The Ground State of Multispin Systems Based on Verdazyl and Nitrene Radicals: An EPR and Quantum-Chemical Study.

In this study, low-temperature EPR spectroscopy and quantum-chemical techniques were employed to investigate multispin systems─1,5-diphenyl-3-(3-nitrenophenyl)-6-oxoverdazyl and 1,5-diphenyl-3-(4-nitrenophenyl)-6-oxoverdazyl─that contain a nitrene center at either a - or -position, respectively. Ground states and magnetic zero-field splitting (ZFS) parameters of these multispin systems were determined by experimental and computational methods. The results indicated that the high-spin quartet state is a ground state, and the quartet-doublet energy gap is close to 10 kcal/mol for the -position of the nitrene group, with ZFS parameters = 0.

N-Heterocycle-coordinated -iodanes as IBX alternatives for alcohol oxidations.

We report the synthesis of novel N-coordinated -iodanes as a unique class of hypervalent iodine compounds. X-ray diffraction analysis revealed their intriguing (pseudo)cyclic structure, showcasing distinctive N⋯I-secondary bonding interactions. We demonstrate the generation of reactive diacetoxy derivatives, which exhibits remarkable efficacy in alcohol oxidation reactions.

Key-to-lock halogen bond-based tetragonal pyramidal association of iodonium cations with the lacune rims of beta-octamolybdate.

The structure-directing "key-to-lock" interaction of double σ-(I)-hole donating iodonium cations with the O-flanked pseudo-lacune rims of [β-MoO] gives halogen-bonded iodonium-beta-octamolybate supramolecular associates. In the occurrence of their tetragonal pyramidal motifs, deep and broad σ-(I)-holes of a cation recognize the molybdate backbone, which provides an electronic pool localized around the two lacunae. The halogen-bonded I⋯O linkages in the structures were thoroughly studied computationally and classified as two-center, three-center bifurcated, and unconventional "orthogonal" I⋯O halogen bonds.

Oxidation Performance of Nano-Layered (AlTiZrHfTa)N/SiN Coatings Deposited by Reactive Magnetron Sputtering.

This work uses the direct current magnetron sputtering (DCMS) of equi-atomic (AlTiZrHfTa) and Si targets in dynamic sweep mode to deposit nano-layered (AlTiZrHfTa)N/SiN refractory high-entropy coatings (RHECs). Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to investigate the effect of Si addition on the oxidation behavior of the nano-layered coatings. The Si-free nitride coating exhibits FCC structure and columnar morphology, while the Si-doped nitride coatings present a FCC (AlTiZrHfTa)N/amorphous-SiN nano-layered architecture.

Toward New Horizons in Verdazyl-Nitroxide High-Spin Systems: Thermally Robust Tetraradical with Quintet Ground State.

High-spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but examples reported to date exhibit limited stability and processability. In this work, we designed the first tetraradical based on an oxoverdazyl core and nitronyl nitroxide radicals and successfully synthesized it using a palladium-catalyzed cross-coupling reaction of an oxoverdazyl radical bearing three iodo-phenylene moieties with a gold(I) nitronyl nitroxide-2-ide complex in the presence of a recently developed efficient catalytic system. The molecular and crystal structures of the tetraradical were confirmed by single crystal X-ray diffraction analysis.

Preparation and X-ray Structural Study of Dibenzobromolium and Dibenzochlorolium Derivatives.

Various five-membered cyclic dibenzobromolium salts (dibenzo[,]bromol-5-ium chloride, nitrate, hydrogen sulfate, dihydrogen phosphate, trifluoroacetate, and tetrafluoroborate) were prepared by diazotization-cyclization of 2'-bromo-[1,1'-biphenyl]-2-amine in solution of appropriate acids. The chlorolium analogues (iodide, trifluoroacetate, and tetrafluoroborate) were obtained by a similar procedure. Additional dibenzohalolium derivatives (dibenzo[,]bromol-5-ium and dibenzo[,]chlorol-5-ium azides, bis(trifluoromethanesulfonyl)imidates, thiocyanates, and trifluoromethanesulfonates) were prepared by anion exchange.

Halogen Bond-Involving Self-Assembly of Iodonium Carboxylates: Adding a Dimension to Supramolecular Architecture.

We designed 0D, 1D, and 2D supramolecular assemblies made of diaryliodonium salts (functioning as double σ-hole donors) and carboxylates (as σ-hole acceptors). The association was based on two charge-supported halogen bonds (XB), which occurred between I sites of the iodonium cations and the carboxylate anions. The sequential introduction of the carboxylic groups in the aryl ring of the benzoic acid added a dimension to the 0D supramolecular organization of the benzoate, which furnished 1D-chained and 2D-layered structures when terephthalate and trimesate anions, correspondingly, were applied as XB acceptors.

