Iron(II) Bis(imidazole) Derivatives of a Binuclear Porphyrin Model

Article pubs.acs.org/IC

Iron(II) Bis(imidazole) Derivatives of a Binuclear Porphyrin Model: Crystal Structures and Mö ssbauer Properties Zhen Yao,† Charles E. Schulz,‡ Nana Zhan,† 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: A new sterically hindered “picket fence-like” porphyrin with chelates for the second metal atom, H2TImPP (TImPP = meso-tetrakis[α,α,α,α-o-(5-imidazolecarboxylaminophenyl)]porphyrinato), is developed and used in the synthesis of four iron(II) bis(imidazole) derivatives, which are characterized by single crystal X-ray and other spectroscopies. The comprehensive studies on the crystal structures revealed noteworthy features including new axial ligand arrangements, deformed porphyrin planes, and strongly tilted pickets which can be rationalized by analysis of the intra- and intermolecular interactions. Solid-state Mössbauer experiments on [Fe(TImPP)(1-MeIm)2] were conducted at several temperatures from 295 to 25 K. The quadrupole splitting (ΔEQ) in the range of 1.01−1.03 mm/s confirmed the low-spin state of the iron.

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INTRODUCTION Cytochrome c oxidases (CcO), a superfamily of proteins, are of particular importance in the process of catalyzing O2 into water.1 The best-conserved subunit (Subunit I) in CcO contains two heme centers.1b The first heme, which is lowspin and bis-histidine coordinated, acts as an electron input device to the second.2 The orientations of the histidines, which can be controlled by various of molecular interactions including hydrogen bonding,3 have strong influences on the function of heme cofactors,4 for example, different histidine conformations can shift the redox potential.5 The second heme (heme a3), which is a binuclear center with a Cu (CuB) as the other metal, is the site of oxygen reduction. Porphyrin models for both of the catalytic heme centers have been developed and investigated.6 For example, Gunter et al. developed a model employing tetradentate chelates for the copper and reported the first binuclear porphyrin crystal structure.7,8 Inspired by these pioneering works, we developed a “picket fence-like” porphyrin, H2TImPP, in which the picket fragments of α,α,α,α-o-(1-methylimidazole-5-carboxylaminophenyl) provide four donor N atoms to bind the second metal atom. Based on this new porphyrin, several iron(III)− copper(II) binuclear complexes have been isolated, and one crystal structure is shown in the Supporting Information (SI).9 In this paper we will focus on the geometric and electronic structures of the bis(imidazole) derivatives of the mononuclear iron(II) porphyrin complexes. Both ferrous and ferric [Fe(Porph)(L)2]0,+ complexes have been studied to understand the correlation between the crystal structures and the spectroscopic and physical properties.10 As a © XXXX American Chemical Society

successful example, the absolute and relative ligand orientations of the ferric bis(imidazole) porphyrinates have been well correlated to the electronic structures.6a,11 For the ferrous [Fe(II)(Porph)(L)2] complexes, several different classes of crystal structures have been recognized according to the porphyrin plane conformations as well as the absolute and relative ligand orientations.12 All the [Fe(II)(Porph)(L)2] complexes reported so far are low-spin states, while two different types of Mössbauer spectra are reported. The first set of species have quadrupole splitting (ΔEQ) values in the range of 0.96−1.27 mm/s. In these complexes, near-planar (e.g., [Fe(TpivPP)(1-MeIm)2])12a or saddled (e.g., [FeTFPPBr8(1MeIm)2])12c porphyrin planes are found. The second set of species show quadrupole splittings greater than ∼1.50 mm/s (e.g., [Fe(TMP)(2-MeHIm)2]).13 In these complexes, ruffled porphyrin planes are found. It has been suggested that the ruffled porphyrin core directly increases the covalency of the bonding interaction between Fe and the porphyrin cores which accounts for the larger quadrupole splittings.14 However, the bis(imidazole) derivatives of the sterically hindered porphyrins are relatively less studied. The only four reported crystal structures are the traditional picket fence porphyrin derivatives [Fe(TpivPP)(R-Im)2] (R-Im = 1-MeIm, 1-EtIm, and 1-VinylIm)12a and the modified picket fence porphyrinate [Fe(MbenTpivPP)(1-MeIm)2].12b Here, we report four iron(II) bis(imidazole) derivatives, three from the new H2TImPP and one from Gunter’s H2TPyPP.15 The Received: August 14, 2017

