Narrow Results

The spectroscopic characterization of peroxo- and hydroperoxo- intermediates of heme proteins and enzymes has long interested scientists studying the structure and function of these important biochemical systems. Until very recently, little progress had been made in studying these fleeting intermediates by vibrational spectroscopic methods. In this brief review, recent studies reporting the Resonance Raman and Infrared spectra of such intermediates and pertinent model compounds are reviewed and compared to corresponding studies utilizing electronic absorption and electron paramagnetic resonance spectrometric methods.

The Mn complexated corrole [T(4-NO₂P)Corr]Mn(py) (3) has been prepared (py = pyridine) where [T(4-NO₂P)Corr] is the trianion of the electron-poor 5,10,15-tris(4-nitrophenyl)corrole (1). The preparation of 3 includes a new synthetic method to form the corrole ligand 1 in a two-step synthesis. The Mn(III) complex gives a parallel mode EPR signal centered around g = 8.2 with six distinct hyperfine lines (A_|| = 139 × 10^-4cm^-1). Electrochemically 3 undergoes one reversible oxidation (E_1/2 = 0.12 V vs Fc) and two reversible reductions (E_1/2 = -1.45, -1.61 V). The oxidation is metal-centered and the product has been characterized by EPR spectroscopy as an S = 3/2Mn(IV) species with no indication for oxidation of the macrocycle. The reductions of complex 3 are ligand based, and at the potential of the second reduction step a stable nitrogen centered radical with g = 2.0055 is generated. Chemical oxidation of 3 by iodosobenzene yields a Mn(IV) complex and epoxidation of cis-stilbene is not catalyzed by the Mn complex.

The synthesis of new metalated diporphyrinylamines is described. The electronic ≪communication≫ through the amino function linking the two porphyrins was clearly demonstrated by electronic spectroscopy. In addition, intramolecular magnetic interactions were measured between two copper(II) ions located in the two linked porphyrins. Compared to the reported value ($J\sim$ -2 K) for Osuka’s triply fused bis-copper(II) porphyrin dimer, a relatively high antiferromagnetic coupling constant was determined in our compound ($J$ = -11 K).

The synthesis of a series of novel tetra-(benzo-24-crown-8)-phthalocyanines (Mg(II), Ni(II) and Co(II)) as well as a modified procedure for the free-base ligand and its Zn(II) and Cu(II) complexes are reported. The tendency of these phthalocyanines to undergo supramolecular cofacial dimerization induced by interaction with a viologen ($N,N$-di(but-3-ynyl)-4,4$\prime$-bipyridinium) was investigated by UV-vis absorption and EPR spectral studies in solution. The nature of the metal cation in phthalocyanine, the concentration, as well as the solvent all influenced the assembly processes.

The synthesis of heterobimetallic coordination compounds by the spontaneous self-assembly approach, where one or both starting metals are in zero-valent or oxide form, is discussed. This chapter concerns the range of examples of heterobimetallic complexes of transition metals, from simple binuclear compounds to large dodecanuclear clusters. Aspects of the synthesis, crystal structures, magnetic properties and catalytic applications are addressed.