Porphyrin Complexes - ACS Publications - American Chemical Society

Article pubs.acs.org/IC

Unique Axial Imidazole Geometries of Fully Halogenated Iron(II) Porphyrin Complexes: Crystal Structures and Mö ssbauer Spectroscopic Studies Bin Hu,† Mingrui He,† Zhen Yao,† Charles E. Schulz,‡ and Jianfeng Li*,† †

College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Yanqi Lake, Huairou District, Beijing 101408, China ‡ Department of Physics, Knox College, Galesburg, Illinois 61401, United States S Supporting Information *

ABSTRACT: The synthesis and characterization of several electronpoor iron(II) porphyrin (FeTFPPBr8) complexes with axial imidazole ligands are reported. The single-crystal X-ray structures have been studied by a combination of crystal packing and Hirshfeld surface calculations, which explained the unusual axial-ligand geometries, e.g., the strong tilt of the Fe−NIm bonds and the imidazole planes. The sixcoordinate [Fe(TFPPBr8)(1-MeIm)2] was studied by multiple-temperature solid-state Mössbauer spectroscopy, which suggested that it is a low-spin complex with δ ∼ 0.32−0.38 mm/s and ΔEQ ∼ 1.0 mm/s.

■

INTRODUCTION Both five- and six-coordinate heme groups are involved in a large variety of biological processes.1 The functions of these complexes are modulated by many factors, which include the nature and geometry of the axial ligands.2 Model complexes have been studied to correlate the geometric structures with their spectroscopic and physical properties. One of the successful examples is the absolute and relative orientations of the axially coordinated planar ligands of ferric porphyrinates.3 For low-spin d6 iron(II) porphyrin complexes, it has been presumed that the axial ligands would align themselves perpendicularly to maximize the π bonding between the π* orbitals of the ligands and the filled dπ orbitals of iron(II). The first structurally characterized iron(II) bis(imidazole)porphyrinate [Fe(TPP)(1-MeIm)2],4,5 however, showed parallel imidazole orientation with a required symmetry of the 2-fold axis and a near-planar porphyrin plane. Subsequently, a number of porphyrin complexes with similar structural features were reported.6 An iron(II) porphyrin complex with mutually perpendicular ligand orientation was eventually reported for [Fe(TMP)(2-MeHIm)2] in 2005.7 The crystal structure showed a very ruffled porphyrin core, and the Mössbauer spectra showed a large ΔEQ of ∼1.7 mm/s.7 These geometric and Mössbauer properties are in sharp contrast to those of [Fe(TPP)(1-MeIm)2] and its analogues, which showed parallel ligand orientation, a near-planar porphyrin plane, and ΔEQ of ∼1.0 mm/s. Although the orientation perpendicular to the porphyrin plane along the heme normal allows better orbital overlap between imidazoles and the iron center,8 it has long been recognized that © XXXX American Chemical Society

the imidazoles always bond to the metal center in a nonidealized fashion.9 The tilt of the imidazole ring could generate strain in the molecule and affect the bonding between the proximal histidine and iron, which consequently influences the reactivity of the distal ligands.10 For deoxy species, an increasing tilt will increase the repulsive forces between the imidazole ligand and heme plane, which weakens the Fe−His bond and lowers the Fe−His stretching frequencies.11 It has been shown that the imidazole tilting is the origin of the increased tetragonal field splitting as well as the tilt of the z axis of the magnetic anisotropy.12 The anisotropic g parameter is reported to increase with a tilt of the imidazole plane and deviation of the dihedral angle between the two imidazole planes.3a,13 It has also been reported that the redox potential of heme can be modulated by histidine conformations.14 Nonbonded intramolecular interactions including hydrogen bonding have been suggested to be the origin of the ligand tilt in proteins;10a in model systems, this has been attributed to crystalpacking effects.15 In many globins, the tilt angles are in the range of 0−10°, while they could be as large as 25°.10a X-ray structural studies showed the tilt angle of the deoxy complexes decreasing from ∼10 to 0° upon binding of the ligands.16 As shown in Scheme 1, the tilt of an imidazole ligand can be described in various ways, which include the tilt of the Fe−NIm vector and the tilt of the imidazole plane, both representing the axial base moving away from the normal to the porphyrin plane. Received: June 6, 2016

A

DOI: 10.1021/acs.inorgchem.6b01364 Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

■

Scheme 1. Description of the ψ, ψ′, θp, and τ Angles of a SixCoordinate [Fe(Porph)(XO)(Im)] Complex (X = O, N, or C)

Article

EXPERIMENTAL SECTION

General Information. All reactions and manipulations were performed under an atmosphere of argon using standard Schlenk techniques unless otherwise noted. All solvents were freeze/pump/ thaw-degassed (three times) prior to use. UV−vis spectra were recorded on a PerkinElmer Lambda-25 spectrometer. Mössbauer measurements were performed on a constant-acceleration spectrometer from 25 to 295 K in zero field using a closed-cycle cryostat (Knox College). Samples for Mössbauer spectroscopy were prepared by immobilization of the crystalline material in Apiezon M grease. Materials. 5,10,15,20-[Tetrakis(pentafluorophenyl)]porphyrin (H2TFPP) was purchased from Frontier Scientific and used as received. The free ligand porphyrin [H2TFPPBr8] and its iron(III) complex [FeIII(TFPPBr8)Cl] were prepared according to published procedures.23 Dichloromethane (Sinopharm Chemical Reagent Co.) was distilled from CaH2 (Greagent); hexanes (Sinopharm Chemical Reagent Co.) were distilled over sodium; ethanethiol (Aladdin), 1methylimidazole (1-MeIm; Acros), and 1-ethylimidazole (1-EtIm; ADMAS) were distilled under an argon atmosphere. 2-Methylimidazole (2-MeHIm; ADMAS) was recrystallized from toluene and dried under vacuum. Synthesis of [Fe(TFPPBr8)(2-MeHIm)]. To a solution of [Fe(TFPPBr8)]Cl (20 mg, 0.012 mmol) in 5 mL of dichloromethane was added via syringe ethanethiol (∼2 mL). The mixture was then stirred under argon at ambient temperature. After 5 h, the reduction was complete (monitored by UV−vis), and the solvent was evaporated under vacuum. Dichloromethane (∼5 mL) was transferred to a Schlenk tube via cannula, and a 2 mL THF solution dissolving 2-MeHIm (3.0 mg, 0.037 mmol) was added via cannula. This mixture was stirred for 4 h to give a clear red solution. Several days later, X-ray-quality crystals were obtained by liquid diffusion using hexanes as the nonsolvent. UV−vis (CH2Cl2): 460, 562, 594 nm. Synthesis of [Fe(TFPPBr8)(1-MeIm)2] (P1̅). [Fe(TFPPBr8)(1MeIm)2] was obtained from a procedure similar to the reported synthesis.24 The black powder [Fe(TFPPBr8)]Cl (50 mg, 0.029 mmol) was dried for 1 h in a Schlenk tube. Dichloromethane (∼10 mL) was transferred into the Schlenk tube via cannula, and 1-MeIm (∼0.3 mL) was added via syringe. This mixture was stirred for 1 h under an argon atmosphere at ambient temperature to give a clear red solution. Several weeks later, X-ray-quality crystals were obtained by liquid diffusion using hexanes as the nonsolvent. UV−vis (CH2Cl2): 360, 458, 563, 593 nm. Synthesis of [Fe(TFPPBr8)(1-MeIm)2] (P21/c). To a solution of [Fe(TFPPBr8)]Cl (20 mg, 0.012 mmol) in 5 mL of dichloromethane was added via syringe ethanethiol (∼2 mL). The mixture was then stirred under argon at ambient temperature. After 5 h, the reduction was

