Five-coordinate iron(lll) porphycenes: 1H NMR, magnetic, and structural studies

Article abstract of DOI:10.1021/ic010725j

Five-coordinate iron(III) 2,7,12,17-tetrapropylporphycene (TPrPc)Fe^IIIX (X = C₆H₅O^-, CI^-, Br^-, I^-, CIO₄^-) complexes have been investigated. The ¹H NMR spectra demonstrate downfield shifts for pyrrole resonances [(TPrPc)Fe^III-(C₆H₅O), 65.3 ppm; (TPrPc)Fe^IIICI, 28.5 ppm] but large upfield ones for (TPrPc)Fe^IIIBr (-7.8 ppm), (TPrPc)Fe^IIIl (-49.4 ppm), and (TPrPc)Fe^IIICIO₄ (-77.1 ppm) (294 K₁ CD₂Cl₂). The pyrrole chemical shifts span the remarkable +70 to -80 ppm range. The variable-temperature ¹H NMR spectra of (TPrPc)Fe^IIIX demonstrate anti-Curie behavior with a sign reversal for (TPrPc)Fe^IIICI. These behaviors are consistent with the admixed S = 3/2, 5/2 ground electronic state with a dominating contribution of the S = 3/2 one. In terms of the chemical shift, (TPrPc)Fe^III(CIO₄) can be considered as an example of the purest S = 3/2 state in the investigated series. The extent of the S = 5/2 contribution in the admixed S = 3/2, 5/2 ground electronic state, as gradated solely the basis of the pyrrole proton paramagnetic shifts, is controlled by the strength of the axial ligand, following the magnetochemical series (Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660). Significantly iron(III) 2,7,12,17-tetrapropylporphycene, soluble in typical organic solvents, can be considered as a universal framework to classify the ligand strength in a magnetochemical series, consistently using the β-H pyrrole paramagnetic shifts as a fundamental criterion. The structure of (TPrPc)Fe^IIICI has been determined by X-ray crystallography. The iron is five-coordinate with bonds of nearly equal length to the four pyrrole nitrogen atoms (Fe-N in the range 1.983(5)-2.006(6) A). The iron lies 0.583(1) A out of the mean plane of the macrocycle and 0.502(5) A out of the mean N₄ plane. In the solid, pairs of molecules are positioned about the center of symmetry so there is face-to-face φ-φ contact. The mean plane separation is 3.38 A, and the lateral shift of the porphycene center along the Fe-N bond is 4.490 A. The distance from one porphycene center to the other is 5.62 A, and the iron-iron separation is 6.304(2) A.

Full text of DOI:10.1021/ic010725j

Inorg. Chem. 2002, 41, 1979−1988
1
Five-Coordinate Iron(III) Porphycenes: H NMR, Magnetic, and Structural
Studies
,†
Krystyna Rachlewicz,† Lechosław Latos-Graz3yn´ski,* Emanuel Vogel,‡ Zbigniew Ciunik,† and
Lucjan B. Jerzykiewicz†
Department of Chemistry, UniVersity of Wrocław, 14 F. Joliot-Curie Street,
Wrocław 50 383, Poland, and Institut fu¨r Organische Chemie, UniVersita¨t zu Ko¨ln,
Greinstrasse 4, D-50939 Ko¨ln, Germany
Received July 9, 2001
Five-coordinate iron(III) 2,7,12,17-tetrapropylporphycene (TPrPc)Fe X(X) C H O-, Cl-, Br-, I-, ClO -) complexes
III
6
5
4
have been investigated. The 1H NMR spectra demonstrate downfield shifts for pyrrole resonances [(TPrPc)Fe -
(C H O), 65.3 ppm; (TPrPc)Fe Cl, 28.5 ppm] but large upfield ones for (TPrPc)Fe Br (−7.8 ppm), (TPrPc)Fe I
(−49.4 ppm), and (TPrPc)Fe ClO (−77.1 ppm) (294 K, CD Cl2). The pyrrole chemical shifts span the remarkable
+70 to −80 ppm range. The variable-temperature 1H NMR spectra of (TPrPc)Fe X demonstrate anti-Curie behavior
with a sign reversal for (TPrPc)Fe Cl. These behaviors are consistent with the admixed S ) 3/2, 5/2 ground
electronic state with a dominating contribution of the S ) 3/2 one. In terms of the chemical shift, (TPrPc)Fe (ClO )
III
III
III
III
6
5
III
4
2
III
III
III
4
can be considered as an example of the purest S ) 3/2 state in the investigated series. The extent of the S )
5/2 contribution in the admixed S ) 3/2, 5/2 ground electronic state, as gradated solely the basis of the pyrrole
proton paramagnetic shifts, is controlled by the strength of the axial ligand, following the magnetochemical series
(Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660). Significantly iron(III) 2,7,12,17-tetrapropylporphycene,
soluble in typical organic solvents, can be considered as a universal framework to classify the ligand strength in
a magnetochemical series, consistently using the â-H pyrrole paramagnetic shifts as a fundamental criterion. The
III
structure of (TPrPc)Fe Cl has been determined by X-ray crystallography. The iron is five-coordinate with bonds of
nearly equal length to the four pyrrole nitrogen atoms (Fe−N in the range 1.983(5)−2.006(6) Å). The iron lies
0.583(1) Å out of the mean plane of the macrocycle and 0.502(5) Å out of the mean N plane. In the solid, pairs
4
of molecules are positioned about the center of symmetry so there is face-to-face π−π contact. The mean plane
separation is 3.38 Å, and the lateral shift of the porphycene center along the Fe−N bond is 4.490 Å. The distance
from one porphycene center to the other is 5.62 Å, and the iron−iron separation is 6.304(2) Å.
Introduction
rin),7,8 offer particularly interesting perspectives in alternation
and control of metalloporphyrin properties.9,10 In this respect
one takes into account the notable changes of their coordi-
nating (NNNN) tetragon geometry.
Porphyrin isomers, which emerged in the past decade,
porphycene,1 corrphycene,2,3 hemiporphycene,4,5 isopor-
phycene,6 and inverted porphyrin (2-aza-21-carbaporphy-
* To whom correspondence should be addressed. E-mail: LLG@
wchuwr.chem.uni.wroc.pl.
(5) Callot, H. J.; Rohrer, A.; Tschamber, T.; Metz, B. New J. Chem. 1995,
19, 155
(6) Vogel, E.; Bro¨ring, M.; Erben, C.; Demuth, R. Angew. Chem., Int.
Ed. Engl. 1997, 36, 353.
† University of Wrocław.
‡ Universita¨t zu Ko¨ln.
(1) Vogel, E.; Ko¨cher, M.; Schmickler, H.; Lex, J. Angew. Chem., Int.
Ed. Engl. 1986, 25, 257.
(7) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak,
T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779.
(2) Sessler, J. L.; Brucker, E. A.; Weghorn, S. J.; Kisters, M.; Scha¨fer,
M.; Lex, J.; Vogel, E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2308.
(3) Aukauloo, M. A.; Guilard, R. New J. Chem. 1994, 18, 1205.
(4) Vogel, E.; Bro¨ring, M.; Weghorn, S. J.; Scholz, P.; Deponte, R.; Lex,
J.; Schmickler, H.; Schaffner, K.; Braslavsky, S. E.; Mu¨ller, M.;
Po¨rting, S.; Fowler, C. J.; Sessler, J. L. Angew. Chem., Int. Ed. Engl.
1997, 36, 1651.
(8) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767.
(9) Sessler, J. L.; Weghorn, S. J. Expanded, Contracted and Isomeric
Porphyrins; Pergamon Tetrahedron Organic Chemistry Series, Vol.
15; Elsevier Science: Oxford, U.K., 1997.
(10) Sessler, J. L.; Gebauer, A.; Vogel, E. Porphyrin Isomers. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: New York, 2000; Vol. 2, p 1.
10.1021/ic010725j CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/12/2002
Inorganic Chemistry, Vol. 41, No. 7, 2002 1979

Rachlewicz et al.
