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)L]·0.5Solv (Solv = (CH)CO, THF, CHCl, CHBr, CHCl) with 2-(1-propyl-1-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazole-3-oxide-1-oxyl (L) under ambient conditions. The conversion of powdered polymeric chain [Cu(hfac)L]·0.

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)- (L ), 2-(1-isopropyl-1H-imidazol-5-yl)- (L ) and 2-(1-butyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L ). The reaction of Cu(hfac) with L in a 1 : 2 ratio yields mononuclear heterospin complexes [Cu(hfac) (L ) ] (L =L , L , L ), which have a similar crystal structure to the "jumping" crystals [Cu(hfac) (L ) ] 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.

Modulating the Magnetic Properties of Copper(II)/Nitroxyl Heterospin Complexes by Suppression of the Jahn-Teller Distortion.

A series of six-coordinate [Cu(L)L][BF] (L = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L 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.

Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions.

We report a multifrequency nuclear magnetic resonance (NMR) study of heterospin complexes [Eu(SQ)L], where SQ is 3,6-di(-butyl)-1,2-semiquinone, L is tetrahydrofuran (THF), pyridine (Py), or 2,2'-dipyridyl (Dipy), and is the number of diamagnetic ligands. Multifrequency NMR experiments allowed us to determine the effective paramagnetic shifts of the ligands (L = THF or Py) and the chemical equilibrium constant for [Eu(SQ)(THF)]. In addition, we have found a strong magnetic field effect on the NMR line broadening, giving rise to very broad NMR lines at high magnetic fields.

First example of a reversible single-crystal-to-single-crystal polymerization-depolymerization accompanied by a magnetic anomaly for a transition-metal complex with an organic radical.

The reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)2] with the stable nitronyl nitroxide 2-(1-ethyl-3-methyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L(a)) resulted in a paired heterospin complex [[Cu(hfac)2]3(μ-O,N-L(a))2][Cu(hfac)2(O-L(a))2]. The crystals of the compound were found to be capable of a reversible single-crystal-to-single-crystal (SC-SC) transformation initiated by the variation of temperature. At room temperature, the molecular structure of [[Cu(hfac)2]3(μ-O,N-L(a))2][Cu(hfac)2(O-L(a))2] is formed by the alternating fragments of the pair complex.

Ligand effects on the ferro- to antiferromagnetic exchange ratio in bis(o-semiquinonato)copper(II).

Heterospin complexes [Cu(SQ)2Py].C7H8, Cu(SQ)2DABCO, and [Cu(SQ)2NIT-mPy].C6H6, where Cu(SQ)2 is bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper(II), DABCO is 1,4-diazabicyclo(2,2,2)octane, and NIT-mPy is the nitronyl nitroxide 2-(pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, have been synthesized.