The tilt of the Fe−NIm vector, conventionally denoted as τ, is defined by the Fe−NIm vector with respect to the heme normal and suggests the nonidealized interactions between the sp2 lonepair orbital of the histidine and the iron dz2 orbital.17 Although less attention has been paid to the tilt of the imidazole plane, several different definitions can be found in the literature: (1) the dihedral angle formed between the imidazole and heme planes, which is denoted by θP;8,13 (2) the tilt of the imidazole plane from the Fe−NIm vector, which is denoted by ψ;18 (3) the tilt of the imidazole plane from perpendicular to the plane of the four porphyrin nitrogen atoms, which is denoted by ψ′.15 In this contribution, we adopt the ψ angle reported by Momenteau et al.18 as the definition of the tilt of the imidazole plane. The first fully halogenated porphyrin structure [Ni(TFPPBr8)] was reported at 1992.19 Recently, this extremely electron-poor porphyrin was used in the isolation of a solid powder of the first {FeNO} heme complex [Co(Cp)2][Fe(TFPPBr8)(NO)].20 Subsequently, single crystals of [Co(Cp)2][Fe(TFPPBr 8 )(NO)] and its {FeNO} precursor [Fe(TFPPBr8)(NO)] were isolated, and their structures were determined at 100 K.21 The structural parameters of the two species suggest a low-spin state of the iron(II) centers, which is in agreement with the multiple-temperature solid-state Mössbauer spectroscopic studies.22 Here, we report the synthesis and characterization of several mono- and bis(imidazole) [Fe(TFPPBr8)] derivatives. The complexes have been studied by single-crystal X-ray, UV−vis, and multiple-temperature Mössbauer spectroscopies.

Table 1. Complete Crystallographic Details for [FeTFPPBr8(2-MeHIm)]·CH2Cl2·THF, [FeTFPPBr8(1-MeIm)2] (P1)̅ , [FeTFPPBr8(1-MeIm)2]·CH2Cl2 (P21/c), and [FeTFPPBr8(1-EtIm)2]

chemical formula fw a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 space group Z temp, K Dcalcd, g cm−3 μ, mm−1 final R indices [I > 2σ(I)] final R indices (all data)

[FeTFPPBr8(2-HMeIm)]·CH2Cl2· THF

[FeTFPPBr8(1-MeIm)2]

[FeTFPPBr8(1-MeIm)2]· CH2Cl2

[FeTFPPBr8(1-EtIm)2]

C53H16Br8Cl2F20FeN6 1898.75 12.3325(7) 17.5209(10) 13.3450(7) 90 92.571(1) 90 2880.6(3) P21/m 2 100(2) 2.189 6.016 R1 = 0.0493, wR2 = 0.1080 R1 = 0.0697, wR2 = 0.1169

C52H12Br8F20FeN8 1823.83 14.4655(5) 14.5702(6) 15.1292(8) 115.772(5) 106.420(3) 90.825(3) 2719.4(2) P1̅ 2 150(2) 2.227 6.272 R1 = 0.0401, wR2 = 0.0815 R1 = 0.0647, wR2 = 0.0907

C53H14Br8Cl2F20FeN8 1908.75 10.7966(5) 26.7015(13) 20.2519(12) 90 102.816(2) 90 5692.9(5) P21/c 4 100(2) 2.227 6.088 R1 = 0.0333, wR2 = 0.0720 R1 = 0.0499, wR2 = 0.0782

C54H16Br8F20FeN8 1851.88 14.3704(8) 14.3747(7) 15.2954(8) 78.4159(16) 63.6903(17) 89.2151(16) 2764.4(3) P1̅ 2 100(2) 2.225 6.172 R1 = 0.0467, wR2 = 0.1023 R1 = 0.0660, wR2 = 0.1100

B


Article

Inorganic Chemistry

[Fe(TFPPBr8)(1-EtIm)2]. A dark-purple plate-shaped crystal with dimensions of 0.21 × 0.15 × 0.08 mm3 was used for structure determination. There were two twin domains (56:44) with a rotation of 179.9° around the (0.001, 0.000, 1.000) reciprocal axis, and TWINBAS28 was used for absorption correction. The asymmetric unit contains one independent porphyrin molecule. A total of 11 atoms [N2, C(A1), C(A2), C(A3), C(A5), C(A8), C(B3), C(B6), C(B8), C(M1), and C(M3)] on the porphyrin core and 10 atoms (C1, C4, C20, C22, C27, C29, F3, F8, F13, and F18) on the benzene rings exhibited unusual thermal motions; thus, those atoms were restrained by “ISOR” commands. Two carbon atoms [C(A8) and C(B8)] of the porphyrin core and two other carbon atoms (C28 and C29) on the benzene ring were restrained by SIMU to constrain the ADPs. Hirshfeld Surface Calculations. Hirshfeld surface and fingerprint plots of [FeTFPPBr8(2-MeHIm)], [Fe(TFPPBr8)(1-MeIm)2] (P21/c and P1̅), and [Fe(TFPPBr8)(1-EtIm)2] were generated using Crystal Explorer 3.129 from the crystal structure coordinates supplied as CIF files. Hirshfeld surface analysis is illustrated in the SI.30 The Hirshfeld surface was calculated at an isovalue of 0.5 e au−3.

complete (monitored by UV−vis), and the solvent was evaporated under vacuum. Dichloromethane (∼5 mL) was transferred into a Schlenk tube via cannula, and 1-MeIm (∼0.1 mL) was added via syringe. This mixture was stirred for 1 h under argon to give a clear red solution. Several days later, X-ray-quality crystals were obtained by liquid diffusion using hexanes as the nonsolvent. UV−vis (CH2Cl2): 360, 458, 563, 593 nm. Synthesis of [Fe(TFPPBr8)(1-EtIm)2]. Reaction procedures similar to those above were performed; hexanes were used as the nonsolvent to diffuse into the reaction solution. Several days later, block crystalline products were collected. UV−vis (CH2Cl2): 362, 460, 564, 596 nm. X-ray Structure Determination. A single-crystal experiment of [Fe(TFPPBr8)(1-MeIm)2] (P1̅) was carried out on an Xcalibur, Eos, Gemini system with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å), and single-crystal experiments of [Fe(TFPPBr8)(2MeHIm)], [Fe(TFPPBr8)(1-MeIm)2] (P21/c), and [Fe(TFPPBr8)(1EtIm)2] were carried out on a Bruker D8 QUEST system with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The crystalline samples were placed in inert oil, mounted on a glass fiber attached to a brass mounting pin, and transferred to the cold dinitrogen gas stream of the diffractometer, and crystal data were collected at 100 or 150 K. The structures were solved by direct methods (SHELXS-2014) and refined against F2 using SHELXL-2014.25 Subsequent difference Fourier syntheses led to the location of all remaining non-hydrogen atoms. All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were idealized with the standard SHELX idealization methods if not remarked upon otherwise below. For the structure refinement, all data were used including negative intensities. The program SADABS26 was applied for absorption correction of [Fe(TFPPBr8)(2-MeHIm)], [Fe(TFPPBr8)(1-MeIm)2] (P21/c), and [Fe(TFPPBr8)(1-EtIm)2]. The data set of [Fe(TFPPBr8)(1-MeIm)2] (P1̅) was corrected by empirical absorption correction using spherical harmonics, implemented in the SCALE3 ABSPACK27 scaling algorithm. Complete crystallographic details, atomic coordinates, anisotropic thermal parameters, and fixed hydrogen atom coordinates are given in the Supporting Information (SI); a brief summary of the crystallographic details is given in Table 1. [Fe(TFPPBr8)(2-MeHIm)]·CH2Cl2·THF. A dark-purple block crystal with dimensions of 0.66 × 0.42 × 0.23 mm3 was used for structure determination. The asymmetric unit contained half of a porphyrin molecule, one THF, and one dichloromethane solvent molecule. Dichloromethane was found to be disordered over two positions, and the site occupancy factors (SOFs) of two disordered moieties were refined by means of “free variable”. Two carbon atoms [C(B2) and C10] on the porphyrin molecule and four carbon atoms of the THF solvent (C1S, C2S, C3S, and C4S) exhibited unusual thermal motions; thus, those atoms were restrained by “ISOR” commands. The two solvent molecules were restrained by “similar Uij” (SIMU) to constrain the anisotropic displacement parameters (ADPs). Six hydrogen atoms (H5, H15, H22, H14A, H14B, and H14C) on the axial ligand were located from the Fourier map. [Fe(TFPPBr8)(1-MeIm)2] (P1̅). A dark-purple block-shaped crystal with dimensions of 2.0 × 1.7 × 0.8 mm3 was used for structure determination. The asymmetric unit contained one independent porphyrin molecule; no solvent molecule was found. [Fe(TFPPBr8)(1-MeIm)2]·CH2Cl2 (P21/c). A dark-purple blockshaped crystal with dimensions of 0.68 × 0.41 × 0.25 mm3 was used for structure determination. The asymmetric unit contained one independent porphyrin molecule and one dichloromethane solvent molecule. One of the chlorine atoms was found to be disordered over two positions, and the SOFs of the disordered moieties were refined by means of “free variable”. The final SOFs were found to be 0.92 and 0.08. A total of 11 atoms (C3, C10, C14, C19, C20, C21, C22, C23, C24, F8, and F18) on the benzene ring of the porphyrin and two other atoms (N2 and Cl2B) exhibited unusual thermal motions; thus, those atoms were restrained by “ISOR” commands. Six carbon atoms (C19, C20, C21, C22, C23, and C24), five fluorine atoms (F16, F17, F18, F19, and F20), and two carbon atoms (C14, C15) on the benzene ring of the porphyrin were restrained by SIMU to constrain the ADPs.

