Seven new crystal structures of 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine (2-bptz) and 3,6-bis(pyridin-4-yl)-1,2,4,5-tetrazine (4-bptz) were determined with inorganic halogen donors (I2 or I3-), organic halogen donors [1,4-diiodotetrafluroobenzene (p-F4DIB) or 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TFTIB)], and the hydrogen-bond donor hydroquinone to investigate how pyridyl orientation and donor type influence supramolecular assembly. Structures formed with molecular iodine, namely, 2,2'-(1,2,4,5-tetrazine-3,6-diyl)dipyridinium bis(triiodide)-3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-diiodine (1/1/1), C12H10N62+·2I3-·C12H8N6·I2 (1), and 4-[6-(pyridin-4-yl)-1,2,4,5-tetrazin-3-yl]pyridinium pentaiodide, C12H9N6+·I5- (2), are dominated by N-H...N hydrogen bonding, with pyridine protonation yielding distinct packing arrangements: 2-bptz forms stacked triads along the a axis, whereas 4-bptz assembles into chains of [H(4-bptz)]+ cations alternating with pentaiodide layers. Replacement of iodine with organoiodines in 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-1,4-diiodotetrafluorobenzene (1/1), C6F4I2·C12H8N6 (3), 3,6-bis(pyridin-4-yl)-1,2,4,5-tetrazine-1,4-diiodotetrafluorobenzene (1/1), C6F4I2·C12H8N6 (4), and 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-1,3,5-trifluoro-2,4,6-triiodobenzene (1/2), C6H4N3·C6F3I3 (5), shifts the primary interactions to C-I...N halogen bonding, producing one-dimensional staggered chains in 2-bptz and linear motifs in 4-bptz, with bifurcated C-I...N interactions in 5 involving both pyridine and tetrazine N atoms. Halogen-halogen and halogen-fluorine interactions further modulate packing and stacking orientations. Reactions with hydroquinone in 3,6-bis(pyridin-2-yl)-1,2,4,5-tetrazine-hydroquinine (2/1), 2C12H8N6·C6H6O2 (6), and 3,6-bis(pyridin-4-yl)-1,2,4,5-tetrazine-hydroquinine (1/1), C12H8N6·C6H6O2 (7), reveal the role of hydrogen bonding in long-range organization: 2-bptz forms discrete triads, whereas 4-bptz generates extended chains propagating through pyridine-phenol interactions. Pyridine-to-tetrazine plane-to-plane angles vary across structures, reflecting the influence of substitution pattern and donor type on molecular geometry. These results demonstrate that subtle changes in pyridyl orientation and the nature of halogen- or hydrogen-bond donors can direct the formation of distinct supramolecular architectures, providing a foundation for the rational design of tetrazine-based crystalline materials with tunable packing and noncovalent interactions.

The role of halide anion identity and the influence of reaction solvent on the resulting halogen-bonded assembly was explored by combining 1,4-diiodo-tetrafluorobenzene (p-F4DIB) with trimethylbenzyl ammonium halides (NMe3BzX, X = Cl, Br, I) in diverse organic solvents. Iodide salts predominantly yielded solvated crystalline products when the salt cocrystallized in an equimolar ratio with p-F4DIB. In solvent systems where the iodides did not crystallize as solvates, the salt:organoiodine ionic cocrystal ratio departed from the 1 : 1 reaction stoichiometry, producing 8 : 3, 4 : 5, or 2 : 3 cocrystals. In contrast, bromide and chloride analogues favored unsolvated forms, with chloride consistently producing a single 1 : 1 motif across multiple solvents. A small number of solvated forms were isolated in the Br and Cl series, typically at matched donor : acceptor ratios. Notably, chloride and bromide salts formed nearly indistinguishable halogen-bonded networks, apart from differences attributable to anion size. These results emphasize the delicate balance between solvent, stoichiometry, and halide identity in directing halogen-bond-driven crystallization.

