Pyridyl Nitrogen Research Articles

Synthesis and optimization of 3D porous polymers for efficient CO2 capture and H2 storage

In this study, a new porous organic polymer (KFUPM-CO2) with intrinsic nitrogen atoms as active sites for CO2 capture was optimized and synthesized via Friedel-Crafts alkylation of triptycene and 2,2-bipyridine. The porous polymer shows a high surface area of 1100 m2/g with a tuned microporosity of less than 1.2 nm, confirmed by NLDFT. KFUPM-CO2 showed a remarkable CO2 sorption capacity of 5.6 mmol/g at 273 K, 3.2 mmol/g at 298 K, and a pressure of 760 mmHg KFUPM-CO2 showed a high enthalpy of adsorption of 43.7 kJ/mol for CO2 with IAST selectivity of CO2/N2 of 127 at 273 K and 97 at 298 K on simulated flue gas composition. Additionally, KFUPM-CO2 exhibited an H2 storage capacity of 1.5 wt. % at 77 K and 860 mmHg Grand Canonical Monte Carlo (GCMC) simulations further revealed that KFUPM-CO2 was mainly stabilized by π-π intra-molecular interactions, and exhibited strong van der Waals attractions to CO2 molecules via the pyridyl nitrogen atoms, resulting in the rapid uptake. The combined advantages of binding 2,2-bipyridine with triptycene provided a robust porous polymer with abundant nitrogen sites, permanent porosity, and thermal stability, rendering KFUPM-CO2 an excellent candidate for CO2 capture and H2 storage technologies.

Conformational stabilisation of a 2-pyridyl imide by n→π* interaction in solid state

ABSTRACT In recent studies, n→π* interactions featuring nucleophilic pyridine have been investigated using Fourier transform microwave spectroscopy and high-level theoretical computations. Examples of n→π* of this type in the solid state, however, are limited. The norbornene-based 2-pyridyl imide 1 is a compound that can adopt two conformers, in which the pyridyl nitrogen is either syn or anti to the norbornane bridge. It would be expected that the syn conformation of imide 1 would be more favourable, as indicated in a previous computational study. Here, tandem crystallographic and additional computational studies provide evidence that the otherwise unfavourable anti conformer of imide 1 becomes favoured upon stabilisation by an n→π* interaction in the solid state.

Redox Activity and Potentials of Bidentate N-Ligands Commonly Applied in Nickel-Catalyzed Cross-Coupling Reactions.

Bidentate N-ligands are paramount to recent advances in nickel-catalyzed cross-coupling reactions. Through comprehensive organometallic, spectroscopic, and computational studies on bi-oxazoline and imidazoline ligands, we reveal that a square planar geometry enables redox activity of these ligands in stabilizing nickel radical species. This finding contrasts with the prior assumption that bi-oxazoline lacks redox activity due to strong mesomeric donation. Moreover, we conducted systematic cyclic voltammetry (CV) analyses of bidentate pyridyl, oxazoline, and imidazoline nitrogen ligands, along with their corresponding nickel complexes. Complexation with nickel shifts the reduction potentials to a more positive region and narrows the differences in redox potentials among the ligands. Additionally, various ligands led to different degrees of bromide dissociation from singly reduced (L)Ni(Ar)(Br) complexes, reflecting varying reactivity in the subsequent activation of alkyl halides, a crucial step in cross-electrophile coupling. These insights highlight the significant electronic effects of ligands on the stability of metalloradical species and their redox potentials, which interplay with coordination geometry. Quantifying the electron-donating, p-accepting properties of these ligands, as well as their effect on catalyst speciation, provides crucial benchmarks for controlling catalytic activity and enhancing catalyst stability.

Preparation and electrochemical properties of nitrogen-doped starch hard carbon anode materials for lithium-ion battery

Here, we report the synthesis of hard carbon materials (CSHs) made from corn starch and their application as an anode in lithium-ion batteries. The study shows that the microstructure and electrochemical properties of CSHs are affected by nitrogen doping. It is found that nitrogen is embedded in the carbon layer with graphite nitrogen, pyridyl nitrogen, and pyrrole nitrogen, so that the surface morphology was changed and reduced the disorder of the materials. The electrochemical test results show that the introduction of nitrogen elements can increase the reversible capacity of the material, with the first discharge capacity reaching above 426.35 mAh g−1, and the rate performance also improves. When melamine and pre-carbonized corn starch are carbonized at a mass ratio of 1:9, the obtained material has a reversible capacity of 122.04 mAh g−1 at a rate of 2 C. During the carbonization process, the nitrogen in melamine is doped into the carbon materials, improving the electrochemical performance of the material.