■

RESULTS The synthesis, crystal structures, and UV−vis and Mössbauer spectra of several five- and six-coordinate halogenated iron(II) porphyrinates, [Fe(TFPPBr8)(2-MeHIm)], [Fe(TFPPBr8)(1MeIm)2] (P1̅ and P21/c), and [Fe(TFPPBr8)(1-EtIm)2], are reported. The formal diagrams of the porphinato cores of 24atom mean planes are given in Figure S1. Labeled Oak Ridge thermal ellipsoid plot (ORTEP) diagrams are given in Figures 1−4 (edge-on views) and Figures S2−S5 (top-down views). The UV−vis spectra are given in Figures S6−S8. A brief summary of the crystallographic data is given in Table 1, and the complete crystallographic details, atomic coordinates, bond distances, and bond angles of these three structures are given in the SI. Mössbauer spectra were measured for solid-state [Fe(TFPPBr8)(1-MeIm)2] from 25 to 295 K, which are given in Figure 7, and they will be discussed subsequently.

■

DISCUSSION Synthesis. The ferric [Fe(TFPPBr8)]Cl can be reduced to iron(II) products in two different pathways, which are illustrated in Scheme 2. In the first method, the addition of excess base ligand L to a solution of [Fe(TFPPBr8)]Cl induced spontaneous autoreduction, which gives air-stable [Fe(TFPPBr8)(L)2] without isolation of four-coordinate [Fe(TFPPBr8)]. This method was reported by Gray and co-workers in the preparation of [Fe(TFPPBr8)(Py)2].24 In this study, EtSH was used to reduce [Fe(TFPPBr8)]Cl to obtain the iron(II) complex (Scheme 2). The resulting four-coordinate [Fe(TFPPBr8)] was isolated and then reacted with base ligands to yield [Fe(TFPPBr8)(L)2] (or [Fe(TFPPBr8)(L)]) or reacted with a diatomic molecule such as

Figure 1. Thermal ellipsoid diagram of [FeTFPPBr8(2-MeHIm)] displaying a partial atom-labeling scheme. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms have been omitted for clarity. C


Article

Inorganic Chemistry

NO or CO to obtain the five-coordinate [Fe(TFPPBr8)(XO)] complex. Structures. The monoclinic crystal form of five-coordinate [FeTFPPBr8(2-MeHIm)] is found in the centrosymmetric space group P21/m with a required 2-fold symmetry. There is a crystallographic mirror plane that passes through the middle of the molecule, i.e., the plane of Np−Fe−Np, and 2-MeHIm ligand. Accordingly, two noteworthy structural features are seen in the ORTEP diagram (Figures 1 and S2), the strongly saddled porphyrin core and the unique orientation of the 2-MeHIm ligand, which is right along the Fe−Np vector; a ligand orientation has never been seen for a porphyrin complex with a hindered imidazole ligand. Table 2 gives the key parameters of all known five-coordinate [FeII(Porph)(L)] and [FeIII(Porph)(L)]+ structures, where L is a hindered imidazole ligand. Listed in the table is the displacement of iron from the mean plane of the 24-atom ΔFe, the absolute ligand orientation given by the dihedral angle between the axialligand plane and the closest Nax−Fe−Np plane, conventionally denoted by φ. Also given is the tilt angle (τ) of the Fe−NIm vector from normal to the porphyrin plane. All of the complexes, including [FeTFPPBr8(2-MeHIm)], are in the high-spin state, as indicated by the large iron out-of-plane displacements [Δ24 > 0.38 for iron(II) and 0.26 Å for iron(III)]. The four iron(III) porphyrinates show relatively smaller Δ24, which is consistent with the shorter (Fe−NP)av distances. Iron(III) complexes also show smaller φ angles ( ∼10°). Except [Fe(TPP)(1-BzylIm)2], where the axial ligand has a “heavy” terminal benzyl group, the rest of the four structures are derived from the extremely electron-poor, fully halogenated porphyrin H2TFPPBr8 and H2TFPPCl8. The strong electron-withdrawing substituent has a substantial influence on the electron density of the metal center;56 thus, π back-donation from iron dπ orbitals to the ligand π* orbital is reduced dramatically, and the σ bonding, which requires donations of lone-pair electrons from a ligand to the dz2 orbital of the metal center, dominates the Fe−NL bonds. As a result, the bonding geometry of the ligand is “flexible”, is governed to a great extent by the environment of the heme, and varies considerably.57 We pick [FeTFPPBr8(1-MeIm)2] (P21/c) as an example to demonstrate the nonbonded interactions surrounding the axial ligands, which has been seen in the case of [FeTFPPBr8(2MeHIm)2]. A partial packing diagram is given in the top panel of Figure 6. It is seen that the two axial ligands on both sides of the porphyrin plane are subjected to nonbonded interactions from the halide atoms of the neighbor porphyrins as well as solvent molecules. On the first porphyrin side, the distances between the imidazole C atoms and F14 or Br8 of the neighbor porphyrins are 3.156 Å (F···C28) and 3.129 Å (F···C27) or 3.464 Å (Br···C27), shorter than the sum of the van der Waals radii for F···C (3.17 Å) and Br···C (3.55 Å).33 The Br8···C27 (3.464 Å) interaction is also evidenced by the 2D fingerprint plot of Br···C interactions (Figure 6d), which are located at the terminals (red circles, di = 1.8 Å and de = 1.7 Å or di = 1.7 Å and de = 1.8 Å) of the two spikes. In addition, the distance from Br8 to the centroid of the imidazole ring is 3.503 Å, corresponding to a distance typical of Br···π interactions.32 This interaction is demonstrated by the shape index of Figure 6b. The red concave region on the imidazole plane and the blue region around the Br8 atom indicate the acceptor and donor atoms, respectively. Two hydrogen bondings are observed for the imidazole ligand on the opposite porphyrin side (Figure 6). As can be seen, the distances and angles between the methyl carbon atom C30 and Cl1 of the methylene chloride solvent and F11 of the neighboring porphyrin are C30−H30B···Cl1 2.679 Å and 149.40° and C30− H30A···F 2.126 Å and 143.22°. These parameters correspond to the values of C−H···Cl and C−H···F interactions.58 The dnorm surface mapped by using a fixed color scale of −0.400 to +1.613 (Figure 6c) and the 2D fingerprint plot (Figure 6e) provide more evidence. The two red spots on the two hydrogen atoms (H30A and H30B) of C30 and the four tips (red and green circles) of the spikes located at di = 1.2 Å and de = 0.9 Å (or di = 0.9 Å and de = 1.2 Å) for H30A and di = 1.6 Å and de = 1.0 Å (or di = 1.0 Å and de = 1.6 Å) for H30B are consistent with hydrogen-bonding interactions. The partial packing diagrams and Hirshfeld dnorm surface of the other two new structures [Fe(TFPPBr8)(1MeIm)2] (P1̅) and [Fe(TFPPBr8)(1-EtIm)2] are given in Figures S9 and S10, which also suggest similarly strong intermolecular interactions of the halide atoms. Consequently, both structural and Hirshfeld surface analysis based on the crystallographic data suggest that the strong electron-withdrawing halide elements on the porphyrin peripheries have substantial effects on the axial-ligand geometries. The

