Protein crystallography is an established method to study the atomic structures of macromolecules and their complexes. A prerequisite for successful structure determination is diffraction-quality crystals, which may require extensive optimization of both the protein and the conditions, and hence projects can stretch over an extended period, with multiple users being involved. The workflow from crystallization and crystal treatment to deposition and publication is well defined, and therefore an electronic laboratory information management system (LIMS) is well suited to management of the data. Completion of the project requires key information on all the steps being available and this information should also be made available according to the FAIR principles. As crystallized samples are typically shipped between facilities, a key feature to be captured in the LIMS is the exchange of metadata between the crystallization facility of the home laboratory and, for example, synchrotron facilities. On completion, structures are deposited in the Protein Data Bank (PDB) and the LIMS can include the PDB code in its database, completing the chain of custody from crystallization to structure deposition and publication. A LIMS designed for macromolecular crystallography, IceBear, is available as a standalone installation and as a hosted service, and the implementation of key features for the capture of metadata in IceBear is discussed as an example.

The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an α2β2 tetrameric enzyme in which the α-chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) active sites, and the β-chain provides the 3-ketoacyl-CoA thiolase (KAT) active site. Linear, medium-chain and long-chain 2E-enoyl-CoA molecules are the preferred substrates of MtTFE. Previous crystallographic binding and modeling studies identified binding sites for the acyl-CoA substrates at the three active sites, as well as the NAD binding pocket at the HAD active site. These studies also identified three additional CoA binding sites on the surface of MtTFE that are different from the active sites. It has been proposed that one of these additional sites could be of functional relevance for the substrate channeling (by surface crawling) of reaction intermediates between the three active sites. Here, 226 fragments were screened in a crystallographic fragment-binding study of MtTFE crystals, resulting in the structures of 16 MtTFE–fragment complexes. Analysis of the 121 fragment-binding events shows that the ECH active site is the `binding hotspot' for the tested fragments, with 41 binding events. The mode of binding of the fragments bound at the active sites provides additional insight into how the long-chain acyl moiety of the substrates can be accommodated at their proposed binding pockets. In addition, the 20 fragment-binding events between the active sites identify potential transient binding sites of reaction intermediates relevant to the possible channeling of substrates between these active sites. These results provide a basis for further studies to understand the functional relevance of the latter binding sites and to identify substrates for which channeling is crucial.

Advances in structural biology have relied heavily on synchrotron cryo-crystallography and cryogenic electron microscopy to elucidate biological processes and for drug discovery. However, disparities between cryogenic and room-temperature (RT) crystal structures pose challenges. Here, Cryo2RT, a high-throughput RT data-collection method from cryo-cooled crystals that leverages the cryo-crystallography workflow, is introduced. Tested on endothiapepsin crystals with four soaked fragments, thaumatin and SARS-CoV-2 3CLpro, Cryo2RT reveals unique ligand-binding poses, offers a comparable throughput to cryo-crystallography and eases the exploration of structural dynamics at various temperatures.

A key prerequisite for the successful application of protein crystallography in drug discovery is to establish a robust crystallization system for a new drug-target protein fast enough to deliver crystal structures when the first inhibitors have been identified in the hit-finding campaign or, at the latest, in the subsequent hit-to-lead process. The first crucial step towards generating well folded proteins with a high likelihood of crystallizing is the identification of suitable truncation variants of the target protein. In some cases an optimal length variant alone is not sufficient to support crystallization and additional surface mutations need to be introduced to obtain suitable crystals. In this contribution, four case studies are presented in which rationally designed surface modifications were key to establishing crystallization conditions for the target proteins (the protein kinases Aurora-C, IRAK4 and BUB1, and the KRAS–SOS1 complex). The design process which led to well diffracting crystals is described and the crystal packing is analysed to understand retrospectively how the specific surface mutations promoted successful crystallization. The presented design approaches are routinely used in our team to support the establishment of robust crystallization systems which enable structure-guided inhibitor optimization for hit-to-lead and lead-optimization projects in pharmaceutical research.

During the automatic processing of crystallographic diffraction experiments, beamstop shadows are often unaccounted for or only partially masked. As a result of this, outlier reflection intensities are integrated, which is a known issue. Traditional statistical diagnostics have only limited effectiveness in identifying these outliers, here termed Not-Excluded-unMasked-Outliers (NEMOs). The diagnostic tool AUSPEX allows visual inspection of NEMOs, where they form a typical pattern: clusters at the low-resolution end of the AUSPEX plots of intensities or amplitudes versus resolution. To automate NEMO detection, a new algorithm was developed by combining data statistics with a density-based clustering method. This approach demonstrates a promising performance in detecting NEMOs in merged data sets without disrupting existing data-reduction pipelines. Re-refinement results indicate that excluding the identified NEMOs can effectively enhance the quality of subsequent structure-determination steps. This method offers a prospective automated means to assess the efficacy of a beamstop mask, as well as highlighting the potential of modern pattern-recognition techniques for automating outlier exclusion during data processing, facilitating future adaptation to evolving experimental strategies.

The availability of highly accurate protein structure predictions from AlphaFold2 (AF2) and similar tools has hugely expanded the applicability of molecular replacement (MR) for crystal structure solution. Many structures can be solved routinely using raw models, structures processed to remove unreliable parts or models split into distinct structural units. There is therefore an open question around how many and which cases still require experimental phasing methods such as single-wavelength anomalous diffraction (SAD). Here, this question is addressed using a large set of PDB depositions that were solved by SAD. A large majority (87%) could be solved using unedited or minimally edited AF2 predictions. A further 18 (4%) yield straightforwardly to MR after splitting of the AF2 prediction using Slice'N'Dice, although different splitting methods succeeded on slightly different sets of cases. It is also found that further unique targets can be solved by alternative modelling approaches such as ESMFold (four cases), alternative MR approaches such as ARCIMBOLDO and AMPLE (two cases each), and multimeric model building with AlphaFold-Multimer or UniFold (three cases). Ultimately, only 12 cases, or 3% of the SAD-phased set, did not yield to any form of MR tested here, offering valuable hints as to the number and the characteristics of cases where experimental phasing remains essential for macromolecular structure solution.