A

DOI: 10.1021/acs.inorgchem.7b02092 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Complete Crystallographic Details for [Fe(TImPP)(1-MeIm)2]·1.6THF, [Fe(TImPP)(1-MeIm)2]·C6H5Cl, 2[Fe(TImPP)(1-EtIm)2]·2C6H6, and [Fe(TPyPP)(1-MeIm)2]·C6H5Cl·C6H14

Chemical formula FW a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Space group Z Cryst. color Cryst. dimensions (mm) Temp (K) Total data collected Unique data Unique obsd data [I > 2σ(I)] GOF (based on F2) Dcalcd, g cm−3 μ, mm−1 Final R indices [I > 2σ(I)] Final R indices (all data)

[Fe(TImPP)(1-MeIm)2]· 1.6THF

[Fe(TImPP)(1-MeIm)2]· C6H5Cl

2[Fe(TImPP)(1-EtIm)2]· 2C6H6

[Fe(TPyPP)(1-MeIm)2]·C6H5Cl· C6H14

C78.4H72.8FeN20O5.60 1440.62 24.1118(13) 24.3986(15) 12.4986(7) 90 101.503(2) 90 7205.2(7) P21/c 4 purple 0.60 × 0.16 × 0.07 100 143064 15910 (Rint = 0.0649) 12121 1.044 1.328 0.278 R1 = 0.0862, wR2 = 0.2311 R1 = 0.1117, wR2 = 0.2486

C78H65ClFeN20O4 1437.80 12.3551(19) 13.423(2) 22.576(3) 73.972(4) 78.505(5) 72.964(5) 3411.9(9) P-1 2 purple 0.29 × 0.22 × 0.10 100 57121 14443 (Rint = 0.0889) 9430 1.024 1.400 0.330 R1 = 0.0704, wR2 = 0.1221 R1 = 0.1551, wR2 = 0.1829

C160H140Fe2N40O8 2862.81 13.4761(5) 22.6814(7) 24.4481(9) 93.9250(10) 104.6200(10) 106.2090(10) 6865.3(4) P-1 2 purple 0.42 × 0.30 × 0.26 100 160708 30283 (Rint = 0.0421) 23337 1.022 1.385 0.290 R1 = 0.0417, wR2 = 0.0970 R1 = 0.0637, wR2 = 0.1094

C88H76ClFeN16O4 1512.94 14.2964(5) 18.3298(7) 28.3226(11) 90 95.9766 90 7381.6(5) C2/c 4 purple 0.29 × 0.46 × 0.58 100 80029 7861 (Rint = 0.0352) 6859 1.038 1.361 0.307 R1 = 0.0406, wR2 = 0.0999 R1 = 0.0498, wR2 = 0.1077

transferred to anhydrous FeCl2 (0.68 g, 5.36 mmol) by cannula. The mixture was stirred at 65 °C for 10 h until the reaction was completed (monitored by TLC, CH3OH:CH2Cl2·NH3). After the solvent was evaporated, the residue was dissolved in CH2Cl2 and washed with portions of diluted hydrochloric acid solution. The organic layer was dried over anhydrous MgSO4 and evaporated. The resulting solid was purified on a silica gel column (300−400 mesh; CH3OH:CH2Cl2· NH3), and the main band was collected. After evaporation, the solid was recrystallized from CH2Cl2-hexanes to give [Fe(TImPP)]Cl 200 mg (0.167 mmol, 61.7%). UV−vis (benzene): 425, 511, 582, 652, 680 nm. Synthesis of [Fe(TImPP)]OH. A CH2Cl2 solution of [Fe(TImPP)]Cl (100 mg, 0.084 mmol) was washed with 2.5% aqueous NaOH (3 × 30 mL) and H2O (50 mL), dried over Na2SO4, and evaporated to dryness. The residue was recrystallized (CH2Cl2hexanes) to give [Fe(TImPP)]OH. UV−vis spectrum (benzene): 422, 577, 627 (sh) nm. Synthesis of [Fe(TImPP)(1-MeIm)2] and [Fe(TImPP)(1-EtIm)2]. [Fe(TImPP)]OH (10 mg, 8.5 × 10−3 mmol) was dried under vacuum for 30 min and dissolved in 3 mL of benzene. One mL of ethanethiol was added to the solution, which was stirred for 2 days and evaporated under vacuum to give a dark purple powder. UV−vis (benzene): 440, 537, 565 nm. The purple solid of [Fe(TImPP)] (10 mg, 8.5 × 10−3 mmol) was dried under vacuum for 30 min and dissolved in 2.5 mL of THF, to which ∼0.15 mL (∼1.7 × 10−3 mol) of 1-MeIm/1-EtIm was added. The mixture was stirred for 20 min and transferred into glass tubes (8 mm × 10 cm) which were layered with hexanes as the nonsolvent. Several days later, X-ray quality block crystals were collected. UV−vis spectrum (benzene): 431, 536, 567 nm. Synthesis of [Fe(TPyPP)(1-MeIm)2]. [Fe(TPyPP)]OH15 (10 mg, 8.5 × 10−3 mmol) was dissolved in 3 mL of benzene, to which 1 mL ethanethiol was added. The solution was stirred for 2 days and evaporated under vacuum to give a dark purple powder. The resulting [Fe(TPyPP)] was dried for additional 30 min and dissolved in 2.5 mL of chlorobenzene. 0.14 mL (1.75 × 10−3 mol) of 1-MeIm was added. The mixture was stirred for 20 min and transferred into glass tubes (8 mm × 10 cm) which were layered with hexanes as the nonsolvent. Several days later, X-ray quality block crystals were collected.

