Russian Chemical Bulletin, International Edition, Vol. 60, No. 12, pp. 2457—2469, December, 2011 2457 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2411—2422, December, 2011. 1066-5285/11/6012-2457 © 2011 Springer Science+Business Media, Inc. "Jumping" crystals: structures and properties of Cu II complexes with N-methylimidazolyl- and N-methyltriazolyl-substituted nitronyl nitroxides V. I. Ovcharenko, E. V. Tretyakov, S. V. Fokin, E. Yu. Fursova, O. V. Kuznetsova, S. E. Tolstikov, G. V. Romanenko, A. S. Bogomyakov, and R. Z. Sagdeev International Tomography Center, Siberian Branch of the Russian Academy of Sciences, 3a ul. Institutskaya, 630090 Novosibirsk, Russian Federation. Fax: +7 (383) 333 1399. E-mail: Victor.Ovcharenko@tomo.nsc.ru To find the factors favorable for the appearance of chemomechanical activity of hetero- spin crystals, a series of new heterospin complexes were synthesized and characterized. It includes [Cu(tfac) 2 L Im 2 ]•2CH 2 Cl 2 , [Cu(tfac) 2 L Im 2 ]•2EtOH, [[Cu(pfu) 2 ] 2 L Im 3 ]•1/2CH 2 Cl 2 , [Cu(pfh) 2 L Im 2 ]•1/2CH 2 Cl 2 , [Cu(piv) 2 L Im 2 ]•2MeOH, [Co(piv) 2 L Im 2 ], [Cu(hfac) 2 L CD 3 2 ], [Cu(hfac) 2 L Tr ] 2 •CH 2 Cl 2 , and [Cu(hfac) 2 L Tr 2 ] (L Im , L CD 3 , and L Tr are N-methylimidazolyl-, N-trideuteriomethylimidazolyl-, and N-methyltriazolyl-substituted nitronyl nitroxides, respectively; tfac, hfac, pfu, pfh, and piv are the charged coordinated diamagnetic ligands 1,1,5,5-tetrafluoropentane-2,4-dionate, 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, 1,1,1,2,2,3,3,4,4,8,8,9,9,10,10,11,11,11-octadecafluoroundecane-5,7-dionate, 1,1,1,5,5,6,6,6- octafluorohexane-2,4-dionate, and 2,2-dimethylpropionate, respectively). The crystal and molecular structures of all compounds were determined. The results of the X-ray diffraction study of the complex [Ni(hfac) 2 L Im 2 ] synthesized earlier are reported. In the solid state of the complexes [Cu(pfh) 2 L Im 2 ] and [Co(piv) 2 L Im 2 ], the paramagnetic ligands are cis-coordinated to the central atom in a monodentate fashion via the donor N atom of the imidazole ring. In the dinuclear complexes [[Cu(pfu) 2 ] 2 L Im 3 ] and [Cu(hfac) 2 L Tr ] 2 , the paramagnetic ligands are also in cis positions but act as bridges through coordination of the donor N atoms of the azole ring and the O atom of the nitronyl nitroxide moiety to different Cu 2+ ions. In the solid complexes [Cu(hfac) 2 L CD 3 2 ], [Cu(hfac) 2 L Tr 2 ], [Cu(tfac) 2 L Im 2 ]•2CH 2 Cl 2 , [Cu(tfac) 2 L Im 2 ]•2EtOH, and [Cu(рiv) 2 L Im 2 ]•2MeOH, the nitronyl nitroxide radicals in the mononuclear heterospin mole- cules are in trans positions. The packing motif in the crystal structures of the complexes [Cu(hfac) 2 L CD 3 2 ], [Cu(tfac) 2 L Im 2 ]•2CH 2 Cl 2 , and [Cu(tfac) 2 L Im 2 ]•2EtOH is the same as that in the previously studied complexes [M(hfac) 2 L Im 2 ] exhibiting chemomechanical activity. Among the complexes under consideration, only crystals of [Cu(hfac) 2 L CD 3 2 ] can exhibit chemomechanical activity, that is to make jumps upon heating or irradiation. The results of the present study suggest that the packing of the solid-state structure plays a key role in the genera- tion of mechanical activity of the crystals. Key words: copper(II) complexes, cobalt(II) complexes, nickel(II) complexes, coordination compounds, X-ray diffraction analysis, structure—property relationships, nitroxide radicals, hexafluoroacetylacetonates, pivalates. Due to relatively high kinetic stability, 2-R-4,4,5,5- tetramethyl-2-imidazoline-3-oxide-1-oxyls (L R ) are readily available spin-labeled materials, 1—5 which are extensively used in the molecular design of magnets. 6—18 In the present study, we focused our attention on the characteristic fea- tures of this type of free radicals. Thus, even upon storage in the dark and at low temperature, all L R gradually lose oxygen and are converted into the corresponding imino nitroxides at a particular rate. The same processes are observed for transition metal coordination compounds with L R . Our experience in the work with these com- pounds shows that the solid-state heterospin complexes [M(hfac) 2 (L R ) n ] (M = Cu, Ni, Co, Mn; hfac is hexafluo- roacetylacetonate) undergo gradual deoxygenation during storage for several years. At the macroscopic level, this is manifested in that the crystals of the complexes, primarily their surface, gradually lose quality. As a result, after long- term storage of the crystals of [M(hfac) 2 (L R ) n ] accompa- nied by their gradual deoxygenation, the crystals become non-transparent, change the color, and undergo cracking. The decomposition of [M(hfac) 2 (L R ) n ] occurs more rap- idly in the light and at high temperatures. The need to monitor the state of the crystals of [M(hfac) 2 (L R ) n ] prompted us to pay attention to unusual