Pollution from plastics is a global problem that threatens the biosphere for a host of reasons, including the time scale that it takes for most plastics to degrade. Biodegradation is an ideal solution for remediating bioplastic waste as it does not require the high temperatures necessary for thermal degradation and does not introduce additional pollutants into the environment. Numerous organisms can scavenge for bioplastics, such as polylactic acid (PLA) or poly-(R)-hydroxybutyrate (PHB), which they can use as an energy source. Recently, a promiscuous PHBase from the thermophilic soil bacterium Lihuaxuella thermophila (LtPHBase) was identified. LtPHBase can accommodate many substrates, including PHB granules and films and PHB block copolymers, as well as the unrelated polymers polylactic acid (PLA) and polycaprolactone (PCL). LtPHBase uses the expected Ser–His–Asp catalytic triad for hydrolysis at an optimal enzyme activity near 70°C. Here, the 1.75 Å resolution crystal structure of apo LtPHBase is presented and its chemical stability is profiled. Knowledge of its substrate preferences was extended to different-sized PHB granules. It is shown that LtPHBase is highly resistant to unfolding, with barriers typical for thermophilic enzymes, and shows a preference for low-molecular-mass PHB granules. These insights have implications for the long-term potential of LtPHBase as an industrial PHB hydrolase and shed light on the evolutionary role that this enzyme plays in bacterial metabolism.

For protein crystals in which more than two thirds of the volume is occupied by solvent, the featureless nature of the solvent region often generates a constraint that is powerful enough to allow direct phasing of X-ray diffraction data. Practical implementation relies on the use of iterative projection algorithms with good global convergence properties to solve the difficult nonconvex phase-retrieval problem. In this paper, some aspects of phase retrieval using iterative projection algorithms are systematically explored, where the diffraction data and density-value distributions in the protein and solvent regions provide the sole constraints. The analysis is based on the addition of random error to the phases of previously determined protein crystal structures, followed by evaluation of the ability to recover the correct phase set as the distance from the solution increases. The properties of the difference-map (DM), relaxed–reflect–reflect (RRR) and relaxed averaged alternating reflectors (RAAR) algorithms are compared. All of these algorithms prove to be effective for crystallographic phase retrieval, and the useful ranges of the adjustable parameter which controls their behavior are established. When these algorithms converge to the solution, the algorithm trajectory becomes stationary; however, the density function continues to fluctuate significantly around its mean position. It is shown that averaging over the algorithm trajectory in the stationary region, following convergence, improves the density estimate, with this procedure outperforming previous approaches for phase or density refinement.

In the search for new active pharmaceutical ingredients, the precise control of the chemistry of cocrystals becomes essential. One crucial step within this chemistry is proton migration between cocrystal coformers to form a salt, usually anticipated by the empirical ΔpKa rule. Due to the effective role it plays in modifying intermolecular distances and interactions, pressure adds a new dimension to the ΔpKa rule. Still, this variable has been scarcely applied to induce proton-transfer reactions within these systems. In our study, high-pressure X-ray diffraction and Raman spectroscopy experiments, supported by DFT calculations, reveal modifications to the protonation states of the 4,4'-bi­pyridine (BIPY) and malonic acid (MA) cocrystal (BIPYMA) that allow the conversion of the cocrystal phase into ionic salt polymorphs. On compression, neutral BIPYMA and monoprotonated (BIPYH+MA−) species coexist up to 3.1 GPa, where a phase transition to a structure of P21/c symmetry occurs, induced by a double proton-transfer reaction forming BIPYH22+MA2−. The low-pressure C2/c phase is recovered at 2.4 GPa on decompression, leading to a 0.7 GPa hysteresis pressure range. This is one of a few studies on proton transfer in multicomponent crystals that shows how susceptible the interconversion between differently charged species is to even slight pressure changes, and how the proton transfer can be a triggering factor leading to changes in the crystal symmetry. These new data, coupled with information from previous reports on proton-transfer reactions between coformers, extend the applicability of the ΔpKa rule incorporating the pressure required to induce salt formation.

The Protein Data Bank (PDB) was established as the first open-access digital data resource in biology and medicine in 1971 with seven X-ray crystal structures of proteins. Today, the PDB houses >210 000 experimentally determined, atomic level, 3D structures of proteins and nucleic acids as well as their complexes with one another and small molecules (e.g. approved drugs, enzyme cofactors). These data provide insights into fundamental biology, biomedicine, bioenergy and biotechnology. They proved particularly important for understanding the SARS-CoV-2 global pandemic. The US-funded Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB PDB) and other members of the Worldwide Protein Data Bank (wwPDB) partnership jointly manage the PDB archive and support >60 000 `data depositors' (structural biologists) around the world. wwPDB ensures the quality and integrity of the data in the ever-expanding PDB archive and supports global open access without limitations on data usage. The RCSB PDB research-focused web portal at https://www.rcsb.org/ (RCSB.org) supports millions of users worldwide, representing a broad range of expertise and interests. In addition to retrieving 3D structure data, PDB `data consumers' access comparative data and external annotations, such as information about disease-causing point mutations and genetic variations. RCSB.org also provides access to >1 000 000 computed structure models (CSMs) generated using artificial intelligence/machine-learning methods. To avoid doubt, the provenance and reliability of experimentally determined PDB structures and CSMs are identified. Related training materials are available to support users in their RCSB.org explorations.

A new polymorph of 1,3-diacetylpyrene has been obtained from its melt and thoroughly characterized using single-crystal X-ray diffraction, steady-state UV–Vis spectroscopy and periodic density functional theory calculations. Experimental studies covered the temperature range from 90 to 390 K and the pressure range from atmospheric to 4.08 GPa. Optimal sample placement in a diamond anvil cell according to our previously presented methodology ensured over 80% data coverage up to 0.8 Å for a monoclinic sample. Unrestrained Hirshfeld atom refinement of the high-pressure crystal structures was successful and anharmonic behavior of carbonyl oxygen atoms was observed. Unlike the previously characterized polymorph, the structure of 2°AP-β is based on infinite π-stacks of antiparallel 2°AP molecules. 2°AP-β displays piezochromism and piezofluorochromism which are directly related to the variation in interplanar distances within the π-stacking. The importance of weak intermolecular interactions is reflected in the substantial negative thermal expansion coefficient of −55.8 (57) MK−1 in the direction of C—H⋯O interactions.

