Hydrosulfide (HS-) coordination in iron porphyrinates

Article abstract of DOI:10.1021/ic901853p

Recent reports of potential physiological roles of hydrogen sulfide have prompted interest in heme-sulfide interactions. Heme - H₂S and/or heme - HS^- interactions could potentially occur during endogenous production, transport, signaling events, and catabolism of H₂S. We have investigated the interaction of the hydrosulfide ion (HS^-) with iron porphyrinates. UV - vis spectral studies show the formation of [Fe(Por(SH)]^-, [Fe(Por)(SH)₂]^2-, and the mixed-ligand species [Fe(Por(Im)(SH)]^-. UV - vis binding studies of [Fe(OEP) and [Fe(T-p-OMePP)] (OEP = octaethylporphyrinate; T-p-OMePP = tetra-p-methoxyphenylporphyrinate) with HS^- allowed for calculation of the formation constants and extinction coefficients of mono- and bis-HS ^- complexes. We report the synthesis of the first HS ^--bound iron(II) porphyrin compounds, [Na(222)][Fe(OEP)(SH)] ·0.5C₆H₆ and [Na(222)][Fe(T-ρ-OMePP)(SH) ·C₆H₅Cl (222 = Kryptofix-222). Characterization by single-crystal X-ray analysis, mass spectrometry, and Moessbauer and IR spectroscopy is all consistent with that of known sulfur-bound high-spin iron(II) compounds. The Fe - S distances of 2.3929(5) and 2.3887(13) A are longer than all reported values of [Fe^II(Por)(SR)]^- species. An analysis of the porphyrin nonplanarity for these derivatives and for all five-coordinate high-spin iron(II) porphyrinate derivatives with an axial anion ligand is presented. In our hands, attempts to synthesize iron(III) HS^- derivatives led to iron(II) species.

Full text of DOI:10.1021/ic901853p

Inorg. Chem. 2010, 49, 1017–1026 1017
DOI: 10.1021/ic901853p
Hydrosulfide (HS-) Coordination in Iron Porphyrinates
Jeffrey W. Pavlik,† Bruce C. Noll,† Allen G. Oliver,† Charles E. Schulz,*,‡ and W. Robert Scheidt*,†
†Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
‡Department of Physics, Knox College, Galesburg, Illinois 61401
Received September 18, 2009
Recent reports of potential physiological roles of hydrogen sulfide have prompted interest in heme-sulfide
interactions. Heme-H2S and/or heme-HS- interactions could potentially occur during endogenous production,
transport, signaling events, and catabolism of H2S. We have investigated the interaction of the hydrosulfide ion (HS-)
with iron porphyrinates. UV-vis spectral studies show the formation of [Fe(Por)(SH)]-, [Fe(Por)(SH)2]2-, and the
mixed-ligand species [Fe(Por)(Im)(SH)]-. UV-vis binding studies of [Fe(OEP)] and [Fe(T-p-OMePP)] (OEP =
octaethylporphyrinate; T-p-OMePP = tetra-p-methoxyphenylporphyrinate) with HS- allowed for calculation of the
formation constants and extinction coefficients of mono- and bis-HS- complexes. We report the synthesis of the first
HS--bound iron(II) porphyrin compounds, [Na(222)][Fe(OEP)(SH)] 0.5C6H6 and [Na(222)][Fe(T-p-OMePP)-
3
(SH)] C6H5Cl (222 = Kryptofix-222). Characterization by single-crystal X-ray analysis, mass spectrometry, and
€
3
Mossbauer and IR spectroscopy is all consistent with that of known sulfur-bound high-spin iron(II) compounds. The
II
-
˚
Fe-S distances of 2.3929(5) and 2.3887(13) A are longer than all reported values of [Fe (Por)(SR)] species. An
analysis of the porphyrin nonplanarity for these derivatives and for all five-coordinate high-spin iron(II) porphyrinate
derivatives with an axial anion ligand is presented. In our hands, attempts to synthesize iron(III) HS- derivatives led to
iron(II) species.
