The interaction of tetrahydrofuran (THF) with thin films of the nitrato complexes Fe-III(Por) (eta(2)-O2NO) [Por = meso-tetraphenylporphyrinato (TPP) and meso-tetratolylporphyrinato (TTP) dianion] at low temperature leads to the formation of the six-coordinate nitrato complex Fe(Por)(THF)(NO3), which was characterized by IR and UV-visible spectroscopies. Formation of the THF adduct was accompanied by nitrate linkage isomerization from bidentate to monodentate coordination. The iron(III) center remains in a high spin state in contrast with the previously observed low-spin nitratonitrosyl complex Fe(TPP)(NO)(eta(1)-ONO2). Upon warming, THF dissociates to restore the initial five-coordinate bidentate nitrato complex.