Homo and heterotrinuclear iron acetates: an experiment for the coordination chemistry laboratory

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.18151820Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Interdisciplinary studies of transition metal compounds in supramolecular systems

In this work the interaction between transition metal complexes and high-molecular weight structures was investigated. We considered pentacyanoferrate (PCF), meso-tetrakis(pentafluorophenyl)porphyrinatomanganese(III) chloride (MnP), linear homopolymers, carbon nanotubes (CNT) and gold nanoparticles (AuNP). The energy of the metal to ligand charge transfer of PCF is shifted when it is coordinated to pyridyl groups of poly(4-vinylpyridine) (P4VP). The amount of coordinated PCF relative to polymer repeating units affects the intrinsic viscosity of the macromolecule solution due to steric hindrance and electrostatic repulsion of the bound PCF groups. Non-coordinated pyridyl groups are still able to interact with e.g. CNT mainly via dispersion interaction, in order to produce a supramolecular aggregate suspended in water/ethanol mixture. Suspended CNT were isolated and Raman spectroscopy revealed no structural damage induced by the non-covalent functionalization process. Glassy carbon electrodes were modified with the hybrid material CNT/P4VP/PCF and further used on the electrocatalytic oxidation of cysteine. The reaction rate constant (8.95x10³ L/mol/s) was determined by chronoamperometry, with linear response within 20.5-151 nmol/L and response time of 0.1 s. MnP was synthesized using ethanol as solvent. The product crystallized in C2/c space group together with three toluene solvent molecules. The dihedral angle between pentafluorophenyl groups and the ruffled tetrapyrrolic ring ranges from 59° to 77°. The use of dimethylformamide as solvent, following procedures frequently reported in literature, results in a mixture of dimethylamine-substituted porphyrins. MnP was associated with pyridyl-functionalized AuNP and deposited over fluoride doped tin oxide electrode. The electrocatalytic oxidation of cysteine was investigated and presented linear response was within 12.2-33.6 µmol/L. Electrodes prepared only with MnP and without AuNP show cyclic voltammograms similar to those from bare electrodes, which evidences the synergism between MnP and AuNP. MnP was employed in the catalytic oxidation of cyclohexene and phenol using hydrogen peroxide and m-chloroperbenzoic acid as oxygen-donor agents, respectively. The presence of poly(acrylic acid) (PAA) in the reaction of the first substrate provided cyclohexene oxide as the only product. Therefore, PAA favors the oxidation in the para position of phenol, which was attributed to the better availability of this position to electrophilic attack due to substrate-polymer hydrogen bonding. Replacement of phenol to methoxybenzene causes the regioselectivity to become invariant to the presence of PAA, which was attributed to the hindrance of hydrogen bonding with the polymer chain. X-ray absorption and electronic spectroscopies do not show evidences of interaction between MnP and PAA chain in solution. The relationship between reactivity and electronic structure of high-valent Mn-oxo porphyrins was investigated by multiconfigurational and density functional methods. In agreement with experimental data, the ground state is a Mn(V) singlet. A triplet state corresponding to the excitation of an electron from the non-bonding 3d orbital to one of the Mn-O pi* orbitals was found to be thermally accessible. Inclusion of solvent effects significantly stabilizes Mn(IV) states with respect to Mn(V). The triplet state displays large oxyl character arising from occupation of Mn-O pi* orbitals and also from diradical character.nrpages: 286status: publishe

Acetatos homo e heterotrinucleares de ferro: um experimento para o laboratório de química de coordenação Homo and heterotrinuclear iron acetates: an experiment for the coordination chemistry laboratory

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

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 <i>meso</i>-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^IVO­(L^•a_2<i>u</i>)⁺ quintet state. The latter state is high-lying in MnO­(P)⁺ but is stabilized by the substitutions of H by F at the <i>meso</i> carbons (where the a_2<i>u</i> 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

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N-Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X-ray Spectroscopic and Crystallographic Investigation

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole- and pyridine-based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu−Nimine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature-dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N Copper I Schiff Base Complexes in Solid and in Solution a Combined NMR, X ray Spectroscopic and Crystallographic Investigation

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole- and pyridine-based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu−Nimine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature-dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state