In this work, regenerated cellulose textile fibers, Ioncell-F, dry-wet spun with different draw ratios, have been investigated by scanning wide-angle X-ray scattering (WAXS) using a mesoscopic X-ray beam. The fibers were found to be homogeneous on the 500 nm length scale. Analysis of the azimuthal angular dependence of a crystalline Bragg spot intensity revealed a radial dependence of the degree of orientation of crystallites that was found to increase with the distance from the center of the fiber. We attribute this to radial velocity gradients during the extrusion of the spin dope and the early stage of drawing. On the other hand, the fiber crystallinity was found to be essentially homogeneous over the fiber cross section.

Ultrahigh-resolution structures provide unprecedented details about protein dynamics, hydrogen bonding and solvent networks. The reported 0.70 Å, room-temperature crystal structure of crambin is the highest-resolution ambient-temperature structure of a protein achieved to date. Sufficient data were collected to enable unrestrained refinement of the protein and associated solvent networks using SHELXL. Dynamic solvent networks resulting from alternative side-chain conformations and shifts in water positions are revealed, demonstrating that polypeptide flexibility and formation of clathrate-type structures at hydro­phobic surfaces are the key features endowing crambin crystals with extraordinary diffraction power.

A significant part of the present and future of optoelectronic devices lies on thin multilayer heterostructures. Their optical properties depend strongly on strain, being essential to the knowledge of the stress level to optimize the growth process. Here the structural and microstructural characteristics of sub-micron a-ZnO epilayers (12 to 770 nm) grown on r-sapphire by metal–organic chemical vapour deposition are studied. Morphological and structural studies have been made using scanning electron microscopy and high-resolution X-ray diffraction. Plastic unit-cell distortion and corresponding strain have been determined as a function of film thickness. A critical thickness has been observed as separating the non-elastic/elastic states with an experimental value of 150–200 nm. This behaviour has been confirmed from ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy measurements. An equation that gives the balance of strains is proposed as an interesting method to experimentally determine this critical thickness. It is concluded that in the thinnest films an elongation of the Zn—O bond takes place and that the plastic strained ZnO films relax through nucleation of misfit dislocations, which is a consequence of three-dimensional surface morphology.

Traditional X-ray methods are extensively applied to commercial cement samples in order to determine their physical and chemical properties. Powder patterns are routinely used to quantify the composition of these phase mixtures, but structure determination becomes difficult because of reflection overlapping caused by the high number of different crystal structures. The fast-growing 3D electron diffraction technique and its related automated acquisition protocols arise as a potentially very interesting tool for the cement industry, since they enable the fast and systematic acquisition of diffraction data from individual particles. In this context, electron diffraction has been used in the investigation of the different crystalline phases present in various commercial clinkers for cement. Automated data collection procedures and subsequent data processing have enabled the structural characterization of the different crystal structures from which the α'H polymorph of Ca2SiO4 (belite) exhibited satellite reflections. Its average crystal structure has been known since 1971 and satellite reflections have been reported previously, yet the modulation was never fully described by means of the superspace formalism. Here, the incommensurately modulated structure is solved and refined using harmonic and crenel functions in the superspace group Pnma(α00)0ss, showing the potential of 3D electron diffraction for systematic crystallographic characterizations of cement. A full description of the different belite polymorphs is provided considering this modulated structure.

The NaZr2P3O12 family of materials have shown low and tailorable thermal expansion properties. In this study, SrZr4P6O24 (SrO·4ZrO2·3P2O5), CaZr4P6O24 (CaO·4ZrO2·3P2O5), MgZr4P6O24 (MgO·4ZrO2·3P2O5), NaTi2P3O12 [½(Na2O·4TiO2·3P2O5)], NaZr2P3O12 [½(Na2O·4ZrO2·3P2O5)], and related solid solutions were synthesized using the organic–inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500°C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr4P6O24 and CaZr4P6O24 was between −1 × 10−6 per °C and 6 × 10−6 per °C from 25 to 1500°C. The crystal structures of the high-temperature polymorphs of CaZr4P6O24 and SrZr4P6O24 with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above ∼1250°C. This work measured thermal expansion coefficients to 1500°C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.

The molecule of anti-epileptic drug lamotrigine [LAM; 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine] is capable of the formation of multicomponent solids. Such an enhanced tendency is related to the diverse functionalities of the LAM chemical groups able to form hydrogen bonds. Two robust synthons are recognized in the supramolecular structure of LAM itself formed via N—H⋯N hydrogen bond: homosynthon, so-called aminopyridine dimer or synthon 1 [R22(8)] and larger homosynthon 2 [R32(8)]. The synthetic procedures for a new hydrate and 11 solvates of LAM (in the series: with acetone, ethanol: two polymorphs: form I and form II, 2-propanol, n-butanol, tert-butanol, n-pentanol, benzonitrile, acetonitrile, DMSO and dioxane) were performed. The comparative solid state structural analysis of a new hydrate and 11 solvates of LAM has been undertaken in order to establish robustness of the supramolecular synthons 1 and 2 found in the crystal structure of LAM itself as well as LAM susceptibility to build methodical solid state supramolecular architecture in the given competitive surrounding of potential hydrogen bonds. The aminopyridine dimer homosynthon 1 [R22(8)] has been switched from para-para (P-P) topology to ortho-ortho (O-O) topology in all crystal structures, except in LAM:n-pentanol:water solvate where it remains P-P. Homosynthon 2 [R32(8)] of the LAM crystal structure imitates in the LAM solvates as a heterosynthon by replacing the triazine nitrogen proton acceptor atoms of LAM with the proton acceptors of solvates molecules.

A few real case examples are presented on how to report magnetic structures, with precise step-by-step explanations, following the guidelines of the IUCr Commission on Magnetic Structures [Perez-Mato et al. (2024). Acta Cryst. B80, 219–234]. Four examples have been chosen, illustrating different types of single-k magnetic orders, from the basic case to more complex ones, including odd-harmonics, and one multi-k order. In addition to acquainting researchers with the process of communicating commensurate magnetic structures, these examples also aim to clarify important concepts, which are used throughout the guidelines, such as the transformation to a standard setting of a magnetic space group.

