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Synthesis and characterization of the iron(III) complexes of tetra-(β,β’-tetramethylene)tetraphenylporphyrin, (TC6TPP)FeCl and (TC6TPP)FeONO2

Liliya A. Yatsunyk, and F. Ann Walker*

Contribution from the Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041

Received date :

Accepted date :

Abstract: The synthesis, NMR and EPR spectroscopic investigation as well as two crystal structures of

(TC6TPP)FeX, where X– = chloride and nitrate are reported. The crystal structure of (TC6TPP)FeCl reveals an

almost equal mixture of saddled and ruffled distortion of the porphyrin as judged by the coefficients of the

lowest-frequency vibrational modes (calculated from Normal-Coordinate Structural Decomposition), while

(TC6TPP)FeONO2 is mainly saddled and more distorted overall. This difference in core structure indicates high

conformational flexibility of the TC6TPP porphyrin ligand. Overall, both (TC6TPP)FeX structures have smaller

deviation from planarity as compared to five coordinate (OMTPP)FeCl and (OETPP)FeCl. Therefore, the

nature and number of peripheral substituents as well as the axial ligand(s) control geometry and conformation

of the porphyrins and fine-tune their spectroscopic properties. EPR data (4.2 K) indicate a predominantly high-

spin (S = 5/2, 97.3%) ground state for (TC6TPP)FeCl and less pure high-spin state (S = 5/2, 80%) for

(TC6TPP)FeONO2. The NMR results support an ideally saddled structure or rapid switching between saddled

and ruffled conformations of (TC6TPP)FeX in solution. The flexibility of the porphyrin core was addressed by

using dynamic NMR spectroscopy. The following kinetic parameters for ring inversion were obtained: ∆H‡ =

24(1) kJ·mol-1, ∆S‡ = –37(3) J·mol-1·K-1 and ∆H‡ = 36(1) kJ·mol-1, ∆S‡ = 20(4) J·mol-1·K-1 for (TC6TPP)FeCl

and (TC6TPP)FeONO2, respectively. This results in low free energies of activation, ∆G298‡ = 35(2) and 30(2)

kJ·mol-1, respectively, indicating extremely high flexibility of the porphyrin core in solution (kex298 > 4.2×106

and 3.8×107 s-1 ).

KEYWORDS: saddled porphyrin, molecular structure, 1H NMR, EPR, spin-admixed, saddle inversion,

kinetics

*Correspondence to: F. Ann Walker, Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA; +(520)621-8645

(office); +(520)626-9300 (fax); awalker@u.arizona.edu.

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INTRODUCTION

The geometry of the porphyrin core plays an important role in the many functions of hemes in biological systems. Highly

nonplanar porphyrins have been shown to possess interesting spectroscopic properties and have been used as models for

heme centers in the electron-transferring cytochromes [1 - 3]. The nonplanarity of the porphyrin core in biological systems is

induced mainly by covalent and non-covalent interaction with protein side chains, while synthetic porphyrins can be made

nonplanar by using many different approaches, one of which is to place bulky substituents on the periphery of the porphyrin

core. Depending on the nature of the substituents used, the spectroscopic properties of model heme compounds can be fine-

tuned. Our group, as well as others, have been involved in elucidating the structures and spectroscopic properties of

(OMTPP)FeIII and (OETPP)FeIII complexes, both of which were reported to be saddled or mainly saddled, with up to 30% of

ruffled deformation, and have a variety of ground states and spectroscopic properties based on the nature of the axial ligands

[1 - 10]. Recently our attention has been drawn to the octaalkyltetraphenylporphyrin complexes with fused hydrocarbon rings

on the β pyrrole positions, TCnTPP (n = 5, 6, and 7). In this case the electronic and steric effects of the substituents can be

carefully controlled. It was shown by molecular mechanics calculations or by crystallography that depending on the number

of carbons in the ring, n, the porphyrin complexes can adopt geometries anywhere from planar to strongly saddled or ruffled

[7, 8, 11]. Namely, NiII tetracyclopentenyltetraphenylporphyrin (tetra-(trimethylene)tetraphenylporphyrin, (TC5TPP)Ni) was

predicted to be planar [7, 8], both NiII tetracyclohexenyl- and tetracycloheptenyltetraphenylporphyrins (tetra-

(tetramethylene)tetraphenylporphyrin, (TC6TPP)Ni [13], and tetra-(pentamethylene)tetraphenylporphyrin, (TC7TPP)Ni),

were predicted to be highly nonplanar, saddled with the average deviation of the core atom from the mean porphyrin plane,

∆24, of 0.57 and 0.66 Å, respectively as compared to (TC5TPP)Ni [7, 8], and NiII tetracyclopentenyltetra(n-pentyl)porphyrin,

(TC5TnPP)Ni, was obtained in a ruffled conformation [11]. At the same time, the dications, H4TC5TPP2+, H4TC6TPP2+, and

H4TC7TPP2+ were all found to be nonplanar due to steric repulsion between the NH protons [7, 11]. Soon afterwards, other

metals, such as CuII, and ZnII were incorporated into these porphyrin complexes [9]. The first experimental proof of the

ability of the molecular mechanics calculations to correctly predict structures of highly substituted porphyrins such as

TCnTPP came from NMR investigations [7,9]. NMR studies of the series of TCnTPPs (with n = 5, 6, and 7) as the free bases,

dications, and NiII complexes had shown that the barrier to ring inversion decreases in the following order OETPP > TC7TPP

> TC6TPP > TC5TPP [9]. Even for (TC6TPP)Ni, which is highly saddled (∆24 = 0.54 Å) [13], the ring inversion is too fast to

be measured by NMR methods, but the free energy of activation, ∆G‡, is estimated from the NMR data to be less than 33

kJ·mol-1 [9], but no temperature is given. Due to the poor solubility of (TC5TPP)Ni, the NMR data were acquired for the

slightly modified complex, (TC5T(3,4,5-OMeP)P)Ni, which has ∆G‡ < 29 kJ·mol-1 [9], but no temperature is given for this

value either. The observed trend indicates that (TC5TPP)Ni should be planar, on average, in solution. However, the crystal

structure of (TC5T(3,4,5-OMeP)P)Ni [9] clearly showed a nonplanar, S4-ruffled geometry in the solid state, with ∆24 = 0.36

Å. This nonplanarity is not as severe as in the case of metal complexes of octaethyltetraphenylporphyrins (OETPP) [1, 10],

and is comparable to that for the tetragonal form of NiII octaethylporphyrin (OEP) [12]. The ruffled distortion of (TC5T(3,4,5-

OMeP)P)Ni is believed to arise mainly from the effect of the small NiII ion and not from the steric repulsion of the peripheral

substituents [11]. In agreement with this, substitution of NiII with the larger metal, CuII, results in a planar porphyrin core,

which was observed in the crystal structure of (TC5T(3,4,5-OMeP)P)Cu [9]. In fact, (TC5T(3,4,5-OMeP)P)Cu [9] is a unique

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example of a planar dodecasubstituted porphyrin. On the other hand, the structure of (TC5TnPP)Ni [11] (with n-pentyl on the

meso-positions instead of phenyl rings) is still ruffled.