Chart 1
Previously, some similarities between metalloporphycenes
and the corresponding metalloporphyrins have been estab-
lished.9,10 In iron(III) porphycene (PcFeIII) chemistry, the
following series of complexes were reported: PcFeIIIX (X
-
) Cl-, Br-, N3 , CH3COO-, CF3COO-, C6H5O-),11,12
[(PcFeIII)]2O,13,14 PcFeIIIR, (R ) aryl ligands),15,16 and [PcFe-
(THF)2]ClO4.17 Using electrochemistry and spectroelectro-
chemistry, it has been demonstrated that porphycene stabi-
lizes high oxidation states of iron in the following systems:
[(Pc•)FeIII]2+,18 [PcFeIVR]+,19 and {[(PcFeIV)]2O}2+.14,18 Iron-
(II) porphycene, when generated electrochemically, was also
found to react spontaneously with dioxygen to give a µ-oxo-
bridged diiron(III) species.18 Introduction of dioxygen into
a toluene-d8 solution of (TPrPc)FeII at 203 K resulted in
formation of a µ-peroxo diiron(III) porphycene, (TPrPc)-
FeIII-O-O-FeIII(TPrPc).20 Reaction of (TPrPc)FeIII-O-O-
FeIII(TPrPc) with nitrogen bases (B, pyridine-d5, 1-meth-
ylimidazole) resulted in a homolytic cleavage of the µ-peroxo
bridge to form the ferryl porphycene B(TPrPc)FeIVO com-
plex.20
probe of the spin density and/or a ground electronic state.
The structural and magnetic susceptibility investigations
corroborated the NMR analysis.
Results
Synthesis. A general route to synthesize (TPrPc)FeIIIX
complexes is a cleavage of the µ-oxo derivative [(TPrPc)-
FeIII]2O with the appropriate acid HX (X ) Cl-, Br-, I-).12
[(TPrPc)FeIII]2O + 2HX f 2(TPrPc)FeIIIX + H2O (1)
1
The H NMR spectra of paramagnetic metalloporphy-
rins21,22 and core-modified metalloporphyrins23 offer a sensi-
tive probe for distinguishing between the various spin,
ligation, and oxidation states of the formed species. Gener-
ally, some essential qualitative similarities of the spectro-
scopic patterns of iron porphyrin and iron porphycenes at
each oxidation state have been detected.12,20 The observed
differences could result either from an altered delocalization
path or from the modifications of the ground electronic state.
Actually both factors may act simultaneously.
Conversion of the chloride ion to the perchlorate ion was
carried out with use of the silver perchlorate.24,25
(TPrPc)FeIIICl + AgClO4 f (TPrPc)FeIIIClO4 + AgCl (2)
(TPrPc)FeIII(C6H5O) has been obtained in the reaction of
(TPrPc)FeIIICl with sodium phenoxide.
(TPrPc)FeIIICl + C6H5ONa f
1
In the present paper we have focused on the H NMR
(TPrPc)FeIII(C6H5 O) + NaCl (3)
characterization of five-coordinate iron(III) 2,7,12,17-tetra-
n-propylporphycene (TPrPc)FeIIIX, X ) C6H5O-, Cl-, Br-,
I-, ClO4- (Chart 1). The â-H pyrrole resonances provideds
similarly to the case of iron(III) tetraarylporphyrinssa direct
Crystal and Molecular Structure of (TPrPc)FeIIICl. The
structure of (TPrPc)FeIIICl has been determined by X-ray
crystallography. The structure displays disorder in the
location of the porphycene macrocycle. The positions of iron-
(III) and the axial chloride are preserved in both forms, but
the macrocycles are rotated by 90° with respect to the axis
defined by Fe-Cl. The perspective view of the major form
is shown in Figure 1.
There is no crystallographically imposed symmetry on the
molecule. A selection of important bond distances and angles
are reported in Table 1. The iron is five-coordinate with
bonds of nearly equal length (Fe-N in the range 1.983(5)-
2.006(6) Å) to the four pyrrole nitrogen atoms. The Fe-N
distances are slightly shorter than determined for typical five-
coordinate high-spin (S ) 5/2) iron(III) porphyrins.26-31
These distances are shorter than those observed for highly
distorted chloroiron(III) porphyrins.32-34 In fact these bond
lengths are in the range determined for the iron(III) porphyrin
with pure S ) 3/2 or admixed S ) 3/2, 5/2 spin states.24,35-40
The corresponding bond distances in chloroiron(III) tetraaza-
porphyrin (pure S ) 3/2)41 and chloroiron(III) phthalocya-
(11) Gisselbrecht, J. P.; Gross, M.; Ko¨cher, M.; Lausmann, M.; Vogel, E.
J. Am. Chem. Soc. 1990, 112, 8618.
(12) Lausmann, M.; Zimmer, I.; Lex, J.; Lueken, H.; Wieghardt, K.; Vogel,
E. Angew. Chem., Int. Ed. Engl. 1994, 33, 736.
(13) Oertling, W. A.; Wu, W.; Lo´pez-Garriga, J.-L.; Kim, Y.; Chang, C.
K. J. Am. Chem. Soc. 1991, 113, 127.
(14) Kadish, K. M.; Boulas, P.; D’Souza, F.; Aukauloo, A. M.; Guilard,
R.; Lausmann, M.; Vogel, E. Inorg. Chem. 1994, 33, 471.
(15) Kadish, K. M.; D’Souza, F.; Van Caemelbecke, E.; Boulas, P.; Vogel,
E.; Aukauloo, A. M.; Guilard, R. Inorg. Chem. 1994, 33, 4474.
(16) Kadish, K. M.; Tabard, A.; Van Caemelbecke, E.; Aukauloo, A. M.;
Richard, P.; Guilard, R. Inorg. Chem. 1998, 37, 6168.
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N.; Nakamura, M. Inorg. Chem. 2001, 40, 3650.
(18) Bernard, C.; Le Mest, Y.; Gisselbrecht, J. P. Inorg. Chem. 1998, 37,
181.
(19) Kadish, K. M.; Tabard, A.; Van Caemelbecke, E.; Aukauloo, A. M.;
Richard, P.; Guilard, R. Inorg. Chem. 1998, 37, 6168.
(20) Rachlewicz, K.; Latos-Graz˘yn´ski, L. Vogel, E. Inorg. Chem. 2000,
39, 3247.
(21) Walker, F. A.; Simonis, U. Biological Magnetic Resonance. In NMR
of Paramagnetic Molecules; Berliner, L. J., Reuben, J., Eds.; Plenum
Press: New York, 1993; Vol. 12, p 133.
(22) Walker, F. A. Proton NMR Spectroscopy of Paramagnetic Metal-
loporphyrins. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 5, p
81.
(23) Latos-Graz˘yn´ski, L. Core Modified Heteroanalogues of Porphyrins
and Metalloporphyrins. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000;
Vol. 2 p 361.
(24) Reed, C. A.; Mashinko, T.; Bentley, S. P.; Kastner, M. E.; Scheidt,
W. R.; Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979, 101, 2948.
(25) Nesset, M. J. M.; Cai, S.; Shokhireva, T. Kh.; Shokhirev, N. V.;
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2000, 39, 532.
1980 Inorganic Chemistry, Vol. 41, No. 7, 2002

FiWe-Coordinate Iron(III) Porphycenes
The macrocycle is not planar as the diagram in Figure 2
shows. The core conformation is a rooflike folding where
the bipyrrolic carbons are displaced with respect to the mean
N4 plane opposite the iron(III). The maximum deviation of
the carbon atom from the N4 plane equals 0.24 Å. The iron
lies 0.583(1) Å out of the mean plane of the macrocycle
and 0.502(5) Å out of the mean N4 plane. However, these
values are notably smaller when compared to two iron(III)
porphycenes structurally characterized till now.12 Namely,
the relevant values equal for [(TPrPc)FeIII]2O 0.84 Å (the
porphycene mean plane) and 0.67 Å (the N4 mean plane)
and for [(T(t-Bu)Pc)FeIII]2O 0.60 Å (the N4 mean plane).12
For these, displacements of high-spin five-coordinate iron
from the porphyrin plane of 0.39-0.62 Å and from the N4
plane of 0.39-0.54 Å are found.26-34 The corresponding
displacement values are typically smaller for the admixed
spin state five-coordinate iron(III) porphyrins.24,35-39
In the solid, pairs of molecules are positioned about the
center of symmetry so there is face-to-face π-π contact.
