Russian Chemical Bulletin, International Edition, Vol. 65, No. 3, pp. 666—674, March, 2016 666 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0666—0674, March, 2016. 10665285/16/65030666 © 2016 Springer Science+Business Media, Inc. Stereo sensitivity of exchange interactions in Ni II and Cu II heterospin complexes with 5formylpyrrolylsubstituted nitroxides* E. M. Zueva, a E. V. Tretyakov, b S. V. Fokin, b G. V. Romanenko, b A. O. Tkacheva, b A. S. Bogomyakov, b O. V. Petrova, c B. A. Trofimov, c R. Z. Sagdeev, d and V. I. Ovcharenko b a Kazan National Technological University, 68 ul. K. Marksa, 420015 Kazan, Russian Federation. Fax: +7 (843) 238 5694. Email: zueva_ekaterina@mail.ru b 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 c A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 ul. Favorskogo, 664033 Irkutsk, Russian Federation. d Kazan (Volga region) Federal University, 18 ul. Kremlevskaya, 420008 Kazan, Russian Federation 5Formylpyrrolylsubstituted nitronyl and imino nitroxide radicals HL 1 and HL 2 were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL 1 ...HL 1 } pairs, the dominant interaction is the ferromagnetic exchange with J/k B = 8.8 K (Hamiltonian H = –2J(S → 1 •S → 2 ). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L 1 ) 2 ], [Cu(L 1 ) 2 ], and [Ni(L 2 ) 2 (MeOH) 2 ]. In the complexes [Ni(L 1 ) 2 ] and [Cu(L 1 ) 2 ], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands. Key words: copper(II) complexes, nickel(II) complexes, nitroxide radicals, pyrrole, Xray diffraction, quantum chemical calculations. Multispin compounds exhibiting magnetic effects under the influence of external stimuli have attracted grow ing interest. 1 Generally, the larger the changes induced by external stimuli in the mutual arrangement of paramag netic centers in the phase under consideration, the stron ger the influence of these stimuli on the magnetic charac teristics of the solid. The magnetic effects induced by small structural changes in heterospin exchange clusters were described in the literature. 2,3 It is clear from general con siderations that this situation is possible; however, it re mains unclear how one can synthesize compounds, in which exchange clusters would be highly sensitive to an insignificant structural reorganization. The usefulness of such compounds is evident because they can serve as high ly efficient sensors for external stimuli. For instance, the solid phase of a Cu II complex with a nitronyl nitroxide radical described recently proved highly sensitive to the applied external pressure. In this case, the spin transition temperature, which abruptly changed under changes in the external pressure, served as an indicator of the applied external stimulus. 4 We thought that the synthesis of transition metal com plexes with polydentate nitroxides, which are favorable for the meridional coordination of the paramagnetic ligand, would provide an approach to the targeted design of he terospin compounds, the exchange clusters of which are sensitive to a small structural reorganization. For this pur pose, we developed a procedure for the synthesis of spin labeled 5formylpyrrole derivatives HL 1 and HL 2 , pre pared heterospin Ni II and Cu II complexes with these de rivatives, studied their structures and magnetic properties, and performed quantum chemical calculations in order to investigate the influence of changes in the mutual orienta * Dedicated to Academician of the Russian Academy of Sciences V. M. Novotortsev on the occasion of his 70th birthday.