The structures of (TC6TPP)Ni [13] and (TC6TPP)Cu [26] are saddled, with the nonplanar distortion being due to steric

interaction of the peripheral substituents, as well as the small size of NiII ion in the case of former complex. The average

deviation of the β-carbons in (TC6TPP)Ni is ± 1.08 Å while the meso-carbons are almost in the porphyrin mean plane (± 0.02

Å). The multiple substituents on the porphyrin core in (TC6TPP)Ni preclude the possibility that strong π-π interaction

between molecules induce the saddled distortion.

In light of these published results and the generally interesting structural and spectroscopic properties of TCnTPP

porphyrin cores we decided to incorporate FeIII into H2TC6TPP in order to compare the properties of (TC6TPP)FeX to those

of saddled (OMTPP)FeCl [6] and (OETPP)FeCl [6, 14]. In this work we carried out a detailed investigation of the NMR and

EPR spectroscopic properties, kinetics of inversion, and structures of the five-coordinate (TC6TPP)FeIII complexes having Cl–

and NO3– as axial ligand. Some of the results obtained in this work have been summarized elsewhere [15], and several bis-

axial ligand complexes of (TC6TPP)FeIII have already been reported as well [4, 5, 16].

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EXPERIMENTAL

Synthesis. (TC6TPP)FeCl was prepared as described earlier [2, 7, 11]. Conversion of (TC6TPP)FeCl to (TC6TPP)FeONO2

was done according to the procedure developed earlier in this laboratory for conversion of chlorides into perchlorates [17].

Namely, 20 mg (0.023 mmol) of (TC6TPP)FeCl was dissolved in a small amount of freshly distilled THF (~ 3 mL) and

heated. Before reflux started, 1.9 mL of 0.012 M solution of AgNO3 in THF (0.023 mmol) was added at once. The mixture

was refluxed for 15 min, cooled to ambient temperature and filtered using a fine or medium frit filter. An equal amount of

freshly distilled toluene was added, and the solvents were removed under vacuum at 50 °C. The residue was dissolved in a

small amount of boiling toluene, and an equal volume of boiling heptane was added. The mixture was cooled to ambient

temperature and then placed in a refrigerator. The next day the crystals obtained were filtered, washed with cold heptane and

dried under vacuum at 60 oC for 4 hours. The crystalline material contained a large amount of toluene. Therefore before

NMR samples were prepared, the crystals were dissolved in 20 mL CH2Cl2, solvent was removed under reduced pressure,

and the residue was vacuum-dried overnight. 1H NMR (CD2Cl2, 300 MHz, 253 K, referenced to the residual solvent peak at

5.32 ppm): δ, ppm, 90.22 (8, CH2(α)1), 83.46 (8, CH2(α)2), 13.02 (4H, o(1)), 10.4 (4H, o(2)), 10.19 (4H, m(1)), 9.67 (4H,

m(2)), 9.09 (4H, p), 5.2 (8H, CH2(β)), and 1.37 (8H, CH2(β)). MS (ESI): [FeTC6TPP]+ m/z = 884, [NO3]- m/z = 62. The

presence of two ortho- and meta-phenyl peaks in the sample of (TC6TPP)FeONO2 indicates C2v symmetry as a result of

nitrate coordination to the central iron, which was shown to be the case from the crystal structure (see later discussion). The

number and position of resonances resembled five-coordinate chloride complexes of (TC6TPP)FeIII [2], (OMTPP)FeIII [6] and

(OETPP)FeIII [6], however, with much larger downfield shifts for the CH2(α) resonances.

Spectroscopic measurements. EPR spectra for the (TC6TPP)FeCl sample in frozen CD2Cl2 solution and the

polycrystalline sample of (TC6TPP)FeONO2 were recorded on a Bruker ESP-300E spectrometer (operating at 9.4 GHz with

100 kHz field modulation) equipped with an Oxford Instruments ESR 900 continuous flow helium cryostat at 4.2 oK.

Variable temperature 1H NMR spectra were acquired on both a Bruker DRX-500 operating at 499.944 MHz and equipped

with 5 mm Nalorac triple gradient probe, and a Varian Unity-300 spectrometer operating at 299.957 MHz and equipped with

a broad-band inverse probe. Samples were prepared by dissolving 5 mg of (TC6TPP)FeX (X⎯ = Cl⎯ and ONO2⎯) in 0.5 ml

CD2Cl2 or CDCl3 in a 5-mm NMR tube (Wilmad WGH-07). Data were acquired in the temperature range from +50 to –93

ºC. The temperature on the Unity-300 was controlled by the variable temperature accessory and was calibrated using the

standard Wilmad methanol sample. 2D data were processed using standard VNMR software. UV-vis spectra were obtained

on a Perkin Elmer Lambda 19 spectrophotometer.

X-ray Crystallography. X-ray-quality crystals of (TC6TPP)FeCl were grow by the liquid diffusion method from the

sample in methylene chloride carefully layered with diethyl ether in an NMR tube in the course of 2-3 days. On the other

hand, obtaining crystals of (TC6TPP)FeONO2 was a complete surprise. This complex was crystallized from methylene

chloride/dodecane in an attempt to obtain crystals of the bis-ligand complex [FeTC6TPP(4-CNPy)2]ONO2.

A dark-blue oblique hexagon of (TC6TPP)FeCl (0.14×0.23×0.47 mm3) and a dark-purple trigonal prism of

(TC6TPP)FeONO2 (0.20×0.20×0.36 mm3) were mounted on glass fibers in random orientation and examined on a Bruker

SMART 1000 CCD detector X-ray diffractometer at 170(2) K. All measurements utilized graphite monochromated Mo Kα

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radiation (λ = 0.71073 Å) with a power setting of 50 kV, 40 mA. Final cell constants and complete details of the intensity

collection and least squares refinement parameters for both complexes are summarized in Table 1.

In both cases a total of 3736 frames at one detector setting covering 0 < 2θ < 60º were collected, having an omega scan

width of 0.2º and an exposure time of 20 seconds per frame. The frames were integrated using the Bruker SAINT software

package's narrow frame algorithm [18]. Initial cell constants and an orientation matrix for integration were determined from

reflections obtained in three orthogonal 5° wedges of reciprocal space. Both structures were solved using SHELXS in the

Bruker SHELXTL (Version 6.0) software package [19]. Refinements were performed using SHELXL and illustrations were

made using XP [19]. Hydrogen atoms were added at idealized positions, constrained to ride on the atom to which they are

bonded and given thermal parameters equal to 1.2 or 1.5 times Uiso of that bonded atom. Empirical absorption and decay

corrections were applied using the program SADABS [20]. Scattering factors and anomalous dispersion were taken from the

International Tables (Vol. C Tables 4.2.6.8 and 6.1.1.4.).

