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New 3-aryl(hetaryl)-1-(benzo[d]thiazol-2-yl)-6-methyl-5-phenylverdazyls were synthesized and characterized by EPR and IR spectroscopies, mass spectrometry, cyclic voltammetry, and X-ray diffraction. The effect of substituents on the spectral and electrochemical properties was studied. It was shown that substituents at position 3 of the verdazyl tetrazine ring, regardless of their nature, cause a significant shift of the oxidation and reduction potentials to the anodic region. The results obtained suggest that the synthesized compounds can be used as an electroactive components in rechargeable organic batteries. [ABSTRACT FROM AUTHOR]

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. For the diradicals, both substantial AF (ΔEST≈−64 cm−1) and FM (ΔEST≥25 and 100 cm−1) intramolecular exchange interactions were observed. The sign of the exchange interaction is determined both by the bridging moiety (para‐ or meta‐phenylene) and by the type of oxoverdazyl block (C‐linked or N‐linked). Upon crystallization, diradicals with the triplet ground state form unique one‐dimensional exchange‐coupled chains with strong intra‐ and weak inter‐diradical ferromagnetic coupling. [ABSTRACT FROM AUTHOR]

A novel design of electroactive components of rechargeable organic batteries based on stable verdazyl radicals bearing various substituents is proposed. 3-Positioned aromatic substituents at the verdazyl moiety affect the reduction potentials and almost do not affect the oxidation potential, while 1-positioned aromatic substituents affect contrariwise the oxidation potential of this radical without any influence on the reduction potential. The acquired electrochemical data allowed us to reveal the structure—potential relationship for the cathodic and anodic processes, which provided the design of triarylverdazyl radicals possessing record-breaking parameters of the "electrochemical gap". [ABSTRACT FROM AUTHOR]

Verdazyl radicals have been obtained from non-symmetric alkadiynyl ethers ofp-hydroxybenzaldehyde. Using these radicals, the effect of the distance between the conjugated diyne fragment and the bulky tetrazinyl substituent on the ability to solid-state polymerization under UV irradiation has been studied. It has been shown that the rate of solid-state polymerization (accompanied by the preservation of the radical site) is increased with an increase in the number of methylene groups in the alkadiyne fragment. [ABSTRACT FROM AUTHOR]

The reactivity of 1,5-diisopropyl-3-(4′-carboxyphenyl)-6-oxoverdazyl H I i -Pr toward divalent metal ions is dominated by the coordination of the carboxylate moiety onto the metal ions. The formula of the compound obtained by the reaction with the earth-alkaline magnesium (II) is [Mg(I i -Pr) 2 ·2H 2 O] n ·0.35H 2 O (I i -Pr –Mg) whereas the reaction with 3d divalent metal ions yields compounds of general formula [M(I i -Pr) 2 (CH 3 OH) 4 ] (M = Mn (I i -Pr –Mn), Co (I i -Pr –Co), Ni (I i -Pr –Ni), Zn (I i -Pr –Zn)). The single-crystal X-ray diffraction analysis of I i -Pr –Mg reveals that the magnesium (II) adduct forms a one-dimensional (1D) coordination polymer with a terminal radical in a bidentate κ(O,O′) coordination mode and a bridging one in a μ − 1κ(O); 1κ (O′) syn – anti mode. The coordination sphere of the magnesium (II) is completed by two water molecules that established H-bonds with the carboxylate moiety of the terminal radicals that further reinforce the 1D coordination polymer. Adjacent chains interact through π-stacking of head-to-tail radicals. The single-crystal X-ray diffraction analysis of I i -Pr –Mn and I i -Pr –Ni reveals that the two compounds are isostructural. They are composed of mononuclear complexes where the divalent metal is surrounded by two radicals coordinated by monodentate carboxylate and four methanol molecules in the equatorial plane. Two methanol ligands act as H-bond donors toward the second oxygen atom of the carboxylate groups. The complexes interact through π-stacking of head-to-tail radicals and H-bonds between the two remaining methanol ligands and the oxygen atom of the oxoverdazyl moieties. In all of the compounds, the exchange interaction is dominated by the weak antiferromagnetic coupling related to the π-stacking of the radicals. [ABSTRACT FROM AUTHOR]

