Investigation of structure of Fe 3+ magnetic center in polyparaphenylene

In the temperature range between 4.2 and 300 K, the EPR spectrum of the impurity Fe 3+ ion in the organic polyparaphenylene has been investigated. An effect developed as an unusual temperature change of Fe 3+ EPR spectrum has been revealed. The EPR spectrum of powder sample consists of two resonance lines. Line 1 with the effective g ‐value equal to g 1 = 4.21 ± 0.05 is of the maximum intensity at T = 4.2 K. With temperature increase, the intensity of line 1 decreases until vanishing. Line 2 is observed over the whole temperature range. For T = 300 K, the g ‐value of line 2 is g 2 = 2.00 ± 0.09. To study the structure of magnetic ion molecular environment and define nonequivalent positions of the magnetic ion in polyparaphenylene, a calculation was done of the energy of Fe 3+ magnetic ion for various possible molecular environments. It is shown that in polyparaphenylene for the Fe 3+ magnetic ion there are two different stationary molecular environments. The obtained model of magnetic ion molecular environment was used to explain the temperature dependence of the EPR spectrum. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002