products have been studied by NMR, single crystal X-ray, UV− vis, and Mössbauer spectroscopies.

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EXPERIMENTAL SECTION

General Information. All experimental operations including the reduction of Fe(III) complexes were carried out using standard Schlenk ware and cannula techniques under argon unless otherwise noted. The 1H NMR spectrum was obtained on a BRUKER AV400 system. UV−vis spectra were obtained on a PerkinElmer Lambda-25 spectrometer. Tetrahydrofuran, benzene, and hexanes (Sinopharm Chemical Reagent) were distilled from sodium and benzophenone; dichloromethane was distilled from CaH2; and chlorobenzene was distilled twice over P2O5 under argon. All solvents were freeze/pump/thaw thrice prior to use. 2,6-Lutidine, 1-methylimidazole, and 1-ethylimidazole were distilled under argon before use. 5-Imidazolecarboxylic acid chloride hydrochloride was prepared according to Collman et al.16 H2TamPP was prepared according to a local modification of the reported synthesis.17 [Fe(TPyPP)]Cl and [Fe(TPyPP)]OH were prepared according to Gunter et al.15 Synthesis of H2TImPP. At room temperature, 2,6-lutidine (0.5 mL) was added to a CH2Cl2 (20 mL) solution of 5-imidazolecarboxylic acid chloride hydrochloride (4 g, 24.60 mmol). A CH2Cl2 solution of H2TamPP (400 mg, 0.60 mmol), was then added dropwise over a period of 1 h, followed by further stirring for 30 min. The mixture was washed with saturated NaHCO3 solution. After drying over Na2SO4 and concentrated, the residue was purified by chromatography on a silica gel column (300−400 mesh, 20 cm; CH3OH:CH2Cl2·NH3 (CH2Cl2·NH3 was prepared by agitation of a 2:1 (v/v) biphasic mixture of CH2Cl2 and 28−30% aqueous NH4OH, separation of the organic layer and drying over Na2SO4) = 1:9). The main band was collected and recrystallized from dichloromethane-hexanes to yield ∼500 mg product (0.45 mmol, 75%). 1H NMR (400 MHz, CDCl3, TMS): δ −2.51 (s, 2H, NHpyrr), 3.51 (s, 12H, CH3), 5.60 (s, 4H, CHIm), 6.91 (s, 4H, CHIm), 7.61 (t, J = 7.5 Hz, 4H, CHaryl), 7.85 (t, J = 7.9 Hz, 4H, CHaryl), 8.11 (d, J = 7.3 Hz, 4H, CHaryl), 8.21 (s, 4H, NH), 8.42 (d, J = 8.2 Hz, CHaryl), 8.89(s, 8H, CHβpyrr). Synthesis of [Fe(TImPP)]Cl. Chlorobenzene solution (30 mL) of H2TImPP (300 mg, 0.271 mmol) and 2,6-lutidine (0.4 mL) was B