Metal-free and atom-efficient protocol for diarylation of selenocyanate by diaryliodonium salts.

We developed an atom- and reaction mass efficient strategy for the preparation of diarylselenides using iodonium salts as reactants. The developed approach allows the obtaining of diarylselenides from the corresponding trimethoxyphenyl-substituted iodonium salts a two-step one-pot reaction sequence. The proposed metal-free methodology is based on the involvement of both iodonium aryl groups for diarylation.

Noncovalent Chelation by Halogen Bonding in the Design of Metal-Containing Arrays: Assembly of Double σ-Hole Donating Halolium with Cu-Containing O,O-Donors.

Five new copper(I) complexes─composed of the paired dibenzohalolium and [CuL] (L = 1,2,4-oxadiazolate) counterions in which O,O-atoms of the anion are simultaneously linked to the halogen atom─were generated and isolated as the solid via the three-component reaction between [Cu(MeCN)](BF), sodium 1,2,4-oxadiazolates, and dibenzohalolium triflates (or trifluoroacetates). This reaction is different from the previously reported Cu-catalyzed arylation of 1,2,4-oxadiazolones by diaryliodonium salts. Inspection of the solid-state X-ray structures of the complexes revealed the strong three-center X···O,O (X = Br, I) halogen bonding occurred between the oxadiazolate moieties and dibenzohalolium cation.

Sweetened Alkylated Verdazyls Effectively Kill Cancer Cells under Light Irradiation.

The development of novel photo-dynamic therapy (PDT) agents enabling to treat the oxygen-deficient tumors is the emerging tasks for the modern medicinal chemistry. Herein, we describe the design and preparation of water-soluble agents for PDT which generate active radical species upon light irradiation. Two conjugates of carbohydrates with 1,2,4,6-substituted-1,4-dihydro-1,2,4,5-tetrazin-3(2H)-ones (AlkVZs) demonstrated high oxygen-independent cytotoxicity on PC-3 and Jurkat cancer cells under light irradiation combining with low toxicity in the dark.

Ligand-free Ullmann-type arylation of oxazolidinones by diaryliodonium salts.

The arylation of azaheterocycles can be considered as one of the most important processes for the preparation of various biologically active compounds. In the present work, we describe a method for the copper-catalyzed -arylation of hindered oxazolidinones using diaryliodonium salts. The method succeeds in good to excellent yields for the arylation of 4-alkyloxazolidinones, including sterically hindered isopropyl- and -butyl-substituted.

Halogen Bonding Involving Gold Nucleophiles in Different Oxidation States.

A single-crystal X-ray diffraction (XRD) study of diaryliodonium tetrachloroaurates (or, in the recent terminology, tetrachloridoaurates), [(-XCH)I][AuCl] (X = Cl, ; Br, ), was performed for (the structure is denoted as to show similarity with the isomorphic structure ) and two polymorphs─ (obtained from MeOH) and (from 1,2-CHCl). Examination of the XRD data for these three structures revealed 2-center C-X···Au (X = Cl and Br) and 3-center bifurcated C-Br···(-) halogen bonding (abbreviated as XB) between the -Cl or -Br atoms of the diaryliodonium cations and the gold(III) atom of [AuCl]. The noncovalent nature of Au-involving interactions, the nucleophilicity of the gold(III) atoms, and the electrophilic role of -X atoms of the diaryliodonium cations in the XBs were studied by a set of complementary computational methods.

Efficient Catalytic Synthesis of Condensed Isoxazole Derivatives via Intramolecular Oxidative Cycloaddition of Aldoximes.

The intramolecular oxidative cycloaddition reaction of alkyne- or alkene-tethered aldoximes was catalyzed efficiently by hypervalent iodine(III) species to afford the corresponding polycyclic isoxazole derivatives in up to a 94% yield. The structure of the prepared products was confirmed by various methods, including X-ray crystallography. Mechanistic study demonstrated the crucial role of hydroxy(aryl)iodonium tosylate as a precatalyst, which is generated from 2-iodobenzoic acid and -chloroperoxybenzoic acid in the presence of a catalytic amount of -toluenesulfonic acid.

Zwitterionic iodonium species afford halogen bond-based porous organic frameworks.

Porous architectures characterized by parallel channels arranged in honeycomb or rectangular patterns are identified in two polymorphic crystals of a zwitterionic 4-(aryliodonio)-benzenesulfonate. The channels are filled with disordered water molecules which can be reversibly removed on heating. Consistent with the remarkable strength and directionality of the halogen bonds (XBs) driving the crystal packing formation, the porous structure is stable and fully preserved on almost quantitative removal and readsorption of water.

