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Artigo em Inglês | MEDLINE | ID: mdl-32715591


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 the corresponding iodoverdazyls with a nitronyl nitroxide-2-ide gold(I) complex with high yields (up to 82%). The synthesized diradicals exhibit high stability and do not decompose in an inert atmosphere up to 180 °C. The magnetic properties of prepared phenylene-coupled diradicals were investigated and magneto-structural correlations were established. For the studied diradicals, both substantial antiferromagnetic (D E ST ¼ -64 cm -1 ) and ferromagnetic (D E ST ³ 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.

Chemistry ; 24(49): 12983-12991, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-29882626


Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN- and XCN- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F- , and SeCN- , the complex [1 a-F]- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C6 F4 Hg)3 , which was characterized by XRD.

Chemistry ; 22(41): 14598-604, 2016 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-27539325


It was shown that dipole-stabilized paramagnetic carbanion lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide can be attached in a nucleophilic manner to either isolated or conjugated aldonitrones of the 2,5-dihydroimidazole 3-oxide and 2H-imidazole 1-oxide series to afford adducts the subsequent oxidation of which leads to polyfunctional mono- and diradicals. According to XRD, at least two polymorphic modifications can be formed during crystallization of the resulting paramagnetic compounds, and for each of them, geometric parameters of the molecules are similar. An EPR spectrum of the diradical in frozen toluene has a complicated lineshape, which can be fairly well reproduced by using X-ray diffraction structural analysis and the following set of parameters: D=14.9 mT, E=1.7 mT; tensor a((14) N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a((14) N)=[0.198 0.198 0.700] mT, and g≈2.007. According to our DFT and ab initio calculations, the intramolecular exchange in the diradical is very weak and most likely ferromagnetic.