The two molecules do not fully overlay. Rather they are
offset as is commonly seen when porphyrin macrocycles
stack over one another. This offset is best seen by referring
to Figure 3, which shows two views of the pair of molecules.
The lower view is oriented so that one looks upon two nearly
parallel planes.
Within this pair, the mean plane separation is 3.38 Å and
the lateral shift of the porphycene center along the Fe-N
bond is 4.49 Å. The distance from one porphycene center to
the other is 5.602 Å, and the iron-iron separation is 6.304-
(2) Å. The shortest C---C contact within this pair is 3.368 Å
and involves C3-C9′. The lateral shift and the mean plane
separation within [(TPrPc)FeIIICl place this molecule at the
border region between I and W groups of the classification
of Scheidt and Lee.29 The I group contains the metallopor-
phyrin with an intermediate degree of π-π overlap. The
continuous decrease of π-π overlap is characteristic for the
W group.
It is interesting to note that the close C---C contact occurs
also in the second pair. This is illustrated in Figure 3. The
shortest C---C separation involves two meso carbons. Within
this pair, the mean plane separation is 3.35 Å and the lateral
shift of the porphycene centers along the iron and C9-C10
midpoint is 7.289 Å. The distance from one porphycene
center to the other is 8.02 Å, and the iron-iron separation
is 7.68 Å. The lateral shift and the mean plane separation
within [(TPrPc)FeIIICl place this molecule in the W group
of the classification of Scheidt and Lee. The Cl atom acts as
an acceptor of two C(sp2)-H‚‚‚Cl hydrogen bonds. Their
geometric parameters (Table 2) suggest that these interactions
are rather weak.43
Crystal and Molecular Structure of (TPrPc)FeII. The
structure of (TPrPc)FeII has been determined by X-ray
crystallography. The perspective view is shown in Figure 4.
A selection of important bond distances and angles are
reported in Table 1. The iron atom is four-coordinate with
Figure 1. Perspective view of (TPrPc)FeIIICl showing 50% thermal
countours.
nines (admixed intermediate-spin state) are equal to 1.929
and 1.945 Å, respectively.42 Importantly the Fe-N bond
distances in (TPrPc)FeIIICl are shorter than found for µ-oxo
diiron(III) porphycene complexes: [(TPrPc)FeIII]2O, 2.052
Å; [(T(t-Bu)Pc)FeIII]2O, 2.056 Å.12 The Fe-Cl distance is
2.2508(9) Å, which is typical for chloroiron(III) porphy-
rins28,31-34 and resembles that for chloroiron(III) phthalo-
cyanine and chloroiron(III) tetraazaporphyrin.41,42
(26) Phillippi, M. A.; Baenziger, N.; Goff, H. M. Inorg. Chem. 1981, 20,
3904.
(27) Gold, A.; Jayaraj, K.; Doppelt, P.; Fischer, J.; Weiss, R. Inorg. Chim.
Acta 1988, 150, 177.
(28) Scheidt, W. R.; Gouterman, M. Ligands, Spin State, and Geometry in
Hemes and Related Metalloporphyrins. In Iron Porphyrins Part I;
Lever, A. B. P., Gray, H., Eds.; Addison-Wesley: Reading, MA, 1983;
p 89.
(29) Scheidt, W. R.; Lee, Y. Struct. Bonding (Berlin) 1987, 64, 1.
(30) Scheidt, W. R.; Finnegan, M. G. Acta Crystallogr. 1989, C45, 1214.
(31) Balch, A. L.; Latos-Graz˘yn´ski, Noll, B. C.; Olmstead, M. M.; Zovinka,
E. P. Inorg. Chem. 1992, 31, 2248.
(32) Cheng, R.-J.; Chen, P.-Y.; Gau, P.-R.; Chen, C.-C.; Peng, S.-M. J.
Am. Chem. Soc. 1997, 119, 2563.
(33) Schu¨nemann, V.; Gerdan, M.; Trautwein, A. X.; Haoudi, N.; Mandon,
D.; Fischer, J.; Weiss, R.; Tabard, A.; Guilard, R. Angew. Chem., Int.
Ed. 1999, 38, 3181.
(34) Mazzanti, M.; Marchon, J.-C.; Wojaczyn´ski, J.; Wołowiec, S.; Latos-
Graz˘yn´ski, L.; Shang, M.; Scheidt, W. R. Inorg. Chem. 1998, 37, 2476.
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1985, 24, 4325.
(36) Gupta, G. P.; Lang, G.; Lee, Y. J.; Scheidt, W. R.; Shelly, K.; Reed,
C. A. Inorg. Chem. 1987, 26, 3022.
(37) Masuda, H.; Taga, T.; Osaki, K.; Sugimoto, H.; Yoshida, Z.-I.; Ogoshi,
H. Inorg. Chem. 1980, 19, 950.
(38) Gonzales, J. A.; Wilson, L. J. Inorg. Chem. 1994, 33, 1543.
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H.; Nasri, H.; Doppelt, P.; Mandon, D.; Fischer, J.; Weiss, R. Inorg.
Chem. 1990, 29, 2741.
(40) Simonato, J.-P.; Pe´caut, J.; Le Pape, L.; Oddou, J.-L.; Jeandey, C.;
Shang, M.; Scheidt, W. R., Wojaczyn´ski, J.; Wołowiec, S.; Latos-
Graz˘yn´ski, L.; Marchon, J.-C. Inorg. Chem. 2000, 39, 3978.
(41) Fitzgerald, J. P.; Haggerty, B. S.; Rheingold, A. L.; May, L.; Brewer,
G. A. Inorg. Chem. 1992, 31, 2006.
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L. Inorg. Chem. 1985, 24, 2040.
(43) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural
Chemistry and Biology; Oxford University Press: Oxford, 1999; pp
215-2221.
Inorganic Chemistry, Vol. 41, No. 7, 2002 1981

Rachlewicz et al.
Table 1. Selected Bond Distances for Iron Porphycene Complexes
(TPrPc)FeII a
(TPrPc)FeIIICla
2.000
[(TPrPc)FeIII]2O12
2.052
(OETAP)FeCl40
1.929(7)
(PPIX)FeClb
(Pc)FeCl41
1.945(4)
Fe-N
1.932(5)
1.898(6)
2.067(6)
Fe-Cl
2.2508(9)
1.929
0.510
2.278(2)
1.897(3)
0.352(3)
2.218(6)
2.007(6)
0.475(10)
2.320(2)
1.871
0.30
N-Ct
0
0.67
Fe-N4 displacement
0
a This work. b Koenig, D. F. Acta Crystallogr. 1965, 18, 663.
Figure 2. Diagram of the macrocyclic core of (TPrPc)FeIIICl. Each atom
symbol has been replaced by a number that represents the perpendicular
displacement (in units of 0.01 Å) of from the mean porphycene plane.
Fe-N bonds of nearly equal length (Fe-N in the range
1.988(6)-1.930(6) Å) to the four pyrrole nitrogen atoms.
Thus, the bond lengths are similar to that found for nickel-
(II) porphycene (1.90 Å).44 The relatively short equatorial
Fe-N bond distances are wholly consistent with the S ) 1
intermediate-spin state of (TPrPc)FeII with an unpopulated
Figure 3. Views of a pair of (TPrPc)FeIIICl molecules showing the overlap
between adjacent molecules in the solid.
Table 2. Lengths (Å) and Angles (deg) of the Hydrogen Bonds
D-H‚‚‚Aa
D‚‚‚A
H‚‚‚A
D-H‚‚‚A
C(10)-H(10)‚‚‚Cl(1i)
3.619 (3)
3.635 (3)
2.79
2.75
146
156
2
2
dx -y orbital. Such an electronic structure has been previously
identified on the basis of 1H NMR spectra.20 The Fe-N bond
distances are slightly shorter than determined for the relevant
four-coordinate intermediate-spin (S ) 1) (OEP)FeII (1.972
Å) and (TPP)FeII (1.996 Å) compounds.45,46 The macrocycle
is planar. The iron lies in the mean plane of the macrocycle.
