Sergio Augusto Venturinelli Jannuzzi

Spin State Energetics and Oxyl Character of Mn-Oxo Porphyrins by Multiconfigurational ab Initio Calculations: Implications on Reactivity

Important electromeric states in manganese-oxo porphyrins MnO(P)(+) and MnO(PF4)(+) (porphyrinato or meso-tetrafluoroporphyrinato) have been investigated with correlated ab initio methods (CASPT2, RASPT2), focusing on their possible role in multistate reactivity patterns in oxygen transfer (OAT) reactions. Due to the lack of oxyl character, the Mn(V) singlet ground state is kinetically inert. OAT reactions should therefore rather proceed through thermally accessible triplet and quintet states that have a more pronounced oxyl character. Two states have been identified as possible candidates: a Mn(V) triplet state and a Mn(IV)O(L(•)a2u)(+) quintet state. The latter state is high-lying in MnO(P)(+) but is stabilized by the substitutions of H by F at the meso carbons (where the a2u orbital has a significant amplitude). Oxyl character and Mn-O bond weakening in these two states stems from the fact that the Mn-O π* orbitals become singly (triplet) or doubly occupied (quintet). Moreover, an important role for the reactivity of the triplet state is also likely to be played by the π bond that has an empty π* orbital, because of the manifest diradical character of this π bond, revealed by the CASSCF wave function. Interestingly, the diradical character of this bond increases when the Mn-O bond is stretched, while the singly occupied π* orbital looses its oxygen radical contribution. The RASPT2 results were also used as a benchmark for the description of excited state energetics and Mn-O oxyl character with a wide range of pure and hybrid density functionals. With the latter functionals both the Mn(V) → Mn(IV) promotion energy and the diradical character of the π bond (with empty π*) are found to be extremely dependent on the contribution of exact exchange. For this reason, pure functionals are to be preferred.

Supramolecular Interactions between Inorganic and Organic Blocks of Pentacyanoferrate/Poly(4-vinylpyridine) Hybrid Metallopolymer

The combination of organic and inorganic molecular building blocks gives rise to hybrid supramolecular materials showing properties from both chemical domains. This work presents the synthesis of metallopolymers made from poly(4-vinylpyridine) (P4VP) and pentacyanoferrate(II) at various polymer repeating unit/[Fe(CN)(5)](3-) ratios (py/Fe) and focuses on the influence of each block on the properties of the other. The solvatochromic shift of the [Fe(CN)(5)](3-) moiety was investigated as a function of the py/Fe ratio and the water molar fraction (X(H(2)O)) of the ethanol/water medium. Asymmetric solvation favoring ethanol was enhanced as the py/Fe ratio increased. The results lead to a modification of the well-established thermodynamical model for asymmetrical solvation and suggest the formation of water-rich domains within the polymer coils with a large number of [Fe(CN)(5)](3-) units. From the macromolecular perspective, the increase of [Fe(CN)(5)](3-) units resulted in higher values of intrinsic viscosity, which is rationalized by the increase of the polymer coil charge density and therefore the increase in hydrodynamic volume due to repulsive electrical forces. Evaluating the intrinsic viscosity of a sample with py/Fe = 25 in solvent mixtures with different water molar fractions, it was found that the hydrodynamic volume is maximized at intermediate X(H(2)O) values, where both the ethanol-soluble uncomplexed polymer block and the water-soluble [Fe(CN)(5)](3-)-pendant units can be suitably solvated, preventing coil shrinkage.

Supramolecular Approach to Decorate Multi-Walled Carbon Nanotubes with Negatively Charged Iron(II) Complexes

Poly(4-vinylpyridine) (P4VP) and P4VP/pentacyanoferrate(II) metallopolymer were used to suspend up to 1 mg mL-1 of multi-walled carbon nanotubes (MWCNT) in ethanol/water mixtures, providing noncolavent decoration of MWCNT with electroactive iron complex. The major interaction between polymer side chains and nanotubes is via π-π stacking, rather than charge-transfer interaction reported for many nitrogenated interacting molecules. Preservation of structural integrity of the nanotubes after functionalization was attested by Raman, which was reflected in the semiconducting character of the dried nanocomposites. Proximity of pentacyanoferrate(II) to MWCNT walls was suggested by its solvatochromic shift of metal-to-ligand charge transfer band attributed to [Fe(CN)5]3− bound to P4VP pyridyl moieties. Electronic microscopy revealed smooth films and good adhesion between MWCNT bundles and the matrix. The procedure described herein can be used to combine unique properties of transition metal compounds able to coordinate to pyridyl groups, with the film-forming ability of P4VP and conductivity provided by MWCNT.

Acetatos homo e heterotrinucleares de ferro: um experimento para o laboratório de química de coordenação

Homo and heterotrinuclear acetates are unique compounds having μ3-oxo bridge and many interesting properties of such compounds are derived from this structure. Some undergraduate inorganic textbooks discuss several aspects of these compounds and we present here an undergraduate experiment for the high-yield synthesis of [Fe2MO(CH3CO2)6(H 2O)3], with M = Fe3+, Co2+ and Ni2+, as well as their characterization using infrared spectroscopy and cyclic voltametry. The proposed experiment gives the opportunity to discuss several concepts of coordination chemistry that follow the characterization techniques, such as: types of acetate coordination, reversibility of electrochemical processes, quelate and trans effects and lability.