Introduction
to 80 ppm of H2S, they had sequential drops in their
metabolic rate and core body temperature, similar to that
observed in animals during the onset of hibernation.10 After
H2S treatment was stopped, vital signs returned to normal,
and no long-term functional or behavioral abnormalities
were observed. This has prompted speculation into the use
of H2S as a means to improving postsurgery and post-trauma
recovery.11
H2S is produced endogenously in mammals by two en-
zymes. Cystathionine γ-lyase is the primary source of physio-
logical H2S in the mammalian cardiovascular system12 and
cystathionine β-synthase (CBS) in the central nervous sys-
tem.13 The endogenous H2S levels in mammalian tissues is
about 15 nM,2 allowing for localized high intracellular gas
concentrations like those observed in NO signaling, wherein
the tissue function is altered upon nanomolar fluctuations.14
At the biological pH of 7.4, dissolved H2S, pKa = 6.9, is
partially deprotonated; the HS-/H2S ratio is 3:1, so one or
more sulfide species could act as ligands to receptor pro-
teins. Neither the binding species nor the receptors for
potential sulfide-protein interactions associated with the
Hydrogen sulfide (H2S) has recently been recognized as a
third possible gasotransmitter, along with NO and CO, and
may play a role in vasodilation, blood pressure regulation,
and neurological health.1-5 Previously known H2S biology
consisted of its malodor and ability to inhibit cytochrome
c oxidase.6 However, the interaction of H2S with mitochon-
drial cytochrome c oxidase is concentration-dependent.7
Endogenously produced H2S has been linked to hippo-
campal long-term potentiation8 as well as neurological dis-
orders such as Down’s Syndrome and Alzheimer’s disease.9
The prospect of suspended animation in animals and humans
is yet another facet of H2S biology. When mice were exposed
*To whom correspondence should be addressed. E-mail: scheidt.1@
nd.edu.
(1) Abe, K.; Kimura, H. J. Neurosci. 1996, 16, 1066.
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Head, A. K.; Whitfield, N. L.; Madden, J. A. J. Exp. Biol. 2006, 209, 4011.
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Acta 1975, 387, 189.
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Mustafa, A.; Mu, W.; Zhang, S.; Snyder, S.; Wang, R. Science 2008, 83, 587.
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r
2009 American Chemical Society
Published on Web 12/28/2009
pubs.acs.org/IC

1018 Inorganic Chemistry, Vol. 49, No. 3, 2010
Pavlik et al.
aforementioned phenomena have been identified; however,
reactions of H2S with heme proteins have been investigated
for quite some time.
was reported by Rizzi et al.25 in 1996; however, the complete
ligand identity and iron oxidation state cannot be verified
˚
from the 1.9-A resolution data. A very recent report suggests
In 1933, Keilin15 reviewed the previous work on
H2S-heme-protein studies, starting with the 1866 report
by Hoppe-Seyler16 of a green compound that formed irre-
versibly upon contact of methemoglobin with H2S in the
presence of oxygen. Haurowitz17 was able to obtain a
molecule that he called “sulpho-hemoglobin” with an ab-
sorption band at 618 nm that is clearly a porphyrin-
based compound. The irreversible product was later sug-
gested to be sulfhemoglobin, wherein the elements of H2S
add across a β-β double bond of a pyrrole.18 Subsequent
NMR studies more firmly established structures of the co-
valently modified sulfur-containing pyrrole of protopor-
phyrin IX.19 This modified pyrrole chemistry accounts for
reports of patients exhibiting green blood and reduced
oxygen transport after ingestion of certain sulfur-containing
compounds.20
Direct interaction of sulfide with the iron center is also
known. In Keilin’s 1933 paper,15 he also presented data that
demonstrated that a new red product could be formed by the
anaerobic reaction of H2S with methemoglobin; this is
commonly believed to be a coordination complex of the
iron(III) porphyrin with sulfide. Neuroglobin, a highly pre-
