Substituent-Guided Cluster Nuclearity for Tetranuclear Iron(III) Compounds with Flat {Fe4(µ3-O)2} Butterfly Core.

The tetranuclear iron(III) compounds [Fe4(µ3-O)2(µ-LZ)4] (1-3) were obtained by reaction of FeCl3 with the shortened salen-type N2O2 tetradentate Schiff bases N,N'-bis(salicylidene)-o-Z-phenylmethanediamine H2LZ (Z = NO2, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe4 bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe4(µ3-O)2} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Feb, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Few. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe4(µ3-O)2} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1-3.

Selective Formation, Reactivity, Redox and Magnetic Properties of MnIII and FeIII Dinuclear Complexes with Shortened Salen-Type Schiff Base Ligands.

The reactivity of the shortened salen-type ligands H3salmp, H2salmen and H2sal(p-X)ben with variable para-substituent on the central aromatic ring (X = tBu, Me, H, F, Cl, CF3, NO2) towards the trivalent metal ions manganese(III) and iron(III) is presented. The selective formation of the dinuclear complexes [M2(µ-salmp)2], M = Mn (1a), Fe (2a), [M2(µ-salmen)2(µ-OR)2)], R = Et, Me, H and M = Mn (3a-c) or Fe (4a-c), and (M2(µ-sal[p-X]ben)2(µ-OMe)2), X = tBu, Me, H, F, Cl, CF3, NO2 and M = Mn (5a-g) or Fe (6a-g), could be identified by reaction of the Schiff bases with metal salts and the base NEt3, and their characterization through elemental analysis, infrared spectroscopy, mass spectrometry and single-crystal X-ray diffraction of 2a·2AcOEt, 2a·2CH3CN and 3c·2DMF was performed. In the case of iron(III) and H3salmp, when using NaOH as a base instead of NEt3, the dinuclear complexes [Fe2(µ-salmp)(µ-OR)(salim)2], R = Me, H (2b,c) could be isolated and spectroscopically characterized, including the crystal structure of 2b·1.5H2O, which showed that rupture of one salmp3- to two coordinated salim- ligands and release of one salH molecule occurred. The same hydrolytic tendency could be identified with sal(p-X)ben ligands in the case of iron(III) also by using NEt3 or upon standing in solution, while manganese(III) did not promote such a C-N bond breakage. Cyclic voltammetry studies were performed for 3b, 4b, 5a and 6a, revealing that the iron(III) complexes can be irreversibly reduced to the mixed-valence FeIIFeIII and FeII2 dinuclear species, while the manganese(III) derivatives can be reversibly oxidized to either the mixed-valence MnIIIMnIV or to the MnIV2 dinuclear species. The super-exchange interaction between the metal centers, mediated by the bridging ligands, resulted in being antiferromagnetic (AFM) for the selected dinuclear compounds 3b, 4b, 5a, 5e,5f, 6a and 6e. The coupling constants J (-2JS1·S2 formalism) had values around -13 cm-1 for manganese(III) compounds, among the largest AFM coupling constants reported so far for dinuclear MnIII2 derivatives, while values between -3 and -10 cm-1 were obtained for iron(III) compounds.

Progressive approach to eruption at Campi Flegrei caldera in southern Italy.

Unrest at large calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms. A classic example is the Campi Flegrei caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption. Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential. An implicit assumption is that the crust relaxes accumulated stress after each episode. Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust. The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the caldera will behave during future unrest.

The "continuum" of a unified theory of diseases.

This essay's theme was inspired by a question asked by a child: 'Why do I get ill?' The question is very interesting, but has no easy answer. This paper discusses a few possible answers to this difficult question. Through the life of a person, from birth to death, there is a "continuum" in the pathological conditions a person may experience. The body, as a whole, suffers deeply any time there is an acute or a chronic condition that is either maltreated or neglected. Chronic and acute diseases in the medical history of a person constitute a rigidly related chain of immune responses in the form of a real "continuum" that at every point in time indicates the end result of this continuum. The idea promoted here is that suppression of diseases, through excess of chemical drugs or other means, many times overwhelms the body's natural defenses and forces the immune system to compromise and start a deeper line of defense, which then constitute the beginning of a new chronic condition. Thus, the original inflammation of an acute condition may continue as a sub-acute inflammatory process on a deeper level. Acute inflammatory conditions must therefore be treated very carefully from their beginnings in childhood in order not to force the immune system to compromise. It is also suggested here that all chronic degenerative conditions have a sub-acute inflammatory character, and that "inflammation" constitutes the main common parameter of all diseases.