Article

Inorganic Chemistry X-ray Structure Determinations. The single crystal experiment was carried out on a BRUKER D8 QUEST system with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The crystal samples were placed in inert oil, mounted on a glass fiber attached to a brass mounting pin, and transferred to the cold N2 gas steam of the diffractometer. Crystal data were collected at 100 K and integrated using a Bruker ApexII system. The structure was solved by direct method (SHELXS-2014) and refined against F2 using SHELXL2014.18 Subsequent difference Fourier syntheses led to the location of all remaining nonhydrogen atoms. All nonhydrogen atoms were refined anisotropically if not remarked upon otherwise below. For the structure refinement, all data were used including negative intensities. All hydrogen atoms were idealized with the standard SHELX idealization methods useless otherwise noted. The program SADABS19 was applied for the absorption correction. Complete crystallographic details, atomic coordinates, anisotropic thermal parameters, and fixed hydrogen atom coordinates are given; a brief summary of crystallographic details is given in Table 1. [Fe(TImPP)(1-MeIm)2] (P21/c). A purple needle crystal with the dimensions of 0.60 × 0.16 × 0.07 mm3 was used for the structure determination. The asymmetric unit contains one bis-ligated [Fe(TImPP)(1-MeIm)2] porphyrin complex and two tetrahydrofuran solvent molecules. All the atoms are ordered including the “picket” atoms and solvent molecules. All nonhydrogen atoms were refined anisotropically. The two THF molecules were restrained by “similar Uij” (SIMU) and “ISOR” commands to constrain the anisotropic displacement parameters (ADPs). All hydrogen atoms except H(B3, H11, H17, H18, H19A, H19B, and H19C and those of the solvent molecules were found in Fourier maps, and all coordinates and isotropic temperature factors were refined. [Fe(TImPP)(1-MeIm)2] (P-1). A purple block crystal with the dimensions of 0.29 × 0.22 × 0.10 mm3 was used for the structure determination. The asymmetric unit contains one bis-ligated [Fe(TImPP)(1-MeIm)2] porphyrin complex and one chlorobenzene solvent molecule. One of the four “pickets” was disordered. Seven atoms (C10, C11, C20, C24, C25, C26, and C33) on the “pickets” exhibited unusual thermal motions and thus were restrained by the “ISOR” command. The 1-MeIm ligand on the unhindered porphyrin side was found to be disordered over two positions, and the site occupancy factors (SOFs) of disordered moieties are refined by means of “free variable”. The final SOFs are found to be 0.52 and 0.48. Four disordered imidazole atoms (N7A, N7B, N8A, and C51B) exhibited unusual thermal motions and thus were restrained by the “RIGU” command. Hydrogen atoms H9B, H52A, H52B, H52C, H52D, H52E, and H52F were found in Fourier maps, and all coordinates and isotropic temperature factors were refined. [Fe(TImPP)(1-EtIm)2]. A purple block crystal with the dimensions of 0.42 × 0.30 × 0.26 mm3 was used for the structure determination. The asymmetric unit contains two bis-ligated [Fe(TImPP)(1-EtIm)2] porphyrin complexes ([Fe(TImPP)(1-EtIm)2]-A and [Fe(TImPP)(1EtIm)2]-B) and two benzene solvent molecules. All the atoms are ordered. All hydrogen atoms except H43A, H43B, and H43C were found in Fourier maps, and all coordinates and isotropic temperature factors were refined. [Fe(TPyPP)(1-MeIm)2]. A purple block crystal with the dimensions of 0.29 × 0.46 × 0.58 mm3 was used for the structure determination. In this structure, the asymmetric unit contains a half porphyrin, a half hexane, and one chlorobenzene solvent molecule. There is a crystallographic two-fold axis passing through the iron atom. The 1MeIm ligand and the chlorobenzene molecule were found to be disordered between two-fold symmetry related sites. The six atoms (C1S, C2S, C3S, C4S, C5S, and C6S) of chlorobenzene were restrained by “similar Uij” (SIMU) to constrain the anisotropic displacement parameters (ADPs). Hydrogen atoms H1, H3A, H3B, H3C, H5, H7A, H7B, and H7C were found in Fourier maps, and all coordinates and isotropic temperature factors were refined. Mö ssbauer Spectroscopy. Mö ssbauer measurements were performed on a constant acceleration spectrometer from 295 to 25 K with an optional small field (Knox College). A red powder of [Fe(TImPP)(1-MeIm)2] was obtained by slow crystallization from the