Toggling the Oxygen Affinity between Anthracenes and Naphthalenes.

We present the design of an anthracenyl⎯naphthyl (ANT⎯NAPH) dyad and its application as a luminescent 4-stage photo switch. Both segments can individually react with singlet oxygen to switch off an optical response. In their initial form the larger ANT component reacts significantly faster and thus an ANTO2⎯NAPH stage is turned on, observed by optical response of the remaining NAPH. To reduce its reactivity, ANT is substituted with two pyridine rings. This concept is first investigated and quantified on ANT and NAPH as separated molecules. Upon protonation the reaction of ANT becomes significantly slower. For the three possible pyridyl isomers this effect increases along the ordermeta<para<ortho. With the pyridyl nitrogen inorthoposition,the reaction completely toggles from ANT to NAPH. Application of this concept on the dyad allows to turn on the ANT⎯NAPHO2stage with optical response of the remaining ANT. The sequence of protonation-oxygenation-neutralization is thereby the only possible way to isolate the unfavored form ANT⎯NAPHO2.In the dyad ANT and NAPH are directly attached and their coupling constitutes a non-oxygenated third stage, where the NAPH luminescence is quenched and ANT luminescence is enhanced. Reaction of both NAPH and ANT to ANTO2⎯NAPHO2constitutes the fourth dark stage.

The binding of diruthenium (II,III) and dirhodium (II,II) paddlewheel complexes at DNA/RNA nucleobases: Computational evidences of an appreciable selectivity toward the AU base pairs

Multiple medicinal strategies involve modifications of the structure of DNA or RNA, which disrupt their correct functioning. Metal complexes with medicinal effects, also known as metallodrugs, are among the agents intended specifically for the attack onto nucleosides. The diruthenium (II,III) and dirhodium (II,II) paddlewheel complexes constitute promising dual acting drugs due to their ability to release the therapeutically active bridging ligands upon their substitution by endogenous ligands. In this paper, we study the structure and the stability of the complexes formed by the diruthenium (II,III) and dirhodium (II,II) paddlewheel complexes coordinated in axial positions with the DNA/RNA nucleobases or base pairs, assuming the attainable metalation at all the accessible pyridyl nitrogens. Dirhodium complexes coordinate at the pyridyl nitrogens more strongly than the diruthenium complexes. On the other hand, we found that the diruthenium scaffold binds more selectively to nucleobase targets. Furthermore, we reveal a tighter coordination of diruthenium complex at the adenine-uracil base pair, compared to adenine-thymine, hence constituting a scarce instance of RNA-selectivity. We envision that the here reported computational outcomes may pace future experiments addressing the binding of diruthenium and dirhodium paddlewheel complexes at either single nucleobases or DNA/RNA fragments.

Piroxicam analogue metal complexes: Synthesis, crystal structures, molecular modeling and biological studies

In recent decades, metal‐based drugs have gained considerable attention all over the world because of their enhanced therapeutic potential. The piroxicam analogue, that is, 2‐Benzyl‐4‐hydroxy‐1,1‐dioxo‐1,2‐dihydro‐1λ6‐benzo [e][1,2] thiazine‐3‐carboxylic acid pyridin‐2‐yl amide 1 was synthesized and coupled with Mn (II), Co (II), Ni (II), Cu (II) and Zn (II) metal ions to isolate complexes 2–6. The N,O‐bidentate chelator coordinated with the metal center via pyridyl nitrogen and amide oxygen atoms by forming six‐membered ring system. Several analytical techniques like UV–Vis, FT‐IR, 1H NMR, magnetic susceptibility, and elemental analysis were performed to confirm the syntheses of the octahedral complexes. The conductance measurement was employed to determine the non‐electrolytic nature of the complexes. The molecular structures of manganese (II) 2, cobalt (II) 3, and zinc (II) 6, complexes were confirmed by single beam X‐ray crystallography revealing the monoclinic crystal system with P21/c space group. The crystallographic data was utilized to carry out the DFT studies, which were found in line with the experimental data. The antioxidant (DPPH, FRAP) and antibacterial activities were performed to determine the therapeutic potential of these synthesized compounds. These studies indicated that understudied compounds have potential as therapeutic agents and they may be used as drug candidates in the future. The in‐silico studies also aligned with the in‐vitro potential of the targeted compounds.