The aromaticity of fourteen 3-oxo-verdazyl (1–8, 15) and Kuhn verdazyl (9–14) radicals with different substituents has been investigated computationally using the gauge-including magnetically induced current-density (GIMIC) method. The strength of the local and global diatropic and paratropic ring current has been obtained by performing numerical integration of the current density flow. Detailed studies of the current densities show that the aromatic character of the verdazyl ring obeys Hückel's aromaticity rule. The cations with formally 6π electrons in the verdazyl ring are weakly aromatic and the anions with 8π electrons are antiaromatic. The verdazyl ring of the neutral radicals is found to be weakly antiaromatic. The studied molecules sustain a significant global diatropic ring current that flows around the verdazyl and the phenyl rings suggesting that there is a strong coupling between the rings. For the 3-oxo-verdazyl cations, the global ring current is weaker. The spin-current density of the radicals is paratropic forming a ring current in the studied 3-oxo-verdazyls, whereas in the Kuhn verdazyls we found that the spin current density is mainly localized on the nitrogens. The calculated ionization potentials are also compared to the values deduced from cyclic voltammetry data. [ABSTRACT FROM AUTHOR]

A general and effective method for the synthesis of 3‐phenylveradzyl radicals bearing a variety of iodophenyl substituents has been developed. The synthesized radicals have been characterized by ESR, UV/Vis spectroscopy, and cyclic voltammetry. Structures of biphenyl‐substituted radicals have been solved by X‐ray crystal structure analysis. The synthesized iodoverdazyls are applicable in the Sonogashira coupling reaction for the preparation of a wide range of ethynyl derivatives. Both N‐2 and C‐6 substituents were functionalized through Sonogashira coupling. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic behavior of the fluorene bridged verdazyl diradicals has been studied theoretically in their neutral and deprotonated states. The deprotonation of C9‐H site of the fluorene ring opens a new coupling pathway, which changes the nature of magnetic coupling. The transmission spectra analysis reveals that the transmission through fluorine has also increased due to the opening of a new coupling path after deprotonation. [ABSTRACT FROM AUTHOR]

The synthesis and crystallization of two verdazyl radicals, 1,5‐dimethyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HIMe and 1,5‐diisopropyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HIiPr, are described. The electrochemical studies reveal that the oxidation of the two radicals is reversible, whereas their reduction is irreversible. The EPR spectrum of both radicals essentially exhibits a nine‐line pattern related to the mean hyperfine interaction of the unpaired electron with the nitrogen atoms of the verdazyl cycle. The single‐crystal X‐ray diffraction of the intermediates towards HIiPr allows a fine description of the cyanoborane adduct, which is the key intermediate of this synthesis. The verdazyl radicals themselves are obtained as single crystals. In the case of HIiPr, depending on the solvent, two polymorphs are crystallized. The structure resolution reveals that, in the solid state, the organization of the verdazyl radicals is governed by both H‐bonding and π–π interactions and is reminiscent of the H‐bonded structures that can be present in solution. Within the 1D π stacks observed in the three compounds, the verdazyl–verdazyl distance varies from 4.88 Å in HIMe to 7.90 Å in HaIiPr. This modulation of the distance strongly influences the antiferromagnetic intermolecular exchange interaction between π‐stacked radicals, which goes from J = –90 cm–1 (H = –JΣSiSi+1) for HIMe to –12.96(3) cm–1 for HbIiPr and –0.92 cm–1 for HaIiPr. [ABSTRACT FROM AUTHOR]