In the course of an investigation of the supramolecular behaviour of copper(II) complexes with the 5-phenyl­imidazole/perchlorate ligand system (`blend') remarkable solvatomorphism has been observed. By employing a variety of crystallization solvents (polar protic, polar/non-polar aprotic), a series of 12 crystalline solvatomorphs with the general formula [Cu(ClO4)2(LH)4]·x(solvent) have been obtained [LH = 5-phenyl­imidazole, x(solvent) = 3.3(H2O) (1), 2(methanol) (2), 2(ethanol) (3), 2(1-propanol) (4), 2(2-propanol) (5), 2(2-butanol) (6), 2(di­methyl­formamide) (7), 2(acetone) (8), 2(tetra­hydro­furane) (9), 2(1,4-dioxane) (10), 2(ethyl acetate) (11) and 1(di­ethyl ether) (12)]. The structures have been solved using single-crystal X-ray diffraction and the complexes were characterized by thermal analysis and infrared spectroscopy. The solvatomorphs are isostructural (triclinic, P1), with the exception of compound 9 (monoclinic, P21/n). The supramolecular structures and the role of the various solvents is discussed. All potential hydrogen-bond functionalities, both of the [Cu(ClO4)2(LH)4] units and of the solvents, are utilized in the course of the crystallization process. The supramolecular assembly in all structures is directed by strong recurring Nimidazole–H⋯Operchlorate motifs leading to robust scaffolds composed of the [Cu(ClO4)2(LH)4] host complexes. The solvents are located in channels and, with the exception of the disordered waters in 1 and the di­ethyl ether in 12, participate in hydrogen-bonding formation with the [Cu(ClO4)2(LH)4] complexes, serving as both hydrogen-bond acceptors and donors (for the polar protic solvents in 2–6), or solely as hydrogen-bond acceptors (for the polar/non-polar aprotic solvents in 7–11), linking the complexes and contributing to the stability of the crystalline compounds.

In recent years, there is a significant interest from the crystallographic and materials science communities to have access to raw diffraction data. The effort in archiving raw data for access by the user community is spearheaded by the International Union of Crystallography (IUCr) Committee on Data. In materials science, where powder diffraction is extensively used, the challenge in archiving raw data is different to that from single crystal data, owing to the very nature of the contributions involved. Powder diffraction (X-ray or neutron) data consist of contributions from the material under study as well as instrument specific parameters. Having raw powder diffraction data can be essential in cases of analysing materials with poor crystallinity, disorder, micro structure (size/strain) etc. Here, the initiative and progress made by the International Centre for Diffraction Data (ICDDR) in archiving powder X-ray diffraction raw data in the Powder Diffraction FileTM (PDFR) database is outlined. The upcoming 2025 release of the PDF-5+ database will have more than 20 800 raw powder diffraction patterns that are available for reference.

Onchocerca volvulus causes blindness, onchocerciasis, skin infections and devastating neurological diseases such as nodding syndrome. New treatments are needed because the currently used drug, ivermectin, is contraindicated in pregnant women and those co-infected with Loa loa. The Seattle Structural Genomics Center for Infectious Disease (SSGCID) produced, crystallized and determined the apo structure of N-terminally hexahistidine-tagged O. volvulus macrophage migration inhibitory factor-1 (His-OvMIF-1). OvMIF-1 is a possible drug target. His-OvMIF-1 has a unique jellyfish-like structure with a prototypical macrophage migration inhibitory factor (MIF) trimer as the `head' and a unique C-terminal `tail'. Deleting the N-terminal tag reveals an OvMIF-1 structure with a larger cavity than that observed in human MIF that can be targeted for drug repurposing and discovery. Removal of the tag will be necessary to determine the actual biological oligomer of OvMIF-1 because size-exclusion chomatographic analysis of His-OvMIF-1 suggests a monomer, while PISA analysis suggests a hexamer stabilized by the unique C-terminal tails.

In the title compound, C15H14N2O2·H2O, the 1H-pyrrole ring makes a dihedral angle of 59.95 (13)° with the phenyl ring. In the crystal, the mol­ecules are connected by C—H⋯O hydrogen bonds into layers parallel to the (020) plane, while two mol­ecules are connected to the water mol­ecule by two N—H⋯O hydrogen bonds and one mol­ecule by an O—H⋯O hydrogen bond. C—H⋯π and π–π inter­actions further link the mol­ecules into chains extending in the [overline{1}01] direction and stabilize the mol­ecular packing. According to a Hirshfeld surface study, H⋯H (49.4%), C⋯H/H⋯C (23.2%) and O⋯H/H⋯O (20.0%) inter­actions are the most significant contributors to the crystal packing.

We report the synthesis and structures of two transition-metal complexes involving 2-(2-hy­droxy­phen­yl)benzimidazole (2hpbi – a ligand of inter­est for its photoluminescent applications), with cobalt, namely, bis­[μ-2-(1H-1,3-benzo­diazol-2-yl)phenolato]bis­[ethanol(thio­cyanato)­cobalt(II)], [Co2(C13H9N2O)2(NCS)2(C2H6O)2], (1), and manganese, namely, bis­[μ-2-(1H-1,3-benzo­diazol-2-yl)phenolato]bis­{[2-(1H-1,3-benzo­diazol-2-yl)phenolato](thio­cyanato)­mang­an­ese(III)} dihydrate, [Mn2(C13H9N2O)4(NCS)2]·2H2O, (2). These structures are two recent examples of a fruitful collaboration between researchers at the Laboratoire de Chimie de Coordination Organique/Organic Coordination Chemistry Laboratory (LCCO), University of Dakar, Senegal and the National Crystallography Service (NCS), School of Chemistry, University Southampton, UK. This productive partnership was forged through meeting at Pan-African Conferences on Crystallography and quickly grew as the plans for the AfCA (African Crystallographic Association) developed. This article therefore also showcases this productive partnership, in celebration of the IUCr's 75 year anniversary and the recent inclusion of AfCA as a Regional Associate of the IUCr.

The asymmetric unit of the title compound, μ-biphenyl-4,4'-di­sulfonato-bis­(aqua­lithium), [Li2(C12H8O6S2)(H2O)2] or Li2[Bph(SO3)2](H2O)2, consists of an Li ion, half of the diphenyl-4,4'-di­sulfonate [Bph(SO3−)2] ligand, and a water mol­ecule. The Li ion exhibits a four-coordinate tetra­hedral geometry with three oxygen atoms of the Bph(SO3−)2 ligands and a water mol­ecule. The tetra­hedral LiO4 units, which are inter­connected by biphenyl moieties, form a layer structure parallel to (100). These layers are further connected by hydrogen-bonding inter­actions to yield a three-dimensional network.