Alkylverdazyls as a Source of Alkyl Radicals for Light-Triggered Cancer Cell Death.

Two alkylated verdazyl radicals (AlkVZs) were investigated as active compounds for photoinitiated controlled MCF-7 cell death. Observed results unambiguously showed that AlkVZ could be a potential structural moiety for the design of a novel family of photodynamic therapy agents. The main advantage of the proposed substances is an oxygen-independent generation of active radicals, which play a pivotal role in the treatment of oxygen-deficient tumors.

Convenient Synthesis of Benziodazolone: New Reagents for Direct Esterification of Alcohols and Amidation of Amines.

Hypervalent iodine heterocycles represent one of the important classes of hypervalent iodine reagents with many applications in organic synthesis. This paper reports a simple and convenient synthesis of benziodazolones by the reaction of readily available iodobenzamides with -chloroperoxybenzoic acid in acetonitrile at room temperature. The structure of one of these new iodine heterocycles was confirmed by X-ray analysis.

Conceptual Developments of Aryldiazonium Salts as Modifiers for Gold Colloids and Surfaces.

Modified colloids and flat surfaces occupy an important place in materials science research due to their widespread applications. Interest in the development of modifiers that adhere strongly to surfaces relates to the need for stability under ambient conditions in many applications. Diazonium salts have evolved as the primary choice for the modification of surfaces.

Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State.

Thermally resistant air-stable organic triradicals with a quartet ground state and a large energy gap between spin states are still unique compounds. In this work, we succeeded to design and prepare the first highly stable triradical, consisting of oxoverdazyl and nitronyl nitroxide radical fragments, with a quartet ground state. The triradical and its diradical precursor were synthesized via a palladium-catalyzed cross-coupling reaction of diiodoverdazyl with nitronyl nitroxide-2-ide gold(I) complex.

Preparation and Synthetic Applicability of Imidazole-Containing Cyclic Iodonium Salts.

A novel approach to the preparation of imidazole-substituted cyclic iodonium salts has been developed via the oxidative cyclization of 1-phenyl-5-iodoimidazole using a cheap and available Oxone/HSO oxidative system. The structure of the new polycyclic heteroarenes has been confirmed by single-crystal X-ray diffractometry, revealing the characteristic structure features for cyclic iodonium salts. The newly produced imidazole-flanked cyclic iodonium compounds were found to readily engage in a heterocyclization reaction with elemental sulfur, affording benzo[5,1-]imidazothiazoles in good yields.

Kinetic investigation of thermal and photoinduced homolysis of alkylated verdazyls.

The on-demand generation of stable organic radicals from the precursors can be considered as an essential challenge for the plethora of applications in various fields of science. In this contribution, we prepared a range of N-(methyl)benzyl derivatives of 6-oxoverdazyl via atom transfer radical addition from moderate to high yields and studied their thermal- and photo-initiated homolysis. The kinetics of homolysis was measured, and the dissociating rate constant k, activation energy E and frequency factor A were estimated.

Ferromagnetically Coupled S=1 Chains in Crystals of Verdazyl-Nitronyl Nitroxide Diradicals.

Thermally stable organic diradicals with a triplet ground state along with large singlet-triplet energy gap have significant potential for advanced technological applications. A series of phenylene-bridged diradicals with oxoverdazyl and nitronyl nitroxide units were synthesized via a palladium-catalyzed cross-coupling reaction of iodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex with high yields. The diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 °C.

Can Plasmon Change Reaction Path? Decomposition of Unsymmetrical Iodonium Salts as an Organic Probe.

Plasmon-assisted transformations of organic compounds represent a novel opportunity for conversion of light to chemical energy at room temperature. However, the mechanistic insights of interaction between plasmon energy and organic molecules is still under debate. Herein, we proposed a comprehensive study of the plasmon-assisted reaction mechanism using unsymmetric iodonium salts (ISs) as an organic probe.

A Weakly Antiferromagnetically Coupled Biradical Combining Verdazyl with Nitronylnitroxide Units.

An antiferromagnetically (AFM) coupled biradical based on oxoverdazyl and nitronylnitroxide was synthesized in 46 % yield using Sonogashira coupling. The obtained heterobiradical evidenced distinct properties of both radical entities in solution. Depending on the solvent, the prepared biradical crystallized in two different forms.

Thermal stability of -heterocycle-stabilized iodanes - a systematic investigation.

The thermal stability of pseudocyclic and cyclic -heterocycle-stabilized (hydroxy)aryl- and mesityl(aryl)-λ-iodanes (NHIs) through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) is investigated. Peak decomposition temperatures ( ) were observed within a wide range between 120 and 270 °C. Decomposition enthalpies (Δ ) varied from -29.