served heme enzyme that occurs throughout the human
central nervous system, regulates oxygen, and perhaps sulfide
as has been shown in vitro, to bind H2S quite tightly.21
However, the best-understood interactions of heme proteins
with H2S are found in marine organisms that inhabit sulfide-
rich environments.22
that H2S, at high concentrations, will reduce the ferric HbI
species.26 There are a few other reports of heme-
protein-H2S interactions in the literature. An optical spec-
tral study of the gill tissue from the bivalve mollusk Solemya
velum led Doeller et al. to conclude that, in this case,
hemoglobin must be converted from the ferrous state to the
ferric state prior to sulfide binding.27 The giant hemoglobin
of Oligobrachia mashikoi can transport oxygen and sulfide
simultaneously.28
These intriguing results for heme proteins prompted us to
investigate iron porphyrinates with the hydrosulfide anion as
a possible ligand. We first note that transition-metal com-
plexes with hydrosulfide or H2S as a ligand are rare. English
et al.29 reported the synthesis of an iron(III) species [Fe(T-p-
OMePP)(SH)] using S þ LiB(C2H5)3H (an unusual source of
HS-). The room temperature X-ray structure revealed a
˚
single axial atom at 2.30 A from iron but without any
evidence for a hydrogen atom. There is, however, a report
of a failure to reproduce this preparation.30 Cai and Holm31
reported the transient formation of a species they believed to
be [FeIII(OEP)(SH)] from the reaction of H2S and
[FeIII(OEP)]2O. The identification was based on an observed
1H NMR meso-hydrogen shift of -50.0 ppm, but the com-
plex quickly reduced to [FeII(OEP)]. Also reported in this
work was [Fe4S4(LS3)-S-Fe(OEP)]m-2, where LS3=1,3,S-
tris[(4,6-dimethyl-3-mercaptophenyl)thio]-2,4,6-tris(p-tolyl-
thio)benzene(3-), which contains an Fe-S-Fe bridge and is
an analogue of certain assimilatory sulfite and nitrite reduc-
tases. Other (nonbiological) transition-metal hydrosulfide
complexes of known structure include [RhCl(H)(SH)-
(P(Ph3)2]2 and [IrCl(H)(SH)(CO)(P(Ph3)2],32 [MnIII(oespz)-
(SH)],33 [Co(cyclam)(SH)]n[ClO4]n and [Ni(μ-SH)(cyclam)]2-
[Ni(SH)2(cyclam)][ClO4],34 trans-[Rh(SH)(CO)(P(Ph3)2],35
and trans-[M(SH)2(dmpe)2]; M = Cr, Fe.36 For H2S,
there are just six structures, all of which are ruthenium(II)
complexes.37-39 One of these, [Ru(IMes)2(CO)(H2S)H2], is
The most studied of these systems are the proteins from the
clam Lucina pectinata, which has several different gill hemo-
globins, of which hemoglobin I in its ferric form binds sulfide.
The function of HbI23 is apparently sulfide delivery to a
symbiotic sulfide-oxidizing bacterium. Kraus et al.24 have
measured electron paramagnetic resonance (EPR) spectra
of the anaerobically formed complexes of H2S with whale
myoglobin (Mb) and L. pectinata hemoglobins I and II (HbI
and HbII). The EPR spectra are consistent with low-spin
iron(III) complexes. The crystal structure of HbI-sulfide
(25) Rizzi, M.; Wittenberg, J. B.; Coda, A.; Ascenzi, P.; Bolognesi, M.
J. Mol. Biol. 1996, 258, 1.
(26) Pietra, R.; Lewis, A.; Leon, R. G.; Casabona, G.; Kiger, L.; Yeh, S.;
Fernandez-Alberti, S.; Marden, M. C.; Cadilla, C. L.; Lopez-Garriga, J.
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Bull. 1988, 175, 388.
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(16) Hoppe-Seyler, F. Zentralbl. Med. Wiss. 1866, 4, 436.
(17) Haurowitz, F. Z. Physiol. Chem. 1926, 151, 130.
(18) (a) Berzofsky, J. A.; Peisach, J.; Blumberg, W. E. J. Biol. Chem. 1971,
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M. J.; La Mar, G. N.; Kauten, R. J. Biochemistry 1987, 26, 6939.
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Miki, K. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 14521.
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(30) Balch, A. L.; Cornman, C. R.; Safari, N.; Latos-Grazynski, L.
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(22) Weber, R. E.; Vinogradov, S. N. Physiol. Rev. 2001, 81, 569.
