Investigation of structure of Fe3+ magnetic center in polyparaphenylene

In the temperature range between 4.2 and 300 K, the EPR spectrum of the impurity Fe3+ ion in the organic polyparaphenylene has been investigated. An effect developed as an unusual temperature change of Fe3+ 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 I 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 Fe3+ magnetic ion for various possible molecular environments. It is shown that in polyparaphenylene for the Fe3+ 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. (C) 2002 Wiley Periodicals, Inc.