Matrix-isolation infrared spectra of oxy(tetraphenylporphyrinato)iron(II) containing CS 2 and SO 2 as axial ligands

Abstract

The IR spectra of cocondensation products of Fe(TPP) with CS 2/Ar exhibit the ν(CS 2) of Fe(TPP)(CS 2) at 1522 cm −1 which is 7 cm −1 lower than that of free CS 2. When Fe(TPP) was cocendensed with O 2/CS 2/Ar, the bands characteristic of Fe(TPP)(CS 2)O 2 (ν(CS 2), 1519 cm −1 and ν(O 2), 1190 cm −1) were observed in addition to those of Fe(TPP)(CS 2) and Fe(TPP)O 2 (ν(O 2), 1195 cm −1). These assignments were confirmed by 12CS 2/ 13CS 2 isotope shifts and warm-up experiments. A S-bonded structure in which the linear CS 2 molecule is weakly coordinated to the Fe atom has been proposed for these adducts. The IR spectra of cocondensation products of Fe(TPP) with SO 2/Ar exhibit bands characteristic of Fe(TPP)(SO 2) (1342, 1146) and Fe(TPP)(SO 2) 2 (1332 and 1142) in addition to those of SO 2 monomer ((1355*, 1351*) and (1152*, 1148*)), SO 2 dimer (1344, 1151) and SO 2H 2O (1343 and 1150 cm −1). Here, the numbers in brackets indicate the SO 2 stretching frequencies, ν 3 and ν 1, respectively, and the asterisks denote those split by the matrix effect. The cocodensation products of Fe(TPP) with O 2/SO 2/Ar exhibit new bands at 1328 (ν 3), 1142(ν 1) and 1188 cm −1 (ν(O 2)). The O-bonded structure in which the bent SO 2 molecule is coordinated to the Fe atom via the terminal oxygen has been proposed, based on small shifts of the ν 3 and ν 1 vibrations upon coordination.