Properties and structures of porphyrexides

The molecular and crystal structures of porphyrexides, viz., 4-amino-2-imino-(1) and (Z)-2-amino-4-bromoimino-5,5-dimethyl-4,5-dihydro-1H-imidazole 1-oxyls (7), and their diamagnetic precursors were determined. Compound 1 is kinetically unstable because it is oxidized with atmospheric oxygen to form (E)-1,2-bis[1-amino-1-(cyanoimino)-2-methyl-propan-2-yl]diazene 1,2-dioxide. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–447, March, 2006.     

2-Imidazoline Nitroxide Derivatives of Cymantrene

The 2-imidazoline nitroxide derivatives of cymantrene—2-(η⁵-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (NNMn) and 2-(η⁵-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (INMn) were synthesized. It was shown that NNMn and INMn exhibit a sufficiently high kinetic stability both in solids and in solutions under normal conditions. Their structural characteristics, magnetic properties and electrochemical behavior are close to Re(I) analogs. This opens the prospect of using paramagnetic cymantrenes as prototypes in the design of Re(I) half-sandwiched derivatives for theranostics, where therapy is combined with diagnostics by magnetic resonance imaging due to the contrast properties of nitroxide radicals.     

Study of the complexes of iron(II) dicyanamide and isothiocyanate with 2-(2-<Emphasis Type="Italic">tert</Emphasis>-butyltetrazol-5-yl)pyridine

Iron(II) dicyanamide and isothiocyanate compounds with 2-(2-tert-butyltetrazol-5-yl)pyridine (L) of the composition [FeL₂(C₂N₃)₂]?2H₂O (I) and [FeL₂(NCS)₂]H₂O (II) are synthesized and studied. The compounds are examined using powder and single crystal XRD (for I), electron (diffuse reflectance spectra) and IR spectroscopy, static magnetic susceptibility. The analysis of the dependence μ_eff(Т) indicates that the exchange interactions of antiferromagnetic nature appear between the iron(II) ions at temperatures below 50 K.     

Synthesis, structure, and properties of nitronyl nitroxyl tetraradical with calix[4]arene framework

A reaction of calix[4]arene tetraaldehyde with 2,3-bis(hydroxyamino)-2,3-dimethylbutane in DMF resulted in the corresponding 1,3-dihydroxyimidazolidine tetraadduct, whose oxidation gave a calix[4]arene (1,3-alternate) bearing four nitronyl nitroxyl-containing substituents at the upper rim.     

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. For the diradicals, both substantial AF (ΔE_ST≈−64 cm⁻¹) and FM (ΔE_ST≥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.     

Effect of increasing pressure on the structure and temperature-induced changes in magnetic properties of heterospin complexes

Russian Chemical Bulletin - The study is concerned with structural rearrangements in the crystals of heterospin complexes Cu(hfac)2 with nitroxide radicals LR (hfac is hexafluoroacetylacetonate, LR...     

Synthesis, structure, and magnetic properties of heterometallic trinuclear complexes {MII��LnIII��MII} (MII = Ni, Cu; LnIII = La, Pr, Sm, Eu, Gd)

Trinuclear heterometallic complexes containing the {M₂Ln(Piv)₆(NO₃)} (M^II = Ni, Cu; Ln^III = Nd, Pr, Sm, Eu, Gd; Piv^? is the anion of pivalic acid) and {Cu₂Ln(Piv)₈)]^? (Ln^III = Eu, Gd) metal cores were synthesized, their structures and magnetic properties were studied. For the most compounds, it was shown that their magnetic properties can be interpreted taking no interaction of the 3d-metal ions and a lanthanide into account. Ferromagnetic exchange interactions were found to exist between the unpaired electrons of the paramagnetic centers in the exchange clusters of the gadolinium-containing heterometallic complexes {M-Gd-M} (M = Ni or Cu).     

Crucial role of paramagnetic ligands for magnetostructural anomalies in "breathing crystals"

Breathing crystals based on polymer-chain complexes of Cu(hfac)(2) with nitroxides exhibit thermally and light-induced magnetostructural anomalies in many aspects similar to a spin crossover. In the present work, we report the synthesis and investigation of a new family of Cu(hfac)(2) complexes with tert-butylpyrazolylnitroxides and their nonradical structural analogues. The complexes with paramagnetic ligands clearly exhibit structural rearrangements in the copper(II) coordination units and accompanying magnetic phenomena characteristic for breathing crystals. Contrary to that, their structural analogues with diamagnetic ligands do not undergo rearrangements in the copper(II) coordination environments. This confirms experimentally the crucial role of paramagnetic ligands and exchange interactions between them and copper(II) ions for the origin of magnetostructural anomalies in this family of molecular magnets.     

Synthesis and structure of polycrystalline adducts of Co(II) azomethine complexes with redox-active 2,4,6,8-tetrakis-(<Emphasis Type="Italic">tert</Emphasis>-butyl)phenoxazin-1-one

The six-coordinate cobalt complexes, C₅₇H_63.50N_4.50O₄Co (IIa), C₆₀H₆₉N₅O₄Co (IIb), C5₈H₆₇N₃O₈Co (IIc), C₅₆H₆₁N₅O₁₀Co (IId), C₅₆H₆₃N₃O₆Co (IIe), C₅₈H₆₆N₄O₆Co (IIf), and C₅₈H₆₃N₇O₈Co (IIg), adducts of high-spin tetrahedral Co(II) bis(salicylaldiminates) (C₂₉H_24.50N_3.50O₂Co (Ia), C₃₂H₃₀N₄O₂Co (Ib), C₃₀H₂₈N₂O₆Co (Ic), C₂₈H₂₂N₄O₈Co (Id), C₂₈H₂₄N₂O₄Co (Ie), C₃₀H₂₇N₃O₄Co (If), and C₃₀H₂₄N₆O₆Co (Ig)) and redox-active 2,4,6,8-tetrakis(tert-butyl)phenoxazin-1-one (L), were synthesized and studied for structure and magnetic properties. Complexes IIa–IIg have octahedral structure (CIF files CCDC nos. 1403920 (IIf), 1403922 (IIg)) and exist in the ground low-spin state (ls-Co^III-SQ), which arises upon intramolecular single-electron redox process in the ligand–metal system. The presence of substituents of different nature in the azomethine ligands of IIa–IIg does not induce any significant changes in their magnetic properties.     

Spin transition in the molecular heterospin complex of Cu(hfac)2 with 4,4,5,5-tetramethyl-2-(1-methylpyrazol-5-yl)-4,5-dihydroimidazole-1-oxyl 3-oxide

The synthesis, structure, and magnetic properties of the products of the reaction for Cu(hfac)₂ (hfac is hexafluoroacetylacetonate) with spin-labeled nitronyl nitroxides 4,4,5,5-tetramethyl-2-(1-R-1H-pyrazol-5-yl)-3-imidazoline-1-oxyl 3-oxides L^5/R (R = Me, Et, Pr, Bu), viz., binuclear complex [Cu(hfac)₂L^5/Me]₂ and chain polymer complexes [Cu(hfac)₂L^5/R]_n, are described. The polymer heterospin chains are built according to “head-to-head” (R = Me, Et, Pr, Bu) and “head-to-tail” (R = Pr, Bu) motifs. Compound [Cu(hfac)₂L^5/Me]₂ is characterized by the ability to reveal the reversible effect of thermally induced spin transition at a temperature about 75 K (without hysteresis). In the set of heterospin Cu^II compounds with spin-labeled pyrazoles, this is the earlier unknown example of a molecular complex exhibiting a similar magnetic anomaly.