Organic materials consisting of two stable charged radicals are rare but fascinating systems. In this communication, we present the first charge transfer complex of a dimethylphenazine radical cation with a furazano[3,4-b]pyrazine-based radical anion. The SC XRD study revealed that the cation-anion (C-A) stacking motif depends on the solvent. Thus, -C-A-C-A- stacks are formed in THF, whereas an -A-A-C-C- stacking pattern is observed in CH2Cl2. Additionally, its features were investigated with PXRD, SQUID and computational methods.

Structures of new heterospin cobalt(II) hexafluoroacetylacetonate complexes (Co(hfac)2) with stable nitronylnitroxyl radicals containing 1-methyl-3-trifluoromethyl- (L1), 1-ethyl-3-trifluoromethyl- (L2), or 1-ethyl-5-trifluoromethylpyrazol-4-yl substituents (L3) are considered. It is shown that the interaction of Co(hfac)2 with L1 and L2 yields a new type of heterospin complexes with the [Co(hfac)2(L)2] stoichiometry, where L is coordinated by the oxygen atom of the nitronyl nitroxide fragment. The interaction with L3 yields a dimeric complex [Co(hfac)2(L3)]2 with paramagnetic ligands performing a bidentate-bridging function due to the coordination of imine N atoms of the pyrazole ring and O atoms of the paramagnetic moiety. Magnetic behavior of [Co(hfac)2(L)2] complexes indicates an antiferromagnetic interaction between the cobalt ion and coordinated nitronyl-nitroxide groups.

The effective approach to the synthesis of heteroradical organic salts based on the paramagnetic difurazanopyrazine derivative and pyridinium-substituted nitronyl nitroxides has been proposed. It was demonstrated that the use of [NNp/mR]I iodides as a cation-radical source in the reaction with NaL(H2O)3 (where L is the anion-radical of bis(1,2,5-oxadiazolo)[3,4-b:3 ',4 '-e]pyrazine) results in reducing L and the formation of solid solutions [NNpMe](L) x (HL)1-x H2O containing both the paramagnetic anion L and its reduced form anion HL. It was found that the use of [NNp/mR]NO3 nitrates allows to avoid the reduction of L, and heteroradical salts [NNp/mR]L can be easily obtained. A single crystal XRD study showed that the solid phases of [NNp/mR]L salts form crystals formed by quartets of anions and cations {NNp/mRLLNNp/mR}. Within the quartets, the distances between the anion-radical planes of L are similar to 3.3 & Aring;, which ensures the presence of antiferromagnetic exchange interactions between them and determines the magnetic properties, in general. It was found that in the [NNmMe]LH2O structure, alternating cationic and anionic radicals are ferromagnetically coupled and form magnetic chains, which are linked into layers by OH2ONL hydrogen bonds. The [NNp/mR]L heteroradical salts represent a new type of paramagnet based on organic fragments with fixed charge and spin states.

The extension of a series of polyalkylpyrazolyl-substituted 2-imidazoline nitronyl nitroxide radicals LR1/R2/R3 (R = Me, Et, Pr, Bu) enables the synthesis of a number of coordination polymers based on copper(II) bis(hexafluoroacetylacetonate) Cu(hfac)2 with LR1/R2/R3. As compared to breathing crystals (Cu(hfac)2 complexes with monoalkyl-substituted nitroxides LR1 with bridging μ2-O,N coordination), the introduction of the second substituent LR1/R2 into the pyrazole ring allows the performance of the tritopic function of the paramagnetic ligand (μ3-O,O,N) and the formation of 1D and 2D polymers with original structures and different combinations of [CuO6], [CuO5N], [CuO4N2], and [CuO5] coordination cores. Only molecular complexes are obtained with single 3-substituted nitroxide LR1/R2/R3–LMe3. The single crystal X-ray diffraction study of the structures of these compounds shows that as in the case of LMe3, an increase in the size of one of substituents in LR1/R2 to Pr or Bu causes an increase in distances between paramagnetic centers in two- and three-spin exchange clusters, and correspondingly, spin transitions are absent.

Spontaneous solvent-controlled solid-state transformations were observed for a series of polymeric chain solvates [Cu(hfac)(2)L-Pr]0.5Solv (Solv = (CH3)(2)CO, 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 (L-Pr) under ambient conditions. The conversion of powdered polymeric chain [Cu(hfac)(2)L-Pr]0.5THF and [Cu(hfac)(2)L-Pr]0.5(CH3)(2)CO complexes, accompanied by the loss of solvent molecules, occurs completely to binuclear [Cu(hfac)(2)L-Pr](2) within a day. On the other hand, in the case of [Cu(hfac)(2)L-Pr]0.5Solv (Solv = CH2Cl2, CH2Br2, CHCl3), the partial transformation into a desolvated 1D polymer [Cu(hfac)(2)L-Pr] or its mixture with [Cu(hfac)(2)L-Pr](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)(2)L-Pr]0.5THF and [Cu(hfac)(2)L-Pr]0.5(CH3)(2)CO 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.

