102149-51-9Relevant academic research and scientific papers
Spin coupling in admixed intermediate-spin iron(III) porphyrin dimers: Crystal structure, m?ssbauer, and susceptibility study of Fe(TPP)(B11CH12)·C7H8
Gupta, Govind P.,Lang, George,Lee, Young Ja,Scheldt, W. Robert,Shelly, Kenneth,Reed, Christopher A.
, p. 3022 - 3030 (2008/10/08)
Susceptibility measurements on Fe(TPP)(B11CH12)·C7H8 (TPP = tetraphenylporphyrinate) in an external field of 0.2 T show that its magnetic moment varies from 2.0 to 4.2 μB over the temperature range 6-300 K. The data were analyzed with Maltempo model spins antiferromagnetically coupled within dimers. Face-to-face pairing of molecules is seen in the crystal structure. The analysis shows that the ground-state quartet S = 3/2 (92%) is mixed with the nearby sextet S = 5/2 (8%) through spin-orbit coupling with an unusually small coupling constant, ξ = 150 cm-1. The exchange interaction within the dimer is estimated to be ～+(3.0 cm-1)S + (combining right arrow above sign)1·S + (combining right arrow above sign)2. Mo?ssbauer spectra were recorded at temperatures varying from 4.2 to 128 K in fields 0-6 T. The chemical shift δ = 0.33 mm/s (Fe) and quadrupole splitting ΔEQ = 4.12 mm/s are temperature-independent and typical of ferric ions in the admixed intermediate-spin state. Mo?ssbauer analysis confirms the exchange interaction between the two spin systems in the dimer. The analysis also provides the rather low contact hyperfine field Pκ/gNβN = 8.7 T/unit spin. The spectra imply intermediate relaxation rates even in fields of 6 T at 4.2 K, the rate increasing with increasing T and decreasing H. All Mo?ssbauer and susceptibility data were fitted with a common parameter set; only the relaxation parameter was varied from one spectrum to another. The [Fe(TPP)(B11CH12)]·C7H8 complex is found to be five-coordinate with the carborane anion as the axial ligand with an open Fe-H-B bridge bond. The Fe-H distance is 1.82 (4) A?, and the Fe-H-B angle is 151 (3)°. The complex also has very short Fe-N bonds: the average distance is 1.961 (5) A?. The complex also exhibits an interaction between pairs of molecules suggestive of a significant π-π interaction. The separation between mean porphinato planes is 3.83 A?. Crystal data for [Fe-(TPP)(B11CHI2)]·C7H8: triclinic, a = 13.660 (2) A?, b = 14.656 (3) A?, c = 13.142 (2) A?, α = 94.85 (1)°, β = 109.63 (1)°, γ = 75.81 (1)°, Z = 2, space group P1, 7446 unique observed data, R1 = 0.079, R2 = 0.092, all observations at 293 K.