Figure 5. Wireframe partial packing diagram (a), Hirshfeld dnorm surface (b), shape index (c), and 2D fingerprint plots showing full (d) and simply Br···N (e) interactions of [FeTFPPBr8(2-MeHIm)].

even larger relative ligand orientation (θ = 80.2°) and shorter axial distance (1.989 Å) than the three traditional picket-fence porphyrin derivatives. Accordingly, more perpendicular ligand orientations correspond to shorter axial-ligand distances and stronger π-bonding interactions. A linear relationship was thus established.45 It is worth noting that all the four of the type II complexes are picket-fence porphyrin derivatives, which have one sterically hindered porphyrin side. The remaining 14 structures of Table 3, including the three new structures, are recognized as the type III species. As can be seen, all of the structures have strongly saddled and/or ruffled porphyrin cores, which preclude the possibility of an inversion center and show dramatically large out-of-plane distances of the iron (Δ24). Interestingly, all of the type III complexes have strong electron-withdrawing groups, e.g., F, Br, and −NO2, on the porphyrin peripheries, which suggests that it might be the nature of the porphyrin that tends to give deformed porphyrin cores.19,23b,46 All but one of the type III structures show nearly perpendicular ligand orientation, in analogy with the type II species. Therefore, it could be generally noted that unless a type I structure can be crystallized, which requires a symmetric porphyrin ligand, a [Fe(Porph)(L′)2] complex prefers to align axial ligands perpendicular to each other, in order to maximize the interactions between iron(II) dπ and the ligand pπ* orbitals, no matter the planar (type II) or distorted (type III) porphyrin conformations. Three new structures show additional unique features. As presented in the ORTEP drawings of Figure 2−4, the axial imidazole ligands tilt dramatically from the heme normal, which is very unusual for a [Fe(Porph)(L′)2] complex. We use two structural parameters to demonstrate these geometric features: F


Article

Inorganic Chemistry Table 3. Key Structural Parameters for [FeII(Porph)(L′)2] (L′ = Nonhindered Planar Nitrogen-Donor Ligands)a complex

Fe S.S.b

core confc

Δ24d,e

[Fe(TPP)(1-VinylIm)2] [Fe(TPP)(1-BzylIm)2] [Fe(TPP)(1-MeIm)2] [Fe(TPP)(Py)2]Py [Fe(TPP)(Py)2] [Fe(TMP)(4-CNPy)2] [Fe(TMP)(3-CNPy)2] [Fe(TMP)(4-MePy)2] [Fe(TMP)(1-MeIm)2] [Fe (OEPOH)(Py)2](1) [Fe (OEPOH)(Py)2](2) [Fe(F8TPP)(DCIm)2]

Ci Ci Ci Ci Ci Ci Ci Ci Ci Ci Ci Ci

near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla near-Pla

3 4 4 4 6 1 2 3 4 2 3 3

[Fe(TpivPP)(1-MeIm)2]

C1

near-Pla

8

[Fe(TpivPP)(1-EtIm)2]

C1

near-Pla

4

[Fe(TpivPP)(1-VinylIm)2]

C1

near-Pla

11

[Fe(MbenTpivPP)(1-MeIm)2]

C1

near-Pla

8

[FeTFPPBr8(1-MeIm)2] (P1̅)

C1

Sad

45

[FeTFPPBr8(1-MeIm)2] (P21/c)

C1

Sad

52

[FeTFPPBr8(1-EtIm)2]

C1

Sad

46

[FeTFPPBr8(Py)2]

C1

Sad

50

[FeTPPBr4(Py)2]

C2

Sad

37

[FeTFPPCl8(1-MeIm)2]

C1

Sad

48

[Fe(OEPy4P)(Py)2]4+

C1

Sad

61

[Fe(tn-OEP)(1-MeIm)2]

C1

Sad

46

[Fe(tn-OEP)(1-MeIm)2] ·THF

C1

Sad

44

[Fe(tn-OEP)(Py)2] (1)

C1

Sad

43

[Fe(tn-OEP)(Py)2] (2)

C1

Sad

49

[Fe(tn-OEP)(3-ClPy)2]

C1

Sad

47

[Fe(tn-OEP)(4-CNPy)2]

C1

Sad

47

[Fe((C3F7)P(Py)2)]

C1

Ruf

30

(Fe−NP)ave,f

Fe−NIme

Type I 2.001(2) 2.004(2) 1.993(9) 2.017(4) 1.998(3) 1.997(12) 1.993(6) 2.039(1) 2.001(2) 2.037(1) 1.993(2) 1.996(2) 1.996(2) 2.026(2) 1.988(2) 2.010(2) 1.990(2) 1.992(2) 1.995(3) 2.017(4) 1.997(6) 2.004(4) 1.9905(6) 2.002(3) Type II 1.992(3) 1.9958(19) 1.9921(18) 1.993(6) 2.0244(18) 1.9940(19) 1.988(5) 1.9979(19) 1.9866(18) 1.994(9) 1.991(3) 1.986(3) Type III 1.986(10) 1.990(5) 1.987(5) 1.974(18) 1.986(3) 2.012(3) 1.994(10) 1.993(5) 1.994(6) 1.963(4) 2.007(7) 2.016(7) 1.976(2) 2.000(3) 2.040(3) 1.981(5) 1.999(5) 1.997(5) 1.953(3) 2.027(3) 2.028(3) 1.982(2) 2.000(3) 2.007(2) 1.985(3) 1.999(3) 2.002(3) 1.961(3) 1.991(3) 2.014(3) 1.961(3) 1.999(3) 2.017(3) 1.962(2) 1.989(2) 2.009(2) 1.986(2) 2.014(2) 2.015(2) 1.958(4) 2.007(6) 1.996(6)

