Foreword to the AfCA collection: celebrating work published by African researchers in IUCr journals.

This virtual collection is a celebration. It is a celebration of crystallography in Africa, and a celebration of the international crystallography community. It commemorates the founding of the African Crystallographic Association (AfCA), which was accepted as the newest Regional Associate of the International Union of Crystallography (IUCr) in 2023, the year of the 75th anniversary of the first IUCr Congress and General Assembly.

Chemistry and crystal engineering.

Recent studies published in the Chemistry and crystal engineering section of IUCrJ emphasize developments both in methodology and techniques as well as the diverse range of classes of compounds being studied and of problems being tackled.

A homochiral coordination polymer of cobalt(II) and L-serine.

A one-dimensional chiral cobalt(II) coordination polymer, namely, catena-poly[[[(S)-2-amino-3-hydroxypropanoato-κN,O]cobalt(II)]-μ-(S)-2-amino-3-hydroxypropanoato-κO,O:N,O], [Co(CHNO)] or Δ-[Co(L-Ser-κN,O)] (L-Ser = L-serine) (1), has been synthesized and characterized using elemental and thermal analyses, IR spectroscopy and single-crystal and powder X-ray diffraction techniques. The asymmetric unit of 1 consists of two serine anions which are coordinated to a Co ion to give three chelate rings. These extend the structure into a helical chain with pendant chelate rings which participate in interchain hydrogen bonding.

Increasing complexity: structural equivalence and combinatorial approaches to preparation of high order cocrystals.

An algorithmic strategy to design stoichiometric quaternary and solid-solution quinary solids is described. The strategy involves recognition of structural inequivalences to generate ternary and quaternary cocrystals which can then be extended to five-component solid solutions through matching of suitable interactions.

Inclusion of Hydroxycinnamic Acids in Methylated Cyclodextrins: Host-Guest Interactions and Effects on Guest Thermal Stability.

There is ongoing interest in exploiting the antioxidant activity and other medicinal properties of natural monophenolic/polyphenolic compounds, but their generally low aqueous solubility limits their applications. Numerous studies have been undertaken to solubilize such compounds via supramolecular derivatization with co-crystal formation with biocompatible coformer molecules and cyclodextrin (CD) complexation being two successful approaches. In this study, eight new crystalline products obtained by complexation between methylated cyclodextrins and the bioactive phenolic acids (ferulic, hydroferulic, caffeic, and -coumaric acids) were investigated using thermal analysis (hot stage microscopy, thermogravimetry, differential scanning calorimetry) and X-ray diffraction.

Synthesis and Characterization of 2D Metal-Organic Frameworks for Adsorption of Carbon Dioxide and Hydrogen.

The reaction of Cd(NO)·4HO and Zn(NO)·6HO with the bipyridyl dicarboxylate ligand Hbpydc (2,2'-bipyridine-4,4'-dicarboxylic acid) afforded two porous metal organic frameworks [Cd(bpydc)(DMF)·2DMF] (JMS-3) and [Zn(bpydc)(DMF)·DMF] (JMS-4). X-ray diffraction studies revealed that both JMS-3 and JMS-4 crystallize in the monoclinic crystal. The MOFs possess 2D interdigited networks with () topology.

Cyclometalation of lanthanum(iii) based MOF for catalytic hydrogenation of carbon dioxide to formate.

The hydrogenation of carbon dioxide (CO) to formic acid is of great importance due to its useful properties in the chemical industry. In this work, we have prepared a novel metal-organic framework (MOF), JMS-1, using bipyridyl dicarboxylate linkers, with molecular formula [La(bpdc)(DMF)] . Network analysis of JMS-1 revealed a new 7-connected topology ().

Cocrystal and Salt Forms of an Imidazopyridazine Antimalarial Drug Lead.

Cocrystallization and salt formation were used to produce new multicomponent forms of a novel antimalarial imidazopyridazine drug lead (MMV652103) that displayed improved physicochemical properties. The drug lead had earlier shown good in vitro potency against multidrug resistant (K1) and sensitive (NF54) strains of the human malaria parasite Plasmodium falciparum, and high in vivo efficacy in both Plasmodium berghei and Plasmodium falciparum mouse models. A major drawback of MMV652103 is its limited aqueous solubility.

Control of crystal structure using temperature and time.

Three novel crystal structures were obtained from iron(III) acetylacetonate and 2,6-pyridinedicarboxylic acid. The structures elucidated were found to be dependent on the temperature and length of time allowed for the reaction. The product of the reaction between iron(III) acetylacetonate and 2,6-pyridinedicarboxylic acid in acetonitrile at room temperature is [FeCHNO]·CHCN, (I).

Supramolecular metallogels constructed from carboxylate gelators.