THF solution of [Fe(TImPP)] and excess 1-MeIm. The product was dried in a vacuum for 2 h and immobilized with a minimum of Apiezon M grease. The sample holder was sealed and used immediately for Mössbauer characterization. Hirshfeld Surface Calculations. Hirshfeld surface and fingerprint plots of [Fe(TImPP)(1-MeIm)2] (P-1) and [Fe(TImPP)(1-EtIm)2]-B were generated using Crystal Explorer 3.120 from the crystal structure coordinates supplied. The Hirshfeld surface analysis is illustrated in SI.21 Hirshfeld surfaces were calculated at an isovalue of 0.5 e au−3.

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RESULTS A new sterically hindered porphyrin and its iron(II) bis(imidazole) derivatives were synthesized. [Fe(TImPP)(1EtIm)2], which contains two porphyrin molecules (A and B) in the asymmetric unit and two forms of [Fe(TImPP)(1MeIm)2] (P21/c and P-1), was characterized by single crystal Xray. [Fe(TPyPP)(1-MeIm)2], which is derived from Gunter’s model,15 was also characterized for comparison. The UV−vis spectra of [Fe(TImPP)]Cl, [Fe(TImPP)]OH, [Fe(TImPP)], and [Fe(TImPP)(1-MeIm)2] are given in Figure S2 of SI. The labeled Oak Ridge thermal ellipsoid plot (ORTEP) diagrams of these complexes with views perpendicular or parallel to the porphyrin planes are given in Figures 1, 2, 6, S5, and S6. Space filling diagrams of [Fe(TImPP)(1-MeIm)2] (P21/c) are given in Figure 4. More quantitative information can be obtained from Figure S4, which shows the detailed displacements of each porphyrin core atom (in units of 0.01 Å) from the 24-atom mean plane. The orientations of the imidazole ligands including

Figure 1. ORTEP diagrams of the [Fe(TImPP)(1-MeIm)2] (P21/c) displaying the atom labeling scheme. Thermal ellipsoids of all atoms are contoured at the 40% probability level. Hydrogen atoms have been omitted for clarity. C


Article

Inorganic Chemistry

selected Mössbauer parameters of [Fe(II)(Porph)(L)2] analogues are given in Table 3.

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DISCUSSION Structures. The first ferrous bis(imidazole) porphyrin structure [Fe(TPP)(1-MeIm)2] was reported in 1978,22 which showed mutually parallel imidazole orientation with a required symmetry of a two-fold axis and a near planar porphyrin conformation. Since then, considerable efforts have been made to understand the geometric and electronic structures of [Fe(II)(Porph)(L)2] complexes, and more than 32 crystal structures have been reported.12b,c Among these species, however, only four sterically hindered porphyrin, complexes are reported.12a,b Table 2 gives key structural parameters of all known ferrous bis(imidazole) complexes with sterically hindered porphyrin. The crystallographically required symmetry at the iron center and the absolute ligand orientation given by the dihedral angle between the axial ligand’s mean plane and the closest Nax−Fe−Np plane (conventionally denoted by φ) are listed. The relative ligand orientation given by the dihedral angle between the two axial ligand’s mean planes (denoted by θ) is also tabulated. It is seen that some common structural features are shared by the new complexes and the previously reported analogues. All species have small metal out of plane displacements with the new complexes showing smaller values (Δ24 ≤ 0.03), which suggests the low-spin state of the iron. The small metal displacements are consistent with the short (Fe−Np)av bond distances which are in a narrow range of 1.984−1.992 Å. Except for [Fe(TImPP)(1-MeIm)2] (P21/c), all the structures show longer axial distances in the hindered porphyrin side than the other side, a feature we have noted for the traditional picket fence porphyrinates.12a The new complexes show some unique characteristics, among which the orientation of the axial ligands is the most noteworthy. ORTEP diagrams of [Fe(TImPP)(1-MeIm)2] (P21/c and P-1) are presented in Figures 1 and 2. We first consider the P21/c form. As can be seen in Table 2, [Fe(TImPP)(1-MeIm)2] (P21/c) has a similar ligand arrangement to the recently reported [Fe(MbenTpivPP)(1MeIm)2].12b Both structures show large φ1 and φ2 angles (27−43°) suggesting the large absolute ligand orientations that nearly bisect the equatorial Np−Fe−Np angles. Both structures also have large θ angles (75−80°) suggesting the mutually nearperpendicular ligand arrangements. In the previously reported [Fe(MbenTpivPP)(1-MeIm)2], the imidazole inside the pocket was governed by the intramolecular interactions, for example, C−H···π interactions between 1-MeIm and the phenyl group, while the “free” imidazole on the unhindered porphyrin side aligned itself perpendicular to the first imidazole to maximize the π-bonding between the filled dπ orbitals of Fe(II) and the π* orbitals of the axial ligands.12a,b Similar situations are seen in [Fe(TImPP)(1-MeIm)2] (P21/c). Several kinds of intramolecular interactions are observed for the imidazole inside the pocket, which are illustrated by a wireframe diagram in Figure 3. The H4A···N16 and H4C···N20 distances are 2.623 and 2.360 Å, both corresponding to the value of (C−)H···N interactions (2.522−2.721 Å).23 The distance between C51 and the centroid of 1-MeIm ligand (Xcent) is 3.568 Å, and the C− H···Xcent angle is 125.4°, corresponding to the values of a (C−)H···π interaction.24 Accordingly, the 1-MeIm was positioned in a specific orientation inside the pocket by the intramolecular interactions. Space-filling models give another

