Highly saddle shaped (porphyrinato)iron(III) iodide with a pure intermediate spin state Mikio Nakamura,* ab Takahisa Ikeue, a Yoshiki Ohgo, a Masashi Takahashi c and Masuo Takeda c a Department of Chemistry, Toho University School of Medicine, Ota-ku, Tokyo 143-8540, Japan. E-mail: mnakamu@med.toho-u.ac.jp b Division of Biomolecular Science, Graduate School of Science, Toho University, Funabashi 274-8510, Japan c Department of Chemistry, Faculty of Science, Toho University, Funabashi 274-8510, Japan Received (in Cambridge, UK) 20th March 2002, Accepted 22nd April 2002 First published as an Advance Article on the web 2nd May 2002 Combined analyses using NMR, EPR and Mössbauer spectroscopy as well as SQUID magnetometry have revealed that highly saddle shaped Fe(OETPP)I adopts an essentially pure intermediate spin state in spite of the coordination of an iodide ligand. Spin states of five-coordinated iron(III) porphyrin complexes are controlled by the ligand field strength of axial ligands. 1 While most of the anionic ligands such as halides and hydroxide lead to the formation of the complexes with high-spin (S = 5/2) state, extremely weak ligands such as ClO 4 2 and SbF 6 2 give the complexes with admixed (S = 3/2, 5/2) spin state. 2 We have recently reported that six-coordinated iron(III) porphyrin com- plexes such as [Fe(OETPP)(4-CNPy) 2 ]ClO 4 and [Fe(OETPP)(THF) 2 ]ClO 4 are in an essentially pure inter- mediate-spin (S = 3/2) state at ambient temperature because of the presence of highly saddle shaped porphyrin rings. 3–5 Fajer and coworkers have also reported that five-coordinated Fe(OETPP)ClO 4 is an essentially pure S = 3/2 complex on the basis of the EPR and crystallographic studies. 6 We thus expected that even five-coordinated iron(III) halides such as Fe(OETPP)I could show the S = 3/2 spin state though the analogous Fe(OETPP)Cl is reported to be in the S = 5/2 spin state with only a small amount of the S = 3/2 spin admixture. 7 Here, we report the spin states of a series of saddle shaped complexes, 1–4, on the basis of the spectroscopic and magnetic results. We also report that Fe(OETPP)I is the first example of the five-coordinated (porphyrinato)iron(III) halide that has an essentially pure intermediate spin state. Complex 2 was prepared according to the literature, 8,9 and was converted to [Fe(OETPP)(OH)] by treatment with aqueous KOH. 1, 3 and 4 were prepared by the addition of perchloric acid to the CH 2 Cl 2 solutions of [Fe(OETPP)(OH)] in the presence of KF, KBr and KI, respectively. 1 H NMR chemical shifts of these complexes exhibit some differences depending on the axial halides as listed in Table 1; the ortho and para signals move downfield while the meta signals shift upfield on going from 1 to 4. Because the pure intermediate spin complexes such as [Fe(OETPP)(4-CNPy) 2 ]ClO 4 and [Fe(OETPP)(THF) 2 ]ClO 4 are characterized by downfield shifted ortho and para signals together with a slightly upfield shifted meta signal, the 1 H NMR results are indicative of the change in spin state from S = 5/2 to S = 3/2 as the axially coordinated F 2 is replaced by Cl 2 , Br 2 and then by I 2 . To obtain much conclusive evidence for the spin state, the EPR spectra were measured in frozen CH 2 Cl 2 solution at 4.2 K as shown in Fig. 1. The g values listed in Table 1 are determined by the computer simulation of the observed spectra. 10 In the case of 4, hyperfine coupling with axially coordinated iodide, 49 G, is clearly observed for the signal at g = 2. The contributions of the S = 3/2 spin state in the admixed S = 3/2, 5/2 system can be estimated as (6 2 g 4 )/2, 11 which are calculated to be 5.0, 4.3, 89 and 94% for 1, 2, 3 and 4, respectively. Thus, the EPR results clearly indicate that, while 1 and 2 are in the S = 5/2 with a small amount of the S = 3/2 spin admixture, 3 and 4 have S = 3/2 with a small amount of the S = 5/2 spin admixture. Table 1 1 H NMR chemical shifts and EPR g values 1 H NMR (CD 2 Cl 2 , 298 K) EPR (CH 2 Cl 2 , 4.2 K) Complexes CH 2 CH 3 o m p g values [Fe(TPP)Cl] a — — 3.8, 6.2 12.0, 12.6 5.8 6.0 6.0 2.0 [Fe(OETPP)F] (1) 24.1, 35.4, 38.4, 45.0 1.6, 3.7 8.1, 10.6 12.9, 13.1 7.0 6.50 5.30 2.00 [Fe(OETPP)Cl] (2) a 20.1, 32.1, 34.8, 49.0 1.8, 3.2 9.1, 11.5 12.2, 12.4 7.5 6.56 5.27 1.97 [Fe(OETPP)Br] (3) 18.1, 32.6, 34.3, 45.8 1.0, 2.3 10.4, 13.5 11.7, 12.2 8.4 4.95 3.50 1.95 [Fe(OETPP)I] (4) 11.9, 29.3, 32.1, 47.3 0.4, 0.9 12.6, 15.8 10.3, 10.8 9.6 4.14 4.14 2.00 [Fe(OETPP)(L 1 ) 2 ] + b 16.2, 42.6 20.7 14.0 5.31 2.0 4.28 3.80 2.08 [Fe(OETPP)(L 2 ) 2 ] + c 14.2, 43.1 0.7 13.0 6.5 9.7 4.01 4.01 2.00 a NMR data cited from ref. 19. b L 1 = 4-CNPy; ref. 4. c L 2 = THF; ref. 5. Fig. 1 EPR spectra of (a) 1, (b) 2, (c) 3 and (d) 4 taken in frozen CH 2 Cl 2 solutions at 4.2 K. This journal is © The Royal Society of Chemistry 2002 1198 CHEM. COMMUN. , 2002, 1198–1199 DOI: 10.1039/b202768b