(Fe−NIm)ave,f

ψg,h

τg,i

φg,j

θg,k

ref

2.004 2.017 1.997 2.039 2.037 1.996 2.026 2.010 1.992 2.017 2.004 2.002

6.4 10.8 1.4 1.7 8.1 3.7 1.4 3.1 4.9 0.1 0.1 1.0

6.0 6.8 2.6 1.8 7.2 2.6 1.8 3.6 5.7 2.6 2.6 3.6

14 26 27.4 34.4 45 40 42 41 40.3 40.4 43.3 14.1

0i 0i 0i 0i 0i 0i 0i 0i 0i 0i 0i 0i

6c 6c 47 48 49 6b 6b 6b 6a 50 50 51

1.9940

1.6 2.0 0.4 7.8 4.8 8.0 0.6 1.4

1.6 2.6 1.1 2.6 2.5 3.9 1.8 0

8.5 21.1 6.6 20.7 11.2 24.6 36.5 26.9

77.2

44

62.4

44

78.5

44

80.2

45

9.7 0.48 8.4 15.8 12.1 16.7 1.2 0.5 0 0 10.1 1.0 0.7 7.6 4.7 2.7 3.7 0.46 0.7 4.2 5.2 4.4 2.6 1.1 4.6 0.4 4.3 1.0

4.8 3.4 7.1 5.9 4.9 5.7 0 1.8 0 0 3.6 1.8 2.5 2.5 0 0 0 0 0 1.8 0 1.8 0 0 2.6 1.8 0 0

38.5 24.5 23.0 15.9 20.6 20.2 1.5 22.2 36.8 33.7 20.9 14.8 11.2 13.3 32.2 23.8 30.0 30.3 38.2 44.2 35.1 36.6 47.2 42.4 42.2 36.2 41.3 46.0

74.0

this work

74.5

this work

74.0

this work

68.3

24

19.2

52

80.7

46a

87.5

53

80.9

54

89.8

54

84.5

46b

87.9

46b

85.5

46b

84.3

46b

87.5

55

2.0092 1.9923 1.989

1.989 1.999 1.994 2.012 2.020 1.998 2.028 2.004 2.001 2.003 2.008 1.999 2.015 2.002

a

Estimated standard deviations are given in parentheses. bSite symmetry of iron. cRuffling (Ruf) or saddling (Sad) deformation; near-Pla indicates an almost planar porphyrin plane. dAveraged displacement of 24 atoms out of the mean plane. eValue in angstroms. fAveraged value. gValue in degrees. h The tilt of the Fe−NIm vector from the plane of the imidazole ligand. iThe tilt of the Fe−NIm vector from normal to the 24-atom mean plane. j Dihedral angle between the plane of the closest Np−Fe−Nax and the ligand plane. kDihedral angle between two axial ligands.

electron-withdrawing substituents have not only induced the σ dominated axial bonds, which facilitate axial-ligand distortion, but also brought forth various intermolecular contacts through nonbonding interactions with the axial ligands. The large size of

the bromine atoms and their roles in creating the saddled porphyrin conformations are also important. Mössbauer Spectra. Temperature-dependent Mössbauer measurements have been done on the crystalline sample of G


Article

Inorganic Chemistry

Figure 7. Mössbauer spectra in the 500 mT field of [FeTFPPBr8(1MeIm)2] at 25, 100, 200, and 295 K. Figure 6. Wireframe partial packing diagram (a), shape index (b), Hirshfeld dnorm surface (c), and 2D fingerprint plot showing Br···C interactions merely (d) and full (e) of [FeTFPPBr8(1-MeIm)2] (P21/c).

ruffling, the decreased Fe−Npor bond distance again yields stronger covalent interactions.59 The large quadrupole splitting is not a necessary result of the short Fe−Npor bond distances. Recently, in the study of picket-fence porphyrin derivatives [Fe(TpivPP)(R-Im)2] (R-Im = 1-MeIm, 1-EtIm, and 1-VinylIm), which show relatively perpendicular ligand arrangements, we claimed that the common structural feature for a complex showing large quadrupole-splitting values is a ruffled porphyrin core and not (absolute and relative) ligand orientations.44 As the first six-coordinate saddled porphyrin complex that was characterized by the Mössbauer spectroscopy, [FeTFPPBr8(1MeIm)2] provides a new example for the species in Table 4. It is seen that the observed isomer shifts (0.32−0.38 mm s−1) show slight temperature dependence and the quadrupole splittings are in a very narrow range of 1.11−1.12 mm s−1, both of which are consistent with the first set of species with near-planar porphyrin planes. Accordingly, it is tentatively concluded that, among the structural features of the planar and/or deformed porphyrin core and the absolute and/or relative axial-ligand orientations, the ruffled core conformation appears to be the only key feature that is known to induce a large quadrupole splitting (>1.5 mm s−1).

[FeTFPPBr8(1-MeIm)2]. Mössbauer data observed for the current complex and the related six-coordinate low-spin species are given in Table 4. Two different systems are recognized in the examination of the quadrupole-splitting values. The first set of species have quadrupole-splitting values in the range of 1.0−1.2 mm s−1, with the imidazole analogues showing smaller values than those of the pyridine. The second set of species, with a bulky 2-substituent on the imidazole ligand, shows quadrupole splitting greater than ∼1.60 mm s−1. On the basis of the structure and Mössbauer study of [Fe(TMP)(2-MeHIm)2],7 where two independent molecules had two axial ligands in a relatively perpendicular orientation, Scheidt and co-workers suggested that for the low-spin iron(II) [Fe(Porph)(L)2] system the quadrupole splitting was sensitive to the relative axial-ligand orientation and larger values of the quadrupole splitting (>1.5 mm s−1) result from the presence of relatively perpendicular ligand orientations, whereas smaller values ( 1.5 mm s−1).

■

Formal diagrams of the porphyrin cores (Figure S1), figures with ORTEP diagrams (Figures S2−S5), UV−vis spectra (Figures S6−S8), wireframe partial packing diagrams and Hirshfeld surfaces of [FeTFPPBr8(1MeIm)2] (P1̅) and [FeTFPPBr8(1-EtIm)2] (Figures S9 and S10), and Hirshfeld surface analysis (PDF) Crystallographic data in CIF format (CIF) Crystallographic data in CIF format (CIF) Crystallographic data in CIF format (CIF) Crystallographic data in CIF format (CIF)

■

ASSOCIATED CONTENT

AUTHOR INFORMATION

Corresponding Author

S Supporting Information *

*E-mail: jfl[email protected].

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01364.

