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Two dinuclear double oxygen-bridged iron(III) complexes made of the Fe2(μ2-OR)2 diamond-core cluster resulting from the coordination between iron(III) cations with calix[4]arene ligands and bearing two lower-rim-appended salicylideneamine (4) or o-methoxy-salicylideneamine coordinating sites (5), connected to the macrocyclic platform via three methylene bridges and displaying a salen-type coordination pocket, were synthesized and characterized using single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), high-resolution mass spectrometry (HRESI-MS), IR, TG-DSC and EA techniques. Independent of the presence of the o-methoxy group in the salicylideneamine moieties, the as-formed complexes contained two nonequivalent iron(III) atoms, both adopting a distorted octahedral coordination N2O4-environment but differing in the cis and trans positions of the nitrogen atoms within the metal coordination sphere, as attested by single-crystal X-ray diffraction and DFT-B3LYP calculations. The possible reason for the observed coordination mode of the macrocyclic ligands is their conformational behavior upon coordination with Fe(III) cations, as confirmed by DFT-B3LYP analysis. 57Fe Mössbauer spectroscopy study showed that both Fe(III) atoms were present in high spin states at room temperature and at 80 K in the studied coordination compounds. The methoxy groups located at the ortho position of the salicylideneamine coordinating fragments were observed to influence the energy of the frontier orbitals, resulting in an increase in the bandgap energy from 1.97 eV to 2.07 eV, as experimentally established by solid-state voltammetry study of 42-Fe2 exp and 52-Fe2 exp, respectively. The interplay between the steric and electronic factors, emerging from the o-methoxy group within coordinating salicylideneamine moieties, seemed to have a negligible effect on the electronic properties of the prepared clusters but significantly impacted the frontier orbital energy distribution, according to both experimental data and theoretical calculations. [ABSTRACT FROM AUTHOR]

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′-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. [ABSTRACT FROM AUTHOR]