We report on a series of eight diaryl-6-oxo-verdazyl radicals containing a tert-butyl group at the C(3) position with regard to their crystal structure and magnetic properties by means of magnetic susceptibility measurements in combination with quantum chemical calculations using a first-principles bottom-up approach. The latter method allows for a qualitative prediction and detailed analysis of the correlation between the solid-state architecture and magnetic properties. Although the perturbation in the molecular structure by varying the substituent on the N-aryl ring may appear small, the effects upon the structural parameters controlling intermolecular magnetic coupling interactions are strong, resulting in a wide spectrum of cooperative magnetic behavior. The non-substituted 1,5-diphenyl- tert-butyl-6-oxo-verdazyl radical features a ferromagnetic one-dimensional spin ladder type magnetic network-an extremely rarely observed phenomenon for verdazyl radicals. By varying substituents at the phenyl group, different non-isostructural compounds were obtained with widely different magnetic motifs ranging from linear and zigzag one-dimensional chains to potentially two-dimensional networks, from which we predict magnetic susceptibility data that are in qualitative agreement with experiments and reveal a large sensitivity to packing effects of the molecules. The present study advances the fundamental understanding between solid-state structure and magnetism in organically based radical systems. [ABSTRACT FROM AUTHOR]

Halogenated 3-aryl-1,5-diisopropyl verdazyl radicals have been shown to undergo Suzuki-Miyaura coupling reactions with a variety of boronic acids to give biaryl-substituted verdazyl derivatives in acceptable to good yields (50-90 %). The successful coupling depends on the halo substituent and the boronic acid, but most boronic acids could be coupled with the iodophenyl verdazyl radical under either ligandless conditions or in the presence of triphenylphosphine. The successful palladium-catalyzed coupling reaction facilitates the incorporation of verdazyl moieties into conjugated systems and can be used to modify the properties of organic materials. The new radicals were characterized by UV/Vis, ESR, and HRMS analysis and, particularly, by electron impact mass spectrometry, which generated the distinctive verdazyl fragmentation pattern. [ABSTRACT FROM AUTHOR]

6-Oxoverdazyl, a π-delocalized stable radical, is considered a central structural element of paramagnetic selforganizing materials. The three available positions on the heterocycle can be substituted with wedge-shaped or rod-like groups in combination with a small substituent, which leads to different molecular architectures and diverse organization of the mesophase. Several of these architectures have been realized experimentally and materials exhibiting columnar and calamitic phases have been obtained. Compounds with some other combination of substituents did not exhibit liquid crystalline behavior. The analysis also indicates some new molecular architectures potentially suitable for the formation of liquid crystalline phases. Finally, results on magnetic susceptibility and photovoltaic measurements of the discotic derivatives are discussed. [ABSTRACT FROM AUTHOR]

Methods for the detection of reactive intermediates such as transient radicals are important in organic chemistry, polymer chemistry, biology or medicine. Along these lines we recently reported that 1,5-diphenyl-6-oxo verdazyl radicals can be used as fluorescent spin sensors. In situ generated C-centered radicals are efficiently trapped by the verdazyls, which in turn undergo transformation from a paramagnetic non-fluorescent state to a diamagnetic fluorescent state. Whereas the N-phenyl substituent in the spin probes is of high importance for obtaining profluorescent behavior, the effect of the C(3)-substituent has not been investigated to date. We herein present the synthesis and characterization of various 1,5-diphenyl-6-oxo-verdazyl radicals bearing differently hybridized C-substituents at the C(3) position. Steady-state and time-resolved fluorescence spectroscopy in solution and in the solid state along with time-dependent density functional theory (TDDFT) calculations reveal that a C(3)-aryl substituent is crucial for obtaining fluorescence after spin trapping. In addition, it is shown that the emission wavelength of the C(3)-aryl substituted verdazyl derivatives can be tuned by selective destabilization of the HOMO and the LUMO.

Condensation of 2,4-diisopropylcarbonobis(hydrazide) bis-hydrochloride with a series of aldoses gives rise to tetrazanes that can be oxidized with potassium ferricyanide to give stable verdazyl radicals in good yield. The radicals are stable under ambient conditions, and are soluble in water and polar organic solvents. Aqueous solutions are stable over a range of both acidic and basic pH and do not react significantly with ascorbic acid or hydrogen peroxide. The radicals quench fluorescence from long lived fluorophores such as pyrene, or when there is an association between the radicals and the fluorophore. These radicals thus provide the foundations of a new series of radical probes and fluorescence quenchers. [ABSTRACT FROM AUTHOR]

