Crystal structure of (diethyl ether-κO)[5,10,15,20-tetra-kis-(2-iso-thio-cyanato-phen-yl)porphyrinato-κ4 N]zinc diethyl ether solvate

The crystal structure of the title compound, [Zn(C48H24N8S4)(C4H10O)]·C4H10O, consists of discrete porphyrin complexes that are located on a twofold rotation axis. The ZnII cation is fivefold coordinated by four N atoms of the porphyrin moiety and one O atom of a diethyl ether mol-ecule in a slightly distorted square-pyramidal environment with the diethyl ether mol-ecule in the apical position. The porphyrin backbone is nearly planar with the metal cation slightly shifted out of the plane towards the coordinating diethyl ether mol-ecule. All four iso-thio-cyanato groups of the phenyl substituents at the meso-positions face the same side of the porphyrin, as is characteristic for picket fence porphyrins. In the crystal structure, the discrete porphyrin complexes are arranged in such a way that cavities are formed in which additional diethyl ether solvate mol-ecules are located around a twofold rotation axis. The O atom of the solvent mol-ecule is not positioned exactly on the twofold rotation axis, thus making the whole mol-ecule equally disordered over two symmetry-related positions.

Crystal structure of (methanol-κO)[5,10,15,20-tetra-kis-(2-amino-phen-yl)porphyrinato-κ4N]zinc(II)-chloro-form-methanol (1/1/1)

In the crystal structure of the title compound, [Zn(C44H32N8)(CH3OH)]·CHCl3·CH3OH, the ZnII cation is coordinated by four porphyrin N and one methanol O atom within a slightly distorted square-pyramidal environment and is shifted out of the porphyrin plane towards the direction of the methanol mol-ecule. The methyl group of the coordinating methanol mol-ecule is disordered over two sets of sites. The porphyrin backbone is nearly planar and the phenyl rings are almost perpendicular to the porphyrin plane. As is typical for picket-fence porphyrins, all four ortho substituents of the meso-phenyl groups (here the amino groups) are facing to the same side of the porphyrin mol-ecule. In the crystal structure, two neighbouring porphyrin complexes form centrosymmetric dimers that are connected via O-H⋯N hydrogen bonding. With the aid of additional N-H⋯N and C-H⋯N hydrogen bonding, these dimers are stacked into columns parallel to [010] that are finally arranged into layers parallel to (001). Between these layers channels are formed where chloro-form solvent mol-ecules are located that are connected to the porphyrin complexes by weak C-H⋯Cl hydrogen bonding. There are additional cavities in the structure where some small residual electron density is found, indicating the presence of disordered methanol mol-ecules, but a reasonable model could not be refined. Therefore the contribution of the electron density associated with the methanol solvent mol-ecule was removed with the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON. Nevertheless, the given chemical formula and other crystal data take into account the methanol solvent mol-ecule.

Iron L-edge X-ray absorption spectroscopy of oxy-picket fence porphyrin: experimental insight into Fe-O2 bonding

The electronic structure of the Fe-O(2) center in oxy-hemoglobin and oxy-myoglobin is a long-standing issue in the field of bioinorganic chemistry. Spectroscopic studies have been complicated by the highly delocalized nature of the porphyrin, and calculations require interpretation of multideterminant wave functions for a highly covalent metal site. Here, iron L-edge X-ray absorption spectroscopy, interpreted using a valence bond configuration interaction multiplet model, is applied to directly probe the electronic structure of the iron in the biomimetic Fe-O(2) heme complex [Fe(pfp)(1-MeIm)O(2)] (pfp ("picket fence porphyrin") = meso-tetra(α,α,α,α-o-pivalamidophenyl)porphyrin or TpivPP). This method allows separate estimates of σ-donor, π-donor, and π-acceptor interactions through ligand-to-metal charge transfer and metal-to-ligand charge transfer mixing pathways. The L-edge spectrum of [Fe(pfp)(1-MeIm)O(2)] is further compared to those of [Fe(II)(pfp)(1-MeIm)(2)], [Fe(II)(pfp)], and [Fe(III)(tpp)(ImH)(2)]Cl (tpp = meso-tetraphenylporphyrin) which have Fe(II)S = 0, Fe(II)S = 1, and Fe(III)S = 1/2 ground states, respectively. These serve as references for the three possible contributions to the ground state of oxy-pfp. The Fe-O(2) pfp site is experimentally determined to have both significant σ-donation and a strong π-interaction of the O(2) with the iron, with the latter having implications with respect to the spin polarization of the ground state.

Structure of an iron(II) dioxygen complex; a model for oxygen carrying hemeproteins

The preliminary structural characterization of a reversible ferrous dioxygen complex is reported. Mono(N-methyl imidazole) (dioxygen) meso-tetra (alpha,alpha,alpha,alpha-o-pivalamidephenyl) porphinatorino(II), [Fe(O(2))-(N-Me imid) (alpha,alpha,alpha,alpha-TpivPP)], 1, isolated from toluene solution, crystallizes in the monoclinic system with four molecules in a unit cell of dimensions a = 18.690 (3), b = 19.514 (3), c = 18.638 (3) A, and beta = 91.00 (1) degrees . R = 0.15 for 841 reflections having F(2) > 3sigma (F(2)). The complex 1 has four pivalamido groups on one side of the porphyrin forming a hydrophobic pocket of 5.4-A depth which encloses coordinated dioxygen. The dioxygen is coordinated "end-on," with a bent Fe-O-O bond. The Fe-O-O plane bisects an N-Fe-N right angle of the equatorial iron porphyrin plane and is four way statistically disordered. In addition there is a crystallographic 2-fold axis through iron, coordinated oxygen, and nitrogen of the axially bound N-methyl imidazole. Thus there are two types of coordinated dioxygen with the Fe-O-O plane either parallel or perpendicular to the trans axial imidazole plane. Corresponding values for the Fe-O-O bond angles are 135-(4) degrees and 137(4) degrees and for the O-O bond lengths are 1.23 (0.08) and 1.26 (0.08) A, with a dihedral angle of 90 degrees between alternative orientations of the Fe-O-O plane. The Fe-O distance is 1.75 (0.02) A and Fe-N (imidazole) is 2.07 (0.02) A, suggesting multiple bond character in the Fe-O moiety. The similarity of the Mössbauer spectrum of the model complex, 1, with oxyhemoglobin indicates that 1 may be a good model for oxygen binding in the oxygen transport hemeproteins.