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 center dot-N-C=N -> O and the imidazole ring in Ln-Pr. This work reports a selective method for the synthesis of N-alkylimidazol-5-yl-substituted nitronyl nitroxides in high yields. And also, a new family of molecular heterospin complexes was obtained by the reaction of new nitroxides and Cu(hfac)2.image

Расширение круга полиалкилпиразолил-замещенных 2-имидазолиновых нитронилнитроксильных радикалов LR1/R2/R3 (R = Me, Et, Pr, Bu) позволило осуществить синтез серии координационных полимеров на основе бис(гексафторацетилацетоната) меди(II) Cu(hfac)2 с LR1/R2/R3. По сравнению с “дышащими кристаллами” – комплексами Cu(hfac)2 с моноалкил-замещенными нитроксилами LR1 с мостиковой m2-O,N координацией, введение в пиразольный цикл второго заместителя – LR1/R2 – дало возможность реализации тритопной функции парамагнитного лиганда (m3-O,O,N) и образования 1D и 2D полимеров оригинального строения с различными комбинациями координационных узлов [CuO6], [CuO5N], [CuO4N2] и [CuO5]. С единственным три-замещенным нитроксилом LR1/R2/R3 – LMe3 получены только молекулярные комплексы. Рентгеноструктурное исследование строения данных соединений показало, что увеличение размера одного из заместителей в LR1/R2 до Pr или Bu, как и в случае LMe3, приводит к увеличению расстояний между парамагнитными центрами в двух- и трехспиновых обменных кластерах и, соответственно, отсутствию спиновых переходов.

Using SC XRD, it was proved that the cyclocondensation of 3,4-diaminofurazan with diethyl-2-oxosuccinate gives two products, being structural isomers – derivatives of furazano[3,4- b ]pyrazin-6-one (2) and furazano[3,4- b ][1,4]diazepin-7-one (6).

Oxidation of 4H,8H-bis(1,2,5-oxadiazolo)[3,4-b:3 ',4 '-e]pyrazine H2L in the presence of Ba or Ca oxide leads to the formation of paramagnetic Ba(II) and Ca(II) salts, respectively. It was shown that the basicity of the reaction mixture plays an important role in the oxidation of H2L. Molecular and crystal structures of [Ba(L)(2)(H2O)(5)]2H(2)O, [Ba-2(L)(HL)(2)(H2O)(6)](L)4H(2)O, [Ba(HL)(H2O)(6)](HL)H2O, and [Ca(L)(H2O)(6)](2)Br-2 were determined. It was found that paramagnetic [Pb(L)(2)(H2O)(5)]2H(2)O can be obtained by H2L oxidation with PbO2 in the absence of alkaline earth metal oxides. It was shown that using two oxidizing agents, PbO2 and Br-2, in the reaction of BaO with H2L allows us to obtain paramagnetic salts with a new anion radical bis(1,2,5-oxadiazolo)[3,4-b:3 ',4 '-e]pyrazine-4-oxyl (L-O) and "singlet diradical" L-O1. It was found that, depending on the synthetic conditions, [Ba(L-O)(2)(H2O)(6)]2H(2)O crystallizes in the form of several polymorphic modifications differing in the angles between the planes of L-O radicals bound to the Ba ion. Quantum chemical analysis revealed that the presence of the N-oxide fragment in L-O leads to a noticeable redistribution of the spin density in comparison with L. The calculated map of the distribution of exchange integrals at different relative displacements in pairs of L-O allows us to give a qualitative insight into the magnetic behavior of anion radical stacks.

Multispin Cu(II)-nitroxide compounds have at-tracted significant interest in the field of molecular magnetism; however, complexes involving more than three spins in a single molecule have rarely been reported. In this work we describe the synthesis and detailed physicochemical study of the solvated six-coordinated five-spin complex [CuL2] (L = 2,2 '-(1H-pyrrole-2,5- diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl)). This complex features a tridentate meridional coordination of the biradical L, resulting in an exchange-coupled cluster of four radical and one Cu(II) spin. The structural and magnetic properties of [CuL2] have been thoroughly investigated using single-crystal X-ray diffraction (XRD), SQUID magnetometry, electron paramagnetic resonance (EPR), Fourier-transform infra -red (FTIR) spectroscopy, and quantum chemical calculations (QCC). An apparently compressed octahedral coordination geometry has been found by XRD, which, however, stems from the superposition of two isomeric structures of elongated octahedral CuN2O4 units. Neither X-ray nor FTIR has revealed any structural transitions in [CuL2] at 8-300 K, whereas the magnetic behavior studied by magnetometry and QCC is governed by temperature-dependent populations of high-spin multiplets. EPR spectroscopy revealed a drastic temperature dependence of the line width in [CuL2], which changes by almost 2 orders of magnitude within 4-300 K. A comparison with EPR and QCC data for close-structure four-and three-spin analogues has revealed an interplay of the temperature-dependent population of high-spin multiplets and intermolecular exchange interactions, which govern the line width in such systems.