ABSTRACT Redox-active 6-oxoverdazyl polymers were synthesized via ring-opening metathesis polymerization (ROMP) and their solution, bulk, and thin-film properties investigated. Detailed studies of the ROMP method employed confirmed that stable radical polymers with controlled molecular weights and narrow molecular weight distributions ( Ð < 1.2) were produced. Thermal gravimetric analysis of a representative example of the title polymers demonstrated stability up to 190 °C, while differential scanning calorimetry studies revealed a glass transition temperature of 152 °C. Comparison of the spectra of 6-oxoverdazyl monomer 12 and polymer 13, including FT-IR, UV-vis absorption, and electron paramagnetic resonance spectroscopy, was used to confirm the tolerance of the ROMP mechanism for the 6-oxoverdazyl radical both qualitatively and quantitatively. Cyclic voltammetry studies demonstrated the ambipolar redox properties of polymer 13 ( E1/2,ox = 0.25 and E1/2,red = −1.35 V relative to ferrocene/ferrocenium), which were consistent with those of monomer 12. The charge transport properties of thin films of polymer 13 were studied before and after a potential of 5 V was applied, revealing a drastic drop in the resistivity from 106−1010 Ω m or more to 1.7 × 104 Ω m and suggesting the potential usefulness of polymer 13 in bistable electronics. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1803-1813 [ABSTRACT FROM AUTHOR]

Novel 1,3-diphenyl-5-(benzothiazol-2-yl)-6-R-verdazyls, stable free radicals, were synthesized from the corresponding formazans by alkylation followed by cyclization and oxidation of the intermediate leucoverdazyls (yields 78–93%). The radicals were characterized by ESR, electronic and IR spectroscopy, mass spectrometry, X-ray diffraction (for one of them) and cyclic voltammetry. The resulting verdazyls are stable under ordinary conditions and are reduced more readily but more difficult to oxidize than the triphenylverdazyl analogue. [ABSTRACT FROM AUTHOR]

A poly(terthiophene) pendant verdazyl radical was prepared via the electrochemical oxidation of either the parent radical or its precursor. Cyclic voltammetry showed a positive shift of the verdazyl radical oxidation potential in the corresponding electroactive poly(verdazyl radical-terthiophene). [ABSTRACT FROM AUTHOR]

Low-spinground states and low-lying excited states of higher spinwere investigated for four pyrene oxoverdazyl monoradicals 1–4and eight pyrene dioxoverdazyl diradicals 5–12. The ground states for quartet andquintet spin symmetries that are in reality excited states were foundin the region of 565–775 nm above the respective electronicground states. We calculated the “adiabatic” magneticexchange coupling constant in the electronic ground state of eachisolated biradical (5–12) by unrestricteddensity functional theory. A number of hybrid functionals such asB3LYP, PBE0, M06, and M06-2X were used. We also used range-separatedfunctionals such as LC-ωPBE and ωB97XD to compare theireffects on the coupling constant and the relative energy of the high-spinstate. Molecular geometries were optimized for the doublet and quartetspin states of every monoradical (1–4), and the broken symmetry and triplet solutions were optimized forevery biradical (5–12), by systematicallyusing 6-311G, 6-311G(d,p), and 6-311++G(d,p) basis sets with eachfunctional. The geometry of each quintet diradical (5–12) was optimized using 6-311G basis set. B3LYPproduced the best spin values. The excited state (quartet or quintet)–groundstate energy difference (ΔE) increases in thepresence of para-phenylene connectors. These energy differences werepredicted here. The nature of spin coupling and consequently the groundstate spin agree with spin alternation rule and the calculated atomicspin population. The adiabatic coupling constants were predicted forthe biradicals (5–12) in their electronicground states. Electron paramagnetic resonance parameters were determinedat 6-311++G** level for the ground state and the quartet state of 1and compared with the available experimental data. Low-lyingexcited states were found for the radical center (oxoverdazyl), pyrene,molecule 1, and diradical 5by time-dependentdensity functional theory (TDDFT) method using B3LYP hybrid, 6-311++G(d,p)basis set, and the molecular geometry in the electronic ground state. Datafrom these calculations were used to discuss possible mechanisms forthe achievement of the high-spin (excited) states in 1and 5and to predict a similar outcome for radicals 2–4and 6–12upon excitation. A comprehensive mechanism for the first excitationis proposed here. In particular, we show that the initial excitationof 1involves large contributions from mixed transitionsbetween pyrene and oxoverdazyl moieties, whereas the initial excitationof 5is basically that of only the pyrene fragment. Subsequentinternal conversion and intersystem crossing are likely to lead tothe high-spin states of lower energy. Sample spin-flip TDDFT calculationswere also done to confirm the energetic location and composition ofthe quartet state of 1and the quintet state of 5. [ABSTRACT FROM AUTHOR]

