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.

Solution-state NMR and X-ray crystallography were used to investigate the complexation of Hg(II) by the tridentate ligand bis [(2-pyridyl)methyl]amine (BMPA). Mercury coordination compounds exhibiting rarely observed solutionstate NMR 1 H 199 Hg satellites were characterized. Temperature and concentration effects on solution-state NMR properties were investigated. The solution-state NMR were correlated with two solid-state structures. The distorted trigonal prismatic complex [Hg(BMPA) 2 ](ClO 4 ) 2 ‚0.5toluene (1) crystallizes in the triclinic space group P1 h with a ) 10.953(5) Å, b ) 12.812(5) Å, c ) 13.006(5) Å, R ) 67.50(3)°, β ) 82.74(3)°, γ ) 67.88(3)°, and Z ) 2. The Hg-N amine bonds are 2.404(4) and 2.350(4) Å and the Hg-N pyridyl bond lengths are similar, ranging from 2.352(4) to 2.557(5) Å. Solution NMR studies are consistent with rapid equilibrium between isomeric trigonal prismatic and facial octahedral forms of this complex. A twisting mechanism is proposed to mediate interconversion. The distorted square planar complex [Hg(BMPA)NCCH 3 ](ClO 4 ) 2 ( 7) crystallizes in the monoclinic space group P2 1 /c with a ) 12.987(2) Å, b ) 17.469(4) Å, c ) 8.886(2) Å, β ) 95.200(12)°, and Z ) 4. The Hg-N amine distance is 2.403 Å, the average Hg-N pyridyl distance is 2.23 Å, and the Hg-N nitrile distance is 2.229 Å. The BMPA ligand is bound to Hg(II) in a meridional fashion with a solvent molecule in the same plane and close associations to two axial perchlorates with Hg-O distances of 2.707(7) and 2.90(2) Å. Solution NMR studies support limited dynamics for a cation with similar interactions between BMPA and Hg(II).

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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.