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 .