At room temperature, the title salt, C7H10NO+·Cl−, is ortho­rhom­bic, space group Pbca with Z' = 1, as previously reported [Zhao (2009). Acta Cryst. E65, o2378]. Between 250 and 200 K, there is a solid-state phase transition to a twinned monoclinic P21/c structure with Z' = 2. We report the high temperature structure at 250 K and the low-temperature structure at 100 K. In the low-temperature structure, the –NH3 hydrogen atoms are ordered and this group has a different orientation in each independent mol­ecule, in keeping with optimizing N—H⋯Cl hydrogen bonding, some of which are bifurcated: these hydrogen bonds have N⋯Cl distances in the range 3.1201 (8)–3.4047 (8) Å. In the single cation of the high-temperature structure, the NH hydrogen atoms are disordered into the average of the two low-temperature positions and the N⋯Cl hydrogen bond distances are in the range 3.1570 (15)–3.3323 (18) Å. At both temperatures, the meth­oxy group is nearly coplanar with the rest of the mol­ecule, with the C—C—O—C torsion angles being −7.0 (2)° at 250 K and −6.94 (12) and −9.35 (12)° at 100 K. In the extended ortho­rhom­bic structure, (001) hydrogen-bonded sheets occur; in the monoclinic structure, the sheets propagate in the (010) plane.

JUAMI, the joint undertaking for an African materials institute, is a project to build collaborations and materials research capabilities between PhD researchers in Africa, the United States, and the world. Focusing on research-active universities in the East African countries of Kenya, Ethiopia, Tanzania and Uganda, the effort has run a series of schools focused on materials for sustainable energy and materials for sustainable development. These bring together early-career researchers from Africa, the US, and beyond, for two weeks in a close-knit environment. The program includes lectures on cutting-edge research from internationally renowned speakers, highly interactive tutorial lectures on the science behind the research, also from internationally known researchers, and hands-on practicals and team-building exercises that culminate in group proposals from self-formed student teams. The schools have benefited more than 300 early-career students and led to proposals that have received funding and have led to research collaborations and educational non-profits. JUAMI continues and has an ongoing community of alumni who share resources and expertise, and is open to like-minded people who want to join and develop contacts and collaborations internationally.

In the title salt, poly[aqua­[μ4-bis­(malonato)borato]sodium], {[Na(C6H4BO8)]·H2O}n or Na+·[B(C3H2O4)2]−·H2O, the sodium cation exhibits fivefold coordination by four carbonyl O atoms of the bis­(malonato)borate anions and a water O atom. The tetra­hedral B atom at the centre of the anion leads to the formation of a polymeric three-dimensional framework, which is consolidated by C—H⋯O and O—H⋯O hydrogen bonds. A Hirshfeld surface analysis indicates that the most significant contacts in the crystal packing are H⋯O/O⋯H (49.7%), Na⋯O/O⋯Na (16.1%), O⋯O (12.6%), H⋯H (10.7%) and C⋯O/O⋯C (7.3%).

The title compound, (C4H12N)[V(C12H8N4O2)O2]·H2O, was synthesized via aerial oxidation on refluxing picolinohydrazide with ethyl picolinate followed by addition of VIVO(acac)2 and di­ethyl­amine in methanol. It crystallizes in the triclinic crystal system in space group Poverline{1}. In the complex anion, the dioxidovanadium(V) moiety exhibits a distorted square-pyramidal geometry. In the crystal, extensive hydrogen bonding links the water mol­ecule to two complex anions and one di­ethyl­ammonium ion. One of the CH2 groups in the di­ethyl­amine is disordered over two sets of sites in a 0.7:0.3 ratio.

The crystal structure of the title compound {systematic name: (4S,4aS,5aR,12aR)-4,7-bis­(di­methyl­amino)-9-[(2,2-di­methyl­propyl­amino)­meth­yl]-1,10,11,12a-tetra­hydroxy-3,12-dioxo-4a,5,5a,6-tetra­hydro-4H-tetra­cene-2-carb­oxamide dihydrate, C29H40N4O7·2H2O} has been solved and refined using synchrotron X-ray powder diffraction data: it crystallizes in space group R3 with a = 24.34430 (7), c = 14.55212 (4) Å, V = 7468.81 (2) Å3 and Z = 9. Most of the hydrogen bonds are intra­molecular, but two classical N—H⋯O inter­molecular hydrogen bonds (along with probable weak C—H⋯O and C—H⋯N hydrogen bonds) link the mol­ecules into a three-dimensional framework. The framework contains voids, which contain disordered water mol­ecules. Keto–enol tautomerism is apparently important in this mol­ecule, and the exact mol­ecular structure is ambiguous.

The title compound, C14H12N4O2·0.5HCl·H2O or H(C14H12N4O2)2+·Cl−·2H2O, arose from the unexpected cyclization of isonicotinoyl-N-phenyl hydrazine carbo­thio­amide catalysed by cobalt(II) acetate. The organic mol­ecule is almost planar and a symmetric N⋯H+⋯N hydrogen bond links two of them together, with the H atom lying on a crystallographic twofold axis. The extended structure features N—H⋯O and O—H⋯Cl hydrogen bonds, which generate [001] chains. Weak C—H⋯Cl inter­actions cross-link the chains. The chloride ion has site symmetry 2. The major contributions to the Hirshfeld surface are from H⋯H (47.1%), Cl⋯H/H⋯Cl (total 10.8%), O⋯H/H⋯O (7.4%) and N⋯H/H⋯N (6.7%) inter­actions.

In the crystal of the title compound, C18H14O10·2H2O, the arene rings of the biphenyl moiety are tilted at an angle of 24.3 (1)°, while the planes passing through the carboxyl groups are rotated at angles of 8.6 (1) and 7.7 (1)° out of the plane of the benzene ring to which they are attached. The crystal structure is essentially stabilized by O—H⋯O bonds. Here, the carboxyl groups of neighbouring host mol­ecules are connected by cyclic R22(8) synthons, leading to the formation of a three-dimensional network. The water mol­ecules in turn form helical supra­molecular strands running in the direction of the crystallographic c-axis (chain-like water clusters). The second H atom of each water mol­ecule provides a link to a meth­oxy O atom of the host mol­ecule. A Hirshfeld surface analysis was performed to qu­antify the contributions of the different inter­molecular inter­actions, indicating that the most important contributions to the crystal packing are from H⋯O/O⋯H (37.0%), H⋯H (26.3%), H⋯C/C⋯H (18.5%) and C⋯O/O⋯C (9.5%) inter­actions.