Notes

The authors declare no competing financial interest. I


Article

Inorganic Chemistry

■

(tetraphenylporphyrinato)Iron(II) Complexes. Inorg. Chem. 1990, 29, 626−633. (7) Hu, C.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Ligand Orientation Control in Low-Spin Six-Coordinate (Porphinato)iron(II) Species. Inorg. Chem. 2005, 44, 4346−4358. (8) Merlino, A.; Howes, B. D.; Prisco, G. d.; Verde, C.; Smulevich, G.; Mazzarella, L.; Vergara, A. Occurrence and Formation of Endogenous Histidine Hexa-Coordination in Cold-Adapted Hemoglobins. IUBMB Life 2011, 63, 295−303. (9) Freeman, H. C. Crystal Structures of Metal−Peptide Complexes. In Advances in Protein Chemistry; Anfinsen, C. B., Edsall, J. T., Anson, M. L., Richards, F.M., Eds.; Academic Press: New York, 1967; Vol. 22, pp 305−308. (10) (a) Mukai, M.; Mills, C. E.; Poole, R. K.; Yeh, S.-R. Flavohemoglobin, a Globin with a Peroxidase-like Catalytic Site. J. Biol. Chem. 2001, 276, 7272−7277. (b) Menyhárd, D. K. Stereoelectronic Control on the Coordination of Substrates to Globin Proteins. The Role of Proximal His93 on the NO Release from Myoglobin. J. Am. Chem. Soc. 1998, 120, 7991−7992. (11) (a) Friedman, J. M.; Scott, T. W.; Stepnoski, R. A.; Ikeda-Saito, M.; Yonetani, T. The Iron-Proximal Histidine Linkage and Protein Control of Oxygen Binding in Hemoglobin. A Transient Raman Study. J. Biol. Chem. 1983, 258, 10564−10572. (b) Sassaroli, M.; Dasgupta, S.; Rousseau, D. L. Cryogenic Stabilization of Myoglobin Photoproducts. J. Biol. Chem. 1986, 261, 13704−13713. (12) Sarma, S.; DiGate, R. J.; Goodin, D. B.; Miller, C. J.; Guiles, R. D. Effect of Axial Ligand Plane Reorientation on Electronic and Electrochemical Properties Observed in the A67V Mutant of Rat Cytochrome b5. Biochemistry 1997, 36, 5658−5668. (13) Vergara, A.; Franzese, M.; Merlino, A.; Vitagliano, L.; Verde, C.; di Prisco, G.; Caroline Lee, H.; Peisach, J.; Mazzarella, L. Structural Characterization of Ferric Hemoglobins from Three Antarctic Fish Species of the Suborder Notothenioidei. Biophys. J. 2007, 93, 2822− 2829. (14) Iverson, T. M.; Arciero, D. M.; Hsu, B. T.; Logan, M. S. P.; Hooper, A. B.; Rees, D. C. Heme Packing Motifs Revealed by the Crystal Structure of the Tetra-Heme Cytochrome c554 from Nitrosomonas Europaea. Nat. Struct. Biol. 1998, 5, 1005−1012. (15) Jameson, G. B. Dioxygen Carriers. In Biological inorganic chemistry; structure and reactivity; Bertini, I. E. A., Ed.; University Science Books: Sausalito, CA, 2007; pp 354−385. (16) (a) Takano, T. Structure of Myoglobin Refined at 2.0 Å Resolution. J. Mol. Biol. 1977, 110, 569−584. (b) Phillips, S. E. V. Structure and Refinement of Oxymyoglobin at 1.6 Å resolution. J. Mol. Biol. 1980, 142, 531−554. (c) Baldwin, J.; Chothia, C. Haemoglobin: The Structural Changes Related to Ligand Binding and its Allosteric Mechanism. J. Mol. Biol. 1979, 129, 175−220. (17) Bangcharoenpaurpong, O.; Schomacker, K. T.; Champion, P. M. Resonance Raman Investigation of Myoglobin and Hemoglobin. J. Am. Chem. Soc. 1984, 106, 5688−5698. (18) Momenteau, M.; Scheidt, W. R.; Eigenbrot, C. W.; Reed, C. A. A deoxymyoglobin model with a sterically unindered axial imidazole. J. Am. Chem. Soc. 1988, 110, 1207. (19) Mandon, D.; Ochenbein, P.; Fischer, J.; Weiss, R.; Jayaraj, K.; Austin, R. N.; Gold, A.; White, P. S.; Brigaud, O. β-Halogenated-pyrrole porphyrins. Molecular structures of 2,3,7,8,12,13,17,18-octabromo5,10,15,20-tetramesitylporphyrin, nickel(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetramesitylporphyrin, and nickel(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl)porphyrin. Inorg. Chem. 1992, 31, 2044−2049. (20) Pellegrino, J.; Bari, S. E.; Bikiel, D. E.; Doctorovich, F. Successful Stabilization of the Elusive Species {FeNO}8 in a Heme Model. J. Am. Chem. Soc. 2010, 132, 989−995. (21) Hu, B.; Li, J. One Electron Makes Differences: From Heme {FeNO}7 to {FeNO}8. Angew. Chem., Int. Ed. 2015, 54, 10579−10582. (22) Hu, B.; Li, J.; et al. Mössbauer Studies on a {FeNO}8 Porphyrin Complex. Unpublished work. (23) (a) Adler, A. D.; Longo, F. R.; Kampas, F.; Kim, J. On the Preparation of Metalloporphyrins. J. Inorg. Nucl. Chem. 1970, 32, 2443−

ACKNOWLEDGMENTS We thank the CAS Hundred Talent Program and National Natural Science Foundation of China (Grant 21371167 to J.L.).

■

REFERENCES

(1) (a) Antonini, E.; Brunori, M. Hemoglobin and Myoglobin in their Reactions with Ligands; North-Holland: Dordrecht, The Netherlands, 1971; Vol. 21. (b) Ghosh, A. The Smallest Biomolecules: Diatomics and their Interactions with Heme Proteins; Elsevier: Amsterdam, The Netherlands, 2008; p 603. (2) (a) Fufezan, C.; Zhang, J.; Gunner, M. R. Ligand Preference and Orientation in b- and c-type Heme-Binding Proteins. Proteins: Struct., Funct., Genet. 2008, 73, 690−704. (b) Zoppellaro, G.; Bren, K. L.; Ensign, A. A.; Harbitz, E.; Kaur, R.; Hersleth, H.-P.; Ryde, U.; Hederstedt, L.; Andersson, K. K. Review: Studies of Ferric Heme Proteins with Highly Anisotropic/Highly Axial Low Spin (S = 1/2) Electron Paramagnetic Resonance Signals with Bis-Histidine and Histidine-Methionine Axial Iron Coordination. Biopolymers 2009, 91, 1064−1082. (3) (a) Walker, F. A. Models of the Bis-Histidine-Ligated ElectronTransferring Cytochromes. Comparative Geometric and Electronic Structure of Low-Spin Ferro- and Ferrihemes. Chem. Rev. 2004, 104, 589−616. (b) Scheidt, W. R.; Reed, C. A. Spin-State Stereochemical Relationships in Iron Porohyrins - Implications for the Hemoproteins. Chem. Rev. 1981, 81, 543−555. (4) (a) Scheidt, W. R.; Kirner, J. F.; Hoard, J. L.; Reed, C. A. Unusal Orientation of Axail Ligands in Metalloporphyrins - MolecularStructure of Low-Spin Bis(2-Methyl-imidazole) (MesoTetraphenylporphyrinato)Iron(III) Perchlorate. J. Am. Chem. Soc. 1987, 109, 1963−1968. (b) Steffen, W. L.; Chun, H. K.; Hoard, J. L.; Reed, C. A. Stereochemistry of Bis(1-Methylimidazole)Iron(II) and Bis(1-Methylimidazole)-Mananese(III) Derivatives of 5,10,15,20-Tetraphenylporphyrin, Fe(TPP)(1-MeIm)2 and Mn(TPP)(1-MeIm)2+. Abstr. Pap. Am. Chem. Soc. 1978, 175, 15−15. (5) Abbreviations. Porphyrins: Porph, a generalized porphyrin dianion; TFPPBr 8 , dianion of 2,3,7,8,12,13,17,18-octabromo5,10,15,20-tetrakis(pentafluorophenyl)porphyrin; TFPP, dianion of meso-tetrakis(2,6-difluorophenyl)porphyrin; OEP, dianion of octaethylporphyrin; TTP, dianion of meso-tetratolylporphyrin; MbenTpivPP, dianion of meso-mono[α-o-(benzenecarboxamido)phenyl]tris(α,α,α-opivalamidophenyl)porphyrin; TpivPP, dianion of α,α,α,α-tetrakis(opivalamidophenyl)porphyrin; TPP, dianion of meso-tetraphenylporphyrin; TMP, dianion of meso-tetramesitylporphyrin; ((C3F7)4)P, dianion of 5,10,15,20-tetrakis(heptafluoropropyl)porphyrin; TPPBr4, dianion of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin; tnOEP, dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetranitroporphyrin; TFPPCl8, dianion of 2,3,7,8,12,13,17,18-octachloro-5,10,15,20tetrakis(pentafluorophenyl)porphyrin; OEPOH, dianion of octaethylmeso-hydroxyporphyrin. Axial ligands: HIm, imidazole; 1-MeIm, 1methylimidazole; 2-MeHIm, 2-methylimidazole; 4-MeHIm, 4-methylimidazole; 1,2-Me2Im, 1,2-dimethylimidazole; 1-AcIm, 1-acetylimidazole; 1-SiMe3Im, 1-(trimethylsilyl)imidazole; 1-VinylIm, 1-vinylimidazole; 1-BzylIm, 1-benzylimidazole; DCIm, 1,5-dicyclohexyl; Im, generalized imidazole; Py, pyridine; 3-ClPy, 3-chloropyridine; 4CNPy, 4-cyanopyridine; 3-CNPy, 3-cyanopyridine; 4-MePy, 4-methylpyridine; 4-NMe2Py, 4-(dimethylamino)pyridine; Pyz, pyrazine. Other: THF, tetrahydrofuran; Np, porphyrinato nitrogen; Nax, nitrogen of axial ligands; EPR, electron paramagnetic resonance; UV−vis, ultraviolet− visible. (6) (a) Meininger, D. J.; Caranto, J. D.; Arman, H. D.; Tonzetich, Z. J. Studies of Iron(III) Porphyrinates Containing Silanethiolate Ligands. Inorg. Chem. 2013, 52, 12468−12476. (b) Safo, M. K.; Nesset, M. J. M.; Walker, F. A.; Debrunner, P. G.; Scheidt, W. R. Models of the Cytochromes. Axial Ligand Orientation and Complex Stability in Iron(II) Porphyrinates: The Case of the Noninteracting dπ Orbitals. J. Am. Chem. Soc. 1997, 119, 9438−9448. (c) Safo, M. K.; Scheidt, W. R.; Gupta, G. P. Axial Ligand Orientation in Iron(II) Porphyrinates. Preparation and Characterization of Low-spin Bis(imidazole)J