In the solid, stacks of molecules are positioned along the a
crystal axis so there is face-to-face π-π contact. The
molecules do not fully overlay. Rather they are offset as is
commonly seen when porphyrin macrocycles stack over one
another. Within the pair, the mean plane separation is 3.5 Å
and the lateral shift of the porphycene centers is 3.8 Å. The
distance from one porphycene center to the other is 5.196
Å. The lateral shift and the mean plane separation within
[(TPrPc)FeII place this molecule in the I group of the
classification of Scheidt and Lee.29
C(20)-H(20)‚‚‚Cl(1ii)
a Code of equivalent symmetry positions: (none) x, y, z; (i) 2 - x, 1 -
y, -z; (ii) 1 - x, -y, -z.
Figure 4. Perspective view of (TPrPc)FeII showing 30% thermal contours.
(44) Vogel, E.; Balci, M.; Pramod, K.; Koch, P.; Lex, J.; Ermer, O. Angew.
Chem., Int. Ed. Engl. 1987, 26, 928.
(45) Collman, J. P.; Hoard, J. L.; Kim, N.; Lang, G.; Reed, C. A. J. Am.
Chem. Soc. 1975, 97, 2676.
(46) Strauss, S. H.; Silver, M. E.; Long, K. M.; Thomson, R. G.; Hudgens,
R. A.; Spartalian, K.; Ibers, J. A. J. Am. Chem. Soc. 1985, 107, 4207.
Although the iron(II) porphycene complex is not the main
topic of this paper, we have found it essential to report its
structural parameters to provide an adequate example of the
2
2
iron porphycene structure with an unpopulated dx -y orbital.
1982 Inorganic Chemistry, Vol. 41, No. 7, 2002

FiWe-Coordinate Iron(III) Porphycenes
Table 3. 1H NMR Data for (TPrPc)FeIIIX Complexes in
a
Dichloromethane-d2
pyrr
meso
R-CH
compound
294 K 203 K 294 K 203 K 294 K 203 K
(TPrPc)FeIII(PhO)
65.3
28.5
95.1 -13.3 -24.1 38.3
55.9
50.8
56.6
43.9
71.3
60.7
81.8
71.0
34.1
-73.4 -15.3 -11.9 39.3
37.2
(TPrPc)FeIIICl
(TPrPc)FeIIIBr
(TPrPc)FeIIII
-7.8 -123.1
-9.3 -10.0 39.0
30.4
-49.4 -127.9
-0.4
-1.4
-6.8 40.5
25.4
(TPrPc)FeIII(ClO4) -77.1 -123.3
-7.5 44 (br) 86.6
73.2
a All chemical shifts relative to that of TMS.
detected for (TPrPc)FeIIIBr, (TPrPc)FeIIII, and (TPrPc)FeIII-
ClO4 (294 K, CD2Cl2). The â-H pyrrole chemical shifts span
the remarkable +70 to -80 ppm range. The upfield
relocation increases in the series C6H5O-, Cl-, Br-, I-, and
-
ClO4 at 294 K in dichloromethane-d2. The â-H pyrrole
chemical shift of (TPrPc)FeIII(C6H5O) (65.3 ppm), although
of the same sign, is smaller than the â-H pyrrole shifts found
in a group of high-spin (TPP)FeX complexes (X ) C6H5O-,
Cl-, Br-, I-) where such a value is practically independent
of the ligand and equals 80 ppm (293 K).21,22,47-49 For
instance, the dissimilarity is clearly pronounced for the chloro
derivatives (TPP)FeIIICl (80 ppm) and (TPrPc)FeIIICl (28.5
ppm).
The variable-temperature 1H NMR spectra of (TPrPc)FeIII-
Cl demonstrate an anti-Curie behavior (Figure 5, traces B
and E). Particularly the downfield shift of the â-H pyrrole
resonance (294 K) is transformed into an upfield shift at the
low-temperature range assuming a 0 ppm value of the
paramagnetic shift at ca. 250 K. The relevant plots of pyrrole
chemical shifts as a function of the inverse temperature are
shown in Figure 6. (The complete plots are included in the
Supporting Information.)
The behavior of the isotropic shift is specific for each
complex. Typically the 1/T dependence is nonlinear. An
attempt of a linear extrapolation with respect to 1/T on the
basis of observed shifts at the lower temperature limit (233-
193 K) resulted in unrealistic intercepts far from the
diamagnetic position. The apparent intercepts of the imposed
straight line for (TPrPc)FeIII(C6H5O), (TPrPc)FeIIICl, (TPrPc)-
FeIIIBr, (TPrPc)FeIIII, (TPrPc)FeIII(ClO4) are -1.3, 433.0,
197.0, 116.0, and 28.0 ppm, respectively.
Figure 5. 1H NMR spectra of (A) (TPrPc)FeIII(C6H5O), (B) (TPrPc)FeIII-
Cl, (C) (TPrPc)FeIIIBr, and (D) (TPrPc)FeIII(ClO4), all measured in
dichloromethane-d2 at 294 K. Inset D′ shows the R-CH2 region of the
spectrum of (TPrPc)FeIII(ClO4) at 203 K. Trace E presents the spectrum of
(TPrPc)FeIIICl measured at 203 K in dichloromethane-d2. Labels: pyrr,
pyrrole H; meso, meso-H; R-CH2, R-methylene of the propyl substituent;
o, m, and p, ortho H, meta H, and para H of the phenoxy ligand.
1H NMR Studies of (TPrPc)FeIIIX. The 1H NMR spectra
of (TPrPc)FeIIIX are shown in Figure 5. The identity of the
pyrrole resonances in these and all other spectra has been
confirmed by a specific deuteration of the pyrrole positions
to yield (TPrPc-d4)FeIIIX. The meso and alkyl resonances
have been assigned by their chemical shifts, intensities, and
relative line widths. The doublet, detected for R-CH2 protons
of n-propyl groups, allowed an unambiguous identification
of the five-coordinate structure for (TPrPc)FeIIIX (where X
-
) PhO-, Cl-, Br-, I-, ClO4 ) in dichloromethane-d2 (Figure
1H NMR spectroscopy of paramagnetic iron porphyrins
provides a particularly useful tool for characterizing the
oxidation/spin/ligation states of the iron.21,22 Recently we
have shown that in the series of iron porphycene derivatives
(TPrPc)FeII, (TPrPc)FeIII-O-FeIII(TPrPc), (TPrPc)FeIII-O-
O-FeIII(TPrPc), and B(TPrPc)FeIVO the positions of the â-H
pyrrole resonances resemble those found for the correspond-
5 and Table 3) and in other solvents used (Table 4).
Such a pattern results from a diasterotopic effect. The
situation is more complex for (TPrPc)FeIIIClO4, where the
fast inversion of iron(III) with respect to the porphycene
plane accounts for a broad singlet of R-CH2 at 294 K in
CD2Cl2 (Figure 5, trace D) and in all other solvents used
with the exception of CDCl3 (Table 4). However, in the slow
exchange limit (203 K), a well-defined doublet has been
detected (Figure 5, inset D′). Remarkably, the sign of the
paramagnetic shift of the (TPrPc)FeIIIX pyrrole resonances
is determined by the choice of an axial ligand. Thus,
downfield shifts have been determined for (TPrPc)FeIII-
(C6H5O) and (TPrPc)FeIIICl, but large upfield ones have been
(47) La Mar, G. N.; Eaton, G. R.; Holm, R. H.; Walker, F. A. J. Am. Chem.
Soc. 1973, 95, 63.
(48) La Mar, G.; Walker, F. A. Nuclear Magnetic Resonance of Paramag-
netic Metalloporhyrins. In The Porphyrins; Dolphin, E., Ed.; Academic
Press: New York, 1979; Vol. IVB, pp 57-161.
(49) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Hrycyk, W.; Pacholska, E.;
Rachlewicz, K.; Szterenberg, L. Inorg. Chem. 1996, 35, 6861.
Inorganic Chemistry, Vol. 41, No. 7, 2002 1983

Rachlewicz et al.