Treatment of 3-(3,4-di­hydroxy­phen­yl)propenoic acid (caffeic acid or 3,4-di­hydroxy­cinnamic acid) with the alkali hydroxides MOH (M = Li, Na) in aqueous solution led to the formation of poly[aqua­[μ-3-(3,4-di­hydroxy­phen­yl)propenoato]lithium], [Li(C9H7O4)(H2O)]n, 1, and poly[aqua­[μ-3-(3,4-di­hydroxy­phen­yl)propenoato]sodium], [Na(C9H7O4)(H2O)]n, 2. The crystal structure of 1 consists of a lithium cation that is coordinated nearly tetra­hedrally by three carboxyl­ate oxygen atoms and a water mol­ecule. The carboxyl­ate groups adopt a μ3-κ3O:O':O' coordination mode that leads to a chain-like catenation of Li cations and carboxyl­ate units parallel to the b axis. Moreover, the lithium carboxyl­ate chains are connected by hydrogen bonds between water mol­ecules attached to lithium and catechol OH groups. The crystal structure of 2 shows a sevenfold coordination of the sodium cation by one water mol­ecule, two monodentately binding carboxyl­ate groups and four oxygen atoms from two catechol groups. The coordination polyhedra are linked by face- and edge-sharing into chains extending parallel to the b axis. The chains are inter­linked by the bridging 3-(3,4-di­hydroxy­phen­yl)propenoate units and by inter­molecular hydrogen bonds to form the tri-periodic network.

The structures of fourteen halochalcogenyl­phospho­nium tetra­halogen­ido­aurates(III), phosphane chalcogenide derivatives with general formula [R13–nR2nPEX][AuX4] (R1 = t-butyl; R2 = isopropyl; n = 0 to 3; E = S or Se; X = Cl or Br) are presented. The eight possible chlorido derivatives are: 17a, n = 3, E = S; 18a, n = 2, E = S; 19a, n = 1, E = S; 20a, n = 0, E = S; 21a, n = 3, E = Se; 22a, n = 2, E = Se; 23a, n = 1, E = Se; and 24a, n = 0, E = Se, and the corresponding bromido derivatives are 17b–24b in the same order. Structures were obtained for all compounds except for the tri-t-butyl derivatives 24a and 24b. Isotypy is observed for 18a/18b/22a/22b, 19a/23a, 17b/21b and 19b/23b. In eleven of the compounds, X⋯X contacts (mostly very short) are observed between the cation and anion, whereby the E—X⋯X groups are approximately linear and the X⋯X—Au angles approximately 90°. The exceptions are 17a, 19a and 23a, which instead display short E⋯X contacts. Bond lengths in the cations correspond to single bonds P—E and E—X. For each group with constant E and X, the P—E—X bond-angle values increase monotonically with the steric bulk of the alkyl groups. The packing is analysed in terms of E⋯X, X⋯X (some between anions alone), H⋯X and H⋯Au contacts. Even for isotypic compounds, some significant differences can be discerned.

The asymmetric unit of the title compound, C25H18N6·H2O, comproses two mol­ecules (I and II), together with a water mol­ecule. The terminal phenyl groups attached to the methyl groups of the mol­ecules I and II do not overlap completely, but are approximately perpendicular. In the crystal, the mol­ecules are connected by N—H⋯N, C—H⋯N, O—H⋯N and N—H⋯O hydrogen bonds with each other directly and through water mol­ecules, forming layers parallel to the (001) plane. C—H⋯π inter­actions between these layers ensure the cohesion of the crystal structure. A Hirshfeld surface analysis indicates that H⋯H (39.1% for mol­ecule I; 40.0% for mol­ecule II), C⋯H/H⋯C (26.6% for mol­ecule I and 25.8% for mol­ecule II) and N⋯H/H⋯N (24.3% for mol­ecules I and II) inter­actions are the most important contributors to the crystal packing.

This study introduces bis­[hexa­kis­(nitrato-κ2O,O')lanthanum(III)] tris­[hexa­aqua­nickel(II)] hexa­hydrate, [La(NO3)6]2[Ni(H2O)6]3·6H2O, with a structure refined in the hexa­gonal space group Roverline{3}. The salt com­prises [La(NO3)6]3− icosa­hedra and [Ni(H2O)6]2+ octa­hedra, thus forming an intricate network of inter­penetrating honeycomb lattices arranged in layers. This arrangement is stabilized through strong hydrogen bonds. Two successive layers are connected via the second [Ni(H2O)6]2+ octa­hedra, forming sheets which are stacked perpendicular to the c axis and held in the crystal by van der Waals forces. The synthesis of [La(NO3)6]2[Ni(H2O)6]3·6H2O involves dissolving lanthanum(III) and nickel(II) oxides in nitric acid, followed by slow evaporation, yielding green hexa­gonal plate-like crystals.

The title compound, [Co(C3H4N2)(C30H30N10)](BF4)2, is a five-coordinate CoII complex based on the neutral ligands tris­[(1-benzyl­triazol-4-yl)meth­yl]amine (tbta) and imidazole. It exhibits a distorted trigonal bipyramidal geometry in which the equatorial positions are occupied by the three N-atom donors from the triazole rings of the tripodal tbta ligand. The apical amine N-atom donor of tbta and the N-atom donor of the imidazole ligand occupy the axial positions of the coordination sphere. Two tetra­fluoro­borate anions provide charge balance in the crystal.

