138 ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2018, Vol. 44, No. 2, pp. 138–146. © Pleiades Publishing, Ltd., 2018. Original Russian Text © A.V. Piskunov, O.Yu. Trofimova, M.S. Piskunova, I.V. Smolyaninov, N.T. Berberova, G.K. Fukin, 2018, published in Koordinatsionnaya Khimiya, 2018, Vol. 44, No. 1, pp. 49–57. Template Assembling of the Pentadentate Redox-Active Ligand in the Coordination Sphere of Tin(IV) A. V. Piskunov a, *, O. Yu. Trofimova a , M. S. Piskunova b , I. V. Smolyaninov c, d , N. T. Berberova d , and G. K. Fukin a a Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, ul. Tropinina 49, Nizhny Novgorod, 603950 Russia b Nizhny Novgorod State Medical Academy, Nizhny Novgorod, Russia c Astrakhan State Technical University, Astrakhan, Russia d Southern Research Center, Russian Academy of Sciences, Rostov-on-Don, Russia *e-mail: pial@iomc.ras.ru Received July 11, 2017 Abstract—Heptacoordinated tin complexes with pentadentate redox-active ligands containing the diiminopyridine fragment combined with two sterically hindered phenolate coordination centers, LSn- Cl 2 and L'SnCl 2 (L and L' are dianions of deprotonated 2,6-bis[2,4-di-tert-butyl-6-(methylidenyl- amino)phenol]pyridine and 2,6-bis[2,4-di-tert-butyl-6-(ethylidenylamino)phenol]pyridine, respec- tively), are synthesized. The molecular and electronic structures of the synthesized compounds were studied by X-ray diffraction analysis (for complex I, CIF file CCDC no. 1557838), a set of spectral meth- ods, and quantum-chemical calculations. The redox properties of the obtained complexes are character- ized by cyclic voltammetry. Keywords: template synthesis, tin(IV), X-ray diffraction analysis, cyclic voltammetry, redox-active ligands DOI: 10.1134/S1070328418020082 INTRODUCTION Schiff bases belong to one of the most universal classes of ligands for molecular design in the coordi- nation chemistry of both transition and non-transition elements. The metal complexes with iminopyridine chelating ligands of this type are being studied actively for several decades [1]. The bi-, tri-, and tetradentate ligands are studied in most detail. At the same time, an increase in the denticity of chelating ligands favors the formation of more stable metal complexes due to pro- viding a higher steric hindrance in the immediate vicinity of the central metal atom. Tin complexes with redox-active ligands, such as o-quinones and their nitrogen-containing analogs, attract attention due to the specific structures and chemical properties of the obtained derivatives. The organotin derivatives of this type can be involved in reactions of oxidative addition and reductive elimination due to the redox-active ligand [2–7]. Increasing interest in these compounds is also caused by prospects of their use in various areas. For example, the o-quinone and o-iminoquinone tin derivatives act as chain growth regulators in the radical polymeriza- tion of the vinyl monomers [8–11]. In addition, the organotin derivatives are biologically active com- pounds and can be used as antimicrobial [12, 13], anti- fungal [14], bactericidal [15, 16], anti-inflammatory [17–19], and other drugs. In this work, we studied the possibility of the syn- thesis of the tin(IV) complexes with the pentadentate redox-active ligands containing the diiminopyridine bridge linking two sterically hindered phenolate frag- ments (Scheme 1). Chelating pentadentate ligands of this type are poorly studied. The zinc [20, 21], cad- mium [22], tin [23], manganese [24], rhenium [25], and cobalt [26] compounds based on these ligands are known at the moment. Six various redox states are theoretically possible for the above indicated pentadentate ligands (Scheme 1). The dianionic (L 2 ) and tetraanionic (L 4 ) species are diamagnetic, whereas the mono- (L 1 ), tri- (L 3 ), and pentaanionic (L 5 ) species are paramagnetic. The neutral ligand (L 0 ) should be biradical in nature.