ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Susceptibility measurements of [Fe(OEP) (3-ClPy)] ⋅ ClO4(OEP=octaethylporphyrinate) in an external field of 1 T show that its magnetic moment varies from 3.36 to 4.58 β over a temperature range of 6–300 K. The data were analyzed with the "Maltempo model'' but could be fitted only when an antiferromagnetic exchange interaction between two neighboring iron atoms within the dimer structure was assumed. The analysis shows that the ground state quartet S=3/2 (81%) is mixed with the nearby sextet S=5/2 (19%) through spin-orbit coupling with an unusually small coupling constant, ζ=150 cm−1. The exchange interaction within the dimer is estimated to be in the range of J=−0.4 to −0.6 cm−1. Mössbauer spectra of a polycrystalline sample of this complex were recorded in a range of temperatures (1.54–128 K) and applied magnetic fields (0–6 T). The analysis of Mössbauer spectra was in excellent agreement with that of susceptibility data. The analysis favors J=−0.6 cm−1. The values of chemical shift, δ=0.36 mm/s (with respect to metallic Fe), and temperature independent quadrupole splitting ΔE=3.23 mm/s, are typical of ferric ions in the admixed-intermediate spin state. Mössbauer analysis also provides the hyperfine coupling constant, P/gNβN =36.3 T/unit spin, a very low value compared with 60 T/unit spin for hemoglobin fluoride. The spectra also show that the system relaxes slowly in the presence of an external field above 5 T at 4.2 K. The rate of relaxation increases if the field is decreased or the temperature is increased. Low temperature spectra with intermediate rates of relaxation could be fitted with the set of parameters mentioned above. Only the direct relaxation process seems to be responsible up to 8 K. The anomalously large value of ΔE and low values of ζ and P are discussed in terms of the formation of molecular orbitals and changing radial wave functions of the 3d orbitals in the admixed-spin states.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.451686