(23) The following abbreviations are used in this paper: HbI, hemoglobin I
from L. pectinata; OEP, dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin;
T-p-OMePP, dianion ofmeso-tetra-p-methoxyphenylporphyrin; TPP; dianion
of meso-tetraphenylporphyrin; TMP, dianion of meso-tetramesitylporphyrin;
TpivPP, dianion of R,R,R,R-tetrakis(o-pivalamidophenyl)porphyrin; Proto IX
DME, dianion of protoporphyrin IX; Por, generalized porphyrin dianion; 222,
1,10-diaza-4,7,13,16,21,24-hexaoxabicyclo[8.8.8]hexacosane; Im, generalized
imidazole; HIm, imidazole; 2-MeHIm, 2-methylimidazole; 1-MeIm, 1-methyl-
imidazole; 2-MeIm, 2-methylimidazolate; cyclam, 1,4,8,11-tetraazacyclo-
tetradecane; oespz, 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetra-
azaporphyrinate dianion; dmpe, 1,2-bis(dimethylphosphino)ethane; IMes, 1,3-
bis(2,4,6-trimethylphenyl)imidazol-2-ylidene.
Organometallics 1990, 9, 2420.
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Soc., Dalton Trans. 1998, 1985.
(34) Pleus, R. J.; Waden, H.; Saak, W.; Haase, D.; Pohl, S. J. Chem. Soc.,
Dalton Trans. 1999, 2601.
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(36) Arif, A. M.; Hefner, J. G.; Jones, R. A.; Koschmieder, S. U. J. Coord.
Chem. 1991, 23, 13.
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Mahon, M. F.; Whittlesey, M. K. Inorg. Chem. 2003, 42, 7695.
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Inorg. Chem. 1997, 36, 5426.
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1992, 114, 922.
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Chem. 1990, 265, 16054.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1019
air-stable and forms a 16-electron species [Ru(IMes)2-
(CO)(SH)2] upon treatment with H2S.37
was placed in a Schlenk flask, to which 10 mL of benzene and
1.0 mL of ethanethiol was added. The mixture was stirred for 2 h
at 60 ꢀC and then 16 h at 25 ꢀC. Benzene and ethanethiol were
removed under vacuum. The flask containing a purple powder
was transferred into a drybox, where 5 mg (0.09 mmol) of NaHS
and 34 mg (0.09 mmol) of Kryptofix(222) were added. The flask
was removed from the drybox, and Schlenk procedures were
resumed. A total of 10 mL of benzene was added, followed by
stirring at 60 ꢀC for 1 h. The mother liquor was divided evenly
between four 7-mm-i.d. glass tubes by cannula transfer. A layer
of 7 mL of hexanes was added to each tube. The tubes were
flame-sealed under a slight vacuum and stored in the dark.
Hexagonal pill-shaped crystals were harvested after 3 weeks.
Yields from the tube reactions were about 42%. Large-scale
We report the binding of HS- to three iron(II) porphyrins,
[Fe(OEP)], [Fe(T-p-OMePP)], and [Fe(TMP)], which was
followed spectrophotometrically, as well as the reaction of
[Fe(TMP)(1-MeIm)2] with HS-. We have been able to
synthesize iron(II) derivatives and report the crystal struc-
tures of two hydrosulfido iron(II) porphyrinates, [Na(222)]-
[Fe(OEP)(SH)] 0.5C6H6 and [Na(222)][Fe(T-p-OMePP)-
3
(SH)] C6H5Cl; both are five-coordinate and high-spin.
3
Attempts to synthesize analogous iron(III) compounds were
unsuccessful; in our hands, HS- reduces iron(III) porphyri-
nates. [Na(222)][Fe(OEP)(SH)] 0.5C6H6 was further char-
3
€
preparations were not attempted. For Mossbauer spectroscopy,
€
acterized by far-IR, mass spectrometry, and Mossbauer
the same procedure was followed except that the hexanes and
mother liquor were mixed together to cause immediate precipi-
tation of the product, which was recovered by filtration and
drying under vacuum.
analysis. Most aspects of the two iron(II) complexes are
similar to those of other five-coordinate anionic iron(II)
porphyrinates, and comparisons are provided.