A series of one dimensional chain complexes [Ln(hfac)3]2·[Cu(hfac)2]2·4(3pyvd)·n-C7H16 (Ln = Gd(1), Tb(2), Dy(3)) containing 2p, 3d and 4f spin carriers have been successfully synthesized and magnetically characterized where the verdazyl radicals represent the bridge linking copper(ii) and lanthanide(iii) ions. Rough estimation of magnetic behaviors of complex 1 revealed that the coupling between a Gd(iii) ion and a radical is weakly ferromagnetic, while alternating-current susceptibilities of complexes 2 and 3 suggest no slow magnetic relaxations exist at low temperature. [ABSTRACT FROM AUTHOR]

The past 17 years have seen the growth of the coordination chemistry of verdazyls—stable free radicals first reported in 1963. Though verdazyls are weakly basic ligands, the ability to synthesize derivatives with chelating substituents, along with the steric similarity of verdazyls to aromatic azine ligands, has resulted in a variety of coordination compounds. Coordination compounds have been reported with Mn2+, Co2+, Ni2+, Cu+, Cu2+, Zn2+, Ru2+, Ag+, Cd2+, Tb3+, Dy3+, Gd3+and Hg2+. These studies have resulted in observations of strong ferromagnetic exchange (up to 400 cm−1), ligand-based redox processes, and non-innocent behavior. On the whole, verdazyls are weakly basic ligands in which the half-filled pi orbital can act as either an electron acceptor or an electron donor. The richness of the metal-verdazyl interaction, along with the structural diversity of verdazyls, provides many further opportunities for novel chemistry, as well as fertile ground for the introduction of undergraduates to research. [ABSTRACT FROM AUTHOR]

Based on the experimental synthesis of organic compound verdazyl radical β -3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl, consisting of four antiferromagnetic couplings, we study the magnetic properties and thermodynamic behaviors for different antiferromagnetic interactions using Green’s function theory. Under different fields, there are five regimes containing two gapless phases and three magnetization plateaus ( M =0, 1/2 and saturated magnetization) distinguished by four critical lines, which are evidenced by the two-site entanglement entropy and closely related to the energy spectra. In addition, we calculate the susceptibility and specific heat, to demonstrate the low-lying excitations at low temperatures. It will provide guidance for us to synthesize varieties of unconventional magnetic materials, and stimulate future studies on quantum spin systems. [ABSTRACT FROM AUTHOR]

Two derivatives of 1,3,5-aryl-6-oxoverdazyl containing two 3,4,5-trioctyloxyphenyl and one 3,4,5-tri((S)-3,7-dimethyloctyloxy)phenyl group in position C(3) (1b) or N(1) (1c) were investigated by thermal, X-ray diffraction and magnetic methods. The results were compared to those obtained for achiral derivative1acontaining three 3,4,5-trioctyloxyphenyl groups. All three compounds exhibit an ordered columnar hexagonal phase,Colh(o), and for chiral derivatives,1band1c, a superstructure with doubled periodicity was found. The introduction of the three chiral alkoxy substituents in1alowered the mesophase stability by about 50 K and induced aColhphase in1c. Thermochromic analysis showed a hypsochromic shift upon formation of theColh(o)phase similar for all three derivatives1(~0.3 eV), which coincides with a 5% drop in effective magnetic moment,μeff, for1c. Analysis of magnetisation data in a range of 2–370 K at 200 Oe revealed weak antiferromagnetic interactions (θ = – 4 K) in theColh(o)phase. [ABSTRACT FROM PUBLISHER]