Figure 2. Edge-on (top) and top-down (middle and bottom) ORTEP diagrams of the [Fe(TImPP)(1-MeIm)2] (P-1) displaying the atom labeling scheme. The axial imidazole on the unhindered side is disordered over two positions which are shown separately in the middle and bottom diagrams. Thermal ellipsoids of all atoms are contoured at the 40% probability level. Hydrogen atoms have been omitted for clarity.

the values of the dihedral angles are also shown. 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 four structures are given. All the hydrogen atoms involved with the intra- and intermolecular interactions are located in the Fourier maps, and all coordinates and isotropic temperature factors were refined. Solid-state Mössbauer spectra of [Fe(TImPP)(1-MeIm)2] measured from 295 K to 25 K are given in Figure 7. The D


Article

Inorganic Chemistry Table 2. Selected Structural Parameters for [Fe(II)(Porph)(L)2]a Δ24c,d

Complex

FeS. S.b

(Fe−Np)avc,e

[Fe(TImPP)(1-MeIm)2] (P21/c)

C1

0.01

[Fe(TImPP)(1-MeIm)2] (P-1)

C1

−0.01

1.9918(27)

[Fe(TImPP)(1-EtIm)2]-A

C1

−0.03

1.9899(26)

[Fe(TImPP)(1-EtIm)2]-B

C1

−0.01

1.990(3)

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

C2

0.00

1.9838(25)

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

C1

0.07

1.994(9)

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

C1

0.04

1.992(3)

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

C1

0.05

1.993(6)

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

C1

0.05

1.988(5)

1.991(7)

Fe−Naxc 1.989(3) 2.007(3) 2.018(3) 2.00(4)j 2.0164(14) 2.0162(14) 2.0135(14) 1.9953(14) 2.023(3) 2.018(3) 1.991(3) 1.986(3) 1.9958(19) 1.9921(18) 2.0244(18) 1.9940(19) 1.9979(19) 1.9866(18)

(Fe−Nax)avc,e 1.998(9) 2.009(9) 2.0163(1) 2.004(9) 2.0205(25) 1.9885(25) 1.9940(19) 2.009(15) 1.992(6)

Core conf.c,f

φ1,2g,h

θg,i

χg,k

ref

Near-Pla (Cm, 0.12) Sad (Cβ, 0.30) Sad (Cβ, 0.29) Sad (Cβ, 0.30) Near-Pla (Cm, 0.19) Near-Pla (Cm, 0.21) Near-Pla (Cm, 0.15) Near-Pla (Cm, 0.09) Near-Pla (Cm, 0.22)

