TY - JOUR
T1 - Difference in spin crossover pathways among saddle-shaped six-coordinated iron(III) porphyrin complexes
AU - Ikeue, Takahisa
AU - Ohgo, Yoshiki
AU - Ongayi, Owendi
AU - Vicente, M. Graça H.
AU - Nakamura, Mikio
PY - 2003/9/8
Y1 - 2003/9/8
N2 - The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L2]+ and [Fe(TBTXP)L2]+ have been examined in solution by 1H NMR, 13C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2]+ and [Fe(TBTXP)(DMAP)2]+ maintain the low-spin (S = 1/2) state, [Fe(OMTPP)(THF)2]+ and [Fe(TBTXP)(THF)2]+ exhibit an essentially pure intermediate-spin (S = 3/2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S = 3/2 to S = 1/2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)PY2]+ reported in our previous paper (Ikeue, T. ; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617-2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L2]+ and [Fe(TBTXP)L 2]+ (L = Py, 4-CNPy) revealed, however, that these complexes adopt the less common (dxz, dyz) 4(dxy)1 electron configuration at low temperature in contrast to [Fe(OETPP)Py2]+ which shows the common (dxy)2(dxz, dyz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (dxz, dyz)4(d xy)1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.
AB - The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L2]+ and [Fe(TBTXP)L2]+ have been examined in solution by 1H NMR, 13C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP) 2]+ and [Fe(TBTXP)(DMAP)2]+ maintain the low-spin (S = 1/2) state, [Fe(OMTPP)(THF)2]+ and [Fe(TBTXP)(THF)2]+ exhibit an essentially pure intermediate-spin (S = 3/2) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S = 3/2 to S = 1/2 as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)PY2]+ reported in our previous paper (Ikeue, T. ; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617-2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L2]+ and [Fe(TBTXP)L 2]+ (L = Py, 4-CNPy) revealed, however, that these complexes adopt the less common (dxz, dyz) 4(dxy)1 electron configuration at low temperature in contrast to [Fe(OETPP)Py2]+ which shows the common (dxy)2(dxz, dyz) 3 electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (dxz, dyz)4(d xy)1 electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.
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U2 - 10.1021/ic0300969
DO - 10.1021/ic0300969
M3 - Article
C2 - 12950204
AN - SCOPUS:0042877156
SN - 0020-1669
VL - 42
SP - 5560
EP - 5571
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 18
ER -