Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations

Abstract

IntroductionInteractions between the paramagnetic ions of transition metals and stable radicals are convenient and effective methods for the synthesis of multispin molecules. These metal-nitroxide systems are often called heterospin systems because they contain paramagnetic centers with both d (or f) odd electrons and centers with p electrons. Paramagnetic centers can differ in the electron spin, g factor, the character of electron spin density delocalization, and heat capacity. The presence of several paramagnetic centers in heterospin molecules has stirred growing interest in their magnetic properties because these compounds are convenient objects for studying the subtle peculiarities of exchange interactions and revealing valuable magnetostructural correlations. That is why coordination chemistry of transition metals with stable nitroxides is an actively developing direction in modern chemistry that contributes to problem solving in the field of molecular magnetism. The results of studies on the synthesis and properties of metal complexes with nitroxides have been considered from different viewpoints and at different times in many monographs and reviews. 1 -19 Importantly, this approach offers the potential for control over the structure of the designed heterospin molecule and the character of interactions between the odd electrons of paramagnetic centers, which is necessary for constructing justifiable magnetostructural correlations. This is one of the factors responsible for the continuous growth of the number of new metal-nitroxide complexes. The Cambridge Structural Database alone contains more than one thousand structurally defined metal-nitroxide systems. 20 Therefore, currently it is impossible and not necessary to collect all available literature data on the synthesis and properties of metal-nitroxide systems in one publication. In any account, a comprehensive review of this kind will already have become incomplete by the time of its publication because new heterospin compounds based on transition metal compounds with nitroxides are being added daily to the list. However, the Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron CompoundsEdited by Robin G. Hicks

Revisiting the Ullman's Radical Chemistry for Phthalocyanine Derivatives

“…Therefore, we soughtt os ynthesize an asymmetric A 3 Btype phthalocyanine bearing in one hand ap rotected formyl group and on the other hand neopentyl bulky group substituents at the peripheralp ositions (5)t or educe aggregation and increasethe solubility in organic solvents. A 3 B-type phthalocyanine classical synthetic methodology consists of the statistically crossover condensation [19] of two appropriate phthalonitrile precursors in different ratio;i no ur case 4,5-dineopentoxyphthalonitrile (2)a nd 4-(5,5-dimethyl-1,3-dioxane-2-yl)-phthalonitrile (1). The synthesis of phthalonitrile 2 wasc arried out on the basis of Leznoff's procedure [20] with substantial modifications (Scheme S1 in the Supporting Information).…”

“…[1,2] Ar enewed interest in their chemistry has comei nt he spotlight because of their involvementi no rganic electrode-active materials [3] or fluorophore-nitroxide hybrid probe. They have been essentially famousa sb uildingb locks in magnetic materials.…”

“…They have been essentially famousa sb uildingb locks in magnetic materials. [1,2] Ar enewed interest in their chemistry has comei nt he spotlight because of their involvementi no rganic electrode-active materials [3] or fluorophore-nitroxide hybrid probe. [4] Imino and nitronyl nitroxide radical derivatives are classically obtained by the Ullman procedure, [5] involving the condensationo f2 ,3-bis(hydroxylamino)-2,3-dimethylbutane (6)w ith an appropriate aldehyde in methanolt og enerate the 1,3-dihydroxyimidazolidine derivative.F or aromatica ldehydes, condensation takes hours at reflux.…”

Pressure-Controlled Migration of Paramagnetic Centers in a Heterospin Crystal

“…A study of the properties of molecular magnets is the subject of active interdisciplinary fundamental research in view of the high potential of their application in various fields of biology and medicine and creation of a new generation of functional materials and spintronic devices. − A wide range of molecular magnets are known in which the structure and functional properties can change under the influence of external factors, for example, irradiation or variation of temperature, pressure, or electromagnetic field, − ,− or during redox processes. ,,, The effect of the external pressure remains least understood. The data of studies that compared the polymorphic transformations induced by temperature variation at different external pressures are especially scarce, ,− though they provide important information about the fundamental properties of objects and serve as a basis for creating energy-independent highly sensitive pressure sensors for space and seismological studies and original devices capable of light emission at increased pressure or work at low temperatures under conditions of underground and deep-sea exploration. ,,,,, …”

A New Method for the Synthesis of Heterospin Complexes

“…They are used in radical-mediated polymerization [3,4], for creating rechargeable organic batteries [5,6], as contrast agents for magnetic resonance imaging [7][8][9] and as organic paramagnets in the synthesis of heterospin molecular magnets [10][11][12][13][14][15][16]. Transition metal complexes with nitroxides were used to create heterospin breathing crystals [17].…”