The uncommon d5 intermediate spin state is found in a series of mfjo-tetraphenylporphyrinatoiron(lll) complexes of general formula Fe(Y) (TPP) where Y is a so-called weak ligand (C104, BF4, PF6, SbF6, and CF3SO3). Synthesis is achieved by AgY metathesis with FeCl(TPP). The spin state is characterized by magnetic moments in the range Mcff = 4. 5-5.3 Mb at 300 K. Detailed studies on the perchlorato derivative further characterize the spin state with a somewhat curved Curie-Weiss plot (4-300 K), Móssbauer data (A£q = 3.5, 5 = 0.38 mm s-1 at 4.2 K), solid-state ESR (g± = 4.75), and a single-crystal X-ray structure on the 0.5w-xylene solvate of Fe(OClC>3)(TPP). Crystal data follow: monoclinic, a = 14.736 (3) Á, b = 15.519 (3) Á, c = 17.506 (3) Á, ß = 95.17 (1)°; space group P2\jn;Z = 4; pcaicd = 1.378, p0bsd = 1.379 g/cm3. The perchlorato ligand is monodentate with an unusually short Fe-0 distance (2.029 (4) Á). The average Fe-N bond distance is 2.001 (5) Á with the iron(lll) atom displaced by an intermediate amount (0.3 Á) from the porphyrin plane. These dimensions are significantly shorter than those of high-spin five-coordinate ferric porphyrins and are consistent with depopulation of the dx2_r2 orbital. The solid-state gj. = 4.75 value together with the magnetic moment, which is greatly in excess of the S = % spin-only value, is interpreted in terms of a quantum mechanically mixed S = %, % state remarkably similar to that of certain low-temperature cytochromes c'. Investigation of the solution behavior of Fe(OClC>3)(TPP) by NMR, ESR, Móssbauer, and visible spectroscopy, however, suggests that a predominantly high-spin species exists in the solution phase. The relevance of axial ligand field strength changes to hemoprotein structure and spin state is discussed with particular reference to the histidine of the cytochromes c'. That a perchlorate ligand causes an intermediate spin complex while chloride, bromide, alkoxide, azide, etc., form high-spin ferric porphyrin complexes leads to the conclusion that perchlorate can be a weaker field ligand than previously supposed, despite relatively good binding. Qualitative crystal field arguments to rationalize the spin state require an interesting compensating dependence of the equatorial ligand field of the porphyrin upon that of the axial ligand.

Nature of Iron(1) and Iron( 0) Tetraphenylporphyrin Complexes. Synthesis and Molecular Structure of (Dibenzo-18-crown-6) bis( tetrahydrofuran)sodium (meso -Tetraphenylporphinato)ferrate and Bis[tris( tetrahydrofuran)sodium] (meso -Tetraphenylporphinato) ferrateA synthetic and structural investigation of the so-called iron(1) and iron (0) tetraphenylporphyrin complexes, [Fe(TPP)]and [Fe(TPP)I2-, resolves a number of the existing ambiguities about their identity. [Fe(TPP)]-has a low-spin S = '12 state and is devoid of axial ligation at least in the solid state where it crystallizes as the purple, air-sensitive [Na(di-benz0-18-crown-6)(THF)~]+ salt. Crystal data: C72H6808N4FeNa, monoclinic, space group P2,/m, a = 12.796 (2) A, b = 21.861 (4) A, c = 12.108 (2) A, p = 103.47 (1)O, Z = 2; Fe-N,(av) = 1.980 (6) A. Analysis of the structural data requires inclusion of substantial iron(I1) r-radical anion character in the previously favored iron(1) formulation. The green dianion [Fe(TPP)I2-has been isolated for the first time. It is diamagnetic and crystallizes in a tightly ion-paired structure where two [Na(tetrahydr~furan)~]+ cations interact with a pair of porphinato nitrogen atoms (Na-N = 2.784 (4), 2.825 (4) A) above and below the porphyrin plane. The porphinato core bond lengths reveal considerable *-radical anion character. Crystal data: C6BH7606N4FeNa2, triclinic, space group Pi, a = 11.877 (3) A, b = 13.242 (3) A, c = 11.242 (2) A, a = 113.69 (2)O, /3 = 110.01 (2)O, y = 77.55 (2)O, 2 = 1; Fe-N,(av) = 1.968 (1) A. Experimental Section as previously described.12 All manipulations were carried out in an inert-atmosphere glovebox University of Southern California. University of Notre Dame. Cohen, I. A,; Ostfeld, D.; Lichtenstein, B. J. Am. Chem. Soc. 1972, 94, Lexa, D.; Momenteau, M.; Mispelter, J. Biochim. Biophys. Acta 1974, 4522-4525. . . 338, 151-163. Kadish, K. M.; Larson, G.; Lexa, D.; Momenteau, M. J. Am. Chem. SOC. 1975, 97, 282-288. Collman, J. P.; Sorrell, T. N.; Dawson, J. H.; Trudel, J. R.; Bunnenburg, E.; Djerassi, C.