Table 4. Solvent Dependence of the Chemical Shifts of the â-Pyrrole and R-CH2 1H NMR Resonances for (TPrPc)FeIIIX Complexesa
dichloromethane- d2 chloroform-d acetonitryl-d3 acetone-d6 benzene-d6
â-pyrr R-CH2 â-pyrr R-CH2
64.9 38.0
toluene-d8
compound
â-pyrr
R-CH2
â-pyrr
R-CH2
â-pyrr
R-CH2
â-pyrr
R-CH2
(TPrPc)Fe(PhO)
64.4
38.3
34.1
39.3
37.2
39.0
30.4
40.5
25.4
44.5b
66.5
46.0
38.2
33.5
40.0
38.9
39.7
35.0
39.2
25.4
39.2b
66.2
52.3
36.9
31.5
40.7
36.6
38.0b
66.7
36.7
31.6
40.4
36.5
38.6
38.0
36.1
31.4
41.4b
34.1
38.7
36.3
38.1
30.5
35.7
21.2
47.4b
30.5b
insoluble
25.6 40.0
(TPrPc)FeCl
(TPrPc)FeBr
(TPrPc)FeI
28.5
-7.8
26.8
-4.6
59.9
36.2
17.0
32.6
36.7
insoluble
-49.4
-76.9
-51.0
-75.2
-66.3
40.0b
30.0b
46.5b
-36.0
-71.1
-23.7
-75.8
38.6
29.4
54.6b
-19.6
-75.7
(TPrPc)Fe(ClO4)
-78.2
a 294 K. b Broad.
to a smaller extent with the π orbitals of porphycene. In the
case of the high-spin iron(III) center both σ an π delocal-
ization routes can operate, resulting in downfield â-H
shifts.21,22,47-49
The intermediate S ) 3/2 ground electronic state should
be characterized by an upfield shift as the low-spin one as
the identical delocalization path is operating. The shift value
is expected to be large as there are two π symmetry unpaired
electrons in the S ) 3/2 state in comparison to that for S )
1/2.21,22,40,50-56
In several cases the pure S ) 5/2 and pure S ) 3/2
electronic states are closely spaced so the spin-orbit coupling
provides the mechanism for mixing them.24,37,57-61 1H NMR
spectra are quite sensitive to the S ) 5/2 and S ) 3/2
contributions in the spin-admixed complexes.25,54,55,61-63 In
addition temperature changes affect the contribution of the
two states with a dramatic effect on the pyrrole proton
shifts.25,32-34,58-60,64 However, the thermal equilibrium be-
tween two pure spin states may result in identical 1H NMR
behavior. Consequently it may be difficult to discriminate
between spin equilibria and spin-admixed states solely on
Figure 6. Pyrrole chemical shift versus 1/T for (A) (TPrPc)FeIII(C6H5O),
(B) (TPrPc)FeIIICl, (C) (TPrPc)FeIIIBr, (D) (TPrPc)FeIIII, and (E) (TPrPc)-
FeIII(ClO4).
ing iron porphyrin derivatives as far as a general pattern is
concerned.20 The R-CH2 resonances of the propyl groups
follow the pattern, but they are downfield shifted practically
in each considered case. Thus, only their relative values of
the paramagnetic shift might be helpful in the spectroscopic
analysis.
The contact shifts are indicative of which iron d orbital
and porphyrin molecular orbital are involved in the transmis-
sion of the unpaired electron in the macrocycle periphery.21,22
The analogous correlation is expected to be valid for iron
porphycenes as well. Generally the ground state of the iron-
(III) porphycene can be related to the following models of
the electronic configuration:
1
the basis of H NMR investigations.25
Several examples of pure S ) 3/2 iron(III) porphyrins have
been reported presenting typically a strong upfield shift for
â-H.25,54,55 Strong upfield chemical shifts have been detected
for (2,4,6-(OMe)3TPP)FeIIIClO4 (-30.6 ppm) (CDCl3, 298
K)24,63 and iron(III) porphyrin with vinyl carbene inserted
(50) Latos-Graz˘yn´ski, L.; Cheng, R.-J.; La Mar, G. N.; Balch, A. L. J.
Am. Chem. Soc. 1981, 103, 4270.
(51) Mansuy, D.; Morgenstern-Baderau, I.; Lange, M.; Gans, P. Inorg.
Chem. 1982, 21, 1427.
(52) Balch, A. L.; Cheng, R.-J.; La Mar, G. N.; Latos-Graz˘yn´ski, L. Inorg.
Chem. 1985, 24, 2651.
(53) Artaud, I.; Gregoire, N.; Leduc, P.; Mansuy, D. J. Am. Chem. Soc.
1990, 112, 6899.
2
3
0
0
2
4
1
2
2
(i) low spin (dxy) (dxzdyz) (dz ) (dx -y ) or (dxzdyz) (dxy) -
(54) Reed, C. A.; Guiset, F. J. Am. Chem. Soc. 1996, 118, 3281.
(55) Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660.
(56) Ikeue, T.; Saitoh, T.; Yamaguchi, T.; Ohgo, Y.; Nakamura, M.;
Takahashi, M.; Takeda, M. Chem. Commun. 2000, 1989.
(57) Dolphin, D. H.; Sams, J. R.; Tsin, T. B. Inorg. Chem. 1977, 16, 711.
(58) Maltempo, M. M. J. Chem. Phys. 1974, 61, 2540.
(59) Maltempo, M. M.; Moss, T. H.; Cusanovich, M. A. Biochim. Biophys.
Acta 1974, 342, 290.
(60) Maltempo, M. M.; Moss, T. H. Q. ReV. Biophys. 1976, 9, 181.
(61) Goff, H. M.; Shimomura, E. J. Am. Chem. Soc. 1980, 102, 31.
(62) Boersma, A. D.; Goff, H. M. Inorg. Chem. 1982, 21, 581.
(63) Goff, H. M., M. Nuclear Magnetic Resonance of Iron Porphyrins. In
Iron Porphyrins Part I; Lever, A. B. P., Gray, H., Eds.; Addison-
Wesley: Reading, MA, 1983; p 237.
0
0
2
2
2
(dz ) (dx -y ) ,
(ii) high spin (dxy) (dxz) (dyz) (dz ) (dx -y ) ,
1
1
1
1
1
2
2
2
2
1
1
1
0
2
2
2
(iii) intermediate spin (dxy) (dxz) (dyz) (dz ) (dx -y ) .
These configurations should be clearly distinguishable by
1H NMR spectroscopy. In the regular low-spin case one can
expect the upfield position of the pyrrole resonances due to
the transmission of the spin density from (dxzdyz)3 to the π
filled orbitals of porphycene. In the less common low-spin
case the pyrrole H resonance should be shifted very little
because of localization of the unpaired electron on the dxy
orbital of iron(III), which, because of its symmetry, overlaps
(64) Toney, G. E.; terHaar, L. W.; Savrin, J. E.; Gold, A.; Hatfield, W. E.;
Sangaiah, R. Inorg. Chem. 1984, 23, 2563.
1984 Inorganic Chemistry, Vol. 41, No. 7, 2002

FiWe-Coordinate Iron(III) Porphycenes
between iron and the pyrrole nitrogen (25.7, -19.7, -23.9,
and -40.5 ppm) (298 K, CDCl3),52 with the most upfield
value determined for (TPP)FeIII(CB11H6Br6) (-62 ppm)
(C6D6, 298 K).55
Thus, the contact shift pattern of (TPrPc)FeIIIX measured
at 203 K of Table 3 reflects extensive spin delocalization
into the π molecular orbital of porphycene similarly to that
found for iron(III) porphyrin complexes. The dominance of
the π spin transfer mechanism can also be taken as direct
2
2
evidence that dx -y is weakly populated or not populated at
this temperature. The 1H NMR spectrum of low-spin
[(TPrPc)FeIII(Im)2]+ measured at 223 K reveals that the
paramagnetic shift of the â-H resonance equals -19.7,
clearly pointing out the difference in the extent of π
delocalization, which is smaller for the S ) 1/2 ground
electronic state in comparison to S ) 3/2 as rationalized
above. The intermediate-spin iron(II) porphycene also dem-
onstrated a strongly upfield shifted pyrrole resonance (-37.52
Figure 7. Temperature dependence of the øMT product for microcrystalline
samples of (TPrPc)FeIIICl (A) and (TPrPc)FeIIIBr (B) in the range 2-300
K.