(TC6TPP)FeCl. The iron atom in (TC6TPP)FeCl is situated on a crystallographic C2 axis; thus only half of the molecule is

unique and present in the asymmetric unit. After completing the initial structure solution it was found that 25% of the cell

volume was filled with disordered solvent that could not be modeled as discrete molecules. According to the NMR spectra,

the crystals contained both water and methylene chloride incorporated into the crystal lattice (see Figure 5 below). Analysis

of solvent voids using Platon [21] gave a volume of 1442.5 Å3/cell. From this point on, atoms in the solvent region were

removed and the solvent region was refined as a diffuse contribution without specific atom positions using the Platon module

SQUEEZE [22]. Eight discrete voids with 177-180 Å3 volumes were found in the unit cell. Each void contained 64-67

electrons yielding a total of 519 electrons per cell. The given electron count and volume can be accounted for by 8 H2O

molecules and 4 CH2Cl2 per unit cell. While not part of the atom list, these are included in the formulas, F000, density and

absorption coefficients. A dramatic improvement was observed in all refinement parameters and indices.

The Fe, as well as the Cl atom attached to it, is disordered between two positions on opposite sides of the porphyrin core in

(TC6TPP)FeCl. The population of both parts was refined freely and independently to 0.85:0.15. The disorder is due to two

different orientations of the porphyrin molecule (with the Fe-Cl bond ‘up’ and ‘down’) on the same crystallographic position

in different unit cells [23]. The orientation and length of the Fe-Cl bond are the only differences between the two parts with

all other bond lengths, angles, and geometry being exactly the same.

(TC6TPP)FeONO2. The porphyrin molecule occupies a general position in the unit cell. One of the cycloalkyl side groups

is disordered over two positions, with the major component having occupancy of 0.671(12) refined freely. Distance restraints

were used to keep the geometry of this disordered group chemically reasonable. As in the case of (TC6TPP)FeCl, the central

iron atom and axial nitrate group are disordered over two positions, with 90% occupancy of the major component refined

freely and independently for both Fe and NO3. A large peak corresponding to the ligated oxygen of the second, minor nitrate

group could be identified clearly using difference Fourier synthesis; the nitrogen, on the other hand, could barely be

distinguished and the remaining oxygen atoms could not be found. Therefore, the minor nitrate group was fixed using the

positions of the Fe, O and N and the geometry of the major component as a guide. The ligated oxygen atom refined with a

reasonable isotropic thermal parameter; the remaining atoms had very large isotropic thermal parameters when freely refined.

This could indicate unresolved rotational disorder of this group around the ligated oxygen atom, which would also explain

the difficulties in locating the atoms. In final refinement cycles a common isotropic thermal parameter was used for the whole

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nitrate group; this refined to a reasonable (if slightly large) value. The two positions of the nitrate group have different

environments, shown in Supporting Information Figure S1.

One molecule of dichloromethane could easily be identified and refined in the structure (using restrained anisotropic

refinement); a significant amount of residual electron density remained, which could not be modeled in a chemically

meaningful way. Instead the residual electron density was treated using SQEEZE [22], which gave a residual electron count

of 314 per unit cell. This was interpreted as a second molecule of dichloromethane per porphyrin molecule.

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RESULTS AND DISCUSSION

Crystallography. (TC6TPP)FeX was obtained in two different crystalline forms with chloride and nitrate as fifth ligand to

iron(III). Atomic coordinates, a table of complete bond length and angles, anisotropic thermal parameters, hydrogen

coordinates and complete torsion angles for both complexes in this study are listed in Tables S1-S10 in the Supporting

Information.

The molecular structures of (TC6TPP)FeCl and (TC6TPP)FeONO2 are presented in the ORTEP plots of Figure 1. The

molecules are nonplanar and adopt an admixture of saddled and ruffled deformations, which are reflected in the deviation of

their β- and meso-carbons from the mean plane. Figure 2 presents the displacement of skeletal atoms from the mean plane

defined by the 24 core atoms of the macrocycle as well as typical bond angles and distances. The structure of (TC6TPP)FeCl

is unique because it combines almost equal amounts of saddled and ruffled distortion. To our knowledge, this is the first

structure with such an interesting core geometry. On the other hand, the porphyrin core of (TC6TPP)FeONO2 is saddled with

a much smaller degree of ruffling distortion. The ruffling of [TC6TPPFe(1-MeIm)2]Cl [2], as measured by the deviation of the

meso-carbons from the mean plane of the porphyrin, is intermediate between that of (TC6TPP)FeONO2 and (TC6TPP)FeCl

(Table 2), which appears to indicate that the porphyrin core of (TC6TPP)FeIII complexes has a large degree of conformational

flexibility.

Shelnutt and coworkers [24] have developed the Normal-Coordinate Structural Decomposition (NSD) method to identify

and quantify the contribution from different types of distortion (saddled, ruffled, etc) to the nonplanar geometry of the

porphyrin core. This allows quantitative comparison of different porphyrin structures. NSD calculations for (TC6TPP)FeCl

resulted in the following lowest energy modes: B2u(sad) = 1.9985, B1u(ruff) = 1.3508, a small domed component, A2u(dome)

= 0.1457, and close to zero values for all the others (Table 2). The obtained values indicate an admixture of saddled and

ruffled conformations with the approximate ratio of these vibrational coefficients of 0.57:0.39. On the other hand, the major

contribution to the nonplanar distortion of (TC6TPP)FeONO2 comes from the B2u mode with 2.8221 coefficient, while the B1u

coefficient is only 0.6028. All other types of nonplanar deformation are substantially smaller. As a result, the relative ratio of

saddled to ruffled contribution is 0.78:0.17. The structure of (TC6TPP)FeONO2 is somewhat more distorted from planarity as

compared to (TC6TPP)FeCl, judging by either the root-mean-square deviation of all the vibrational coefficients, Doop, (2.8884

vs. 2.4166) or the average displacements of the 24 core atoms, ∆24 (0.48 vs. 0.40 Å). In order to look at the complete

picture, the data for [TC6TPPFe(1-MeIm)2]Cl [2] are also included in Table 2. The porphyrin core in [TC6TPPFe(1-

MeIm)2]Cl is the least distorted from planarity among the three complexes (∆24 = 0.29 Å) but has 0.68:0.32 of saddling to

ruffling contribution in its structure [2].

In comparison to the iron(III) complexes of TC6TPP, those of OMTPP and OETPP also show a wide range of degrees of

saddle and ruffle distortion. While the degree of saddle distortion increases markedly in the order TC6TPP < OMTPP <

OETPP, the contribution of ruffling to the individual molecules varies widely. Two molecules of [OMTPPFe(4-Me2NPy)2]Cl

obtained from different solvents exhibit ratios of 0.68:0.30 and 0.91:0.06 [2], while the one molecule of [OMTPPFe(4-

CNPy)2]Cl has a ratio of 0.79:0.17 [4]. For OETPPFeIII structures, that of [OETPPFe(4-Me2NPy)2]Cl has a ratio of 0.80:0.17

[1], and the six molecules in the two structures of [OETPPFe(4-CNPy)2]Cl obtained from different solvents exhibit relative

ratios ranging from 0.83:0.15 to 0.96:0.01 [4]. Such large ranges of saddled to ruffled ratios demonstrate clearly that even the

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most highly distorted [OETPPFe(L)2]Cl complexes can adopt a large range of porphyrin ring conformations. Thus it is not

surprising to find two quite different core conformations for the much more flexible (TC6TPP)FeCl and (TC6TPP)FeONO2

molecules.