43.2, 32.0

75.1

74.5

tw

88.2 (44.0) 74.0

57.5

tw

58.7

tw

11.2, 30.3

39.9

56.3

tw

11.2, 17.9

68.4

tw

36.5, 26.9

28.1 28.8 80.2

68.7

12b

8.5, 21.1

77.2

69.7

12a

6.6, 20.7

62.4

67.1

12a

11.2, 24.5

78.5

73.4

12a

6.2, 8.0 (35.0) 8.2, 8.3

a (Porph = (modified) picket fence porphyrins, L = 1-MeIm, 1-EtIm, 1-VinylIm). Estimated standard deviations are given in parentheses. bSite symmetry of Fe. cValue in Å. dDisplacement of iron from the 24-atom mean plane of the porphyrin core; a positive number indicates a displacement toward the imidazole ligand. eAveraged value. fNumber in parentheses is the largest displacement of the methine carbons (Cm) or pyrrole β carbons (Cβ) from the 24-atom mean plane for ruffling (Ruf) or saddling (Sad) deformation, respectively; near-Pla indicates an almost planar porphyrin plane in a centrosymmetric or (modified) picket fence structures. gValue in degrees. hDihedral angle between the plane of the closest Np−Fe−Nax and the ligand plane. iDihedral angle between two axial ligands. jAveraged value of two disordered ligands. kDihedral angle between the 24-atom mean plane and phenyl plane of picket.

Interestingly, the second form of [Fe(TImPP)(1-MeIm)2] (P-1) shows quite different ligand orientations from [Fe(TImPP)(1-MeIm)2] (P21/c). As seen in Figure 2, a “rotational” disorder appearing as two orientational parts is found for the imidazole on the unhindered porphyrin side. This “rotational” disorder is unusual for a [Fe(Porph)(L)2] structure, compared to the more common “swing” disorder which is involved with the crystallographically required symmetry, as happened to [Fe(TPyPP)(1-MeIm)2] and the diatomic ligand adducts, for example, [Fe(TpivPP)(1-MeIm)(O2)].25 The two “rotational” imidazole parts of [Fe(TImPP)(1-MeIm)2] (P-1) are crystallographically independent (ratio 0.52:0.48), thus showing distinct geometric parameters. The first imidazole pair is very comparable to those of [Fe(TImPP)(1-EtIm)2]-A, for example, similarly small φ1,2 (6−8°) and near perpendicular θ angles (88.8 and 74.0°, Table 2). Small φ1 angles have been observed for the traditional picket fence analogues [Fe(TpivPP)(1-MeIm)2] (8.5°) and [Fe(TpivPP)(1EtIm)2] (6.6°), a result of the steric demands on the picket side of the porphyrin which require the imidazole plane to eclipse the Np−Fe−Np vector.12a On the other porphyrin side, similarly small φ2 angles along the second Np−Fe−Np vector are observed, and a large θ angles is yielded. Again, the axial ligand arrangements are well consonant with the conclusion that for the closed subshell configuration of low-spin d6 Fe(II) porphyrinates, two planar axial ligands would prefer to align themselves in mutually perpendicular planes to maximize the πbonding interactions between the filled dπ orbitals of Fe(II) and the π* orbitals of the ligands.12a,c The second imidazole pair of [Fe(TImPP)(1-MeIm)2] (P-1) and the second molecule in [Fe(TImPP)(1-EtIm)2] (B) shared some common features. Both structures show small φ1 angles (8.0−11.2), large φ2 angles (30−36°), and small θ angles 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. (19) Sheldrick, G. M. Program for Empirical Absorption Correction of Area Detector Data; Universität Göttingen: Germany, 1996. (20) Wolff, S. K.; Grimwood, D. J.; Mckinnon, J. J.; Turner, M. J.; Jayatilaka, D.; Spackman, M. A. CrystalExplorer (Version 3.1); University of Western Australia: Perth, Western Australia2012. (21) (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. (22) 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, 1. (23) Taylor, R.; Kennard, O. Crystallographic Evidence for the Existence of CH···O, CH···N and CH···Cl Hydrogen Bonds. J. Am. Chem. Soc. 1982, 104, 5063−5070. (24) Brandl, M.; Weiss, M. S.; Jabs, A.; Sühnel, J.; Hilgenfeld, R. CH···π-Interactions in Proteins. J. Mol. Biol. 2001, 307, 357−377. (25) Li, J.; Noll, B. C.; Oliver, A. G.; Schulz, C. E.; Scheidt, W. R. Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: J


Iron(II) Bis(imidazole) Derivatives of a Binuclear Porphyrin Model

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