**5. Conclusion**

210 Current Trends in X-Ray Crystallography

Fig. 24. The dependences of the positions of the absorption bands relating to the ClCu charge transfer (CT) on the degree of distortion of the anionic polyhedron (= 1 – 2)

Fig. 25. The dependence of magnetic properties of bifolded hexchlorodicuprates(II) on the

folding -angle and the bridging -angle (O'Brien et al., 1988).

(Koval'chukova et al., 2009a).

Anionic halocuprate(II) complexes are of a great interest for scientists because of the areas of their application. They show a large variety in composition and coordinational geometry, and may be presented by mononuclear CuX22- species (X = Cl, Br) or form Cu2X62- dimers which can exist separately or be arranged in polymeric [Cu2Cl6 2-] chains. Dimeric structures may exist as planar, twisted, or folded fragments. The coordination number of Cu(II) can change from 4 (tetrahedrons with different degrees of tetrahonal distortion or planar square configuration) to 5 (from the square pyramidal to the trigonal-bipyramidal configurations) and even 6 (more or less distorted octahedra). More complicated structures can also exist despite the event they were out of our interest.

Among the factors controlling on the type and finer details of coordination mode of Cu(II) there is the nature of the cation which neutralizes the negative charge of halocuprate(II) species, i.e. cation size, shape, flexibility, as well as the ability of formation of H-bonds. The nature of the halide atom (Cl or Br) affects the type of the structure much less. Unfortunately the influence of the organic cation on the features of the structure of halocuprates(II) is not unequivocal, and the determination of the crystalline structures not available at every instant. The relationship between the structure and spectral or magnetic properties appeared to be helpful by the prediction of the features of coordination modes, and physical properties as well as possible areas of the application of newly synthesized halocuprates(II).