The most upfield position of the meso-H resonance (Table
3) is observed for (TPrPc)FeIII(C6H5O), with the largest S )
5/2 contribution in the series. (TPrPc)FeIII(ClO4) demonstrates
a less upfield shifted meso-H position than any compound
in the group. This observation leads to the conclusion that
the S ) 5/2 state locates more of the positive spin density at
the meso position than the S )3/2 one does.
2
2
ppm) at 293 K accounted for by depopulation of the dx -y
2
2
1
1
0
2
2
2
orbital in the (dxy) (dz ) (dxz) (dyz) (dx -y ) electronic struc-
ture.20
Considering the values of the chemical shifts and pro-
nounced non-Curie behavior of the pyrrole as well as meso
signals demonstrated in the variable-temperature experiments,
one can conclude that the (TPrPc)FeIIICl, (TPrPc)FeIIIBr, and
(TPrPc)FeIIII complexes reveal the admixed S ) 3/2, 5/2
ground electronic state, with a dominating contribution of
the S ) 3/2 one. Once temperature increases the S ) 5/2
contribution gains importance as clearly illustrated by the
positive deviation from the Curie law for all pyrrole
resonances and the values of the intercepts found for the
forced linear extrapolations.
Magnetization Measurements. The magnetization prop-
erties of microcrystalline samples of (TPrPc)FeIIICl and
(TPrPc)FeIIIBr have been investigated to evaluate the spin
state of the iron centers. Figure 7 illustrates the temperature
dependence of the product of molar susceptibility and
temperature.
The Curie-Weiss plot of (TPrPc)FeIIICl is not strictly
linear. The plot of øMT demonstrates that this value varies
in the relatively small range 3.4-3.8 cm3 K mol-1 (µeff
)
In terms of the chemical shift (TPrPc)FeIII(ClO4) and
recently reported [(TPrPc)FeIII(THF)2]ClO4)17 can be con-
sidered as examples of the purest S ) 3/2 state in the series
where the corresponding shift sets the limits at any temper-
ature considered. The high-spin limit behavior is exemplified,
at least at 294 K, by (TPrPc)FeIII(C6H5O). Apart from the
distinctive downfield pyrrole resonance position, we have
identified axial ligand resonances at (ortho) -115.47 ppm,
(meta) 89.16 ppm, and (para) -104.18 ppm (294 K, CD2-
Cl2). The resonance assignments for this ligand are based
on the previous assignments of phenoxy complexes, intensi-
ties of the resonances, and line widths.65-67 These values
are slightly smaller when compared to those found for (TTP)-
FeIII(C6H5O): ortho, -118.4 ppm; meta, 95 ppm; para,
-109.7 ppm (298 K, C7D8).67 The detected differences reflect
some contribution of the S ) 3/2 state in the ground
electronic state of (TPrPc)FeIII(C6H5O). As determined for
the corresponding aryloxy iron(III) porphyrin complexes, the
opposite signs of the shifts for meta versus ortho and para
5.2-5.5 µB) at the 50-300 K limits. These values are two
low for high-spin iron(III) (4.37 cm3 K mol-1 or 5.9 µB)
and too high for the intermediate-spin (1.87 cm3 K mol-1 or
3.9 µB) assignment. At lower temperatures the øMT product
decreases to 1.32 cm3 K mol-1 (3.25 µB) at 2.1 K. Such a
behavior of magnetic susceptibility might be expected in the
framework of the admixed S ) 3/2, 5/2 spin model, with a
dominating S ) 5/2 contribution, presuming that the complex
presents a zero-field splitting component to account for the
low-temperature limit.39 The possibility of a spin-spin
interaction can be instrumental as well since the minimum
distances between adjacent paramagnetic centers are rela-
tively small. The crystal structure of (TPrPc)FeIIICl shows
the arrangement of the molecules in double layers with
opposite orientation of the Fe-Cl bonds in the neighboring
layers and a very short interlayer distance of 3.38 Å (Figure
2). On this basis, the reason for the magnetic properties can
be related to interactions between oppositely oriented
molecules inside the double layers. However, a detailed
analysis of the ground electronic state has not been carried
out. The microcrystalline samples obtained in the bulk
syntheses may be polymorphic, and they may contain a
mixture of structurally similar species38 or reveal different
effects of solvation.54,55 Thus, examination of (TPrPc)FeIIIX
with bulk physical probes such as magnetic susceptibility
affords a resultant measurement for the different species
protons are indicative of π spin density on the aryloxy ligand
65-67
2
2
and require that the iron(III) dx -y orbital is half-occupied.
(65) Goff, H. M.; Shimomura, E. T.; Lee, Y. J.; Scheidt, W. R. Inorg.
Chem. 1984, 23, 315.
(66) Pyrz, J. W.; Roe, A. L.; Stern, L. J.; Que, L., Jr. J. Am. Chem. Soc.
1985, 107, 614.
(67) Arasasingham, R. D.; Balch, A. L.; Hart, R.; Latos-Graz3yn´ski L. J.
Am. Chem. Soc. 1990, 112, 7566.
Inorganic Chemistry, Vol. 41, No. 7, 2002 1985

Rachlewicz et al.
which may be present in the samples. Actually the existence
of two crystallographically distinct orientations of the
disordered (TPrPc)FeIIICl molecules has been determined by
X-ray crystallography. Preliminary Mo¨ssbauer data reveal
the presence of high-spin and admixed spin components.68
Remarkably the plot of the reciprocal magnetic suscepti-
bility for (TPrPc)FeIIIBr demonstrates strong deviation from
linearity, with a well-defined inflection at ca. 100 K. The
temperature dependence of the product of molar susceptibility
and temperature is shown in Figure 7. The value of the øMT
corresponding physicochemical parameters determined for
-
(TPrPc)FeIIIX (X ) C6H5O-, Cl-, Br-, I-, ClO4 ) fit the
admixed ground electronic state characteristics.
The theoretical analysis based on crystal field theory
indicates that increasing tetragonal distortion in ferric tet-
raphenylporphyrin (e.g., decreasing axial field strength) will
eventually stabilize the intermediate-spin state (S ) 3/2)
2
when the dz orbital is close in energy to the dxy, dxz, and dyz
2
2
orbitals and singly occupied, and the dx -y is considerably
higher in energy and vacant.58-60,74 A preference between
high- and intermediate-spin states depends also on the energy
product decreased smoothly from 2.87 cm3 K mol-1 (µeff
)
4.7 µB) at 298 K to 1.83 cm3 K mol-1 (µeff ) 3.9 µB) at 50
K. Such a behavior can be related to the quantum-mechanical
admixed S ) 3/2, 5/2 spin state.39 At the 50-4 K limits the
øMT product decreases below the 1.87 cm3 K mol-1 pure
spin value to approach 0.45 cm3 K mol-1 at 4 K. A decrease
of the value of the øMT product can be expected if the ground
electronic state of the complex presents a zero-field splitting
component.40,69,70 At the very low-temperature limit we have
found a behavior deviating from the Curie-Weiss law,
indicating possible antiferromagnetic interactions resembling
those detected for (TPP)FeIII(B11CH12).36
2
2
separation between the dx -y and dxy orbitals. It provides
another potential instrument for stabilizing the pure inter-
2
2
mediate-spin state (S ) 3/2) via an increase of the dx -y
orbital energy, which is controlled by the field strength of
the equatorial ligand. Consequently the mixed-spin and nearly
pure intermediate-spin states found for the chloroiron(III)
complexes of phthalocyanine42 and tetraazaporphyrin,41
respectively, are related to the stronger interaction of these
2
2
macrocycles with the iron dx -y orbital, due to their smaller
hole relative to that of the porphyrins. Thus, the combination
of a weak axial field and a small tetramethylchiroporphyrin
porphyrin ((TMCP)H2) hole in the [(TMCP)FeIII(C2H5OH)2]+
and [(TMCP)FeIII(C2H5OH)(H2O)]+ species resulted in a
ground state which is an intermediate-spin or nearly inter-
mediate-spin state (S ) 3/2).40
Discussion
In general the results of our investigations are all in accord
with the admixed S ) 3/2, 5/2 ground electronic state in the
series of five-coordinate iron(III) porphycene complexes.