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)2LF]2 {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)2LF]n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LF) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)2LF]2 have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand LF. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)2LF]2, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)2LF]2 and [Ni(hfac)2LF]2, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)2LF]2 showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (JMn-ON = −84.1 ± 1.5 cm−1, JCo-ON = −134.3 ± 2.6 cm−1, and JNi-ON = −276.2 ± 2.1 cm−1; H^=−2JS⃑^MS⃑^NO). Notably, the magnetization of [Mn(hfac)2LF]2 having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)2LF]n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {ONO–Cu(II)–ONO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (JCu-ON = 14.8 ± 0.3 cm−1).

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.

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.

The structures of hexafluoroacetylacetonate complexes of Cu(II)–Cu(hfac)2– with nitroxide radicals LR1/R2, where R1 and R2 are alkyl substituents in the 1,3-pyrazole moiety are studied by X-ray crystallography. It is found that solid phases of all [Cu(hfac)2LR1/R2] are formed by polymeric chains whose common structural motif is a ditopic bridging coordination of paramagnetic ligands in the head-to-head fashion. The study of the temperature structure dynamics and the related change in the temperature dependence of the effective magnetic moment of the complex shows that changes in both R1 and R2 can substantially affect not only the possibility of the appearance of magnetic anomalies on the temperature curve of the effective magnetic moment but also its shape.

The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L1) and iminonitroxide (L2) diradicals (HL1 is 2,2′-(1H-pyrrole-2,5diyl)-bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl; HL2 is 2,2′-(1H-pyrrole-2,5-diyl)-bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl) are studied. It is established that in all synthesized compounds, a tridentate meridional coordination of paramagnetic ligands is responsible for a distorted octahedral environment of the metal ion. In $$[M\text{L}_{2}^{n}]$$ bis-chelates, the metal ion environment is an octahedron compressed along the NPyr–M–MPyr axis. When one of the ligands in the $$[\text{CuL}_{2}^{\,2}]$$ molecule is replaced by a reduced L2H monoradical, a typical Cu(II) environment in the form of elongated octahedron arises in [CuL2L2H]. It is found that in $$[M\text{L}_{2}^{\,1}]$$ complexes with bis-nitronyl nitroxide, the character of the temperature dependence of the effective magnetic moment μeff(T) is determined by antiferromagnetic exchange in coordinated diradicals. In $$[M\text{L}_{2}^{\,2}]$$ complexes with iminonitroxides, ferromagnetic exchange interactions between unpaired electrons of the metal ion and diradicals dominate.

The structure of previously unknown compounds NH4(HL•)(HL)·3H2O and NH4(L•)x(HL)1x·H2O (L• is a radical anion, HL is a deprotonated difurazanopyrazine derivative, HL• is a product of difurazanopyrazine oxidation) prepared by the oxidation of difurazanopyrazine (H2L) in aqueous ammonia is described. It is established that the shortest distances between the neighboring {L} in NH4(HL•)(HL)·3H2O and NH4(L•)x(HL)1–x·H2O fall within a fairly narrow range of 3.15-3.30 Å, despite the fact that they have substantially different stackings of {L} fragments. The bond lengths and bond angles of molecules {L} in all the studied compounds differ insignificantly. The energy of interaction between the paramagnetic centers in ammonium difurazanopyrazine salts is sharply diminished due to the decreased content of paramagnetic particles and, consequently, increased distances between these particles.

Crystalline Cs salts with the difurazanopyrazine radical anion are synthesized: Cs(L • )(H 2 O) 2 -I, Cs(L • )(H 2 O) 2 -II, Cs 2 (L • ) 2 (HL • )(H 2 O), Cs 3 (L • ) 3 (L •• ) 2 (H 2 O) 3 . In the solid phase, Cs ions are surrounded by water molecules and are located between the stacks of difurazanopyrazines, forming a framework. The study of the structure and magnetic properties of the compounds shows that Cs(L • )(H 2 O) 2 -I represents a metastable phase that transforms into Cs(L • )(H 2 O) 2 -II on cooling and differs from the initial compound by a shift of radical anions relative to each other in the stacks. It is found that in Cs(L • )(H 2 O) 2 -II there is strong antiferromagnetic exchange between paramagnetic centers.