As a crystallographer, nothing is sadder than failed crystal growth. As an “experienced” crystallographer (a basketball ref couldn't hand signal my number of years), I’ve thrown away more than my share of oily smudges (always according to established hazardous waste procedures, of course). Fortunately, my students are more curious than I. Recently we reported the first halogen-bonding-based deep eutectic solvent, which consisted of a mixture of 1,3-dithiane and o- diiodotetrafluorobenzene – a system that simply refused to cooperate during crystal growth (Peloquin et al. Angew Chem, Int. Ed.2021, 60, 22983–22989). Based on this result and memories of many other liquid samples, we have been exploring a number of different systems, most consisting of tetraalkylammonium triiodides with a variety of organoiodines. As it turns out, many of these systems that resist crystal growth are doing exactly what they are “supposed” to do. Most of these are pseudo binary systems with two or more eutectic points and at least one cocrystalline composition (see phase diagram below). The preparation and characterization of these systems by thermal analysis and, in the case of cocrystals, structural characterization will be discussed. Efforts to correlate halogen bonding in triiodide-based cocrystals with halogen bonding in triiodide-based deep eutectic solvents are now in progress.

In the title compound, C20H9F21O3, a central sp 3-hybridized carbon atom is decorated with three hepta-fluoro-2-meth-yloxy(cyclo-pent-1-ene) arms and a methyl group. The primary packing is determined by C-F⋯F-C inter-actions, forming [001] chains, which are consolidated via weaker C-F⋯F-C and C-H⋯F-C contacts. A Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing: this revealed that the largest contribution to the surface contacts arises from F⋯F inter-actions (53.5%), followed by F⋯H/H⋯F (34.5%) and F⋯C/C⋯F (7.1%).

In the title compound, C20H9F21O3, a central sp3-hybridized carbon atom is decorated with three heptafluoro-2-methyloxy(cyclopent-1-ene) arms and a methyl group. The primary packing is determined by C—F...F—C interactions, forming [001] chains, which are consolidated via weaker C—F...F—C and C—H...F—C contacts. A Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing: this revealed that the largest contribution to the surface contacts arises from F...F interactions (53.5%), followed by F...H/H...F (34.5%) and F...C/C...F (7.1%).

In the title compound, C11H10F4N2O2, the conformation about the N—C—C—O bond is gauche [torsion angle = 61.84 (13)°]. In the crystal, N—H...O hydrogen bonds link the molecules into [010] chains, which are cross-linked by C—H...F and C—H...π contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing. This analysis showed that the largest contribution to the surface contacts arises from F...H/H...F interactions (35.6%), followed by O...H/H...O (17.8%) and H...H (12.7%).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Utilizing the N-heterocyclic chalcogenones hexahydro-1,3-bis(2,4,6- trimethylphenyl)-2H-1,3-diazepine-2-thione (SDiazMesS) and hexahydro-1,3-bis(2,4,6-trimethylphenyl)-2H-1,3-diazepine-2-selone (SDiazMesSe) as halogen-bond acceptors, a total of 24 new cocrystals were prepared. The solid-state structures of the parent molecules were also determined, along with those of their acetonitrile solvates. Through the reaction of the chalcogen atom with molecular diiodine, a variety of S-I-I and Se-I-I fragments were formed, spanning a wide range of I-I bond orders. With acetone as a reaction solvent, molecular diiodine causes the oxidative addition of acetone to the chalcogen atom, resulting in new C-S, C-Se and C-C covalent bonds under mild conditions. The common halogen-bond donors, iodopentafluorobenzene, 1,2-, 1,3- and 1,4-diiodotetrafluorobenzene, 1,3,5-trifluorotriiodobenzene and tetraiodoethylene resulted in halogen-bond-driven cocrystal formation. In most cases, the analogous SDiazMesS and SDiazMesSe cocrystals are isomorphic.