[Na(222)][Fe(T-p-OMePP)(SH)] C6H5Cl. To a Schlenk flask
3
Experimental Section
were added 40 mg (0.025 mmol) of [Fe(T-p-OMePP)]2O, 12 mL
of chlorobenzene, and 1.0 mL of ethanethiol. The mixture was
stirred for 2 h at 60 ꢀC and then 16 h at 25 ꢀC. Chlorobenzene
and ethanethiol were removed under vacuum. The flask con-
taining a purple powder was transferred to a drybox, where
4.5 mg (0.08 mmol) of NaHS and 32 mg (0.09 mmol) of
Kryptofix(222) were added. After removal of the flask from
the drybox, Schlenk procedures were resumed and 12 mL of
chlorobenzene was added. This slurry was stirred at near boiling
for 1 h in an oil bath until a brown-green solution resulted.
Stirring and heating were terminated, and the reaction vessel
remained undisturbed in the oil bath for 40 h. Purple needle-like
crystals were collected by filtration of the reaction solution and
were washed with hexanes. The yield was approximately 30%.
X-ray Crystallographic Studies. For [Na(222)][Fe(OEP)-
General Information. All manipulations for the preparation
of the five-coordinate iron(II) porphyrin derivatives were car-
ried out under argon using a double-manifold vacuum line,
Schlenkware, and cannula techniques. Benzene and hexanes
were distilled over sodium benzophenone. Chlorobenzene was
stirred over concentrated sulfuric acid, washed with a dilute
Na2CO3 solution, dried with Na2SO4, and then distilled over
P2O5. Octaethylporphyrin (H2OEP) was synthesized from for-
maldehyde and 3,4-diethylpyrrole.40 [Fe(OEP)Cl] was prepared
according to a modified Adler preparation,41 and [Fe(OEP)]2O
was prepared from [Fe(OEP)Cl]. [Fe(T-p-OMePP)]2O and
[Fe(TMP)(OH)] were also prepared by the same general proce-
dure. All other chemicals were used as received from Aldrich
or Fisher.
(SH)] 0.5C6H6, a crystal was placed in inert oil to reduce air
€
Mossbauer measurements were performed on a constant-
3
exposure and cut by a razor blade to 0.5 ꢀ 0.4 ꢀ 0.3 mm. Crystal
data were collected and integrated using a Bruker Apex system,
with graphite-monochromated Mo KR radiation (λh=0.701 73
acceleration spectrometer from 4.2 to 300 K with an optional
small field and in a 9 T superconducting magnet system (Knox
€
College). Samples for Mossbauer spectroscopy were prepared
˚
A) at 100 K (700 Series Oxford Cryostream). The program
by immobilization of the crystalline material in Apiezon M
grease.
SADABS43 was applied for absorption corrections. The struc-
ture was solved by direct methods in SHELXS-97.43 All struc-
tures were refined using SHELXL-97.43 All non-hydrogen
atoms were found after successive full-matrix least-squares
refinement cycles on F2 and then refined with anisotropic
thermal parameters. Most hydrogen-atom positions were idea-
lized with a riding model and fixed thermal parameters [Uij =
1.2Uij(eq) or 1.5Uij(eq)] for the atom to which they are bonded.
The exceptions are the sulfur-bound hydrogen atoms, which
were refined freely, with and without constraints for compari-
Anhydrous NaHS. Anhydrous sodium hydrosulfide was pre-
pared by a method described in Inorganic Substances Handbook
with minor modifications.42 In a drybox, each side of a 1 g cube
of sodium was shaved to a shiny surface. The resulting cube was
cut in half, and each half was pressed into a 1.5-mm-thin sheet
using a spatula. If the sheets are not sufficiently thin, the interior
sodium may be inaccessible for the reaction. The sheets were
loosely rolled around the spatula and placed in a Schlenk tube.
At the Schlenk line, 15 mL of benzene was added, and
the mixture was stirred under an H2S atmosphere for 2 days.
The head gas was replaced several times with fresh H2S during
the reaction. Benzene was removed under vacuum, and the white
powder NaHS was collected and stored under inert conditions.