The core conformation of (TC6TPP)Fe+ combines the characteristic features of both saddled and ruffled distortions; as in

the saddled conformation, alternate pyrrole rings are displaced above and below the porphyrin mean plane (Figure 3), and at

the same time, as in a ruffled conformation, the meso-carbons are not in the porphyrin mean plane but are displaced above

and below it by ± 0.47, ± 0.26, and ± 0.21 Å, for (TC6TPP)FeCl, [TC6TPPFe(1-MeIm)2]Cl [2], and (TC6TPP)FeONO2,

respectively. The high deviation of the meso-carbons is in accord with a strong twist of the adjacent pyrrole rings, which

results in an uneven deviation of adjacent β-Cs (∆∆Cβ = 0.40, 0.23, 0.18 Å, respectively) [25]. However, in a typical ruffled-

only structure the adjacent β-Cs of a given pyrrole ring are on opposite sides of the porphyrin mean plane. Unlike the

(TC6TPP)FeIII structures discussed herein, (TC6TPP)NiII [13] and (TC6TPP)CuII [26] are purely saddled (the average

deviation of the meso-Cs, ∆|Cm| = ± 0.02 and ± 0.008 Å, respectively, and ∆|Cβ| = ± 1.08 and ± 1.028 Å, respectively) and

somewhat more distorted from planarity (∆24 = 0.54 and 0.50 Å, respectively). The latter might be due to the small size of

the NiII ion, except that the CuII ion should be larger because of the dx2-y2 electron. Hence we conclude that the range of

porphyrin ring conformations observed for various metal (and their ligand) complexes of TC6TPP are simply indicative of the

high degree of flexibility of this nonplanar porphyrin.

Since the saddled distortion is substantially less pronounced in (TC6TPP)FeIII as compared to (TC6TPP)NiII, the angles

between adjacent and opposite pyrrole rings are also smaller than the same angles in the NiII complex. For adjacent rings they

average 29.4(1), 33.3(2), and 34.5º for (TC6TPP)FeCl, (TC6TPP)FeONO2 and (TC6TPP)NiII [13], respectively, and for

opposite pyrrole rings 41.2(1), 47.6(1), and 49.6º. Individually, each pyrrole ring is nearly planar. Further evidence of the

planarity of the pyrroles comes from the small Cα-Cβ-Cβ-Cα dihedral angles whose values ranges from 4.6(3) to 5.8(3)º for

(TC6TPP)FeCl and 1.3(3) to 3.0(3)º in (TC6TPP)FeONO2.

The average dihedral angles of the phenyl rings with the mean macrocycle plane are 67.9(1), 47.1 and 44.9º for

(TC6TPP)FeCl, (OMTPP)FeCl [6] and (OETPP)FeCl [6], respectively and thus correlate with the increasing degree of

saddled distortion in iron(III) chloride complexes in the order listed. The same is true when the complexes with the TC6TPP

core are compared. The dihedral angle between the phenyls and the porphyrin mean plane decreases in the order of

increasing saddled distortion: [TC6TPPFe(1-MeIm)2]Cl [2] > (TC6TPP)FeCl > (TC6TPP)FeONO2 > (TC6TPP)NiII [13] (71.8

> 67.9 > 54.9 > 50.0º). However, the bond length between the meso-carbons and phenyl rings stays clearly single, 1.501(5),

1.504(4), 1.495(4), 1.488(6) Å, respectively.

The average Fe-NP distances expand from 2.005(3) Å in the low-spin [TC6TPPFe(1-MeIm)2]Cl [2] to 2.014(2) and

2.052(2) Å for mainly high-spin (TC6TPP)FeONO2 and (TC6TPP)FeCl, respectively. Substantially longer Fe-Np distances in

(TC6TPP)FeCl are a result of the repulsive effect of the unpaired electron in the FeIII dx2-y2 orbital on the porphyrin nitrogens.

However, the differences in the Fe-Np bond length between [TC6TPPFe(1-MeIm)2]Cl and the five coordinate (TC6TPP)FeX

complexes do not seem too dramatic due to the fact that the former complex is the most planar of the three (TC6TPP)FeIII,

with the average displacement of the 24 core atoms (∆24) of only 0.29 Å vs 0.40 and 0.48 Å, for (TC6TPP)FeCl and

(TC6TPP)FeONO2, respectively. As was observed earlier [27], there is an inverse correlation between the degree of

nonplanar distortion and the length of the Fe-Np bond. In general, the Fe-Np bond length in typical low-spin FeIII porphyrin

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complexes is on the order of 1.96-1.99 Å [2]. The Fe-Np distances in other mainly high-spin dodecasubstitutediron(III)

porphyrins are 2.031(5) in (OETPP)FeCl and 2.034(5) Å in (OMTPP)FeCl [6]. Both of them are shorter as compared to the

Fe-Np distance in (TC6TPP)FeCl due to the fact that latter is the most planar of the three.

As was already discussed in the Experimental section, the porphyrin macrocycles in both (TC6TPP)FeX were modeled as

having two orientations, with the fifth axial ligand (Cl or NO3) pointing in opposite directions, occupying the same

crystallographic position in two different unit cells. The populations of the two parts were refined roughly to 9:1 in both

complexes. All data presented are for the major component only. Unlike in the six-coordinate FeIII porphyrins, where the

central metal atom is in the porphyrin mean plane, in five coordinate (TC6TPP)FeIII complexes the iron atom is significantly

out of the porphyrin mean plane by 0.530(1) and 0.359(1) Å for the main component of (TC6TPP)FeCl and

(TC6TPP)FeONO2, respectively. The same values for the minor component are 0.575(5) and 0.453(8) Å. The displacement of

the Fe atom from the porphyrin mean plane in (TC6TPP)FeCl is close to that in (OEP)FeCl (0.53 Å) [28, 29], (OMTPP)FeCl

(0.51 Å) [6], and somewhat larger as compared to the same displacement in (OETPP)FeCl (0.43 and 0.48 Å) [6, 14]. The

axial Fe-Cl bond distance, 2.234(2) Å, is in good agreement with the same distances in (OEP)FeCl [28, 29], (OMTPP)FeCl

[6] and (OETPP)FeCl [6] (2.235(1), 2.24(3), and 2.242(2) Å, respectively). The Fe-O distance in (TC6TPP)FeONO2 is

substantially shorter 1.996(3) Å, due to the lower effective radius of oxygen.

