New crystalline phase of (octaethylporphinato)nickel(II): effects of .pi.-.pi. interactions on molecular structure and resonance Raman spectra

An in-situ Raman study of the effect of the support for adsorbed iridium-chelates in catalysing oxygen reduction

“…This decrease in 7r change causes a contraction of the porphyrinato core. The bands that reflect this are the vl0 (1624 cm-~), ~,19 (1579 cm -]) and v3 (not visible in our spectrum) bands and the oxidation state marker band u4 (1391 cm -]) [21,22]. These are therefore called core size markers, but vl0 and v4 are also sensitive to the oxidation state of the metal ion.…”

“…But, by influencing the core size of the macrocycle, the position of the iridium with respect to the macrocycle ring might be varied. It has been found for NiOEP, by Brennan et al [21], that an increase in 7r-~ interaction causes a decrease in 7r charge density in the porphyrin ring. This decrease in 7r change causes a contraction of the porphyrinato core.…”

Critical Re-evaluation of the O−H Bond Dissociation Enthalpy in Phenol

“…Meyer reported X-ray data for a tetragonal form of NiOEP, 10 Cullen and Meyer followed this with data for a triclinic form (later referred to as the triclinic A form), 11 and Shelnutt and coworkers reported X-ray data for a second triclinic form, called triclinic B. 12 It is well-known that nickel(II) porphyrins have a tendency to deviate from planarity. 13 This deviation from planarity is attributed to the combination of the Ni-N bond being too short to fit the central cavity of a planar pophyrin and the presence of substituents on the periphery of the macrocycle.…”

“…14 The bond shortening is accommodated by ruffling of the porphyrin ring, an effect which has been observed crystallographically and spectroscopically. 12,14,15 Although a large amount of experimental data has been reported for NiOEP, there has not been an attempt to characterize this system quantum mechanically. In this paper we report the results of density functional theory (DFT) energy calculations and geometry optimizations for selected planar and ruffled conformers of NiOEP.…”

“…In this study we concentrate on the energies and geometries of four conformers (Figure 2). These conformers were chosen because X-ray crystallography data has been reported for three of them, [10][11][12] and the fourth has been used as a model in other NiOEP studies. 7b The detailed vibrational analysis will be presented in future publication.…”