1. (3S,4S)-3-Ethyl-4-hydr-oxy-3-(3-methoxy-phen-yl)-1-methyl-azepan-1-ium d-tartrate dihydrate
Xing-Hai Wang, Bo Chao, Zhui-Bai Qiu Acta Crystallogr Sect E Struct Rep Online. 2008 Apr 2;64(Pt 5):o784. doi: 10.1107/S1600536808005898.
In the title compound, C(16)H(26)NO(2) (+)·C(4)H(5)O(6) (-)·2H(2)O, a meptaz-inol derivative, three C atoms of the azepane ring are disordered over two positions, with site-occupancy factors of 0.80 and 0.20; the major disorder component adopts a twist-chair conformation, while the minor component has a chair conformation. The benzene ring is axially substituted on the heterocyclic ring, resulting in a folded conformation of the cation. The absolute configuration was determined with reference to d-tartaric acid. The crystal structure is stabilized by an extensive network of intra- and inter-molecular O-H⋯O hydrogen bonds.
2. The ephemeral dihydrate of sulfanilic acid
Stefanie Langenstück, Chenchen Zhao, Ulli Englert Acta Crystallogr C Struct Chem. 2018 Jan 1;74(Pt 1):7-12. doi: 10.1107/S2053229617016886. Epub 2018 Jan 1.
Evaporation of an aqueous solution of sulfanilic acid (systematic name: 4-aminobenzene-1-sulfonic acid) at 273 K affords a crystalline dihydrate, C6H7NO3S·2H2O. The organic molecule exists as a zwitterion; two zwitterions are aligned in an antiparallel fashion about a crystallographic centre of inversion. They interact directly via two N-H...O hydrogen bonds between the ammonium group of one zwitterion and the sulfonate group of its symmetry-related counterpart, and their aromatic rings are π-stacked, with an interplanar distance of 3.533 (3) Å. One of the cocrystallized water molecules connects the resulting pairs into layers and the second crosslinks the layers into a three-dimensional network. All H atoms connected to N or O atoms find acceptors in suitable geometries. In the resulting crystal, polar and hydrogen-bond-dominated slabs alternate with stacks of organic arene rings. Although the new dihydrate shows efficient space filling, with a packing coefficient of 75.7%, it is unstable and undergoes fast desolvation at room temperature. In this process, the orthorhombic ansolvate forms as a pure phase.
3. Hydro-nium 4-oxo-1,4-dihydro-pyridine-3-sulfonate dihydrate
Zhi-Biao Zhu, Shan Gao, Seik Weng Ng Acta Crystallogr Sect E Struct Rep Online. 2009 Oct 10;65(Pt 11):o2687. doi: 10.1107/S1600536809040641.
2-Hydroxy-pyridine when treated with concentrated sulfuric acid is sulfonated at the 3-position to yield the title hydrated salt, H(3)O(+)·C(5)H(4)NO(3)S(-)·2H(2)O. In the crystal structure, the cations, anions and uncoordinated water mol-ecules are linked by extensive O-H⋯O and N-H⋯O hydrogen bonds into a three-dimensional network. The crystal studied is a non-merohedral twin with a twin component of 36%.