Theoretical calculations on the effect of nonplanarity indicate that in highly distorted porphyrins the highest occupied

molecular orbital should be destabilized with respect to the lowest unoccupied molecular orbital, resulting in a red shift of the

first visible absorption band as well as the Soret band [7]. When the molecular structures of (TC6TPP)FeCl, (OMTPP)FeCl

[6], and (OETPP)FeCl [6] are compared, the former has the smallest and the latter has the largest deviation from planarity

(∆24 = 0.40, 0.53, and 0.58 Å, respectively). For all complexes, the Soret band is split and appears at 397 and 427, 398 and

436, and 399 and 442 nm for (TC6TPP)FeCl, (OMTPP)FeCl, and (OETPP)FeCl, respectively (Table 3). The degree of

nonplanar distortion correlates well with the position of the Soret band: (TC6TPP)FeCl, the most planar, has a blue shifted

second Soret maximum as compared to the Soret bands in (OMTPP)FeCl, and (OETPP)FeCl. Therefore, UV/vis data that are

easily acquired can be useful in estimation of the relative degree of nonplanar distortion in similar porphyrin complexes.

Crystallographic and UV/vis data are in good agreement with the kinetics studies of ring inversion in (TC6TPP)FeCl,

(OMTPP)FeCl, and (OETPP)FeCl [16].

EPR and Variable Temperature NMR Studies of (TC6TPP)FeCl and (TC6TPP)FeONO2. The EPR spectrum (X-

band, 4.2 K, frozen CD2Cl2 solution) of (TC6TPP)FeCl is shown in Figure 4 and is indicative of a predominantly high-spin (S

= 5/2) ground state. It is characterized by gx = 6.60, gy = 5.29 (g⊥ = (gx + gy)/2 = 5.95), and gz =1.98, and is similar to the 77

K EPR spectra of (OMTPP)FeCl [6], and almost identical to the 4.2 and 10 K EPR signals of (OETPP)FeCl [1, 6, 14]. The

second g-value, 5.29, which is between 6 (pure HS) and 4 (pure IS), indicates an admixture of the intermediate spin state, IS,

(S = 3/2) into the HS ground state. The amount of the IS state was calculated to be 2.7% according to the equation of

Maltemo and Moss [30]. Similar values (4-10%) were obtained for (OETPP)FeCl [14, 15] and (0-1.25%) for (OMTPP)FeCl

[15]. The EPR spectrum of polycrystalline (TC6TPP)FeONO2 consists of broad signals at 6.2, 5.0 (g⊥ = (gx + gy)/2 = 5.60),

and 2.0 that are also indicative of a quantum mechanical spin-admixed (HS/IS) spin state, but with 20% S = 3/2 character,

substantially more than found for the chloride complex.

10

NMR experiments were performed in the temperature range from +50 to –93 ºC. The main purpose of the NMR

experiments was to obtain information about the ground state of the complexes at ambient temperatures, as well as their

geometry in solution, and the kinetics of inversion of the nonplanar porphyrin macrocycle. An example of the 1H NMR

spectrum of (TC6TPP)FeCl at 25 ºC is presented in Figure 5 and shows two resonances for all types of protons except p-

phenyl-H. The same is true for (TC6TPP)FeONO2. This is consistent with the C2v symmetry of the porphyrin complex in

solution and Cl– and ONO2− being bound to the iron(III), as is evident from the crystal structures as well. Peak assignment

was accomplished on the basis of DQF-COSY experiments, and by comparison of the 1D spectra with the corresponding

spectra for (OMTPP)FeCl [16] and (OETPP)FeCl [1, 16]. The chemical shifts of all resonances at two temperatures, +30 and

–70 ºC are presented in Table 4, including the values of the relaxation times, T1.

The proton chemical shifts of (TC6TPP)FeCl show non-linear temperature dependence, which was analyzed with the two-

level temperature-dependent fitting program developed in our laboratory [31, 32], and presented in detail elsewhere (Figures

S11 of [15]). According to the fitting results, (TC6TPP)FeCl adopts the intermediate spin ground state, S = 3/2, with excited

state, S = 5/2, lying 260 cm-1 higher in energy [15]. The temperature dependence of (TC6TPP)FeONO2 was investigated in

this work, and the plot of the chemical shifts and their fit to the Temperature Dependent Fitting, TDFw, program [31, 32] is

shown in Figure S3 of the Supporting Information. Again, it is found that the ground state has S = 3/2 and the excited state,

which lies 349 cm-1 higher in energy, has S = 5/2 character; however, the spin densities at the pyrrole-CH2 positions are

larger for the ground than for the excited state. Thus, the chemical shifts for CH2(α) observed at 30 oC for (TC6TPP)FeONO2

are larger than those for the chloride complex (Table 4). The ground and excited state results are not in agreement with the

EPR data for either (TC6TPP)FeCl or (TC6TPP)FeONO2. However, it should be remembered that EPR data were obtained at

4.2 K, while NMR data were obtained at much higher temperatures, where the ground and excited states can be different due

to chemical equilibria between the possible spin states.

The large downfield shifts of the CH2(α) protons (54.7, 53.0 and 72.6, 67.8 ppm at +30 ºC for (TC6TPP)FeCl and

(TC6TPP)FeONO2, respectively) are due to the presence of an unpaired electron in each π-type orbital (dxz and dyz) as well as

significant population of the σ-type dx2-y2 orbital for the two complexes. The meso-phenyl-H chemical shift differences for

(TC6TPP)FeCl, δm – δp and δm – δo, are larger (5.45 and 5.04 ppm, respectively, at +30 ºC) than the same chemical shift

differences for (TC6TPP)FeONO2 (1.38 and –0.76 ppm, respectively, at +30 oC). This suggests a relatively large amount of

positive π spin density at the meso-carbons (i.e., the same sign as the spin density on the metal) for (TC6TPP)FeCl, but not for

(TC6TPP)FeONO2. As shown previously by Cheng and coworkers [33], if the metal is significantly out of the plane of the

porphyrin ring, the a2u(π) orbital, which also has large spin density at the meso-positions, can interact with the unpaired

electron in the metal dz2 orbital and lead to spin transfer. Since the iron is further out-of-plane in the chloride (0.530 Å) as

compared to the nitrate complex (0.359 Å), this leads to significantly more spin delocalization through the dz2–a2u(π) bonding

interaction to the meso-carbons and their phenyl substituents in (TC6TPP)FeCl. In comparison, the small meso-phenyl-H

chemical shift differences for (TC6TPP)FeONO2, with δm – δp positive (+1.38 at +30 and +0.24 ppm at –70 ºC) and δm – δo

negative (–0.76 at +30 and –3.20 ppm at –70 ºC), indicate a metal electron configuration that has little or no spin density at

the meso-carbons, in agreement with the nodal properties of the 3e(π) orbital of the porphyrin, probably due to the smaller

out-of-plane position of the iron. Thus the phenyl-H chemical shifts for (TC6TPP)FeONO2 are consistent with the dπ

contribution plus the dipolar contribution to the paramagnetic shift, combined with the ring-current shift difference between

11

the phenyl-ortho and -meta protons as described recently [34]. A similar pattern of phenyl-H shifts is observed for porphyrin

complexes with axial ligands that give rise to the S = 1/2 (dxy)2(dxz,dyz)3 ground state [34].