Article

Inorganic Chemistry 2445. (b) Birnbaum, E. R.; Hodge, J. A.; Grinstaff, M. W.; Schaefer, W. P.; Henling, L.; Labinger, J. A.; Bercaw, J. E.; Gray, H. B. 19F NMR Spectra and Structures of Halogenated Porphyrins. Inorg. Chem. 1995, 34, 3625−3632. (24) Grinstaff, M. W.; Hill, M. G.; Birnbaum, E. R.; Schaefer, W. P.; Labinger, J. A.; Gray, H. B. Structures, Electronic Properties, and Oxidation-Reduction Reactivity of Halogenated Iron Porphyrins. Inorg. Chem. 1995, 34, 4896−4902. (25) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (b) R1 = ∑||Fo| − |Fc||/∑|Fo| and wR2 = {∑[w(Fo2 − Fc2)2]/∑[wFo4]}1/2. The conventional R factors R1 are based on F, with F set to zero for negative F2. The criterion of F2 > 2σ(F2) was used only for calculating R1. R factors based on F2(wR2) are statistically about twice as large as those based on F, and R factors based on all data will be even larger.. (26) M, S. G. Program for Empirical Absorption Correction of Area Detector Data; Universität Göttingen: Göttingen, Germany, 1996. (27) CrysAlispro; Oxford Diffraction Ltd.: Oxfordshire, U.K., 2010. (28) M, S. G. Twinabs. Universität Göttingen: Göttingen, Germany, 2005. (29) Wolff, S.; Grimwood, D.; McKinnon, J.; Turner, M.; Jayatilaka, D.; Spackman, M. CrystalExplorer, version 3.1; University of Western Australia: Crawley, Australia, 2012. (30) (a) Spackman, M. A.; Jayatilaka, D. Hirshfeld surface analysis. CrystEngComm 2009, 11, 19−32. (b) Spackman, M. A.; McKinnon, J. J. Fingerprinting Intermolecular Interactions in Molecular Crystals. CrystEngComm 2002, 4, 378−392. (c) McKinnon, J. J.; Jayatilaka, D.; Spackman, M. A. Towards Quantitative Analysis of Intermolecular Interactions with Hirshfeld Surfaces. Chem. Commun. 2007, 3814− 3816. (31) Hu, C.; Roth, A.; Ellison, M. K.; An, J.; Ellis, C. M.; Schulz, C. E.; Scheidt, W. R. Electronic Configuration Assignment and the Importance of Low-Lying Excited States in High-Spin ImidazoleLigated Iron(II) Porphyrinates. J. Am. Chem. Soc. 2005, 127, 5675− 5688. (32) (a) Schollmeyer, D.; Shishkin, O. V.; Ruhl, T.; Vysotsky, M. O. OH-π and halogen-π Interactions as Driving Forces in the Crystal Organisations of Tri-bromo and Tri-iodo Trityl Alcohols. CrystEngComm 2008, 10, 715−723. (b) Paton, A. S.; Lough, A. J.; Bender, T. P. A Role for π-Br Interactions in the Solid-state Molecular Packing of Parahalo-phenoxy-boronsubphthalocyanines. CrystEngComm 2011, 13, 3653−3656. (33) Bondi, A. van der Waals Volumes and Radii. J. Phys. Chem. 1964, 68, 441−451. (34) Pimentel, G. C.; Sederholm, C. H. Correlation of Infrared Stretching Frequencies and Hydrogen Bond Distances in Crystals. J. Chem. Phys. 1956, 24, 639−641. (35) (a) Hirshfeld, F. L. Bonded-atom Fragments for Describing Molecular Charge Densities. Theor. Chim. Acta 1977, 44, 129−138. (b) Wang, R.; Dols, T. S.; Lehmann, C. W.; Englert, U. The Halogen Bond Made Visible: Experimental Charge Density of a very short Intermolecular Cl···Cl donor-acceptor contact. Chem. Commun. 2012, 48, 6830−6832. (36) Hu, C.; Noll, B. C.; Piccoli, P. M. B.; Schultz, A. J.; Schulz, C. E.; Scheidt, W. R. Hydrogen Bonding Effects on the Electronic Configuration of Five-Coordinate High-Spin Iron(II) Porphyrinates. J. Am. Chem. Soc. 2008, 130, 3127−3136. (37) Ellison, M. K.; Schulz, C. E.; Scheidt, W. R. Structure of the Deoxymyoglobin Model Fe(TPP)(2-MeHIm) Reveals Unusual Porphyrin Core Distortions. Inorg. Chem. 2002, 41, 2173−2181. (38) Hu, C.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Hydrogen Bonding Influence of 1,10-Phenanthroline on Five-Coordinate HighSpin Imidazole-Ligated Iron(II) Porphyrinates. Inorg. Chem. 2008, 47, 8884−8895. (39) Hu, C.; An, J.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Electronic Configuration of High-Spin Imidazole-Ligated Iron(II) Octaethylporphyrinates. Inorg. Chem. 2006, 45, 4177−4185. (40) Guilard, R.; Perrot, I.; Tabard, A.; Richard, P.; Lecomte, C.; Liu, Y. H.; Kadish, K. M. Metalloprophyrins Containing σ-bonded Nitrogen