Serendipity still plays a role in gel discovery as the prediction of gel formation is difficult. This work explores the role of ligand, metal salt, solvent, and temperature in the formation of a low molecular mass carboxylate iron(iii) system. The influence of each component is discussed.

Fe(III) Protoporphyrin IX Encapsulated in a Zinc Metal-Organic Framework Shows Dramatically Enhanced Peroxidatic Activity.

Two MOFs, [HN(CH)][Zn(TATB)(HCOO)]·HN(CH)·DMF·6HO (1) and Zn-HKUST-1 (2), were investigated as potential hosts to encapsulate Fe(III) heme (Fe(III) protoporphyrin IX = Fe(III)PPIX). Methyl orange (MO) adsorption was used as an initial model for substrate uptake. MOF 1 showed good adsorption of MO (10.

Encapsulation of the Antioxidant R-(+)-α-Lipoic Acid in Permethylated α- and β-Cyclodextrins: Thermal and X-ray Structural Characterization of the 1:1 Inclusion Complexes.

The naturally occurring compound α-lipoic acid (ALA) is implicated in manifold critical biological roles and its potent antioxidant properties and potential for treatment of various diseases have led to its widespread use as a dietary supplement. However, shortcomings of poor aqueous solubility and low thermal stability have hampered its development as a medicinal agent, prompting the use of cyclodextrins (CDs) to address these problems. The paucity of published structural data on the nature of the interactions between ALA and CDs motivated the present study, which describes the synthesis and X-ray structural elucidation of crystalline inclusion complexes between the biologically relevant R-(+)-α-lipoic acid (RALA) and the host molecules permethylated α-CD (TMA) and permethylated β-CD (TMB).

Inclusion complexes of 2-methoxyestradiol with dimethylated and permethylated β-cyclodextrins: models for cyclodextrin-steroid interaction.

The interaction between the potent anticancer agent 2-methoxyestradiol (2ME) and a series of cyclodextrins (CDs) was investigated in the solid state using thermal analysis and X-ray diffraction, while the possibility of enhancing its poor aqueous solubility with CDs was probed by means of equilibrium solubility and dissolution rate measurements. Single crystal X-ray diffraction studies of the inclusion complexes between 2ME and the derivatised cyclodextrins heptakis(2,6-di-O-methyl)-β-CD (DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-CD (TRIMEB) revealed for the first time the nature of the encapsulation of a bioactive steroid by representative CD host molecules. Inclusion complexation invariably involves insertion of the D-ring of 2ME from the secondary side of each CD molecule, with the 17-OH group generally hydrogen bonding to a host glycosidic oxygen atom within the CD cavity, while the A-ring and part of the B-ring of 2ME protrude from the secondary side.

Thermal, X-ray Structural, and Dissolution Characteristics of Solid Forms Derived from the Anticancer Agents 2-Methoxyestradiol and 2-Methoxyestradiol-3,17-O,O-Bis-Sulfamate.

The aim of the study was to generate alternative solid forms of 2-methoxyestradiol (2ME) and its sulfamoylated derivative 2-methoxyestradiol-3,17-O,O-bis-sulfamate (2MES), both of which are potent anticancer agents with no significant history of solid-state investigation. Screening for polymorphs and solvates by a variety of procedures yielded four distinct species: a crystalline form of 2ME, an amorphous form of 2ME, a chloroform solvate 2ME·(CHCl3 )2 , and the hemihydrate of the bis-sulfamate, 2MES·(H2 O)0.5 .

Inclusion of trans-resveratrol in methylated cyclodextrins: synthesis and solid-state structures.

The phytoalexin trans-resveratrol, 5-[(1E)-2-(4-hydroxyphenyl)ethenyl]-1,3-benzenediol, is a well-known, potent antioxidant having a variety of possible biomedical applications. However, its adverse physicochemical properties (low stability, poor aqueous solubility) limit such applications and its inclusion in cyclodextrins (CDs) has potential for addressing these shortcomings. Here, various methods of the attempted synthesis of inclusion complexes between trans-resveratrol and three methylated cyclodextrins (permethylated α-CD, permethylated β-CD and 2,6-dimethylated β-CD) are described.

Inclusion of the insecticide fenitrothion in dimethylated-β-cyclodextrin: unusual guest disorder in the solid state and efficient retardation of the hydrolysis rate of the complexed guest in alkaline solution.

An anhydrous 1:1 crystalline inclusion complex between the organophosphorus insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl)phosphorothioate] and the host compound heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) was prepared and its structure elucidated by single-crystal X-ray diffraction. This revealed two independent host molecules in the asymmetric unit. In one of these, the cavity is occupied by two disordered guest components (distinguishable as rotamers with respect to the P-OAr bond) while in the other, three distinct guest components with site-occupancies 0.

Topological studies of three related metal-organic frameworks of GdIII and 5-nitroisophthalate.

