Crystal chemistry of coordination compounds with anionic ligands based on stable nitroxide radicals

Abstract

Due to a recent expansion of research into metal complexes with stable NR connected with prospects for the production of a radically new class of magnetic materials [50, 51], a great amount of data has been accumulated, in particular, on CC with anionic NR ligands. But until recently there were no reviews analyzing the structural features of these compounds. The reason for this is, evidently, dissimilarity of both the NR ligands and the CC based on them. The systematic studies on the synthesis, crystal structures, and magnetic properties of CC with 3-imidazoline NR permitted analysis of the crystallochemical structure of compounds. As the present paper is virtually the first publication that overviews structural studies of CC with NR, we did not undertake to give a complete analysis of the “structure-property” relationship. Nevertheless, the structural data obtained for CC with 3-imidazoline NR allow one to make some correlations between the character of exchange interactions and the electronic and spatial structure of CC [6, 7, 31]. It is known that to choose an exchange cluster model, one needs information on the relative arrangement of PMC. But the quantum-chemical calculations of the electronic states of a system require exact data on the stereochemistry of a coordination unit and mutual arrangement of PMC. Besides, it should be noted that the relationship between crystal symmetry (centrosymmetric or acentric space group) and magnetic properties will not become adequate unitl crystal structure and symmetry studies have been carried out in a magnetic field at appropriate temperatures, i.e., under conditions of measurement of magnetic parameters for compounds of a given class. In the near future, this research will certainly be continued, both in the field of synthesis of CC with 3-imidazoline NR and preparation of their single crystals, and in the field of studies on their structure, magnetic and other physical properties, as well as of quantum-chemical calculations.