ChemInform Abstract: New Crystalline Phase of (Octaethylporphinato)nickel(II). Effects of .pi±pi. Interactions on Molecular Structure and Resonance Raman Spectra.

Abstract

A new (third) crystalline phase of Ni(OEP) has been isolated and characterized by a single-crystal X-ray diffraction study and single-crystal resonance Raman spectroscopy. Single-crystal Raman measurements were also performed on the two previously described phases and the Raman spectra of the three phases compared. Differences in Raman spectra between the current new phase and the previously reported triclinic phase are interpreted in terms of ..pi..-..pi.. interactions found for this new phase. These spectral differences are also compared to solution Raman data that had been previously reported on aggregated and monomeric porphyrin derivatives. The bands most affected are the core-size marker bands v/sub 10/, v/sub 19/, and v/sub 3/ and the oxidation-state marker band v/sub 4/ where ..pi..-..pi.. interaction leads to increases of 2.5-4.3 cm/sup -1/. These Raman shifts are consistent with a decrease in the core size, and the crystal structure confirms this interpretation. The two crystallographically distinct Ni-N bond distances in the new crystalline phase are 1.946 (4) and 1.958 (4) A, with the shorter distance along the one-dimensional stack axis of the complex. The observed interplanar spacing between porphyrin planes is 3.44 A, and the Ni...Ni separation is 4.80 A. Crystal data: triclinic; space group P anti 1;more » a = 13.302 (6), b = 13.342 (11), c = 4.802 (2) A; ..cap alpha.. = 92.21 (2), ..beta.. = 93.52 (4), ..gamma.. = 113.43 (6)/sup 0/; Z = 1; V = 778.7 A/sup 3/.« less