Axial Ligands. 2. Synthesis and Characterization of Iron(III) Tetrazolato and Triazolato Porphyrin Complexes. Molecular Structure of (5Methyltetrazolato)(2,3,7,8,12,13,17,18-octaethylporphinato)iron(III). Inorg. Chem. 1991, 30, 27−37. (41) Li, J.; Noll, B. C.; Oliver, A. G.; Schulz, C. E.; Scheidt, W. R. Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: Structural and Mössbauer Investigations. J. Am. Chem. Soc. 2013, 135, 15627−15641. (42) Scheidt, W. R.; Geiger, D. K.; Lee, Y. J.; Reed, C. A.; Lang, G. Characterization of five-Coordinate Mono(imidazole) (porphinato)Iron(II) Complexes. J. Am. Chem. Soc. 1985, 107, 5693−5699. (43) Ikezaki, A.; Takahashi, M.; Nakamura, M. Models for Cytochromesć: Observation of an Extremely Labile Spin State in Monoimidazole Complexes of Saddle-Shaped Iron(III) Porphyrinates. Angew. Chem., Int. Ed. 2009, 48, 6300−6303. (44) Li, J.; Nair, S. M.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different? Inorg. Chem. 2008, 47, 3841− 3850. (45) He, B.; Schulz, C. E.; Li, J. Synthesis and Characterization of a Modified ″picket fence″ Porphyrin Complex - Stronger π Bonding Interactions Between Fe(II) and Axial Ligands. Dalton Trans. 2015, 44, 13651−13661. (46) (a) Patra, R.; Sahoo, D.; Dey, S.; Sil, D.; Rath, S. P. Switching Orientation of Two Axial Imidazole Ligands between Parallel and Perpendicular in Low-Spin Fe(III) and Fe(II) Nonplanar Porphyrinates. Inorg. Chem. 2012, 51, 11294−11305. (b) Patra, R.; Bhowmik, S.; Ghosh, S. K.; Rath, S. P. Effects of axial pyridine coordination on a saddle-distorted porphyrin macrocycle: stabilization of hexa-coordinated high-spin Fe(iii) and air-stable low-spin iron(ii) porphyrinates. Dalton Trans. 2010, 39, 5795−5806. (47) Guan, Y.; Powell, D. R.; Richter-Addo, G. B. Crystal Structure of Bis(1-methyl-1H-imidazole-κN3)(5,10,15,20-tetraphenylporphyrinatoκ4N)iron(II)-1-methyl-1H-imidazole (1/2). Acta Crystallogr., Sect. E 2015, 71, m57−m58. (48) Li, N.; Petricek, V.; Coppens, P.; Landrum, J. Structure of Bis(pyridine)(5,10,15,20-tetraphenylporphyrinato)Iron(II)-pyridine Solvate, [Fe(C44H28N4)(C5H5N)2].2C5H5N. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1985, 41, 902−905. (49) Li, N.; Coppens, P.; Landrum, J. Electron Density Studies of Porphyrins and Phthalocyanines. 7. Electronic Ground State of Bis(pyridine) (meso-tetraphenylporphinato)Iron(II). Inorg. Chem. 1988, 27, 482−488. (50) Rath, S. P.; Olmstead, M. M.; Balch, A. L. Reactions of mesoHydroxyhemes with Carbon Monoxide and Reducing Agents in Search of the Elusive Species Responsible for the g = 2.006 Resonance of Carbon Monoxide-Treated Heme Oxygenase. Isolation of Diamagnetic Iron(II) Complexes of Octaethyl-meso-hydroxyporphyrin. Inorg. Chem. 2004, 43, 6357−6365. (51) Lucas, H. R.; Meyer, G. J.; Karlin, K. D. Carbon Monoxide and Nitrogen Monoxide Ligand Dynamics in Synthetic Heme and Heme− Copper Complex Systems. J. Am. Chem. Soc. 2009, 131, 13924−13925. (52) Scheidt, W. R.; Noll, B. C. Dipyridine(2,3,12,13-tetrabromo5,10,15,20-tetraphenylporphyrin)Iron(II) Pyridine Solvate. Acta Crystallogr., Sect. E: Struct. Rep. Online 2006, 62, m1892−m1894. (53) Renner, M. W.; Bochot, C.; Héroux, A.; Mansuy, D.; Battioni, P. Structural, Electrochemical, and Spectroscopic Properties of a Class of Dodecasubstituted Iron Porphyrins Bearing Four Positive Charges Close to the Metal. Eur. J. Inorg. Chem. 2007, 2007, 2426−2433. (54) Patra, R.; Chaudhary, A.; Ghosh, S. K.; Rath, S. P. Axial Ligand Orientations in a Distorted Porphyrin Macrocycle: Synthesis, Structure, and Properties of Low-Spin Bis(imidazole)iron(III) and Iron(II) Porphyrinates. Inorg. Chem. 2010, 49, 2057−2067. (55) Moore, K. T.; Fletcher, J. T.; Therien, M. J. Syntheses, NMR and EPR Spectroscopy, Electrochemical Properties, and Structural Studies of [5,10,15,20-Tetrakis(perfluoroalkyl)porphinato]iron(II) and -Iron(III) Complexes. J. Am. Chem. Soc. 1999, 121, 5196−5209. (56) (a) Yoshimura, T.; Toi, H.; Inaba, S.; Ogoshi, H. Iron(III) Porphyrins Substituted with Highly Electron-withdrawing TrifluorK


Article

Inorganic Chemistry omethyl Groups: Electronic Absorption, MCD, and EPR spectral study. Inorg. Chem. 1991, 30, 4315−4321. (b) Bhyrappa, P.; Krishnan, V. Octabromotetraphenylporphyrin and its Metal Derivatives: Electronic Structure and Electrochemical Properties. Inorg. Chem. 1991, 30, 239− 245. (c) Giraudeau, A.; Callot, H. J.; Jordan, J.; Ezhar, I.; Gross, M. Substituent effects in the electroreduction of porphyrins and metalloporphyrins. J. Am. Chem. Soc. 1979, 101, 3857−3862. (57) (a) Das, T. K.; Couture, M.; Guertin, M.; Rousseau, D. L. Distal Interactions in the Cyanide Complex of Ferric Chlamydomonas Hemoglobin. J. Phys. Chem. B 2000, 104, 10750−10756. (b) Lou, B.S.; Snyder, J. K.; Marshall, P.; Wang, J.-S.; Wu, G.; Kulmacz, R. J.; Tsai, A.-L.; Wang, J. Resonance Raman Studies Indicate a Unique Heme Active Site in Prostaglandin H Synthase. Biochemistry 2000, 39, 12424− 12434. (58) (a) Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga, D. Crystal Forms of Hexafluorophosphate Organometallic Salts and the Importance of Charge-Assisted C−H···F Hydrogen Bonds. Organometallics 1998, 17, 296−307. (b) Taylor, R.; Kennard, O. Crystallographic Evidence for the Existence of C−H···O, C−H···N and C−H··· Cl Hydrogen Bonds. J. Am. Chem. Soc. 1982, 104, 5063−5070. (59) Grodzicki, M.; Flint, H.; Winkler, H.; Walker, F. A.; Trautwein, A. X. Electronic Structure, Porphyrin Core Distortion, and Fluxional Behavior of Bis-Ligated Low-Spin Iron(II) Porphyrinates. J. Phys. Chem. A 1997, 101, 4202−4207. (60) Kobayashi, H.; Maeda, Y.; Yanagawa, Y. Mössbauer Spectra of Iron Tetraphenylporphyrins. Bull. Chem. Soc. Jpn. 1970, 43, 2342−2346. (61) Polam, J. R.; Wright, J. L.; Christensen, K. A.; Walker, F. A.; Flint, H.; Winkler, H.; Grodzicki, M.; Trautwein, A. X. Valence Electron Cloud Asymmetry from Two Points of View: A Correlation between Mössbauer Quadrupole Splittings and 57Fe NMR Chemical Shifts of Diamagnetic Iron(II) Porphyrinates. J. Am. Chem. Soc. 1996, 118, 5272−5276. (62) Dolphin, D.; Sams, J. R.; Tsin, T. B.; Wong, K. L. Synthesis and Mössbauer Spectra of Octaethylporphyrin Ferrous Complexes. J. Am. Chem. Soc. 1976, 98, 6970−6975.

L


Porphyrin Complexes - ACS Publications - American Chemical Society

Recommend Documents