The admixed S ) 3/2, 5/2 state, investigated in detail for
five- and six-coordinate iron(III) porphyrins and five-
coordinate iron(III) phthalocyanines and iron(III) tetraaza-
porphyrin, demonstrates magnetic properties that are dis-
tinctively contained in the range between the limits of the
pure S ) 3/2 and S ) 5/2 states. These include magnetic
moments between 3.9 and 5.9 µB and EPR gieff values
between 4 and 6.21,22,54,55,70-72 Mo¨ssbauer quadrupole splitting
values are contained in the 3-4.2 mm/s range for the S )
3/2 state, and this value decreases with increasing S ) 5/2
character in the spin-admixed state.54,68,57,73 The â-H pyrrole
shift values of (TPP)FeIIIX shift dramatically upfield with
increasing S ) 3/2 character.21,22,54,55,61-63 Evidently, the
The present investigation emphasizes the resemblance and
fundamental differences between iron porphycenes and iron
porphyrins observed at the five-coordinate iron(III) level.
Using the strength of the equatorial ligand as the criterion,
one can place porphycene on the borderline between por-
phyrins and tetraazaporphyrins,41 i.e., in the position adjacent
to phthalocyanines.42
The rather simple picture for the (TPrPc)FeIIIX group
detected in dichloromethane-d2 solutions by 1H NMR is more
complex in the solid state. One has to notice that the delicate
balance typical for the admixed spin state is controlled apart
from the nature of the axial and equatorial contributions and
by external factors. This opinion is clearly supported by the
observation of a strong solvent effect in the 1H NMR spectra
of (TPrPc)FeIIIX (Table 4). The replacement of the solvent
(68) Preliminary Mo¨ssbauer data collected for the (TPrPc)FeIIICl complex
presented a rather complex picture. The spectrum measured at 293 K
consists of two doublets [(A) ∆Eq ) 0.0, δ ) 0.33; (B) ∆Eq ) 1.50,
δ ) 0.23 (mm s-1)]. The temperature decrease to 10 K preserves the
number of species although the spectroscopic parameters change
markedly [(A) ∆Eq ) 1.03, δ ) 0.32; (B) ∆Eq ) 2.83, δ ) 0.26 (mm
s-1)]. The first set of parameters has been assigned to the admixed
electronic state form and the second to the high-spin component. The
∆Eq value of the admixed form increased from 1.50 to 2.83 mm s-1
once the temperature was lowered from 293 to 10 K as expected for
such an electronic structure.39,69
(69) Keutel, H.; Ka¨pplinger, I.; Ja¨ger, E.-G.; Grodzicki, M.; Schu¨nemann,
V.; Trautwein, A. X. Inorg. Chem. 1999, 38, 2320.
(70) Mitra, S. Magnetic Susceptibility of Iron Porphyrins. In Iron Porphy-
rins Part II; Lever, A. B. P., Gray, H., Eds.; Addison-Wesley:
Reading, MA, 1983; p 1.
1
typically used in our H NMR investigations, i.e., dichlo-
romethane-d2 by toluene-d8, causes a marked increase of the
S ) 5/2 character in the admixed ground electronic state as
demonstrated by a downfield relocation of the pyrrole
resonances including the spectacular change of the sign of
the isotropic shift seen for (TPrPc)FeIIIBr (Table 4). Thus, a
solid-state effect such as intermolecular coupling, effect of
solvation, etc. may considerably change the electronic
structure compared to these detected in solution. The solid-
state or frozen-solution data presented in this paper are
generally consistent with the presence of the admixed ground
electronic spin state. In the case of (TPrPc)FeIIICl the
admixed spin form is accompanied by a high-spin state as
found by Mo¨ssbauer68 and EPR75 spectroscopy. The decrease
of the øMT product for (TPrPc)FeIIICl and (TPrPc)FeIIIBr
(71) Palmer, G. Electron Paramagnetic Resonance of Hemoproteins. In Iron
Porphyrins Part II; Lever, A. B. P., Gray, H., Eds.; Addison-Wesley:
Reading, MA, 1983; p 43.
(72) Bominaar, E. L.; Ding, X.-Q.; Gismelseed, A.; Bill, E.; Winkler, H.;
Trautwein, A. X.; Nasri, H.; Fischer, J.; Weiss, R. Inorg. Chem. 1992,
31, 1845.
(73) Kostka, K. L.; Fox, B. G.; Hendrich, M. P.; Collins, T. J.; Rickard,
C. E. F.; Wright, L. J.; Mu¨nck, E. J. Am. Chem. Soc. 1993, 115, 6746.
(74) Boominar, E. L.; Block R. J. Chem. Phys. 1991, 95, 6712.
1986 Inorganic Chemistry, Vol. 41, No. 7, 2002

FiWe-Coordinate Iron(III) Porphycenes
Table 5. Summary of Crystal Data for (TPrPc)FeIIICl (1) and
(TPrPc)FeII (2)
derivatives in the 300-50 K temperature limits indicates the
decreasing S ) 5/2 contribution once the temperature has
been decreasing. Consequently the X-ray data of (TPrPc)-
FeIIICl measured at 110 K can be considered as characteristic
for the admixed electronic structure of iron(III) porphycene.
Significantly the extent of the S ) 5/2 contribution in the
admixed S ) 3/2, 5/2 ground electronic state, as gradated
solely on the basis of the pyrrole proton paramagnetic shifts,
is controlled by the strength of the axial ligand and increases
in the series ClO4- < I- < Br- < Cl- < C6H5O-. This order
reflects the basic features of the magnetochemical series
introduced by Reed and co-workers.54,55,76 Elements of this
idea were noted much earlier by Reed24 and Goff.62,63
Originally the method for ranking ligand field strength was
based on the degree of S ) 3/2, 5/2 admixture caused by an
axial ligand in five-coordinate iron(III) tetraphenylporphyrin,
applying the paramagnetic shift of the â-H pyrrole resonance
as a major criterion. Since stronger ligands, e.g., I-, Br-,
and Cl-, produced analogous high-spin iron(III) porphyrin
complexes, the series could be extended only by changing
the equatorial ligand (from porphyrin to phthalocyanine) and
as a consequence resorting to other physicochemical probes.
Thus, the magnetic moment, zero-field splitting, and quad-
rupole splitting were used as measured in the solid state,
bearing, however, the burden of possible solid-state effects.54
Finally the following series, represented here in its shorter
1
2
empirical formula
mol wt
T, K
C32H36N4ClFe
576.95
100(2)
0.71073
triclinic
P?1
9,496(2)
12.281(2)
13.338(3)
112.22(3)
97.85(3)
96.76(3)
1401.9(5)
1
1.345
598
0.661
10413
6514
496
0.0417
1.069
0.0959
C32H36N4Fe
532.50
100(2)
0.71073
triclinic
P?1
5.196(1)
9.857(2)
12.506(3)
81.17(3)
84.85(2)
89.29(3)
630.4(2)
1
1.403
282
0.628
4090
2674
171
0.0875
0.95
0.2024
λ, Å
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Dc, Kg m-3
F(000)
µ(Mo KR), mm-1
no. of data
no. of unique data
no. of params
R1a
S
wR2a
a Observation criterion I > 2σ(I), R1 ) ∑||Fo| - |Fc| |/∑|Fo|, wR2 )
{∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
2
2
2
range of the ligand field to be covered including that
characterized previously by iron(III) phthalocyanines. Such
a suitability has been demonstrated here for the representative
set of axial ligands. The proposed probe is very sensitive
and at present covers the +65.31 to -77.12 ppm paramag-
netic shift span (294 K). The demonstrated solvent depen-
dence of the paramagnetic shift may be conceivably used as
an additional tool to discriminate fine differences between
axial ligands.