Copper perchlorate catalyzed oxidative cyclisation of a novel bishydrazone ligand, formation of an unusual copper complex and in vitro biological implications

A novel hexadentate bishydrazone ligand, 1,10-bis(di(2-pyridyl)ketone) adipic acid dihydrazone (H2L1) is synthesized and characterized. With copper perchlorate as a catalytic oxidant, the ligand undergoes oxidative cyclisation and resulted in the formation of an unusual copper complex [Cu(L1a)2Cl]ClO4 (1), where L1a is 3-(2-pyridyl)triazolo[1,5-a]-pyridine. The Cu(II) complex was characterized physicochemically, while the molecular structure was confirmed by single crystal X- ray diffraction. In the complex cation, copper(II) is in a distorted trigonal bipyramidal coordination environment, surrounded by two triazolo nitrogen atoms and two pyridyl nitrogen atoms of L1a and a chloride atom. The relevant non covalent intermolecular interactions of the complex quantified using Hirshfeld surface analysis reveals that the O···H/ H···O (27.2%) contacts has the highest contribution. The solution phase bandgaps of the compounds were calculated using Tauc plot, whereas the solid-state band gaps were calculated by Kubelka-Munk model. DFT studies of the compounds indicate that the theoretical calculations corroborate with the experimental data. DPPH antioxidant activity assay of the synthesized compounds showed that the proligand H2L1 has a lower IC50 value (24.1 μM) than that of complex 1 (29.7 μM). The in vitro antibacterial activity was evaluated against Escherichia coli and Staphylococcus aureus, which revealed that complex 1 have excellent activity against E. coli, much as the standard ciprofloxacin. The cytotoxic efficacy investigation of the compounds against A549 (lung) adenocarcinoma cells suggested that H2L1 has more anticancer activity (IC50 value of 149.08 μM) than that of complex 1(IC50 value of 176.70 μM).

Understanding the Selective Extraction of the Uranyl Ion from Seawater with Amidoxime-Functionalized Materials: Uranyl Complexes of Pyrimidine-2-amidoxime

The study of small synthetic models for the highly selective removal of uranyl ions from seawater with amidoxime-containing materials is a valuable means to enhance their recovery capacity, leading to better extractants. An important issue in such efforts is to design bifunctional ligands and study their reactions with trans-{UO2}2+ in order to model the reactivity of polymeric sorbents possessing both amidoximate and another adjacent donor site on the side chains of the polymers. In this work, we present our results concerning the reactions of uranyl and pyrimidine-2-amidoxime, a ligand possessing two pyridyl nitrogens near the amidoxime group. The 1:2:2 {UO2}2+/pmadH2/external base (NaOMe, Et3N) reaction system in MeOH/MeCN provided access to complex [UO2(pmadH)2(MeOH)2] (1) in moderate yields. The structure of the complex was determined by single-crystal X-ray crystallography. The UVI atom is in a distorted hexagonal bipyramidal environment, with the two oxo groups occupying the trans positions, as expected. The equatorial plane consists of two terminal MeOH molecules at opposite positions and two N,O pairs of two deprotonated η2 oximate groups from two 1.11000 (Harris notation) pmadH− ligands; the two pyridyl nitrogen atoms and the –NH2 group remain uncoordinated. One pyridyl nitrogen of each ligand is the acceptor of one strong intramolecular H bond, with the donor being the coordinated MeOH oxygen atom. Non-classical Caromatic-H⋯X (X=O, N) intermolecular H bonds and π–π stacking interactions stabilize the crystal structure. The complex was characterized by IR and Raman spectroscopies, and the data were interpreted in terms of the known structure of 1. The solid-state structure of the complex is not retained in DMSO, as proven via 1H NMR and UV/Vis spectroscopic techniques as well as molar conductivity data, with the complex releasing neutral pmadH2 molecules. The to-date known coordination chemistry of pmadH2 is critically discussed. An attempt is also made to discuss the technological implications of this work.

Bis[μ-bis-(pyridin-2-yl)methanone oxime-κ3N:,N',N'']bis-[di-acetato-κ2O,O';κO-zinc(II)

The structure of the title complex, [Zn2(C2H3O2)4(C11H9N3O)2], is triclinic containing half of the mol-ecule in the asymmetric unit. Each zinc atom is coordinated to a pyridyl and oxime nitro-gen from one di-2-pyridyl ketone oxime (dpko) ligand and a third nitro-gen from the other dpko pyridyl ring. Additionally, each zinc is coordinated to two acetato anions, one of which is bidentate and the other monodentate. The uncoordinated oxygen of the monodentate acetato group is involved in a hydrogen bond with the oxime hydrogen. The packing in the crystal is assisted by weak C-H⋯O inter-actions between acetato groups and neighboring pyridyl rings.

