Electron spin resonance studies of silver complexes of octaethylporphyrin cocrystallized with fullerenes: Observation of triplet spin states due to magnetic dipolar interactions

Electron spin resonance (ESR) studies have been performed on newly synthesized Ag^II complexes of octaethylporphyrin (oep) cocrystallized with fullerenes (C₆₀ and C₇₀) using single crystals and polycrystals between 4 and 300 K. We have observed the fine structure in the ESR spectra of Ag^II(oep)C₆₀; the fine structure is ascribed to the triplet spin states due to magnetic dipolar interactions between S=1/2 spins of Ag^II ions in adjacent oep molecules. The analysis of the angular dependence of the g value and fine-structure splitting width for Ag^II(oep)C₆₀ single crystals determines the angle between the Ag-Ag direction and the normal of the Ag-oep plane as 37°. The results of Ag^II(oep)C₇₀ are similar to those of Ag^II(oep)C₆₀. The spin susceptibility of all complexes almost obeys the Curie law, indicating the exchange interactions between the spins of Ag ions are negligible in the temperature region measured.