ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2010, Vol. 36, No. 6, pp. 401–429. © Pleiades Publishing, Ltd., 2010. Original Russian Text © V.A. Kogan, V.V. Lukov, I.N. Shcherbakov, 2010, published in Koordinatsionnaya Khimiya, 2010, Vol. 36, No. 6, pp. 403–432. 401 INTRODUCTION The study of the electronic structures and proper- ties of polynuclear complexes is one of the main research areas in modern coordination chemistry. A large group of polynuclear complexes is constituted by compounds containing so-called exchange-coupled paramagnetic transition metal ions or exchange clus- ters. Finding a correlation between the exchange parameters and the structural features of such com- plexes plays a key role in the understanding of the magnetic properties of exchange clusters and, conse- quently, for solution of structural chemical problems by magnetic methods. In addition, this approach pro- vides the theoretical basis for the synthesis of clusters with desired magnetic characteristics and ultimately for targeted modification of magnetoactive materials. Accurate description of even the simplest representa- tives of exchange-coupled systems (binuclear com- plexes) is impossible without simultaneously consider- ing a vast variety of electronic and geometrical factors that are decisive for the strength of exchange effects between paramagnetic centers. Fundamentally, this can be done by studying the physicochemical proper- ties of systematic series of polynuclear complexes with similar compositions and structures through variation of a few separate factors, the others being maintained relatively constant. A convenient class of coordination compounds that open up large scope for such analysis are transition metal complexes with organic hydrazine derivatives [1, 2]. In this review, we tried to systematize the known literature data for bi- and polynuclear com- plexes with ligands based on both organic hydrazine derivatives and Schiff bases, oximes, and related sys- tems with similar ligating properties. A separate sec- tion of this review is devoted to the study of binuclear metal chelates with 2,6-diformyl-4-R-phenols as ligands and to comparative analysis of the magne- tochemical behavior of bi- and polynuclear complexes in which the paramagnetic centers are linked by sym- metric and asymmetric bridging fragments with sub- stantially different electronic and geometrical struc- tures. MAGNETOCHEMICAL STUDY OF THE STRUCTURES OF BINUCLEAR METAL CHELATES WITH AZOMETHINES AND HYDRAZONES. A CONCEPT OF GEOMETRICAL MODELING OF EXCHANGE FRAGMENTS It is known that the possibility of describing exchange couplings in polynuclear complexes, which is performed (as for any quantum-mechanical system) in terms of the so-called effective, or phenomenologi- cal, Hamiltonian [3–5], implies separation of the exchange effects theory into two interrelated areas: (1) revealing of the type of the exchange Hamilto- nian from the most general considerations and devel- opment of a method for its solution with the aim of finding the magnetochemical parameters by compar- ing the calculated and experimental properties. This is a subject of the so-called phenomenological theory of exchange couplings; (2) calculation of exchange parameters on the basis of electronic structure theory (i.e., determination of their numerical values or expressions in terms of orbital energies, overlap integrals, and other quantum- mechanical characteristics used to describe the struc- ture of matter), which is the subject of microscopic exchange theory. Since investigations in the former area are based on the initial conditions that are well justified theoreti- cally and relatively simple for implementation (espe- cially in the isotropic approximation), the majority of publications on magnetochemical topics is related to this area. At the same time, almost all relevant studies Magnetic Exchange in Bi- and Polynuclear Complexes of Transition Metals with Hydrazones and Azomethines V. A. Kogan, V. V. Lukov*, and I. N. Shcherbakov Southern Federal University, Rostov-on-Don, Russia *E-mail: vlukov@mail.ru Received October 14, 2009 Abstract—Magnetic exchange data for bi- and polynuclear complexes of transition metals with hydrazones, Schiff bases, oximes, and related systems were generalized and systematized. A correlation between the elec- tronic and geometrical structures of the complexes and characteristic exchange effects was discussed. A sys- tematic analysis of magnetostructural correlations in such complexes was performed. DOI: 10.1134/S1070328410060011