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An oxalate complex of vanadyl(IV) (Bu4N)2[VO(C2O4)2] (I) was synthesized and used as a vanadium precursor. The synthesis and characterization of the double complex salts [Pt(NH3)4][VO(H2O)(C2O4)2]·2H2O (III) and {[Pt(NH3)4][VO(C2O4)2]}n (IV) were carried out. The complexes obtained were characterized by IR and diffuse reflectance spectroscopy, single-crystal and powder X-ray diffraction, and EPR. The magnetic properties of I, III, and IV were also studied. The process of thermal decomposition of the synthesized complexes in reducing and inert atmospheres was studied, and the composition of the released gases was determined. Thermal decomposition of the salts in a hydrogen atmosphere at 600 °C resulted in the formation of a bimetallic solid solution, Pt0.6V0.4. [ABSTRACT FROM AUTHOR]

Spontaneous solvent-controlled solid-state transformations were observed for a series of polymeric chain solvates [Cu(hfac)2LPr]·0.5Solv (Solv = (CH3)2CO, THF, CH2Cl2, CH2Br2, CHCl3) with 2-(1-propyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LPr) under ambient conditions. The conversion of powdered polymeric chain [Cu(hfac)2LPr]·0.5THF and [Cu(hfac)2LPr]·0.5(CH3)2CO complexes, accompanied by the loss of solvent molecules, occurs completely to binuclear [Cu(hfac)2LPr]2 within a day. On the other hand, in the case of [Cu(hfac)2LPr]·0.5Solv (Solv = CH2Cl2, CH2Br2, CHCl3), the partial transformation into a desolvated 1D polymer [Cu(hfac)2LPr] or its mixture with [Cu(hfac)2LPr]2 takes much longer time. The magnetic behavior of the isostructural solvates is highly sensitive to the included solvent molecules. The complexes with THF, CH2Cl2, CH2Br2, and CHCl3 undergo a transition to a magnetically ordered state below 4 K, a phenomenon reported for the first time for the polymeric chain Cu(II) complexes with a "head-to-tail" motif. [Cu(hfac)2LPr]·0.5THF and [Cu(hfac)2LPr]·0.5(CH3)2CO undergo a spin transition at 190 K, which is induced by the transformation of the Cu atom environment. In the case of the THF solvate, the increase in the distances between the Cu and oxygen atoms leads to enhanced ferromagnetic exchange interactions, while in the acetone solvate, the nitroxide coordination type changes from axial to equatorial at certain coordination sites, resulting in the emergence of strong antiferromagnetic exchange. [ABSTRACT FROM AUTHOR]

A series of pyridyl‐substituted nitronyl nitroxides was synthesized and structurally characterized. A comprehensive magnetochemical and quantum chemical study of extended raw of the nitroxides with different substituents R in the pyridine fragment was performed. It was shown, that temperature‐dependent magnetic properties are determined by the short contacts between nitroxide groups of adjacent molecules as well as between nitroxide group and methyl substituents in the pseudo axial positions of imidazoline fragments. Quantum chemistry allows to select the appropriate model of exchange cluster for analysis of experimental magnetic data and evaluation of the exchange interaction parameters. For NN–PyCl the "order‐disorder" transition was detected by means of low temperature XRD. The difference in the experimental and calculated exchange interaction energies may serve as an indicator of temperature‐induced structural rearrangements. For instance, for methyl substituted nitronyl nitroxide NN‐PyMe structural transformations and significant changes in exchange interaction energies were observed. [ABSTRACT FROM AUTHOR]

Valence tautomeric complexes (VT) are promising systems for creating molecular devices. From this viewpoint, valence tautomeric complexes with a hysteresis loop on the magnetic curve are of special interest as potential memory elements. The hysteresis loop is a consequence of retarded structural rearrangements which investigation is an actual problem. Recently, we have described a new VT transition taking place in a bis-dioxolene cobalt complex with imino-pyridine having a TEMPO substituent (A. A. Zolotukhin, et al., Inorg. Chem., 2017, 56, 14751-14754). Valence tautomeric transformation occurs with a hysteresis loop and is accompanied by a phase transition. The phase transition taking place during cooling is accompanied by crystal destruction. This fact makes it impossible to monitor the structural changes responsible for the hysteresis loop. The current research attempts to resolve this problem. A nickel compound of the same composition (TEMPO-imino-pyridine)Ni(3,6-DBSQ)2 was synthesized and characterized. It was established to be isostructural with the cobalt complex. It was used as an inert matrix for the dilution of the VT cobalt complex. The number of solid solutions with Co/Ni ratios of 1: 1, 1: 2, 1: 4, and 1: 8 was obtained. Variable temperature magnetic susceptibility measurements show that VT transformation with a hysteresis loop takes place in all solid solutions. The hysteresis loop is shifted to low temperatures primarily due to the shifting of its low-temperature boundary with dilution. The hysteresis width does not change significantly with dilution. DSC detected that transformations are accompanied by phase transitions at different temperatures at cooling and heating. The phase transition at the first cooling occurs at slightly lower temperatures compared with subsequent cycles. These temperatures correspond to the transition temperatures detected from the magnetic curves. The phase transition during the first cooling is accompanied by crystal destruction. Physical destruction takes place in the crystals of all solid solutions. X-ray diffraction powder patterns confirm that phase transition is accompanied by considerable reorganization of the crystal structure typical for the first order transitions. The unit cell volume of solid solutions is larger than that of pure complexes. Especially calculated crystal invariom indicated that the "lattice energy" in a solid solution is the lowest compared with that in "pure" nickel and cobalt complexes. [ABSTRACT FROM AUTHOR]

