Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL1) in organic solvents formed trinuclear complex [Co3(Piv)2L12L22]·Solv (Solv is Me2CO and/or C7H16 and CH3CN) containing both nitroxide L1 and the product of its single-electron reduction, nitrone L2. The formation of [Co3(Piv)2L12L22] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L1 to L2 led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL12L2] and [FeL12L2]·Me2CO

Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL1) in organic solvents formed trinuclear complex [Co3(Piv)2L12L22]·Solv (Solv is Me2CO and/or C7H16 and CH3CN) containing both nitroxide L1 and the product of its single-electron reduction, nitrone L2. The formation of [Co3(Piv)2L12L22] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L1 to L2 led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL12L2] and [FeL12L2]·Me2CO

Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL¹) in organic solvents formed trinuclear complex [Co₃(Piv)₂L¹₂L²₂]·Solv (Solv is Me₂CO and/or C₇H₁₆ and CH₃CN) containing both nitroxide L¹ and the product of its single-electron reduction, nitrone L². The formation of [Co₃(Piv)₂L¹₂L²₂] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L¹ to L² led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL¹₂L²] and [FeL¹₂L²]·Me₂CO

Thermally Induced Spin Transitions in Nitroxide−Copper(II)−Nitroxide Spin Triads Studied by EPR

Thermally induced spin transitions in a family of heterospin polymer chain complexes of Cu2+ hexafluoroacetylacetonate with two pyrazole-substituted nitronyl nitroxides are studied using electron paramagnetic resonance (EPR) spectroscopy. The structural rearrangements at low temperatures induce spin transitions in exchange-coupled spin triads of nitroxide−copper(II)−nitroxide. The values of exchange interactions in spin triads of studied systems are typically on the order of tens to hundreds of inverse centimeters. The large magnitude of exchange interaction determines the specific and very informative peculiarities in EPR spectra due to the predominant population of the ground state of a spin triad and spin exchange processes. The variety of these manifestations depending on structure and magnetic properties of spin triads are described. EPR is demonstrated as an efficient tool for the characterization of spin transitions and for obtaining information on the temperature-dependent sign and value of the exchange interaction in strongly coupled spin triads

A Copper–Nitroxide Adduct Exhibiting Separate Single Crystal-to-Single Crystal Polymerization–Depolymerization and Spin Crossover Transitions

A complex <i>cascade of solid-state processes</i> initiated by variation of temperature was found for the heterospin complex [Cu­(hfac)₂L^Me/Et] formed in the reaction of copper­(II) hexafluoroacetylacetonate [Cu­(hfac)₂] with stable nitronyl nitroxide 2-(1-methyl-3-ethyl-1<i>H</i>-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1<i>H</i>-imidazole-3-oxide-1-oxyl (L^Me/Et). The cooling of the compound below 260 K initiated a solid-state chemical reaction, which led to a depolymerization of chains and formation of a pair heterospin complex [Cu­(hfac)₂L^Me/Et₂]­[[Cu­(hfac)₂]₃L^Me/Et₂]. Further decrease in temperature below 144 K led to a spin transition accompanied by a drastic decrease in the effective magnetic moment from 2.52 to 2.24 μ_B. When the compound was heated, the order of effects was reversed: at first, the magnetic moment abruptly increased, and then the molecular fragments of the pair cluster united into polymer chains. Two hysteresis loops correspond to this cascade of temperature-induced structural transformations on the experimental dependence μ_eff(<i>T</i>): one at high (<i>T</i>↑ = 283 K and <i>T</i>↓ = 260 K) and the other at low (<i>T</i>↑ = 161 K, <i>T</i>↓ = 144 K) temperature. The spin transitions were also recorded for the [[Cu­(hfac)₂]₃L^Bu/Et₂] and [[Cu­(hfac)₂]₅L^Bu/Et₄] molecular complexes, which are models of the trinuclear fragment of the {[Cu­(hfac)₂]₃L^Me/Et₂} pair cluster