Medforth et al. [11] have shown that NMR spectroscopy can be a useful tool for assessing the solution structures of

nonplanar porphyrin complexes by utilizing the number and position of proton resonances at different temperatures.

However, this assumes that the rate of interconversion of the possible structures is slow on the NMR time scale. In the

crystalline state (TC6TPP)FeCl adopts an almost equal mixture of saddled and ruffled geometry, while (TC6TPP)FeONO2 is

close to being just saddled, but as is shown below, the rate of interconversion of nonplanar conformations is extremely rapid

in both of these complexes (> 106 s-1). Although we might be able to use the para-phenyl protons to investigate the nonplanar

conformation of the porphyrin ring, in fact only one resonance is observed for para-phenyl protons even at –93 oC, and thus

the purely saddled conformation or rapid interconversion of ruffled and saddled forms on the NMR time scale are apparent.

In either case, the effective symmetry in solution, as observed by NMR spectroscopy, is definitely higher than that of the

crystalline state.

Determination of Porphyrin Ring Inversion Rates by Dynamic NMR Spectroscopy. If porphyrin ring inversion were

frozen on the NMR time scale, four different magnetic environments should be resolved for CH2(α) protons of both 5-

coordinate complexes. In a simplified way they can be viewed as the following: ‘up-up’ (pyrrole ring and CH2(α) protons

point toward the axial ligand), ‘up-down’ (pyrrole ring points toward the axial ligand and CH2(α) points away from the axial

ligand), ‘down-up’ (pyrrole ring points away from the axial ligand but CH2(α) points toward the axial ligand) and finally,

‘down-down’ (pyrrole ring and CH2(α) point away from the axial ligand). This is shown in the ORTEP plot of the crystal

structure of (TC6TPP)FeCl (Figure 6). Since only two CH2(α) peaks are observed in the NMR spectrum of both

(TC6TPP)FeX at any temperature, we can conclude that ring inversion of both the cyclohexene rings and the porphyrin ring is

very fast on the NMR time scale. The two observed CH2(α) resonances are attributed to diastereotopic methylene protons

that point up (toward the axial chloride or nitrate, earlier denoted as ‘up-up’ and ‘up-down’) and down (away from the axial

ligand, ‘down-up’ and ‘down-down’). Unfortunately, it is impossible to cool the sample to the temperature where all four

CH2(α) resonances are resolved. Similarly, macrocycle inversion cannot be frozen out for the analogous (TC6TPP)Ni

complex [13], even though its crystal structure shows a very nonplanar saddled conformation. For the two FeIII complexes of

this study, when the temperature is lowered, slower ring inversion causes broadening of the CH2(α) resonances, which

coalesce below, but close to –93 ºC. This broadening of the CH2(α) resonances is used to study the ring inversion kinetics of

the five-coordinate (TC6TPP)FeIII complexes.

The rate of ring inversion in (TC6TPP)FeCl was estimated by DNMR techniques utilizing standard line shape analysis [35

- 37]. Since the procedure of calculation has been described in detail elsewhere [16], only the specific results and any

differences are discussed here. First, the linewidth of both CH2(α) resonances of (TC6TPP)FeCl was plotted versus 1000η/T

(Figure 7A). As the temperature is lowered, the downfield CH2(α)1 proton signal broadens more than its upfield counterpart,

CH2(α)1, as is seen in Figure 7A. The nearly flat, high temperature part of this plot was fit to a line (Wo = 82.3 + 10780η/T)

and extrapolated into the lower temperature regime where the rate of ring inversion can be measured using DNMR

techniques. The difference between the measured linewidth, W*, and the extrapolated linewidth in the absence of exchange,

Wo, represents the increase of the linewidth due to the presence of chemical exchange, excluding the influence of other

factors. Next, the difference in frequency, ∆ν, between the two types of diastereotopic CH2(α) protons has to be obtained

12

from the two-level fit to the Curie plot [31, 32]. However, the ring inversion is very fast on the NMR time scale, and the

sample cannot be cooled to a low enough temperature to bring the system to the slow- or no-exchange regime, which

precludes measurements of ∆ν. Instead, we start with the assumption that the minimum difference in the chemical shifts, ∆ν,

must be at least as large as the maximum linewidth for the two CH2(α) resonances observed, or 3648 Hz for CH2(α)1 (–90

ºC) and 1833 Hz for CH2(α)2 (–93 °C). For larger values of ∆ν the calculated rate constant would simply be scaled by the

factor of (∆ν/3648)2 for CH2(α)1 and (∆ν/1833)2 for CH2(α)2. Thus, our assumption will not affect the calculated ∆H‡,

although it will affect ∆S‡ and kex. Results for both methylene resonances are in very good agreement and lead to the

following kinetic parameters: ∆H‡ = 29(1) kJ·mol-1, and ∆S‡ = –14(4) J·mol-1·K-1.

The danger of the constant ∆ν assumption is in the fact that for all known octaalkyltetraphenyliron(III) porphyrin

complexes for which the ring inversion was measured and which can be cooled to the slow or no-exchange regime [16] the

values of ∆ν are not constant but rather are temperature dependent. This is an intrinsic property of paramagnetic complexes.

Therefore, in order to make the calculations more correct we constructed two lines for each CH2(α)1 (δ = δ(CH2(α)1) ±

12.16/2 ppm) and CH2(α)2 (δ = δ(CH2(α)2) ± 6.11/2 ppm) (where 12.16 and 6.11 ppm are the linewidths in ppm at 300 MHz

for CH2(α)1 and CH2(α)2 at –90 and –93 ºC, respectively). This was done using the expanded (two-level) Curie fit (Figure

S11 of [15]) and the NMR Temperature Dependence Fitting, TDFw, program [31]. All constructed lines (Figure S2A and B)

intersect at the diamagnetic position (2.31 ppm) at 1/T = 0. More detailed description of the fitting process used is included in

the figure caption of Supporting Information Figure S2.

With the above assumptions, the values of kex for the ring inversion of (TC6TPP)FeCl were calculated in the temperature

range from –10 to –93 °C and the Eyring plot shown in Figure 7B was constructed. Data obtained for both CH2(α)

resonances are in good agreement with each other and result in the following activation parameters: ∆H‡ = 24(1) kJ·mol-1 and

∆S‡ = –37(3) J·mol-1·K-1, a smaller value of ∆H‡ and more negative value of ∆S‡ than obtained with the constant ∆ν

assumption discussed above. These values predict that at 25 ºC the free energy of activation, ∆G‡, is 35(2) kJ·mol-1 and the

minimum rate of ring inversion in (TC6TPP)FeCl is 4.2×106 s-1.