The reaction of 5-nitroisophthalic acid (H(2)NIA) with Gd(NO(3))(3)·6H(2)O in DMF afforded three new metal-organic frameworks: [Gd(NIA)(1.5)(DMF)(2)]·DMF (I), [Gd(2)(NIA)(3)(DMF)(4)]·xH(2)O (II) and [Gd(4)(NIA)(6)(DMF)(5.5)(H(2)O)(3)]·4DMF·H(2)O (III).

A new class of thermo- and solvatochromic metal-organic frameworks based on 4-(pyridin-4-yl)benzoic acid.

Using 4-(pyridin-4-yl)benzoic acid, 44pba (1) as a ligand, two new metal-coordination networks [Co(4)(44pba)(8)](n)·[(DMF)(3)·(EtOH)(0.25)·(H(2)O)(4)](n) (2) and [Ni(4)(44pba)(8)](n)·[(DMF)(3.5)·(EtOH)·(H(2)O)(1.

Benzoic acid-3,4-bis-[(pyridin-3-ylmeth-yl)amino]-cyclo-but-3-ene-1,2-dione (1/2).

In the title co-crystal, C(16)H(14)N(4)O(2)·2C(7)H(6)O(2), the 3,4-bis-[(pyridin-3-ylmeth-yl)amino]-cyclo-but-3-ene-1,2-dione squareamide mol-ecules assemble into chains along the b axis via N-H⋯O hydrogen bonds. The benzoic acid mol-ecules then hydrogen bond to the pyridine rings via O-H⋯N hydrogen bonds, supported by weaker C-H⋯O hydrogen bonds, forming extended ribbons. The asymmetric unit consists of a half squareamide mol-ecule, sitting on a special position around a twofold axis, and one benzoic acid mol-ecule on a general position.

Crystallization of toxic glycol solvates of rifampin from glycerin and propylene glycol contaminated with ethylene glycol or diethylene glycol.

This study was initiated when it was suspected that syringe blockage experienced upon administration of a compounded rifampin suspension was caused by the recrystallization of toxic glycol solvates of the drug. Single crystal X-ray structure analysis, powder X-ray diffraction, thermal analysis and gas chromatography were used to identify the ethylene glycol in the solvate crystals recovered from the suspension. Controlled crystallization and solubility studies were used to determine the ease with which toxic glycol solvates crystallized from glycerin and propylene glycol contaminated with either ethylene or diethylene glycol.

Effect of cyclodextrins on the reactivity of fenitrothion.

The hydrolysis reaction of fenitrothion was studied in water containing 2% dioxane and in the presence of native cyclodextrins (α-, β- and γ-CD) and two commercially available modified derivatives, namely, permethylated β- and α-cyclodextrin (TRIMEB and TRIMEA, respectively). The kinetics of the reaction in the presence of TRIMEA could not be measured because the complex formed is insoluble and precipitated even at low concentration. On the other hand, the reaction is only weakly affected by the presence of α-CD.

New polymorphs of isonicotinamide and nicotinamide.

For each of the well-known co-crystal formers, isonicotinamide and nicotinamide, a new polymorph, obtained during attempted co-crystallisation experiments, has been fully characterized and its stability relationship with previously reported forms established.

Anionic zinc-trimesic acid MOFs with unusual topologies: reversible hydration studies.

The reaction of 1,3,5-benzenetricarboxylic acid (H(3)BTC) with ZnSO(4).6H(2)O in a DMF-water solution afforded two new metal-organic frameworks [Zn(6)(mu(3)-OH)(2)(BTC)(4)(DMF)(2.5)(H(2)O)(2)].

Solid-state structures and thermal properties of inclusion complexes of the organophosphate insecticide fenitrothion with permethylated cyclodextrins.

The X-ray crystal structures and thermal stabilities of the inclusion complexes formed between the organophosphate insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate] and the host compounds TRIMEA and TRIMEB (permethylated alpha- and beta-cyclodextrins, respectively) are reported. In the complex (TRIMEA)(2).fenitrothion 1, the guest phosphate ester group is disordered and the molecule is fully encapsulated within a novel TRIMEA dimer in which the secondary rims of the two host molecules are in close contact.

Investigation of the inclusion of the herbicide metobromuron in native cyclodextrins by powder X-ray diffraction and isothermal titration calorimetry.

We report the formation of inclusion complexes between the phenylurea herbicide metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea] and beta- and gamma-cyclodextrin in the solid state. Formation of crystalline inclusion complexes by the kneading method was confirmed by powder X-ray diffraction and further structural characterization using the principles of isostructurality followed. In addition, DeltaH degrees , DeltaS degrees , DeltaG degrees and the association constants (K) at 298K were determined for complex formation in solution using isothermal titration calorimetry.