Copper(ii) self-assembled clusters of bis((pyridin-2-yl)-1,2,4-triazol-3-yl)alkanes. Unusual rearrangement of ligands under reaction conditions

Abstract

Reaction of two structurally related bridging ligands bis[5-(2-pyridyl)-1,2,4-triazole-3-yl]methane (H2L1) and bis[5-(2- pyridyl)-1,2,4-triazole-3-yl]ethane (H2L2) with copper(II) salts resulted in a surprising wide variety of the complex structures [Cu2(H2L1)Cl2]Cl2·4CH3OH (1), [Cu4L14]∙4H2O (2), [Cu(H2L2)(ClO4)2] (3) and [Cu3(OH)Na2(L')6](ClO4)·5H2O·C3H6O (4), where HL' is 3,5-bis-(pyridin-2-yl)-1,2,4-triazole, which were structurally characterized by the X-ray diffraction method. Complexes 1 and 2 were prepared on H2L1 basis and have binuclear and tetranuclear structure respectively, demonstrating strong impact of type of counter anion on coordination mode of the ligand. In contrast, the reaction between Cu(ClO4)2 6H2O and H2L2 led to preparation of mononuclear complex 3. Reaction of H2L2 with Cu(ClO4)2 in alkaline conditions led to oxidative rearrangement of the ligand and the homoleptic pentanuclear complex 4 with anionic ligand L' was prepared. Magnetic properties were studied for compounds 1, 2 and 4 and for all of them the antiferromagnetic interactions between the Cu atoms were confirmed and analyzed by spin Hamiltonian formalism. Furthermore, the occurrence of the antisymmetric exchange was confirmed in 4. The magnetic data analysis was supported by the X-band EPR measurements performed for complexes 1, 2 and 4.