The calculation of the rate of ring inversion for (TC6TPP)FeONO2 was done similarly to that of (TC6TPP)FeCl, using the

TDFw plot (Figure S3) and the results are presented in Figure 7B. The following kinetics parameters were obtained: ∆H‡ =

36(1) kJ·mol-1 and ∆S‡ = 20(4) J·mol-1·K-1. These values predict that at 25 ºC the free energy of activation, ∆G‡, is 30(2)

kJ·mol-1 and the minimum rate of ring inversion is 3.8×107 s-1. As one can see from the plot, Figure 7B, the

(TC6TPP)FeONO2 inverts more rapidly at high temperatures as compared to its chloride counterpart but at –75 ºC the lines

intersect and below that temperature the situation reverses. The flexibility of both (TC6TPP)FeX are second to highest (after

[TC6TPPFe(4-CNPy)2]ClO4) among different octaalkyltetraphenylporphinatoiron(III) complexes [16] and comparable to the

flexibility of four-coordinate NiII complexes of TC5TPP, TC5T(3,4,5-OMeP)P, and TC6TPP that have free energies of

activation for ring inversion less than 33 kJ·mol-1 [7, 9], but at unreported temperatures. The ring inversion/axial ligand

rotation rates of two six-coordinate low-spin iron(III) complexes of TC6TPP have been studied previously, [TC6TPPFe(4-

Me2NPy)2]Cl [16], and [TC6TPPFe(4-CNPy)2]ClO4 [4]. The activation parameters found in these cases were ∆H‡ = 30(1) and

24(4) kJ·mol-1, respectively, and ∆S‡ = –16(6) and –20(20) J·mol-1·K-1, respectively, which predict values of ∆G‡298

= 34(3)

and 30(10) kJ·mol-1, respectively, and the minimum rates of ring inversion/axial ligand rotation at 25 oC are 6.3×106 and

13

3.8×107 s-1, respectively. The temperature-dependent plots of ln kexh/kBT vs. inverse temperature for these two complexes are

included in Figure 7B. It can be seen that for the two 6-coordinate complexes the ∆H‡ values are bracketed by those of the

two 5-coordinate complexes, the ∆S‡ are all small (too small, considering the assumptions made in obtaining these values, to

be meaningfully interpreted), and the rates of ring inversion are extremely high. Based on the comparison of the activation

parameters for the 5- and 6-coordinate complexes, there is no obvious additional barrier due to rotation of the pyridine

ligands.

In comparison to other octaalkyltetraphenylporphyrinatoiron(III) complexes (those of OMTPP, F20OETPP and OETPP)

[16], the rates and activation parameters for porphyrin inversion of (TC6TPP)FeIII again indicate the extreme flexibility of the

latter porphyrinate core: the ∆H‡ values for the three un-bridged octaalkyltetraphenylporphyrinate complexes range from 45

to 47 to 56 kJ·mol-1 (OMTPP)FeCl, (OETPP)FeCl and (F20OETPP)FeCl, respectively, as compared to (TC6TPP)FeCl (24

kJ·mol-1), while 6-coordinate low-spin complexes of (OETPP)FeIII have ∆H‡ values ranging from 49 to 63 kJ·mol-1 [16], as

compared to [TC6TPPFe(4-Me2NPy)2]+ (30 kJ·mol-1) [16]; ∆S‡ values for most of these complexes are in general small and

either positive or negative, as seen for the (TC6TPP)FeIII complexes of the present study, and thus no major conclusions can

be made concerning the observed values, which follow no particular patterns and are in many cases of the same order of

magnitude as the probable errors in the measured values, considering the necessary assumptions made in obtaining the values

of ∆ν.

In conclusion, the first synthesis and detailed characterization of 5-coordinate predominantly HS complexes of

TC6TPPFeIII porphyrins are presented. The crystal structures and NMR studies reveal high conformational flexibility of the

mainly saddled porphyrin core of these complexes.

Acknowledgements: The support of this research by the National Institute of Health, grant DK31038, the National

Science Foundation, grant CHE9610374 (X-ray diffractometer grant), and the University of Arizona Molecular Structure

Laboratory are gratefully acknowledged. The authors thank Dr. Alice Dawson for her help in structure refinement of

(TC6TPP)ONO2. This paper is dedicated to Professor Hisanobu Ogoshi on the occasion of his 70th birthday.

14

Table 1. Summary of Crystal Data and Intensity Collection Parameters.

Molecule (TC6TPP)FeCl٠2CH2Cl2٠4H2O (TC6TPP)FeONO2٠2CH2Cl2

Empirical formula C62 H64 Cl5 Fe N4 O4 C62 H56 Cl4 Fe N5 O3

Formula weight 1162.27 1116.77

Crystal system Monoclinic Orthorombic

Space group C2/c Pbca

a, Å 16.247(2) 16.3376(16)

b, Å 14.0010(18) 24.001(2)

c, Å 25.376(3) 26.699(3)

β, deg 99.236(4) 90

Volume, Å3 5697.4(13) 10469.3(18)

Z 4 8

Density (calc), g/cm3 1.355 1.417

Absorption coeff., mm-1 0.551 0.546

F(000) 2428 4648

Crystal dimension, mm3 0.47 × 0.23 × 0.14 0.36 × 0.20 × 0.20

θ limits, deg 1.63 to 26.74 1.53 to 27.06

Limiting indices -19 ≤ h ≤ 20, -17 ≤ k ≤ 17,

-31 ≤ l ≤ 31

-20 ≤ h ≤ 20, -30 ≤ k ≤ 30,

-34 ≤ l ≤ 34

Reflections utilized 29073 118127

Independent reflections 5871 [Rint = 0.0536, Rσ = 0.055] 11449 [Rint = 0.0903, Rσ = 0.054]

Redundancy 4.95 10.3

Reflection with I>2σ(I) 4190 (71.4 %) 7327 (64 %)

Completeness, % 96.7 99.7

Min/max transmission 0.844 0.900

Data/restraints/parameters 5871/0/310 11449/39/709

GoF on F2 1.036 1.028

Final R indices [I>2σ(I)] R1 = 0.0640, wR2 = 0.1376 R1 = 0.0604, wR2 = 0.1550

15

R indices (all data) R1 = 0.1026, wR2 = 0.1528 R1 = 0.1008, wR2 = 17.26

Largest diff. peak and hole, e/Å3 0.567, -0.319 0.626, -0.509

RMS dif. density, e/Å3 0.053 0.064

16

Table 2. Normal-Coordinate Structural Decomposition (NSD) [24] of Distortion Modes of TC6TPPFeIII Complexes.

Compound Doop B2u,

Saddle

B1u,

Ruffle

A2u,

Dome

Eg(x),

Wave(x)

Eg(y)

Wave(y)

A1u,

Propeller

∆24, Å |∆Cm|, Å ∆∆Cβa Å Sad/Ruf

(TC6TPP)FeCl 2.4166 1.9985 1.3508 0.1457 0.0000 0.0000 0.0095 0.40 ± 0.47 0.40 1.48

(TC6TPP)FeONO2 2.8884 2.8221 0.6028 0.0215 0.0260 0.1180 0.0108 0.48 ± 0.21 0.18 4.68

[TC6TPPFe(1-MeIm)2]Cl 1.7721 1.6073 0.7463 0.0010 0.0000 0.0000 0.0007 0.29 ± 0.26 0.23 2.15

a) ∆∆Cβ is the average differnce between the deviations of adjacent β-Cs, which reflect twisting of the pyrrole ring and therefore, the degree of ruffled deformation of the porphyrin

core.