Solid NaHS is sparingly soluble in benzene or chlorobenzene. At
higher concentrations, dissolution of the NaHS-Kryptofix
mixture in chlorobenzene required 24 h of stirring. The resulting
son. For [Na(222)][Fe(T-p-OMePP)(SH)] C6H5Cl, disorder
3
was found in one peripheral p-methoxyphenyl group with two
orientations and three ethylene groups of the 222; three posi-
tions of the chlorobenzene solvate around an inversion center
were required for a complete description. The sulfur-bound
hydrogen atom in this case was refined freely, without
constraints.
Mass Spectroscopy. In a drybox, isolated crystals of
[Na(222)][Fe(OEP)(SH)] 0.5C6H6 with a combined mass of
solution had a light-blue tint, consistent with the possible
2-
presence of small amounts of polysulfide ions such as S3
[Na(222)][Fe(OEP)(SH)] 0.5C6H6. Standard Schlenk proce-
.
3
∼1 mg were dissolved in 500 μL of tetrahydrofuran. The
solution was drawn into an airtight syringe, removed from the
drybox, and injected into a JEOL AX505HA triple-quadrupole
mass spectrometer with electrospray sample ionization and
time-of-flight detection. Both negative- and positive-ion-mode
spectra were collected for m/z 0-2000.
3
dures were followed. A total of 50 mg (0.04 mmol) of [Fe(OEP)]2O
(40) Milgram, B. C.; Eskildsen, K.; Richter, S. M.; Scheidt, W. R.;
Scheidt, K. A. J. Org. Chem. 2007, 72, 3941.
(41) (a) Adler, A. D.; Longo, F. R.; Kampus, F.; Kim, J. J. Inorg. Nucl.
Chem. 1970, 32, 2443. (b) Buchler, J. W. In Porphyrins and Metalloporphyrins;
Smith, K. M., Ed.; Elsevier Scientific Publishing: Amsterdam, The Netherlands,
1975; Chapter 5.
IR Spectroscopy. IR spectra were collected on a Nicolet
Nexus 670 FT-IR with 2 cm-1 resolution equipped with EZ
(42) Lidin, R. A. Inorganic Substances Handbook; Begel House Inc.: New
York, 1996; p 284.
(43) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, A64, 112.

1020 Inorganic Chemistry, Vol. 49, No. 3, 2010
Pavlik et al.
Table 1. Brief Crystallographic Data and Data Collection Parameters
[Na(222)][Fe(OEP)(SH)] 0.5C6H6
3
[Na(222)][Fe(T-p-OMePP)(SH)] C6H5Cl
3
formula
fw, amu
[C36H45FeN4S]-, [C18H36N2NaO6]þ 0.5C6H6
1060.21
21.9682(4)
23.7269(4)
24.1203(6)
116.676(1)
11234.2(4)
P21/n
8
1.254
4552
0.367
0.47 ꢀ 0.39 ꢀ 0.34
Mo KR, 0.710 73
100(2)
[C48H37FeN4O4S]-, [C18H36N2NaO6]þ C6H5Cl
1333.75
12.3987(5)
25.3197(10)
21.7450(8)
95.392(2)
6796.2(5)
P21/n
4
1.304
2808
0.361
0.33 ꢀ 0.13 ꢀ 0.12
Mo KR, 0.710 73
100(2)
3
3
˚
a, A
˚
b, A
˚
c, A
β, deg
3
˚
V, A
space group
Z
Dc, g/cm3
F(000)
μ, mm-1
cryst dimens, mm
˚
radiation (λh, A)
temperature, K
total data collected
abs corrn
unique data
unique obsd data [I > 2σ(I)]
refinement method
final R indices [I > 2σ(I)]
final R indices (all data)
398 321
90 934
semiempirical from equivalents
37 293 (Rint = 0.046)
27 137
semiempirical from equivalents
11 972 (Rint = 0.044)
8963
full-matrix least squares on F2
R1 = 0.0456, wR2 = 0.1118
R1 = 0.0761, wR2 = 0.1346
full-matrix least squares on F2
R1 = 0.0691, wR2 = 0.1934
R1 = 0.0922, wR2 = 0.2164
Omnic ESP, version 5.2a, software. Mid-IR spectra were col-
lected from KBr pellets and far-IR from CsI pellets. All pellets
were prepared in a drybox and then analyzed immediately. The
CsI pellet was analyzed again after 24 h of air exposure for
[Na(222)][Fe(OEP)(SH)] 0.5C6H6. A far-IR spectrum was also
collected on a similarly prepared, 57Fe-enriched crystalline
3
sample of [Na(222)][Fe(OEP)(SH)] 0.5C6H6.
