Pressure-Controlled Migration of Paramagnetic Centers in a Heterospin Crystal

Abstract

A study of the single-crystal-to-single-crystal transformation induced by temperature variation for the chain polymer Cu­(II) complex with nitronyl nitroxide showed that an increase in the hydrostatic pressure of up to ∼0.07 GPa completely changes the intracrystalline displacements of molecules relative to one another. This, in turn, significantly affects the interaction energy of the unpaired electrons of the paramagnetic centers and hence the form of the temperature dependence of the magnetic susceptibility χT. The cooling of crystals under normal conditions causes a rearrangement of the intrachain exchange clusters {>N–•O–Cu­(II)–O•–N<} accompanied by a shortening of the distances between the paramagnetic centers. This changes the character of exchange interactions and generates multistage spin transitions. An increase in the hydrostatic pressure leads to a drastic change in the O···O distances between the nitroxyl fragments of adjacent chains, an increase in the antiferromagnetic exchange between them, and complete suppression of spin transitions.

1,2,5-Thiadiazole 1,1-dioxides and Their Radical Anions: Structure, Properties, Reactivity, and Potential Use in the Construction of Functional Molecular Materials

“…The oxo- and dioxothiadiazoles can be easily reduced to stable radical anions [ 21 ] and are therefore of potential use to the molecular magnetism community. However, this group of compounds seems to be completely omitted as potential building blocks for the construction of molecule-based magnetic materials [ 22 , 23 ] compared to other organic radicals (nitronyl nitroxides [ 24 , 25 , 26 , 27 ], verdazyl [ 28 , 29 , 30 ], semiquinones [ 31 , 32 ], or TCNE and TCNQ derivatives [ 33 , 34 ]) which have been used extensively to obtain all-organic magnets [ 35 ], Single Molecule Magnets [ 36 , 37 ], or Single Chain Magnets (SCMs) [ 24 , 38 , 39 , 40 , 41 ], among many other functional magnetic materials. This review focuses on 1,2,5-thiadiazole 1,1-dioxides ( Figure 1 a) and their radical anions [ 42 ], which constitute perhaps the prime example of the dioxothiadiazole family, and summarizes the current state-of-the-art in the field of 1,2,5-thiadiazole 1,1-dioxides with the aim of shedding light on the extraordinary possibilities and applications of this heterocyclic moieties with respect to the design and preparation of switchable/functional molecular materials.…”

Influence of the Increasing Number of Organic Radicals on the Structural, Magnetic, and Electrochemical Properties of the Copper(II)–Dioxothiadiazole Family of Complexes

“…5 Among many different functionalities of radical-based magnetic compounds, the following seem to be the most popular: electronic conductivity, 12−14 long-range magnetic ordering, 15−19 valence tautomerism, 6,20−22 photomagnetism, 20,23−28 luminescence, 29−32 and single molecule and single chain magnet behavior (SMM and SCM). 3,33−36 Even though the library of organic radicals is enormous, 3,20,37−40 only a few classes dominate the field of molecular magnetism, and these are verdazyls, 41,42 nitronyl nitroxides, 43,44 semiquinones, 45,46 and TTF, TCNE, and TCNQ derivatives. 47−52 The popularity of these four groups is dictated by their stability, chemical tunability, coordination abilities promoting strong magnetic interactions, and electro- chemical properties providing electron transfer and enabling various types of switching properties.…”

“…Even though the library of organic radicals is enormous, ,,− only a few classes dominate the field of molecular magnetism, and these are verdazyls, , nitronyl nitroxides, , semiquinones, , and TTF, TCNE, and TCNQ derivatives. − The popularity of these four groups is dictated by their stability, chemical tunability, coordination abilities promoting strong magnetic interactions, and electrochemical properties providing electron transfer and enabling various types of switching properties.…”

Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase

“…Coordination chemistry of transition metals with nitroxides is one of the actively developing trends in modern chemistry, which make an important contribution to the solution of problems in molecular magnetism. − This group of compounds includes known ferro- and ferrimagnets; − numerous compounds exhibiting a spin-crossover-like behavior; compounds capable of performing the functions of switches and actuators; − breathing crystals exhibiting single-crystal-to-single-crystal phase transitions; − crystals with mechanical activity; , and sensor compounds possessing high sensitivity to included solvent molecules, , minor intramolecular displacements, or external hydrostatic pressure. − This paper reports on a new effect: a spin transition arising from the generation of a new multispin compound in the metastable phase. This effect was found in our study of the mixed-ligand complex of Cu­(II) hexafluoroacetyl acetonate with the imidazolyl-substituted nitronyl nitroxide L 5Et (Chart ).…”