17

Table 3. Kinetic and UV-vis parameters for (TC6TPP)FeCl, (OMTPP)FeCl and (OETPP)FeCl.

Molecule TC, ºCa ∆G‡C,a kJ·mol-1 λ Soret, nm

(OETPP)FeCl 100 (100)b 69 (66) 399; 442 (396; 444)

(OMTPP)FeCl –26 (–30) 43 (42) 398; 436 (396; 436)

(TC6TPP)FeCl ≤ –93 ≥ 30c 397; 427

a) TC is the coalescence temperature and ∆G‡C is the free energy of activation at TC

b) Data in parenthesis are taken from [6]; data not in parenthesis are taken from [16].

c) This work.

18

Table 4. Chemical shift assignments and T1 for (TC6TPP)FeX (X = Cl and ONO2) at 30 and –70 ºC.

(TC6TPP)FeCl (TC6TPP)FeONO2

T = 30 ºC T = –70 ºC T = 30 ºC T = –70 ºC

Peak

assignment

Shift, ppm T1, ms Shift, ppm Shift, ppm T1, ms Shift, ppm

CH2(α)1 54.65 4.1(1) 88.93 72.58 7.6(1) 117.00

CH2(α)2 53.04 3.8(1) 83.94 67.77 7.7(1) 107.34

m(1) 13.19 13.9(3) 16.96 10.19a Overlapped 10.14

m(2) 12.80 12.8(3) 16.01 9.93 ~37(1) 9.44

o(1) 9.21 1.3(3) 14.50 11.68 5.5(1) 14.78

p 7.55 18.3(2) 8.59 8.68 81.0(3) 9.55

CH2(β)1 7.00 6.45(8) 10.89 4.99 20.4(4) 5.43

o(2) 6.70 Overlapped 8.71a 9.97a Overlapped 11.20

CH2(β)2 5.61 7.06(12) 7.91 2.07 20.7(3) 0.28

Av (δm – δp) 5.45 – 7.90 1.38 – 0.24

Av (δm – δo) 5.04 – 4.88 –0.76 – –3.20

a) Values calculated from the two-level Curie fit [15]. Peaks are either too broad to be observed or overlapped at given temperature.

19

Fig. 1 ORTEP diagram of the porphyrin macrocycle with the numbering scheme for crystallographically unique atoms for A)

(TC6TPP)FeCl and B) (TC6TPP)FeONO2. Thermal ellipsoids are shown at 50% probability. H-atoms are omitted for simplicity.

A

B

20

42

82

54

12-1

47

-90

-49

4

-3-52

-47 53 C5

C10

C10a

C5a

1.444(4) 1.372

(4)

1.370(3)

1.40

5(4)

2.061(2)

2.044(2)127.91(6)

107.7(2)

127.

3(2)

124.

4(2)

109.1(2)

107.0

(2)

123.5(2)

Ia II

IIIa

88

105

47

724

20

-104

-82

-22

-11-51

-23

-101

-87

-25

-8-45

-18

79

97

49

1325

24

36 C5

C10

C20

C15

III II

IIV

1.451(4) 1.359

(4)1.

394(

4)

2.022

(2)

2.025(2)

125.0(2)

107.2(2)

127.

4(2)

123.

4(2)

109.5(2)

106.1

(2)122.7(2)

1.992(2)

2.015(2)

1.454(4)

Fig. 2 Formal diagram showing the displacement of the atoms in units of 0.01 Å, from the mean plane of

the 24-atom core for A) (TC6TPP)FeCl and B) (TC6TPP)FeONO2. Selected bond lengths and angles are

shown only for major component (85-90 % populated).

A

B

21

-1.0

-0.5

0.0

0.5

1.0

disp

lace

men

t in

Å

(TC6TPP)FeCl

-1.0

-0.5

0.0

0.5

1.0(TC

6TPP)FeONO

2

disp

lace

men

t in

Å

-1.0

-0.5

0.0

0.5

1.0 [TC6TPPFe(1-MeIm)2]Cl

disp

lace

men

t in

Å

Fig. 3 Linear displays of the out-of-plane deviations of the core atoms from the 24-atom mean porphyrin plane for three TC6TPP

complexes.

22

1000 2000 3000 4000 5000 6000

(TC6TPP)FeCl in CD2Cl26.60

5.29

1.98

[G]

Fig. 4 EPR spectrum of (TC6TPP)FeCl at 4.2 K in frozen CD2Cl2.

23

Fig. 5 500 MHz NMR spectrum of (TC6TPP)FeCl at 25 ºC in CD2Cl2.

CH2(α)1 CH2(α)2

CH2(β)1 CH2(β)2

o(2)o(1)

p

m(1) m(2)

Solv.H2O

α

β

CH2(α)1 CH2(α)2

CH2(β)1 CH2(β)2

o(2)o(1)

p

m(1) m(2)

Solv.H2OCH2(α)1 CH2(α)2

CH2(β)1 CH2(β)2

o(2)o(1)

p

m(1) m(2)

Solv.H2O

α

β

24

Fig. 6 ORTEP plot of the crystal structure of (TC6TPP)FeCl. Thermal ellipsoids are shown at 50% probability. Phenyl rings are

omitted for clarity.

‘up-up’

‘up-down’

‘down-down’

‘down-up’

‘up-up’

‘up-down’

‘up-up’

‘up-down’

‘down-down’

‘down-up’

‘up-up’

‘up-down’

25

0 2 4 6 8 10 12 14 16

0

1000

2000

3000

4000

CH2(α)1 CH2(α)2

(TC6TPP)FeCl

Lin

ewid

th, W

* , Hz

η*1000/T

A

26

3.5 4.0 4.5 5.0 5.5

-22

-20

-18

-16

-14

-12

ln(k

exh/

k BT

)

1000/T, K-1

[TC6TPPFe(4-Me2NPy)2]+

(TC6TPP)FeONO2 (TC6TPP)FeCl

[TC6TPPFe(4-CNPy)2]+

Fig. 7 A) Temperature dependence of the linewidths, W*, of the two CH2(α) resonances in (TC6TPP)FeCl. The linear fitting that

corresponds to the linewidth, Wo, (in the absence of chemical exchange) is shown as a straight line. It includes the contribution

from solvent viscosity, magnetic field inhomogeneity, truncation of the FID, window (multiplier) function and other parameters.

B) Eyring plot of the kinetic data for porphyrin ring inversion in (TC6TPP)FeX (X⎯ = Cl⎯, NO3⎯), [TC6TPPFe(4-Me2NPy)2]Cl

[16] and [TC6TPPFe(4-CNPy)2]ClO4 [4] in CD2Cl2.

B

27

References

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28

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