Crystal structure, tautomerism and photostability of 2-(2-pyridyl)-phenalene-1,3-dione

Tautomerism of cyclic β-diketones has been of scientific interest for decades due to the practical applications it can render, from sensors to photostable materials. In this work the tautomerism of 2-(2-pyridyl)-phenalene-1,3-dione (PPD) was studied in solid state, in solution, and in gas phase through a combination of experimental and theoretical methods. Single-crystal X-ray diffraction analysis of PPD revealed its existence in diketo form in the solid state with protonated pyridyl nitrogen that is stabilized by the intramolecular hydrogen bond of N-H···O type. A very large Stokes shift was observed in the emission spectra in DMSO (ca. 177 nm) and in ethanol (ca. 160 nm), indicating on possible excited-state intramolecular proton transfer (ESIPT) process. DFT calculations in ground state (gas phase and water medium) and in the excited singlet state (B3LYP-6311++G(d,p)) agree very well with the experimental data and suggest reverse order of the possible OH and NH tautomers in the ground and the excited singlet state, namely the diketo NH tautomer is the most stable one in the ground state whereas in the excited singlet state the enol OH form is more stable. The photostability of PPD was estimated by irradiation experiments that were performed in comparison with 2-acetylindan-1,3-dione (2AID), which is a compound with proven high photostability in ethanol and fast ESIPT. The data showed that unlike 2AID, the 2-(2-pyridyl)-phenalene-1,3-dione exhibits lower photostability in ethanol. These results could suggest that either the ESIPT process is not the only transformation that takes place in the excited state of PPD, or it is not as fast as the one of 2AID.

Photoactivated Pyridine Directed Fluorination through Hydrogen Atom Transfer.

We have established hydrogen atom transfer (HAT) as the key player in a directed, photopromoted fluorination of pyridylic groups. The Lewis basic pyridyl nitrogen directs amine radical dication propagated HAT and Selectfluor fluorination of various ortho substituents in a highly regioselective manner with little to no side product formation. A variety of pyridines and quinolines were employed to showcase the directing capability of the nitrogen atom. Additionally, both experimental and computational data are provided that illuminate how this mechanism differs from and complements prior work in the area.

Synthesis, structural characterization and DFT calculations of a diphenyl-2-pyridylphosphine complex of copper(II)

The reaction of Cu(NO3)2·3H2O with a potentially bidentate P,N-donor ligand, diphenyl-2-pyridylphosphine (PPh2Py), in 1:2 molar ratio resulted in formation of a κ 2N,O-chelated complex, [Cu(κ 2N,O-P(O)Ph2Py)2(NO3)2] (1). A single-crystal X-ray study confirmed the formation of a five-membered κ 2N, O-chelate involving pyridyl nitrogen and phosphine oxide oxygen donor sites. A DFT study was carried out on 1 to understand the chelate ring expansion process upon oxidation with PPh2Py. DFT analysis revealed that 1 contains a relatively strong M-N bond compared to its M-P bond, facilitating the oxidation of the P atom followed by chelate ring expansion.

Synthesis, crystal structures, photophysical and antibacterial properties of Ag(I) and Zn(II) coordination polymers based on a flexible bisacylhydrazone ligand

A flexible bisacylhydrazone ligand (H4L) was designed and synthesized from the condensation reaction of dialdehyde 3,3′-thiobis(methyiene)-bis-(5-methyl-salicylaldehyde) (b) with isonicotinic hydrazide. In the DMSO/methanol solution, two coordination polymers (CPs), formulated as {[Ag(H4L)NO3]·DMSO·2H2O}n (CP 1) and {[Zn2(H2L2-)2]·3DMSO·3H2O}n (CP 2), were synthesized from H4L with Ag(I) or Zn(II) ions, respectively. These two CPs were characterized via elemental analysis, FT-IR spectra, and single crystal X-ray determination. The results show that CP 1 exists as a 1D looped-chain polymer, while CP 2 exists as a 2D sheet polymer. The coordination configurations of the two CPs were analyzed and compared in detail, which disclose the terminal pyridyl nitrogen atoms exhibit obviously stronger coordination ability compared to other sites. In addition, photophysical, electrochemical and antibacterial properties of H4L and the two CPs were investigated.

