Solntsev P. Fused pyridazines a new class of ligands for synthesis of coordination polymers

The thesis is devoted to synthesis and investigation of metal ion complexes with a new class of polydentate nitrogen-donor ligands – condensed pyridazino[4,5-d]pyridazines. The coordination compounds of Cu(I), Cu(II), Zn(II), Cd(II) and Co(II) were prepared reacting the components in nonaqueous media and over 50 crystal structures were determined from X-ray diffraction data. Comparative analysis of the structures reveals significance of metal ion nature, properties of the counter anions (halogenides, NCS-, N(CN)2-, NO3-, ClO4-, S2O62-, SiF62-), crystallisation conditions and volume of aliphatic substituents of the ligands as potential design factors. In spite of the inherent electron deficiency of the condensed 19heterocycle, all four available nitrogen atoms are functional as lone pair donors for supporting either coordination or hydrogen bonds. However, the electronic factors were particularly prevalent since the ligand capacity was sensitive to ability of metal ions for sustaining efficient back-bonding. Therefore, in zinc(II) and cadmium(II) complexes the pyridazines typically act as outer-sphere groups, for copper(II) they were bidentate-bridging, while in copper(I) complexes the ligands manifest tetradentate coordination. In the latter case, complementary pyridazine and halogenide bridges were involved for generation of hybrid organic/inorganic frameworks comprising CuX helices or finite patterns in the form of di-, tri- and tetranuclear clusters (CuX)n or macrocycles Cu12I12. The structures feature control over assembly of homochiral or racemic frameworks and formation of three- and four-fold helices for sustaining tri- and tetragonal channelled architecture. CuX open frameworks possess thermal stability up to 350°C and may be suited for gas adsorption applications. Many of the examined structures demonstrate an intrinsic role of shape-complementary relations between the components, as was revealed by Cu(II) complexes adopting a unique sodalite-like structure with giant (>4100 A) crystal cages.