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^n-Pr ), 2-(1-isopropyl-1H-imidazol-5-yl)- (L^i-Pr ) and 2-(1-butyl-1H-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^n-Bu ). The reaction of Cu(hfac)₂ with L^R in a 1 : 2 ratio yields mononuclear heterospin complexes [Cu(hfac)₂ (L^R )₂ ] (L^R =L^n-Pr , L^i-Pr , L^n-Bu ), which have a similar crystal structure to the "jumping" crystals [Cu(hfac)₂ (L^Me )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 (L^n-Pr )₂ ] can be obtained, and magnetic properties of [Cu(hfac)₂ (L^n-Pr )₂ ] strongly depend on the angle between the planes of the paramagnetic fragment O•-N-C=N→O and the imidazole ring in L^n-Pr .