The title compound, C12H16N2O, is a hy­droxy-substituted mono­amine alkaloid, and the primary metabolite of the naturally occurring psychedelic compound psilocybin. Crystalline forms of psilocin are known, but their characterization by single-crystal structure analysis is limited. Herein, two anhydrous polymorphic forms (I and II) of psilocin are described. The crystal structure of polymorphic Form I, in space group P21/c, was first reported in 1974. Along with the redeterm­ination to modern standards and unambiguous location of the acidic H atom and variable-temperature single-crystal unit-cell determinations for Form I, the Form II polymorph of the title compound, which crystallizes in the monoclinic space group P21/n, is described for the first time. The psilocin mol­ecules are present in both forms in their phenol–amine tautomeric forms (not resolved in the 1974 report). The mol­ecules in Forms I and II, however, feature different conformations of their N,N-dimethyl ethyl­ene substituent, with the N—C—C—C link in Form I being trans and in Form II being gauche, allowing the latter to bend back to the hydroxyl group of the same mol­ecule, leading to the formation of a strong intra­molecular O—H⋯N hydrogen bond between the hydroxyl moiety and ethyl­amino-nitro­gen group. In the extended structure of Form II, the mol­ecules form one-dimensional strands through N—H⋯O hydrogen bonds from the indole group to the oxygen atom of the hydroxyl moiety of an adjacent mol­ecule. Form II exhibits whole-mol­ecule disorder due to a pseudo-mirror operation, with an occupancy ratio of 0.689 (5):0.311 (5) for the two components. In contrast, Form I does not feature intra­molecular hydrogen bonds but forms a layered structure through inter­molecular N—H⋯O and O—H⋯N hydrogen bonds.

Crystal formation of penta­sodium nona­deca­cesium tetra­cosa­tungstate(VI) heneikosahydrate, Na5Cs19[W24O84]·21H2O, was successfully achieved by the conversion of [H2W12O42]10− through the addition of excess Cs+. The crystal structure comprising the toroidal isopolyoxidometalate is presented, as well as its Raman spectrum. Na5Cs19(H2O)21W24O84 crystallizes in the rhombohedral space group Roverline{3} with an obverse centering. The title compound represents the addition of a new member to the isopolytungstate family with mixed alkali counter-ions and contains rarely observed five-coordinate tungsten(VI) atoms in the [W24O84]24− anion (site symmetry C3i) arising from the conversion mediated by Cs+ counter-ions.

The mol­ecular structure of tricarbon­yl[η4-6-exo-(tri­phenyl­phosphino)cyclo­hepta-2,4-dien-1-one]iron(0) tetra­fluoro­borate di­chloro­methane hemisolvate, [Fe(C28H22O4)(CO)3]BF4·0.5CH2Cl2, as determined by single-crystal X-ray diffraction is reported. The two independent tricarbon­yl[η4-6-exo-(tri­phenyl­phosphino)cyclo­hepta-2,4-dien-1-one] iron(0) cations and their corresponding anions form dimers, which constitute the asymmetric unit of the structure parallel to the (100) plane. Solid-state stability within that asymmetric unit as well as between neighboring dimeric units is afforded by C—H⋯O and C—H⋯F hydrogen bonds and C—H⋯π and Y—X⋯π (Y = B, C; X = F, O) inter­actions, which yield diperiodic sheets and a three-dimensional extended network.

The crystal structure of 1,2,3,4-tetra­hydro­isoquinolin-2-ium (2S,3S)-3-carb­oxy-2,3-di­hydroxy­propano­ate monohydrate, C9H12N+·C4H5O6−·H2O, at 115 K shows ortho­rhom­bic symmetry (space group P212121). The hydrogen tartrate anions and solvent water mol­ecules form an intricate diperiodic O—H⋯O hydrogen-bond network parallel to (001). The tetra­hydro­isoquinolinium cations are tethered to the anionic hydrogen-bonded layers through N—H⋯O hydrogen bonds. The crystal packing in the third direction is achieved through van der Waals contacts between the hydro­carbon tails of the tetra­hydro­isoquinolinium cations, resulting in hydro­phobic and hydro­philic regions in the crystal structure.

Reaction of thorium(IV) nitrate with 2-[(4-phenyl-1H-1,2,3-triazol-1-yl)meth­yl]pyridine (L) yielded (LH)2[Th(NO3)6] or (C14H13N4)2[Th(NO3)6] (1), instead of the expected mixed-ligand complex [Th(NO3)4L2], which was detected in the mass spectrum of 1. In the structure, the [Th(NO3)6]2− anions display an icosa­hedral coordination geometry and are connected by LH+ cations through C—H⋯O hydrogen bonds. The LH+ cations inter­act via N—H⋯N hydrogen bonds. Hirshfeld surface analysis indicates that the most important inter­actions are O⋯H/H⋯O hydrogen-bonding inter­actions, which represent a 55.2% contribution.

Propane-1,3-diaminium squarate dihydrate, C3H12N22+·C4O42−·2H2O, results from the proton-transfer reaction of propane-1,3-di­amine with squaric acid and subsequent crystallization from aqueous medium. The title compound crystallizes in the tetra­gonal crystal system (space group P4bm) with Z = 2. The squarate dianion belongs to the point group D4h and contains a crystallographic fourfold axis. The propane-1,3-diaminium dication exhibits a C2v-symmetric all-anti conformation and resides on a special position with mm2 site symmetry. The orientation of the propane-1,3-diaminium ions makes the crystal structure polar in the c-axis direction. The solid-state supra­molecular structure features a triperiodic network of strong hydrogen bonds of the N—H⋯O and O—H⋯O types.

In the structure of the title salt, {[Ba(μ3-C3H2N3O2)2(μ-H2O)(H2O)]·H2O}n, the barium ion and all three oxygen atoms of the water mol­ecules reside on a mirror plane. The hydrogen atoms of the bridging water and the solvate water mol­ecules are arranged across a mirror plane whereas all atoms of the monodentate aqua ligand are situated on this mirror plane. The distorted ninefold coord­ination of the Ba ions is completed with four nitroso-, two carbonyl- and three aqua-O atoms at the distances of 2.763 (3)–2.961 (4) Å and it is best described as tricapped trigonal prism. The three-dimensional framework structure is formed by face-sharing of the trigonal prisms, via μ-nitroso- and μ-aqua-O atoms, and also by the bridging coordination of the anions via carbonyl-O atoms occupying two out of the three cap positions. The solvate water mol­ecules populate the crystal channels and facilitate a set of four directional hydrogen bonds. The principal Ba–carbamoyl­cyano­nitro­somethanido linkage reveals a rare example of the inherently polar binodal six- and three-coordinated bipartite topology (three-letter notation sit). It suggests that small resonance-stabilized cyano­nitroso anions can be utilized as bridging ligands for the supra­molecular synthesis of MOF solids. Such an outcome may be anti­cipated for a broader range of hard Lewis acidic alkaline earth metal ions, which perfectly match the coordination preferences of highly nucleophilic nitroso-O atoms. Thermal analysis reveals two-stage dehydration of the title compound (383 and 473 K) followed by decomposition with release of CO2, HCN and H2O at 558 K.