Synthesis, crystal structures, and NMR (1H, 13C) spectroscopy of PdII/HgII complexes with N, S-donor thiosemicarbazone/heterocyclic-2-thione ligands

The reaction of 2-benzoylpyridine thiosemicarbazone, {(C6H5)(py-N1)C2=N2-N3H-C1(=S)-N4H2, bzpytscH}, with palladium(II) chloride in acetonitrile yielded a heteroleptic complex, [Pd(N1,N2,S-bzpytsc)Cl] (1), in which the thio-ligand coordinated through pyridyl nitrogen (N1), azomethine nitrogen (N2) and sulfur as terdentate anion (N,N,S-bzpytsc–). In another reaction, pyrimidine-2-thione (pymtH) with mercury(II) chloride in CH3CN-DMF mixture formed a homoleptic compound, [Hg(N,S-pymt)2] (2), similar to the literature report of formation of a homoleptic compound, [Hg(κ1S-pyt)2], from HgCl2 and pytH in CH3CN-DMF. A reaction of mercury(II) bromide with pyridine-2-thione (pytH) in CH3CN-DMF mixture did not remove the bromides and rather yielded a heteroleptic complex of composition, [HgBr2(κ1S-pytH)2] (3). NMR (1H, 13C NMR) spectroscopy and infrared spectroscopy of 1–4 as well as crystal structures of 1, 3, and 4 are reported.

Vanadium Complexes Derived from O,N,O-tridentate 6-bis(o-hydroxyalkyl/aryl)pyridines: Structural Studies and Use in the Ring-Opening Polymerization of ε-Caprolactone and Ethylene Polymerization

Interaction of [VO(OiPr)3] with 6-bis(o-hydroxyaryl)pyridine, 2,6-{HOC(Ph)2CH2}2(NC5H3), LH2, afforded [VO(OiPr)L] (1) in good yield. The reaction of LNa2, generated in-situ from LH2 and NaH, with [VCl3(THF)3] led to the isolation of [VL2] (2) in which the pyridyl nitrogen atoms are cis; a regioisomer 3∙2THF, in which the pyridyl nitrogen atoms are trans, was isolated when using [VCl2(TMEDA)2]. The reaction of the 2,6-bis(o-hydroxyalkyl)pyridine {HOC(iPr)2CH2}2(NC5H3), L1H2, with [VO(OR)3] (R = nPr, iPr) led, following work-up, to [VO(OR)L1] (R = nPr (4), iPr (5)). Use of the bis(methylpyridine)-substituted alcohol (tBu)C(OH)[CH2(C5H3Me-5)]2, L2H, with [VO(OR)3] (R = Et, iPr) led to the isolation of [VO(μ-O)(L2)]2 (6). Complexes 1 to 6 have been screened for their ability to act as pre-catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL), and rac-lactide (r-LA) and compared against the known catalyst [Ti(OiPr)2L] (I). Complexes 1, 4–6 were also screened as catalysts for the polymerization of ethylene (in the presence of dimethylaluminium chloride/ethyltrichloroacetate). For the ROP of ε-CL, in toluene solution, conversions were low to moderate, affording low molecular weight products, whilst as melts, the systems were more active and afforded higher molecular weight polymers. For δ-VL, the systems run as melts afforded good conversions, but in the case of r-LA, all systems as melts exhibited low conversions (&lt;10%) except for 6 (&lt;54%) and I (&lt;39%). In the case of ethylene polymerization, the highest activity (8600 Kg·mol·V−1bar−1h−1) was exhibited by 1 in dichloromethane, affording high molecular weight, linear polyethylene at 70 °C. In the case of 4 and 5, which contain the propyl-bearing chelates, the activities were somewhat lower (≤1500 Kg·mol·V−1bar−1h−1), whilst 6 was found to be inactive.

