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1. Crystal engineering of a 1:1 5-fluorocytosine–4-hydroxybenzaldehyde cocrystal: insights from X-ray crystallography and Hirshfeld analysis

   https://doi.org/10.1107/S2056989025004463  

   Sangavi, Marimuthu; Mohana, Marimuthu; Butcher, Ray J; McMillen, Colin D (June 2025, Acta Crystallographica Section E Crystallographic Communications)

   The 1:1 cocrystal of 5-fluorocytosine (5FC) and 4-hydroxybenzaldehyde (4HB), C₄H₄FN₃O·C₇H₆O₂has been synthesized and its structure characterized by single-crystal X-ray diffraction and Hirshfeld surface analysis. The compound crystallizes in the monoclinicP2₁/cspace group. A robust supramolecular architecture is stabilized by N—H...O, N—H...N, C—H...O and C—H...F hydrogen bonds, formingR₂²(8),R₄⁴(22),R₆⁶(32), andR₈⁸(34) ring motifs. The N—H...O and N—H...N hydrogen bonds form strong directional interactions, contributing to theR₂²(8) andR₈⁸(34) motifs through dimeric and extended ring structures. O—H...O interactions link 5FC and 4HB molecules, generating anR₆⁶(32) ring that enhances the packing. Weaker C—H...F bonds help form theR₄⁴(22) tetrameric motif, supporting the overall three-dimensional supramolecular framework. Additionally, C—F...π interactions between the fluorine atom and the aromatic ring add further to the crystal cohesion. Hirshfeld surface analysis and two-dimensional fingerprint plots confirm that O...H/H...O contacts are the most significant, highlighting the central role of hydrogen bonding in the stability and organization of the crystal structure. 

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2. 2-Chloro-4-hydroxyanilinium chloride

   https://doi.org/10.1107/S2414314625008934  

   Bai, Sindhu V; Mensah, Patrick F; Li, Guoqiang; Fronczek, Frank R; Uppu, Rao M (October 2025, IUCrData)

   The title compound, C₆H₇ClNO⁺·Cl⁻, crystallizes in orthorhombic space groupPnmawith both cations and anions lying on a mirror plane in the crystal. The C—Cl distance is 1.7289 (6) Å, the C—N distance is 1.4590 (8) Å, and the C—O distance is 1.3617 (8) Å. Parallel molecules form stacks with interplanar spacing 3.1473 (2) Å, but slipped by 1.97 Å. The NH₃⁺substituent donates three intermolecular hydrogen bonds to chloride ions having N...Cl distances in the range 3.1514 (6)–3.3019 (2) Å, and the OH group donates an intermolecular hydrogen bond to chloride with O...Cl distance 3.0671 (6) Å. The chloro substituent and OH group do not accept hydrogen bonds from NH or OH. 

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3. A 1:1 flavone cocrystal with cyclic trimeric perfluoro- o -phenylenemercury

   https://doi.org/10.1107/S2056989024005346  

   Novikov, Egor M; Castañeda, Raúl; Fonari, Marina S; Timofeeva, Tatiana V (July 2024, Acta Crystallographica Section E Crystallographic Communications)

   The title compound, systematic name tris(μ₂-perfluoro-o-phenylene)(μ₂-3-phenyl-4H-chromen-4-one)-triangulo-trimercury, [Hg₃(C₆F₄)₃(C₁₅H₁₀O₂)], crystallizes in the monoclinicP2₁/nspace group with one flavone (FLA) and one cyclic trimeric perfluoro-o-phenylenemercury (TPPM) molecule per asymmetric unit. The FLA molecule is located on one face of the TPPM acceptor and is linked in an asymmetric coordination of its carbonyl oxygen atom with two Hg centers of the TPPM macrocycle. The angular-shaped complexes pack in zigzag chains where they stackviatwo alternating TPPM–TPPM and FLA–FLA stacking patterns. The distance between the mean planes of the neighboring TPPM macrocycles in the stack is 3.445 (2) Å, and that between the benzo-γ-pyrone moieties of FLA is 3.328 (2) Å. The neighboring stacks are interdigitated through the shortened F...F, CH...F and CH...π contacts, forming a dense crystal structure. 

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4. Bis(diisobutylammonium) tetrachloridobis[3-(trifluoromethyl)phenyl]stannate

   https://doi.org/10.1107/S2414314623009136  

   Song, Xueqing; Li, William (October 2023, IUCrData)

   The asymmetric unit in the title salt, (C₈H₂₀N)₂[SnCl₄(C₇H₄Cl₂F₃)₂], features a di-isobutylammonium cation in a general position and a diorganotin tetrachloride dianion,i.e. tetrachloridobis(3-trifuoromethylphenyl)stannate(IV), located on a centre of inversion; the Sn^IVatom is octahedrally coordinated. In the crystal, charge-assisted N⁺—H...Cl hydrogen bonds along with C—H...F contacts occur within supramolecular layers that interdigitate along thea-axis direction. 

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5. Syntheses and crystal structures of three triphenylsulfonium salts of manganese(II), iron(III) and cobalt(II)

   https://doi.org/10.1107/S2056989025006668  

   Callaway, Waylan; Elterman, Matthew; Krasilnikov, Nikita; Roberts, Gavin; Rutan, Davis; Spencer, Ty; Padgett, Clifford W; Lynch, Will E (August 2025, Acta Crystallographica Section E Crystallographic Communications)

   Bis(triphenylsulfonium) tetrachloridomanganate(II), (C₁₈H₁₅S)₂[MnCl₄] (I), triphenylsulfonium tetrachloridoferrate(III), (C₁₈H₁₅S)[FeCl₄] (II), and bis(triphenylsulfonium) tetrachloridocobaltate(II), (C₁₈H₁₅S)₂[CoCl₄] (III), crystallize in the monoclinic space groupsP2₁/n[(I) and (III)] andP2₁/c[(II)]. Compounds (I) and (III) each contain two crystallographically independent triphenylsulfonium (TPS⁺) cations in the asymmetric unit, whereas (II) has one. In all three compounds, the sulfonium centers adopt distorted trigonal–pyramidal geometries, with S—C bond lengths falling roughly in the 1.78–1.79 Å range and C—S—C angles observed at about 101 to 106°. The [MCl₄]ⁿ⁻anions (M= Mn²⁺, Fe³⁺, Co²⁺;n= 2,1,2) adopt slightly distorted tetrahedral geometries, withM—Cl bond lengths in the 2.19–2.38 Å range and Cl—M—Cl angles of approximately 104–113°. Hirshfeld surface analyses shows that H...H and H...C contacts dominate the TPS⁺cation environments, whereas H...Cl and shortM—S interactions link each [MCl₄]ⁿ⁻anion to the surrounding cations. In (I) and (III), inversion-centered π–π stacking further consolidates the crystal packing, while in (II) no π–π interactions are observed. 

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