A novel synthetic approach has been employed to synthesize a series of new nitronyl nitroxides: 2‐(1‐propyl‐1H‐imidazol‐5‐yl)‐ (Ln−Pr), 2‐(1‐isopropyl‐1H‐imidazol‐5‐yl)‐ (Li−Pr) and 2‐(1‐butyl‐1H‐imidazol‐5‐yl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazole‐3‐oxide‐1‐oxyl (Ln−Bu). The reaction of Cu(hfac)2 with LR in a 1 : 2 ratio yields mononuclear heterospin complexes [Cu(hfac)2(LR)2] (LR=Ln‐Pr, Li‐Pr, Ln‐Bu), which have a similar crystal structure to the "jumping" crystals [Cu(hfac)2(LMe)2] that exhibit chemomechanical activity. It was shown that an increase in the alkyl substituent R leads to changes in the crystal packing of the molecules and the absence of chemomechanical activity. Furthermore, it was found that two polymorph modifications of the heterospin complex [Cu(hfac)2(Ln−Pr)2] can be obtained, and magnetic properties of [Cu(hfac)2(Ln−Pr)2] strongly depend on the angle between the planes of the paramagnetic fragment O•–N‐C=N→O and the imidazole ring in Ln−Pr. [ABSTRACT FROM AUTHOR]

High‐spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but those synthesized to date possess limited stability and processability. In this work, we have designed a tetraradical based on the Blatter's radical and nitronyl nitroxide radical moieties and successfully synthesized it by using the palladium‐catalyzed cross‐coupling reaction of a triiodo‐derivative of the 1,2,4‐benzotriazinyl radical with gold(I) nitronyl nitroxide‐2‐ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X‐ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C under an inert atmosphere and exhibits reversible redox waves at −0.54 and 0.45 V versus Ag/AgCl. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed by using high‐level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl‐nitronylnitroxide tetraradical is a new milestone in the field of creating high‐spin systems. [ABSTRACT FROM AUTHOR]

A new binuclear "paddle-wheel" complex, [Co2(bhbz)4(EtOH)2]·4EtOH (1, Hbhbz-3,5-di(tert-butyl)-4-hydroxybenzoic acid); an isostructural zinc complex (2); a and magnetically diluted sample of [Zn1.93Co0.07(bhbz)4(EtOH)2]·4EtOH (3) were obtained. Molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. DFT calculations for 1 indicate strong Co-Co antiferromagnetic exchange interactions in the binuclear fragment. It was shown that when one paramagnetic ion in the binuclear molecule is replaced by a diamagnetic zinc(II) ion, the remaining cobalt(II) ion can be considered as an isolated center with magnetic anisotropy, the parameters of which are determined by ab initio calculations. Magnetic properties for samples 1 and 3 were investigated and analyzed in detail. [ABSTRACT FROM AUTHOR]

Novel nitronyl nitroxides, namely 2-(3-iodoethynylphenyl)- and 2-(4-iodoethynylphenyl)-4,4,5,5-tetramethyl-imidazoline-3-oxyl-1-oxides, were prepared by condensation of appropriate aldehydes with 2,3-bis(hydroxylamino)-2,3-dimethylbutane followed by oxidative treatment with NaIO4. Crystal and molecular structures of the obtained paramagnets were studied by single-crystal X-ray diffraction. In the crystals, the radicals are assembled into zigzag chains in which the radical building blocks are linked by intermolecular I⋯N–O halogen bonding. Magnetic analyses revealed that in both nitronyl nitroxides, the radicals are weakly coupled. Nonetheless, spin–spin interactions in the 3-iodoethynyl isomer are antiferromagnetic, and the coupling is stronger than that in the 4-iodoethynyl derivative, in which the exchange interaction is ferromagnetic. DFT calculations in combination with MEP, NCIplot, and QTAIM analyses were used to evaluate and characterize the structure-directing halogen bonding interactions observed in the solid state of both compounds. [ABSTRACT FROM AUTHOR]

Ditopic di-o-quinone with a resorcinol bridge exhibits the ability to self-assemble in a reaction with copper, giving a cage-like binuclear complex that, due to the cofacially placed metal ions, is capable of encapsulation of different solvent molecules as guest ligands. Notably, the geometry of the internal cavity of this complex adjusts depending on the coordinating properties of the encapsulated molecule (mono- or bidentate). A feature of this species is that the cage-forming units are copper(II) bis-semiquinonate moieties, capable of undergoing ligand-centered redox transformations. Electrochemical and EPR spectroscopy studies showed that there is a channel for intramolecular electronic exchange interactions between the redox centres of the molecule. [ABSTRACT FROM AUTHOR]