plicable as well to ordered ones and the conclusions drawn from such an analysis are not dependent on the potential chosen, as long as a reasonable function is employed. Acknowledgment. We are grateful to Ms. Pnina Dauber for carrying out many of the calculations presented here. This work was supported in part by a grant (to J.B.) from the Israel Academy of Science. References and Notes(1) (a) (c) unpublished results. J. Bernstein, unpublished results. (a) A. T. Hagler and S. Lifson, J. Am. Chem. Soc., 96,5327 (1974); (b) A. T. Hagler, L. Leiserowitz, and M. Tuval, ibid., 98, 4600 (1978); (c) A. T. Hagler and S. Lifson, Acta Ctystallogr., Sect. 6, 30, 1336 (1974); (d) A. T. Hagler, E. Huler, and S. Lifson, J. Am. Chem. SOC., 96, 5319 (1974). D. E. Williams, Acta Ctystalbgr., Sect. A, 30, 71 (1974). 0. Kennard et al., Ed., "Molecular Structures and Dimensions", N. V. A. Oosthoek's Uitgevers Mij. Utrecht, 1972, pp S2-S3. E. Giglio, Nature (London), 222, 339 (1969). A. T. Kitaigorodskii, Adv. Struct. Res. Diffr. Methods, 3, 225 (1970). A. T. Hagler and L. Leiserowitz, "On the Amide Hydrogen Bond and the Anomalous Packing of Adipamide", submitted for publication. Subsequent listings of energy contributions are given for the three potentials in the same order. Abstract: The synthesis and definitive characterization of the first examples of six-coordinate high-spin ferric porphyrin complexes are reported. Perchlorato(tetraphenylporphyrinato)iron(III) reacts with various weak field ligands L (sulfoxides, dimethylformamide, triphenylphosphine oxide, pyridine N-oxide) to give isolable crystalline derivatives [ FeL2( tetraphenylporphyrin)]C104. Magnetic, Mossbauer, ESR, and structural data support a high-spin state assignment and certain properties parallel those of aquomethemoglobin. The crystal structure of bis(tetraEethy1ene sulfoxide)(tetraphenylporphinato)iron( I I I ) perchlorate, FeN4C52H&20&1, has been determined: space group P I ; Z = 2; a = 14.003 ( 5 ) , b = 15.246 ( 5 ) , c = 12.108 (3) A; a = 11 3.20 ( 2 ) , p = 89.24 (2), y = 76.67 (4)'; 7586 reflections, Mo Ka; R I = 0.076, R2 = 0.089 with final datafparameter ratio of 13.2.In contrast to all other known high-spin ferric porphyrins the iron atom is precisely located in the plane of an expanded porphyrin core with mean Fe-N 2.045 ( 5 ) A. The axial tetramethylene sulfoxide ligands are 0-bound with F e -0 2.069 (3) and 2.087 (3) A, respectively, in the two independent half-molecules of the unit cell.