The synthesis of the title compound, [Zn(C4H6N2)6](NO3)2, is described. This complex consists of a central zinc metal ion surrounded by six 1-methyl­imidazole ligands, charge balanced by two nitrate anions. The complex crystallizes in the space group Poverline{3}. In the crystal, the nitrate ions are situated within the cavities created by the [Zn(N-Melm)6]2+ cations, serving as counter-ions. The three oxygen atoms of the nitrate ion engage in weak C—H⋯O inter­actions. In addition to single-crystal X-ray diffraction analysis, the complex was characterized using elemental analysis, 1H NMR, 13C NMR, and FTIR spectroscopy.

The mol­ecular salt sulfamethoxazolium {or 4-[(5-methyl-1,2-oxazol-3-yl)sulf­amo­yl]anilinium methyl sulfate monohydrate}, C10H12N3O3S+·CH3O4S−·H2O, was prepared by the reaction of sulfamethoxazole and H2SO4 in methanol and crystallized from methanol–ether–water. Protonation takes place at the nitro­gen atom of the primary amino group. In the crystal, N—H⋯O hydrogen bonds (water and methyl­sulfate anion) and inter­molecular N—H⋯N inter­actions involving the sulfonamide and isoxazole nitro­gen atoms, link the components into a tri-dimensional network, additional cohesion being provided by face-to-face π–π inter­actions between the phenyl rings of adjacent mol­ecules. A Hirshfeld surface analysis was used to verify the contributions of the different inter­molecular inter­actions, showing that the three most important contributions for the crystal packing are from H⋯O (54.1%), H⋯H (29.2%) and H⋯N (5.0%) inter­actions.

The title compound, (C9H8NO)[CuCl3(C7H5NO4)]·2H2O, was prepared by reacting CuII acetate dihydrate, solid 8-hy­droxy­quinoline (8-HQ), and solid pyridine-2,6-di­carb­oxy­lic acid (H2pydc), in a 1:1:1 molar ratio, in an aqueous solution of dilute hydro­chloric acid. The CuII atom exhibits a distorted CuO2NCl3 octa­hedral geometry, coordinating two oxygen atoms and one nitro­gen atom from the tridentate H2pydc ligand and three chloride atoms; the nitro­gen atom and one chloride atom occupy the axial positions with Cu—N and Cu—Cl bond lengths of 2.011 (2) Å and 2.2067 (9) Å, respectively. In the equatorial plane, the oxygen and chloride atoms are arranged in a cis configuration, with Cu—O bond lengths of 2.366 (2) and 2.424 (2) Å, and Cu—Cl bond lengths of 2.4190 (10) and 2.3688 (11) Å. The asymmetric unit contains 8-HQ+ as a counter-ion and two uncoordinated water mol­ecules. The crystal structure features strong O—H⋯O and O—H⋯Cl hydrogen bonds as well as weak inter­actions including C—H⋯O, C—H⋯Cl, Cu—Cl⋯π, and π–π, which result in a three-dimensional network. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing involving the main residues are from H⋯Cl/Cl⋯H inter­actions, contributing 40.3% for the anion. Weak H⋯H contacts contribute 13.2% for the cation and 28.6% for the anion.

The title compound, a hydrate of 3,5-di­amino-1,2,4-triazole (DATA), C2H5N5·H2O, was synthesized in the presence of sodium perchlorate. The evaporation of H2O from its aqueous solution resulted in anhydrous DATA, suggesting that sodium perchlorate was required to precipitate the DATA hydrate. The DATA hydrate crystallizes in the P21/c space group in the form of needle-shaped crystals with one DATA and one water mol­ecule in the asymmetric unit. The water mol­ecules form a three-dimensional network in the crystal structure. Hirshfeld surface analysis revealed that 8.5% of the inter­molecular inter­actions originate from H⋯O contacts derived from the incorporation of the water mol­ecules.

The reaction of Zn(ClO4)2·6H2O with Na3SbS4·9H2O in a water/aceto­nitrile mixture leads to the formation of the title compound, (μ-tetra­thio­anti­monato-κ2S:S')bis­[(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ4N)zinc(II)] perchlorate 0.8-hydrate, [Zn2(SbS4)(C10H24N4)2]ClO4·0.8H2O or [(Zn-cyclam)2(SbS4)]+[ClO4]−·0.8H2O. The asymmetric unit consists of two crystallographically independent [SbS4]3– anions, two independent perchlorate anions and two independent water mol­ecules as well as four crystallographically independent Zn(cyclam)2+ cations that are located in general positions. Both perchlorate anions and one cyclam ligand are disordered and were refined with a split mode using restraints. The water mol­ecules are partially occupied. Two Zn(cyclam)2+ cations are linked via the [SbS4]3– anions into [Zn2(cyclam)2SbS4]+ cations that are charged-balanced by the [ClO4]− anions. The water mol­ecules of crystallization are hydrogen bonded to the [SbS4]3– anions. The cations, anions and water mol­ecules are linked by N—H⋯O, N—H⋯S and O—H⋯S hydrogen bonds into a three-dimensional network. Powder X-ray diffraction proves that a pure sample had been obtained that was additionally investigated for its spectroscopic properties.

The title hydrated mol­ecular salt, C19H15N4+·Cl−·2.5H2O, has two tri­phenyl­tetra­zolium cations, two chloride anions and five water mol­ecules in the asymmetric unit. The cations differ in the conformations of the phenyl rings with respect to the heterocyclic core, most notably for the C-bonded phenyl ring, for which the N—C—C—C torsion angles differ by 36.4 (3)°. This is likely a result of one cation accepting an O—H⋯N hydrogen bond from a water mol­ecule [O⋯N = 3.1605 (15) Å], while the other cation accepts no hydrogen bonds. In the extended structure, the water mol­ecules are involved in centrosymmetric (H2O)2Cl2 rings as well as (H2O)4 chains. An unusual O—H⋯π inter­action and weak C—H⋯O and C—H⋯Cl hydrogen bonds are also observed.