The synthesis and characterization of two new N,N′-diarylverdazyl radical ligands and their corresponding PdCl2 complexes are described. One of the two radicals is of the “Kuhn verdazyl” structure type and was made by adaptation of standard synthetic procedures for this class of verdazyl. The N,N′-diphenyl-6-oxoverdazyl was prepared by hydrolysis of a related tetrazane; the resulting N,N′-diphenylcarbohydrazide was condensed with pyridinecarboxaldehyde and then oxidized to the verdazyl according to standard protocols. Square planar PdCl2 complexes of both verdazyls were prepared by reactions of the radicals with PdCl2 in acetonitrile solution. The structural, spectroscopic, and electrochemical properties of the new verdazyl ligands and their Pd complexes are reported; generally the distinct ligand-centred properties associated with each verdazyl type carry over into the properties of the complexes. The electrochemical studies reveal ligand-centred oxidation and reduction processes; despite the minimal extent of spin delocalization onto Pd in the metal complexes, large shifts in oxidation and reduction potentials (relative to those of the free verdazyl ligands) are discussed. [ABSTRACT FROM AUTHOR]

We have succeeded in synthesizing single crystals of the verdazyl radical β-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl. The ab initio molecular orbital calculation indicates the formation of an S=1/2 Heisenberg antiferromagnetic chain with fourfold magnetic periodicity consisting of three types of exchange interactions. We successfully explain the magnetic and thermodynamic properties based on the expected spin model by using the quantum Monte Carlo method. Furthermore, we reveal that the alternating and unique Ising ferromagnetic chains become effective in the specific field regions and observe a cooperative phenomenon caused by the magnetic order and quantum fluctuations. These results demonstrate that the verdazyl radical could form an unconventional spin model with interesting quantum behavior and provide a way to study a variety of quantum spin systems. [ABSTRACT FROM AUTHOR]

Transformations of functional groups, such as OCH2Ph, OCOPh, NO2 and I, in 1,3,5-triphenyl-6-oxoverdazyls 1a-1e were investigated in order to expand the range of synthetic tools for incorporation of the verdazyl system into more complex molecular architectures and to increase spin delocalization. Thus, Pd-catalyzed debenzylation of the OCH2Ph group or basic hydrolysis of the OCOPh group gave the phenol functionality, which was acylated, but could not be alkylated. Orthogonal deprotection of diphenol functionality was also demonstrated in radical 1c. Pt-catalyzed reduction of the NO2 group led to the aniline derivative, which was acylated. Attempted C-C coupling reactions to iodophenyl derivatives 1e and 5e were unsuccessful. Selected verdazyl radicals were characterized by EPR and electronic absorption spectroscopy, and results were analyzed with the aid of DFT computational methods. [ABSTRACT FROM AUTHOR]

Abstract: Reactions of ZnCl2 with tridentate ligands based either on a 2,2′-bipyridine-substituted verdazyl radical (1) or a 2,6-pyridine-linked verdazyl diradical (2) give trigonal bipyramidal complexes 1·ZnCl2 and 2·ZnCl2, respectively in which the Zn–N bonds to the verdazyl nitrogen atoms are considerably longer than the Zn–N (pyridine) bonds. Electronic and EPR spectroscopy and magnetic susceptibility studies indicate that the perturbation of the verdazyl chromophore in the two Zn complexes is small. However, the redox properties of the Zn complexes are substantially different from those of the free ligand. The oxidation and reduction potentials of the verdazyl radical 1 both shift to more positive potentials in 1·ZnCl2. Voltammetry studies of diradical complex 2·ZnCl2 reveal substantial changes: reduction of the two verdazyl moieties in the complex occurs in a stepwise manner, whereas in the free ligand the two verdazyls have nearly identical reduction potentials. Oxidation of 2·ZnCl2 appears to lead to hemilabile behavior, i.e. the verdazyl–Zn bonds are broken reversibly upon oxidation, based on the voltammetric profile and also based on spectroscopic studies of the neutral and oxidized form of this complex. [Copyright &y& Elsevier]