-
-
form, has been determined: SbF6 < H2O < ClO4
<
-
-
-
CF3SO3 < BF4 < ReO4 < I- < Br- < OH- ≈ Cl- <
OAc- < OPh(p-NO2) - < OPh- < F- < RS-.55 The reversal
of the H2O and OH- ligand field strengths on the magne-
tochemical series relative to the spectrochemical series has
been discussed.55 The magnetochemical series reflects the
ligand field effect dominated by σ-bonding and electrostatic
interactions.55 Evans and Reed commented55 that in the
(TMCP)FeIIIBr (84.6 ppm), (TMCP)FeIIICl (90.7 ppm), and
(TMCP)FeIII(OH) (91.9 ppm) groups (X ) Cl-, Br-, OH-)
the averaged pyrrole proton shifts (given in parentheses)35
suggest the magnetic ordering Br- < Cl- ≈ OH-.55 We have
found it important to make the point that the recently reported
[(TMCP)FeIII(C2H5OH)2]+ (-30.7 ppm) and [(TMCP)FeIII-
(D2O)2]+ (-35.0 ppm) complexes demonstrated averaged
â-H pyrrole shifts (in parentheses) which follow the tet-
raarylporphyrin series.40 In particular the reversal of the H2O
and OH- ligand field strengths has been independently
confirmed.
Experimental Section
Reagents. The free 2,7,12,17-tetra-n-propylporphycene [(TPrPc)-
H2] was prepared using the reported method.1 (TPrPc-d4)H2 was
obtained as previously described.20 Insertion of iron followed a
known route to produce [(TPrPc)FeIII]2O, which was subsequently
cleaved with HX acids to produce (TPrPc)FeIIIX (X ) Cl, Br,
I).12,13,20 The respective sample was dried under vacuum to remove
traces of water.
Conversion from the chloride anion to the perchlorate anion
followed the published methods.24,25
Caution! The perchlorate salts are potentially explosive when
heated or shocked. They should be handled in milligram quantities.
Samples of (TPrPc)FeIII(C6H5O) were obtained by addition of
an excess of the sodium phenoxide to (TPrPc)FeIIICl in toluene
solution, sonication, and filtration to remove sodium phenoxide and
sodium chloride following the procedure for an analogous iron-
(III) porphyrin derivative.66
(TPrPc)FeII was obtained by reduction of (TPrPc)FeIIICl in CH2-
Cl2 with an aqueous solution of sodium dithionite.20 Crystals were
grown by very slow evaporation of the dichloromethane layer under
a water solution of the reducing agent in a closed vial under purified
nitrogen in a glovebox.
X-ray Data Collection and Refinement. Crystals of (TPrPc)-
FeIIICl were prepared by diffusion of hexane into the dichlo-
romethane solution contained in a thin tube.
Crystal data for (TPrPc)FeIIICl and (TPrPc)FeII are given in Table
5, together with refinement details. Both crystals were mounted
In terms of the magnetochemical series, the iron(III) 1,7,-
12,17-tetrapropylporphycene, soluble in typical organic
solvents, can be considered as an alternative and universal
framework to classify the ligand strength in a magne-
tochemical series, consistently using the â-H pyrrole para-
magnetic shift as a fundamental criterion. It allows the whole
(75) The EPR spectra of (TPrPc)FeIIICl (toluene, 7 K) are accounted for
by two species. Effective g values of the first component (g1 ) 6.18,
g2 ) 5.80, g3 ) 2.00) are characteristic for an S ) 5/2 ground
electronic state with zero-field splitting and a rhombic contribution
to the ligand field. The second component (g1 ) 4.31, g2 ) 4.17, g3
) 2.00) reveals features typical for the admixed spin state with the
domination of the S ) 3/2 contribution.23,24,38-40,55,60,63,69,71
(76) Reed, C. A. Inorg. Chim. Acta 1997, 263, 95.
Inorganic Chemistry, Vol. 41, No. 7, 2002 1987

Rachlewicz et al.
onto a glass fiber and then flash-frozen to 100 K (Oxford
Cryosystem-Cryostream cooler). Preliminary examination and
intensity data collections were carried out on a Kuma KM4CCD
κ-axis diffractometer with graphite-monochromated Mo KR radia-
tion. Crystals were positioned 65 mm from the KM4CCD camera.
A total of 612 frames were measured at 0.75° intervals with a
counting time of 35 s for (TPrPc)FeIIICl and 30 s for (TPrPc)FeII.
The data were corrected for Lorentz and polarization effects. No
absorption correction was applied. Data reduction and analysis were
carried out with the Kuma Diffraction (Wrocław) programs. The
structures were solved by direct methods (program SHELXS9777)
and refined by the full-matrix least-squares method on all F2 data
using the SHELXL9778 programs. Disorder exists in the complex
(TPrPc)FeIIICl. Molecules have two different orientations (4:1) in
the unit cell, but the Fe(1) and Cl(1) atoms have identical
coordinates in both cases. These molecules differ by rotation along
the Fe(1)-Cl(1) bond by 90°. Non-hydrogen atoms from molecules
with primary orientation were refined with anisotropic displacement
parameters and isotropically in molecules with secondary orientation
using the instruction SAME; coordinates of the hydrogen atoms
were calculated using the geometry of the molecules and were
refined as riding groups for both orientations of (TPrPc)FeIIICl. In
the complex (TPrPc)FeII all non-hydrogen atoms were refined with
anisotropic thermal parameters. The carbon-bonded hydrogen atoms
were included in the calculated positions and refined using a riding
model.
contribution, and the molar susceptibility corresponds to the
resulting magnetization per mole and per magnetic field unit. The
diamagnetic contribution of the sample was evaluated using Pascal’s
constants.
NMR Spectroscopy. 1H NMR spectra were recorded on a Bruker
AMX 300 spectrometer operating in the quadrature mode at 300
MHz. The residual 1H NMR resonances of deuterated solvents were
used as a secondary reference.
Acknowledgment. Financial support from the State
Committee for Scientific Research KBN of Poland (Grant 3
T09A 155 15) and the Foundation for Polish Science is
kindly acknowledged.
Supporting Information Available: Figures S1-S5, temper-
ature dependence of the 1H NMR chemical shifts of some protons
for (TPrPc)FeIII(ClO4), (TPrPc)FeIIICl, (TPrPc)FeIIIBr, (TPrPc)FeIIII,
and (TPrPc)FeIII(PhO), Figure S11, various views of (TPrPc)FeIII-
Cl, Table S11, crystal data and structure refinement for (TPrPc)-
FeIIICl, Table S12, atomic occupancy factors, coordinates, and
equivalent/isotropic displacement parameters (Å2) for (TPrPc)FeIII-
Cl, Table S13, bond lengths (Å) and angles (deg) for (TPrPc)FeIII-
Cl, Table S14, torsion angles (deg) for (TPrPc)FeIIICl, Table S15,
lengths (Å) and angles (deg) of the hydrogen bonds for (TPrPc)-
FeIIICl, Table S16, least-squares planes for (TPrPc)FeIIICl, Figure
S21, various views of (TPrPc)FeII, Table S21, crystal data and
structure refinement for (TPrPc)FeII, Table S22, atomic occupancy
factors, coordinates, and equivalent/isotropic displacement param-
eters (Å2) for (TPrPc)FeII, Table S23, bond lengths (Å) and angles
(deg) (TPrPc)FeII, Table S24, torsion angles (deg) (TPrPc)FeII, and
crystallographic data in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
Magnetization Measurements. The solid-state magnetization
of (TPrPc)FeIIICl and (TPrPc)FeIIIBr was measured under helium
on a Quantum Design MPMS SQUID magnetometer from 2 to 300
K at a field of 0.5 T. The sample was contained in a Kel-F bucket.
The bucket was measured independently at the same field and
temperatures. The raw data were corrected for the sample holder
(77) Sheldrick, G. M. SHELXS97, program for solution of crystal structures,
University of Go¨ttingen, Germany, 1997.
(78) Sheldrick, G. M. SHELXL97, program for crystal structure refinement,
University of Go¨ttingen, Germany, 1997.
IC010725J
1988 Inorganic Chemistry, Vol. 41, No. 7, 2002