that the anisotropy of intermolecular interactions in the crystal structure results in an anisotropic strain generated upon the action of hydrostatic compression. Periodic density functional theory calculations were carried out by considering an isotropic external pressure, the results showing good agreement with the experimental findings. The bulk modulus of the crystal was obtained from the equations of state, being 7 (1) GPa for experimental data and 6.8 (5) GPa for theoretical data.