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A series of six-coordinate [Cu(L)L1][BF4]2 (L1 = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L1 ligand spins is enhanced by an L coligand with distal methyl substituents, which is attributed to a sterically induced suppression of its Jahn–Teller distortion.

The paramagnetic salts (NH3But)1 and [K(NH2But)2]1, where 1 is the 3-oxyl-4,4,5,5-tetramethyl-2-oxoimidazolidin-1-olate anion, were isolated for the first time in the individual state. The crystal structure of [K(NH2But)2]1 involves polymer chains formed by hydrogen bonding between anions 1 and [K2(NH2But)4]2+ cation dimer fragments. The magnetic properties of [K(NH2But)2]1 are well described by the quasi-isolated dimer model with spins S = 1/2 coupled by weak exchange interactions via [K2(NH2But)4]2 fragments in polymer chains.

An effective procedure has been developed for the synthesis of the potassium salt of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide-2-carboxylic acid K(1). The salts of 4,4,5,5-tetramethyl-1-oxyl-4,5-dihydro-1H-imidazole-2-carboxylic acid X(2) are kinetically much more stable than K(1). Due to this, a series of heterospin complexes Cu(2)2(CH3OH)2, Cu(2)2(H2O)2, Cu(2)2, Co(2)2(CH3OH)2, Ni(2)2(H2O)2, Ni(2)2(py)2, and Ni(2)2(dipy) · H2O were isolated. For K(2), Cu(2)2(CH3OH)2, and Ni(2)2(py)2, crystal and molecular structure has been determined. For Cu(2)2 and Ni(2)2(bipy), cooperative magnetic ordering has been recorded at 16.6 and 4.6 K, respectively.

Three approaches to the synthesis of (R)-2-(1-hydroxy-4,4,5,5-tetraalkylimidazolidin-2-ylidene)ethanones 1 are described: (a) condensation of 1,2-bishydroxylamines with β-ketoaldehyde synthons, (b) treatment of metallated 1-hydroxy-2-methyl-4,5-dihydroimidazoles with esters, and (c) 1,3-dipolar cycloaddition between 1-hydroxy-4,5-dihydroimidazole-3-oxide and DMAD. The reactivity of 1 with electrophiles has been studied. The exocyclic methylene (enamine) carbon atom is shown to be the major site of electrophilic attack. Synthesized chloro-substituted 1-hydroxy-2-acetylideneimidazolidines react with sodium cyanide to form the corresponding nitriles. Oxidation of these nitriles occurs with formation of persistent vinyl nitroxides, which are of interest as potential paramagnetic ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Methods for the synthesis of a new family of nitronylnitroxides, iminonitroxides, and their precursors with 2-hydroxyphenyl or 3-hydroxypyridin-2-yl substituents in the side chain have been developed. Five heterospin chelates of Cu(II) with deprotonated iminonitroxides have been isolated. Their structure and magnetic properties have been studied. In all complexes, ferromagnetic intramolecular exchange interactions take place (J∼40–350 cm−1).

The first nitronyl nitroxides containing tetrazole substituents: sodium salt of 2-(1H-tetrazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (Na(2)), 2-(1-methyl-1H-tetrazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (3), and 2-(2-methyl-2H-tetrazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl (4) have been synthesized. The structures of 2–4 were confirmed by X-ray analysis. For 2, a tendency to form highly dimensional structures by interaction with transition metals has been found. MnII tends to form diamond-like packing with 2 using [Mn(H2O)6]2+ and [Mn(2)3]− building blocks. NiII forms layered structures from the binuclear cations with the aid of the bridging nitroxide [En2Ni(2)NiEn2]3+ and H-bonded ClO4 − groups.