A Series of New Manganese(II) Polynuclear Complexes Based on Nitrothiacalix[4]arenes: The Study of Interplay between Macrocycle Platform Flexibility and Structural Diversity of Coordination Compounds

Four new manganese(II) complexes, based on dinitro and tetranitrothiacalix[4]arenes, were synthesized and characterized from structural points of view in the crystalline phase. It was revealed that thiacalix[4]arenes decorated with two and four electron withdrawing groups, when combined with MnCl2, afforded the formation of similar tetranuclear complexes 1 and 2a with two non-equivalent metal ions and a rhombic geometry of the metallic cluster core. The distortion of the coordination sphere of metal cations within the obtained complexes was found to be dependent on the number of nitro groups located at the upper rim of the macrocyclic backbone, adopted in cone conformation. The tetranuclear complex 2b of a different type, displaying the formation of a dinuclear cluster core, crystallized in a non-centrosymmetric space group was obtained, when tetranitrothiacalix[4]arene, adopted in a partial cone conformation, was involved in coordination with manganese(II) cations. The switching of coordination behavior for the macrocyclic ligand in 2b was achieved due to the presence of upper-rim-disposed electron-withdrawing nitro groups, increasing the flexibility of the macrocyclic backbone by breaking the H-bonding between the OH phenolate moieties within the ligand structure. Finally, the use of 2,2 & PRIME;-bipyridine as an auxiliary ligand in coordination with tetranitrothiacalix[4]arene and manganese(II) cations led to the third type complex formation 3, where the macrocycle platform adopted in a 1.2-alternate conformation.