Abstract: 3-Nitroformazans react with bis(1,1,1,5,5,5-hexafluroacetylacetonato)palladium to afford monometallic complexes. The complexes were characterized via X-ray crystallography, cyclic voltammetry, and electronic spectroscopy. The nature of the aryl substituents on the formazan ligands had a profound effect on the structure and spectroscopy of the complexes, with o-substituted aromatic rings twisted with respect to the ligand, while the p-tolyl substituted derivative adopted a planar structure. The complexes undergo irreversible reductions near −1V versus Fc/Fc+. [Copyright &y& Elsevier]

Abstract: The synthesis, structure, and magnetic properties of a dinuclear Co(II) complex of a tridentate verdazyl radical are presented. The reaction of a tetrazane containing a 4,6-bis(2-pyridyl)-pyrimid-2-yl substituent with cobalt chloride hexahydrate in aerated solution leads to in situ oxidation of the tetrazane to a verdazyl radical which is coordinated to Co(II) in a tridentate manner. The second tridentate coordination site of the verdazyl remains vacant. The crystal structure reveals the complex to be dimeric, with the cobalt ions linked by two bridging chlorides. The structure of Co2Cl2 core is highly asymmetric, with two short (2.3317Å) and two long (2.744Å) Co–Cl bonds. There are relatively short intermolecular contacts between coordinated verdazyl radicals in the solid state. Magnetic susceptibility data from 2 to 300K suggest intramolecular ferromagnetic interactions, and modeling of the high-temperature data produced a best fit with J Co–verdazyl of +20cm−1. [Copyright &y& Elsevier]

Abstract: Stable organic radicals have received much attention as building blocks for the construction of molecular magnetic materials because they are readily functionalized using modern synthetic techniques. In this context, the nitroxide radical family has been the dominant class of radicals in molecular magnetochemistry. However, other stable radical systems have also been explored. One such example is the verdazyl family of radicals. Their high chemical stability and synthetic versatility make verdazyls one of the more attractive alternatives to nitroxides in molecular magnet design. This article reviews the magnetism of verdazyl-based systems, including through-bond coupling in polyradicals, coordination complexes and intermolecular interactions in the solid state. [Copyright &y& Elsevier]

We successfully synthesized single crystals of the verdazyl radical 2-Cl-3,6-F2-V [=3-(2-chloro-3,6-difluorophenyl)-1,5-diphenylverdazyl], which is a rare model compound with an S=½ Heisenberg antiferromagnetic (HAF) honeycomb lattice. Ab initio molecular orbital calculations indicate two dominant AF interactions, forming a slightly distorted honeycomb lattice. We explain the magnetic susceptibility and the magnetization curve up to the saturation field based on the expected spin model using the quantum Monte Carlo method. In the low-temperature regions, we found a phase transition to an AF ordered state at about 0.77 K for the zero field and obtained the magnetic field-temperature phase diagram from the magnetic susceptibility and the specific heat for various magnetic fields. Through the analysis considering the effect of lattice distortion on magnetic behavior, we confirm that the lattice distortion of the present model is small enough that it does not affect the intrinsic behavior of the uniform S=½ HAF honeycomb lattice. [ABSTRACT FROM AUTHOR]

We demonstrate an advanced spin-system design using a hybrid spin consisting of a strongly coupled metal ion and verdazyl radical. Ab initio calculation, magnetization, and ESR measurements evidenced the first realization of an S=2 ferromagnetic-antiferromagnetic alternating chain with Ising anisotropy in a Mn-verdazyl complex [Mn(hfac)2]·(o-Py-V) [hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate; o-Py-V = 3-(2-pyridyl)-1,5-diphenylverdazyl]. Furthermore, we find an anomalous change in magnetization at 1/4 of the saturation value, which is probably a manifestation of the quantum nature of the system. [ABSTRACT FROM AUTHOR]