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C H z = C H -C H = C H 2 ) , 4.600 (m, 1, CH2==CH-CH=CH2), 1.380 (d, 9, zJHp = 7.3 Hz, PMe,), 0.957 (d, 9, zJHp s 6.7 Hz, PMe,'), 2.23, 1.44, 1.15, 1.00,0.842, -0.161,-0.807, -0.919 (m, 1, olefinic resonances). The 4.826-and 4.600-ppm resonances coalesce at 75 f 10 OC [Av = 62 f 5 Hz, AG' = 17 i 1 kcal mol-']. I3C NMR (toluene-d,, 67.89 MHz, -30 "C): 94.87 (d, ' J C H = 160 Hz, CHzjCH-CH=CH2), 92.57 (d, 'JCH = 163 Hz, CH2=CH--CH=CH2), 51.79 (tt, ' J c p = 5.6 Hz, 'JCH = 147 Hz, CH2=CH2), 43.40 (ddd, 2Jcp = 5.7 Hz, 'JcH = 155 and 148 Hz, CHz=CHz), 34.75 (ddd, 2Jcp = 7.8 Hz, 'JCH = 141 and 149 Hz, CH2=CH-CH=CH2), 30.19 (tt, 2Jcp CHz=CH-CH=CHz), 14.92 (qd, ' J c p 8.2 Hz, 'JCH i i : 150 Hz, 21.6 Hz, 'JcH = 130 Hz, PMe3), 13.54 (qd, ' J c p = 23.3 Hz, 'JcH = 130 Hz, PMe,'). I3C NMR (15.0 Hz, 60 "C): ethylene carbon atom resonances coalesce [T, = 60 f 10 OC, Av = 129 & 5 Hz, AG* = 16 f 1 kcal mol-']. 13C NMR (15.0 MHz, 100 "C): 93.95 (s, CHz=CH-CH=CH2), 47.8 (br s, CHz= CHI), 33.1 (s, CHz=CH-CH=CHz), 14.9 ppm (d, lJcp i i : 12 Hz, PMe3). IIP NMR (CDCI,, 109.3 MHz, -30 "C): 6 2.0 (s) and -8.3 (s) (major isomer), 2.5 (9) and -7.8 (s) (minor isomer). The ratio of the major to minor isomer was 2:l at -30 OC for this sample in this solvent. (14) Ta( 1,Ibutadieae) ( C2H4) (Et) ( PMe3)2. Ta(C4H6)(C2H4) (CI)-(PMe3)2 (1.25 g, 2.77 mmol) was dissolved in ether (25 mL), and the solution was cooled to -78 OC. A 4.7"sample of a 1.18 M LiCzHS (excess) in benzene solution was added slowly by syringe. The reaction mixture was warmed to 25 OC, stirred for 30 min, and filtered. The solvent was removed in vacuo, and the residue was recrystallized from minimal pentane; yield 0.6 g (49%).Anal. Calcd for TaC14H33Pz: C, 37.84; H, 7.48. Found: C, 37.23; H, 7.32. 'H NMR (toluene-& 270 MHz, -40 "C): 6 4.92 (m, CH2= CH-CH=CH2), 3.46 (m, CHz=CH-CH=CH2), 1.30 (d, 2JHp = 6 Hz,PMe3),0.87(d,2J~pii:6H~,PMe~),1.55,1.16,0.76,-0.16,and -0.37 (m, olefinic and CHz resonances), -0.05 (t. 'JHH = 7.7 Hz, CHzCH3). "C NMR (toluene-d,, 67.89 MHz, -40 OC): major isomer, 102.3 (d, 'JCH = 157 Hz, CHz=CH-CH=CHz), 89.0 (d, ' J C H Hz, CHZ=CH-CH=CH2), 48.6 ppm (tt, 'JCp = 5.7 Hz, ' J C H = 146 Hz, CH2=CHz), 42.1 (td, 2 J c p = 4.8 Hz, ' J C H = 149 Hz, C H y C H z ) , 33.9 (td, 2 J c p = 5.8 Hz, 'JcH = 150 Hz, CHZ-CH--CH=CH2), 33.6 (t, 'JCH = 116 Hz, CHZCH,), 25.1 (td, 2 J c p = 9.0 Hz, ' J c H 149 Hz, CHz=CH-CH=CHz), 15.0 (qd, ' J c p = 17.7 Hz, ' J C H 130 Hz, 163 PMe,), 13.5 (qd, ' J c p = 19.4 Hz, 'JCH EZ 130 Hz, PMe,'), 5.8 ppm (q, 'JCH 123 Hz, CHZCH,); minor isomer, 94.4 (CHz=CH-CH=CHz), 1.55 ppm (CHzCH3). (Other signals could not be found in this sample.) j'P NMR (toluene -d,, 109.3 MHz, -47 OC): 6 -6.4 (s) and -11.4 (s) (major isomer), -6.0 (s) and -1 1.9 (s) (minor isomer). The ratio of the major to minor isomer was 3:l at -47 OC and 1:l at 30 OC. (CHz=CH=CH