Synthesis, structures, and gas adsorption properties of Hg(II) and Cd(II) complexes constructed from two acylhydrazone ligands with multiple coordination sites

Two chain-like acylhydrazone ligands (L1 and L2) were synthesized from Schiff base condensation reaction of 3,3′-(1,4-piperazine-bis-(methylene)-bis-(2-hydroxy-5-methylbenzaldehyde)) (b) with isonicotinic hydrazide or nicotinic hydrazide, respectively. In the presence of Hg(II) or Cd(II) ions and in DMF/methanol solution, three complexes, formulated as {[Hg3L1Br6]·4DMF}n (1), {[Hg2L2I4]·2DMF}n (2), and [Cd4(L2)2I8(H2O)2]·4DMF (3), were synthesized and further characterized via elemental analysis, FT-IR spectra and single-crystal X-ray diffraction. Complex 1 exists as a 1D zag-zig chain polymer and complex 2 exists as a 1D looped chain polymer. Complex 3 exists as a rare tetranuclear structure. The structural differences of the three complexes and the coordination competition among the coordination sites were analyzed, and the results showed that the pyridyl nitrogen atoms have an obvious coordination ability prior to other sites. Furthermore, gas adsorption measurements were carried out, which show that the three complexes exhibit good adsorption capacity towards CH3OH over N2, H2, O2, and CO2.

Stoichiometry-controlled chirality inversion in the amide-linked zinc bisporphyrinates induced by amino acid esters

We investigated chirality transfer processes with two amide-linked zinc bisporphyrinates as hosts and chiral amino acid esters as guests. The linkers in these hosts contain a coordination site (pyridyl nitrogen or amino nitrogen). CD spectra were measured after titration of these zinc bisporphyrinates with amino acid esters. The CD spectra show that the signals were inverted during the titration. This result suggests that there is a two-step chirality induction process, which is most likely dominated by the corresponding 1:1 and 1:2 host-guest complexes. In the 1:1 complexes, the pyridyl nitrogen or amino nitrogen in the linkers is coordinated with zinc. NMR spectra confirmed such coordination interactions. Theoretical calculations also confirmed the corresponding chirality induction and inversion. This work provides a useful strategy to tune chirality transfer processes by introducing an extra coordination site in the linker.

Impact of Internal Charge Transfer on the Photophysical Properties of Pyridine-Fused Phosphorus-Nitrogen Heterocycles.

The phosphaquinolinone scaffold has been previously studied as a modular core for a variety of fluorescent species where use of substituent effects has focused on increasing or decreasing electron density in the core rings. We now report the synthesis and analysis of several pyridine-containing phosphaquinolinone species exhibiting notable linear conjugation from the aryl-substituent to electron-withdrawing pyridyl nitrogen. Varying the nature of the aryl substituent from electron-withdrawing to electron-donating leads to the generation of an internal charge-transfer (ICT) band in the absorbance spectrum, which becomes the dominant absorbance in terms of intensity in the most electron-rich -NMe2 example. This heterocycle exhibits improved photophysical properties compared to others in the set including high quantum yield and considerably red-shifted emission. The enhanced ICT can be observed in the X-ray data where a rare example of molecule co-planarity is observed. Computational data show increased localization of negative charge on the pyridyl nitrogen as the electron-donating character of the aryl-substituent increases.

Anticooperativity and Competition in Some Cocrystals Featuring Iodine-Nitrogen Halogen Bonds.

Phenomena such as anticooperativity and competition among non-covalent bond donors and acceptors are key considerations when exploring the polymorphic and stoichiomorphic landscapes of binary and higher-order cocrystalline architectures. We describe the preparation of four cocrystals of 1,3,5-trifluoro-2,4,6-triiodobenzene with N-heterocyclic compounds, namely acridine, 3-aminopyridine, 4-methylaminopyridine, and 1,2-di(4-pyridyl)ethane. The cocrystals, which are characterized by single-crystal and powder X-ray diffraction experiments, all show moderately strong and directional iodine⋅⋅⋅nitrogen halogen bonds with reduced distance parameters ranging from 0.79 to 0.92 and carbon-iodine⋅⋅⋅nitrogen bond angles ranging from 165.4(3) to 175.31(7)°. The cocrystal comprising 1,3,5-trifluoro-2,4,6-triiodobenzene and acridine provides a relatively rare example where all three halogen bond donor sites form halogen bonds with three acceptor molecules, overcoming an anticooperative effect. This effect manifests itself through the lengthening of non-halogen-bonded C-I bonds, weakening their potential to form halogen bonds. The effect is only observed once two halogen bonds have been formed to 1,3,5-trifluoro-2,4,6-triiodobenzene; one such bond does not appear to be adequate. Among the four cocrystals studied, competition between the pyridyl nitrogen atoms and the amine nitrogen atoms suggests that the former are the preferred halogen bond acceptors. Analysis by Hirshfeld fingerprint plots and 13 C and 19 F magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy provides additional insights into the prevalence of various short contacts in the crystal structures and into the spectral response to halogen-bond-induced cocrystallization.