“Jumping” crystals: structures and properties of CuII complexes with N-methylimidazolyl- and N-methyltriazolyl-substituted nitronyl nitroxides

Abstract

To find the factors favorable for the appearance of chemomechanical activity of heterospin crystals, a series of new heterospin complexes were synthesized and characterized. It includes [Cu(tfac)2LIm2]·2CH2Cl2, [Cu(tfac)2LIm2]·2EtOH, [[Cu(pfu)2]2LIm3]·1/2CH2Cl2, [Cu(pfh)2LIm2]·1/2CH2Cl2, [Cu(piv)2LIm2]·2MeOH, [Co(piv)2LIm2], [\( Cu(hfac)_2 L^{CD_3 } _2 \)], [Cu(hfac)2LTr]2·CH2Cl2, and [Cu(hfac)2LTr2] (LIm, \( L^{CD_3 } \), and LTr 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)2LIm2] synthesized earlier are reported. In the solid state of the complexes [Cu(pfh)2LIm2] and [Co(piv)2LIm2], 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]2LIm3] and [Cu(hfac)2LTr]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 Cu2+ ions. In the solid complexes \( Cu(hfac)_2 L^{CD_3 } _2 \) , [Cu(hfac)2LTr2], [Cu(tfac)2LIm2]·2CH2Cl2, [Cu(tfac)2LIm2]·2EtOH, and [Cu(piv)2LIm2]·2MeOH, the nitronyl nitroxide radicals in the mononuclear heterospin molecules are in trans positions. The packing motif in the crystal structures of the complexes \( Cu(hfac)_2 L^{CD_3 } _2 \) , [Cu(tfac)2LIm2]·2CH2Cl2, and [Cu(tfac)2LIm2]·2EtOH is the same as that in the previously studied complexes [M(hfac)2LIm2] 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 generation of mechanical activity of the crystals.