Solvent-controlled solid-state phase transitions of a heterospin Cu(II) complex with imidazolyl-substituted nitronyl nitroxide.

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

Pyridyl-Substituted Nitronyl Nitroxides: Comprehensive Magnetochemical and Quantum Chemical Study.

A series of pyridyl-substituted nitronyl nitroxides was synthesized and structurally characterized. A comprehensive magnetochemical and quantum chemical study of extended raw of the nitroxides with different substituents R in the pyridine fragment was performed. It was shown, that temperature-dependent magnetic properties are determined by the short contacts between nitroxide groups of adjacent molecules as well as between nitroxide group and methyl substituents in the pseudo axial positions of imidazoline fragments. Quantum chemistry allows to select the appropriate model of exchange cluster for analysis of experimental magnetic data and evaluation of the exchange interaction parameters. For NN-PyCl the "order-disorder" transition was detected by means of low temperature XRD. The difference in the experimental and calculated exchange interaction energies may serve as an indicator of temperature-induced structural rearrangements. For instance, for methyl substituted nitronyl nitroxide NN-PyMe structural transformations and significant changes in exchange interaction energies were observed.

Microgravity-like Crystallization of Paramagnetic Species in Strong Magnetic Fields.

The crystallization of paramagnetic species in a magnetic field gradient under microgravity-like conditions is an area of interest for both fundamental and applied science. In this paper, a setup for the crystallization of paramagnetic species in the magnetic field up to 7 T generated by a superconducting magnet is described. The research includes calculations of the conditions necessary to compensate for the gravitational force for several types of paramagnetic substances using the magnetic field of superconducting magnets (4.7 T, 7 T, 9.4 T, and 16.4 T). Additionally, for the first time, the crystallization of copper sulfate and cobalt sulfate, as well as a mixture of copper sulfate and cobalt sulfate under gravitational force compensation in a superconducting magnet, was performed. This paper experimentally demonstrates the feasibility of growing paramagnetic crystals within the volume of a test tube on the example of copper and cobalt sulfate crystals. A comparison of crystals grown from the solution of a mixture of copper and cobalt sulfates under the same conditions, with and without the presence of a magnetic field, showed changes in both the number and size of crystals.

Novel pyridyl-substituted nitronyl nitroxides as potential antiarrhythmic and hypotensive agents with low toxicity and enhanced stability in aqueous solutions.

This study explores the antiarrhythmic and hypotensive potential of pyridyl-substituted nitronyl nitroxides derivatives, uncovering the crucial role of a single carbon moiety of the pyridine cycle alongside radical and charged oxygen centers of the imidazoline fragment. Notably, the introduction of fluorine atoms diminished the antiarrhythmic effect, while the most potent derivatives featured the nitronyl nitroxide pattern positioned at the third site of the pyridine cycle. Gender-dependent responses were observed in lead compounds LCF3 and LMe, with LMe inducing temporary bradycardia and hypotension specifically in female rats, and LCF3 causing significant blood pressure reduction followed by rebound in females compared to milder effects in males. Mechanistic insights point towards ß1 adrenoceptor blockade as an underlying mechanism, supported by experiments on isolated rat atria. This research underscores the interplay between structure, cardiovascular effects and gender-specific responses, offering insights for therapeutic strategies for treating free radical-associated cardiovascular disorders.

N-Alkylimidazol-5-yl-substituted Nitronyl Nitroxides and Their Mononuclear Cu(II) Complexes: Synthesis, Structure and Magnetic Properties.

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•-N-C=N→O and the imidazole ring in Ln-Pr .