To probe reaction kinetics and polymer decomposition, energetic filaments composed of aluminum (Al) and poly(vinylidene fluoride) (PVDF) with varying hexafluoropropylene (HFP) content are tested for processability and combustion characteristics. Rheological and crystallization findings indicate that the Al‐binder interfacial interactions are disrupted by HFP content. Thermal analysis shows that fuel consumption scales with Al particle size due to the diffusion‐driven Al‐fluoropolymer reaction regardless of HFP concentration. Char yield analysis shows that more solid product is retained in samples with smaller particle diameters, which further reflects the diffusive nature of both Al‐PVDF and Al‐P(VDF‐HFP) reactions. Burn rates reveal two competing mechanisms for reaction efficiency: 1) accelerated binder decomposition through Al‐PVDF interactions and 2) more energetic fluorination due to higher fluorine content in the P(VDF‐HFP) binders. Finally, powder X‐ray diffraction (PXRD) patterns show that AlF3 is the primary product from self‐propagating burns. However, in larger Al particle sizes, filaments are unable to burn completely and result in high levels of Al2O3 and Al4C3 formation, which indicates that these binders are not amenable with low surface area, metallic fuels. These findings aim to improve fluorinated feedstock selection for potential binder candidates in energetic additive manufacturing (AM).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Through the combination of heterocyclic thiones with variation in the identity of the heterocyclic elements, namely, imidazolidine-2-thione, 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 2-mercaptobenzoxazole, and 2-mercaptobenzothiazole with the common halogen-bond donors 1,2-, 1,3-, and 1,4-diiodotetrafluorobenzene, 1,3,5-trifluorotriiodobenzene, and tetraiodoethylene, a series of 18 new crystalline structures were characterized. In most cases, N-H...S hydrogen bonding was observed, with these interactions in imidazole-containing structures typically resulting in two-dimensional motifs (i.e. ribbons). Lacking the second N-H group, the thiazole and oxazole hydrogen bonding resulted in only dimeric pairs. C-I...S and C-I...I halogen bonding, as well as C=S...I chalcogen bonding, served to consolidate the packing by linking the hydrogen-bonding ribbons or dimeric pairs.

Utilizing the facile addition–elimination reaction of thiosemicarbazide with acetone or aldehydes, nine thiosemicarbazones were synthesized. Aldehydes were chosen which contain additional heteroatoms to increase the diversity of possible intermolecular interactions. Further, the thiosemicarbazone synthesis was conducted in situ with one of the common halogen bond donors 1,2-, 1,3-, or 1,4-diiodotetrafluorobenzene, 1,3,5-trifluoro-2,4,6-triiodobenzene, or tetraiodoethylene. These reactions resulted in the characterization of 12 new cocrystals showcasing halogen bonding. The dimerization of two thiosemicarbazone units through a pair of N‒H···S hydrogen bonds was a universal feature of the solid-state structures in this series, with the hydrogen bond network often extending these motifs into chains. The organoiodines serve to link chains through either I···S or I···N halogen bonding, or less commonly, S···I chalcogen bonding. This variety of intermolecular interactions leads to the formation of double-stranded chains, ribbons, and sheets. Utilizing the facile addition–elimination reaction of thiosemicarbazide with acetone or aldehydes, nine thiosemicarbazones were synthesized, seven of which were isolated as cocrystals with common halogen bond donors. Significant N–H···S hydrogen bonding was observed in all, with S···I halogen and chalcogen bonding contributing to the long-range packing in the cocrystals.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Reaction between RuCl2(PPh3)3 and 1,2-diphenylhydrazine resulted in rearrangement and coordination of ortho-semidine. The product, RuCl2(PPh3)2(κ2-NH2-1,2-C6H4-NHPh), was characterized spectroscopically and the molecular structure was conclusively determined using X-ray crystallography. Computational chemistry was employed to probe the energetics surrounding the rearrangement reaction and product.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The reactivity of the prominent ruthenium(II) catalyst and precursor, RuCl2(PPh3)3, was explored with hydrazine and its derivatives. The reactions produced 6-coordinate ruthenium(II) products that bond with the hydrazine moiety in bridging (NH2NH2 or NH2NHMe), end-on (NH2NHMe, NH2NHPh, or NH2NMe2), or side-on (NH2NMe2) fashions. The products have been characterized by single crystal X-ray diffraction and 31P NMR spectroscopy. With NH2NH2, the dimeric product, [RuCl2(PPh3)2]2(mu-N2H4)2, was formed under all conditions used. For other hydrazines, the reaction stoichiometry governed product formation to yield either bimetallic or monomeric products. When the RuCl2(PPh3)3 to hydrazine derivative ratio was 1:1 or lower, bimetallic complexes were formed while a 1:2 ratio produced monomeric compounds. The exception to the latter occurs with the production of the monomeric compound, RuCl2(PPh3)2(eta 2-NH2NMe2), that forms employing a 1:1 ratio. In addition to stoichiometry, steric factors and hydrogen bonding played a significant role in dictating the bonding mode of hydrazines. The bimetallic complexes were further reacted to yield the corresponding monomeric products, adopting the form RuCl2(PPh3)2(L)2 (L = NH2NHMe, NH2NHPh, or NH2NMe2). Reactions utilizing less than a 1:2 ratio of RuCl2(PPh3)3 to NH2NMe2 produced a mixture of products that appear to be in equilibrium. DFT calculations were performed to gain insight into the reaction energetics and molecular stability.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.