3
UV-Vis Binding Studies. Binding studies of HS- in the form
of solutions of Na(222)HS were carried out by the reaction of
[Fe(OEP)], [Fe(T-p-OMePP)], or [Fe(TMP)] in order to deter-
mine the stoichiometry, bonding constants, and spectral proper-
ties. Displacement reactions of [Fe(TMP)(1-MeIm)2] with
Na(222)HS were also performed. Complete experimental details
are given in the Supporting Information.
Results
The interaction of the HS- ion with iron(II) porphyrinates
has been established by a series of UV-vis observations on
solutions of iron(II) porphyrinates with varying amounts of
added NaHS. These data were interpreted as demonstrating
the formation of both five-coordinate [Fe(Por)(SH)]- and
Figure 1. Thermal ellipsoid plot (50% probability ellipsoids) of anion 1
in [Na(222)][Fe(OEP)(SH)] 0.5C6H6 at 100 K. In this and other figures
3
and tables, the following atom-naming convention has been used: Q(n),
Q(ny), and Q(nyy), where Q is the atom type, n refers to anion 1 or 2, and y
and yy are further numbers and letters needed to completely specify the
atom. Thus, similar atoms in the two anions have the same name except
for the digit n. Hydrogen atoms (except where bound to sulfur) are
omitted for clarity.
six-coordinate [Fe(Por)(SH)2]2-
.
Two different five-coordinate [Fe(Por)(SH)]- derivatives
have been crystallized and structurally characterized. Both
are five-coordinate high-spin species with an axial hydro-
sulfide ligand. Brief crystallographic data and intensity
information are given in Table 1. [Na(222)][Fe(OEP)-
The OEP complex has also been characterized by electro-
€
spray mass, far-IR, and Mossbauer spectroscopy. As shown
in Figure 2, the negative-ion-mode mass spectrum for
[Na(222)][Fe(OEP)(SH)] 0.5C6H6 exhibits a series of peaks,
(SH)] 0.5C6H6 crystallizes with two porphyrin anions, two
3
3
m/z 619.3, 621.3, 622.3, and 623.3, with relative peak heights
similar to those of the natural abundance isotopic distribu-
tion for [Fe(OEP)(SH)]-, as shown by the red bars. Also
shown in Figure 2 for comparison are the expected isotopic
variant m/z and relative intensities for [Fe(OEP)(Cl)]- as blue
sodium cryptand cations, and a benzene solvate molecule in
the asymmetric unit of the structure. The independent por-
phyrinate anions in the asymmetric unit will be referred to
as 1 and 2. Thermal ellipsoid plots of the two anions are given
in Figures 1 and S1 in the Supporting Information. A
diagram of the contents of the asymmetric unit of the
structure is given in Figure S2 in the Supporting Information.
A similar five-coordinate species was also found for
€
bars. Mossbauer spectra for [Na(222)][Fe(OEP)(SH)], mea-
sured from 25 to 200 K, were consistent with the high-spin
iron(II) state assigned to the complexes.
[Na(222)][Fe(T-p-OMePP)(SH)] C6H5Cl, and a thermal
3
Discussion
ellipsoid plot of the porphyrinate anion is presented in Figure
S3 in the Supporting Information. Complete lists of bond
distances and angles forall species are given in the Supporting
Information.
Spectral Studies. The UV-vis spectra of [FeII(T-p-
OMePP)] with varied concentrations of HS- exhibit large
spectral changes consistent with the formation of new

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1021
shoulder markedly increases in intensity and becomes a
sharp peak at 447 nm with maximum intensity at an HS-/
Fe ratio of near 2.5. The initial 420 nm peak drops
substantially in intensity with increasing HS- concentra-
tion until it has approximately half the intensity of the 447
peak and is slightly shifted to 423 nm at an HS-/Fe ratio
of near 2.5. Increasing HS- concentrations lead to the
final position of the Soret band at 419 nm along with a less
intense band at 454 nm. The Q-band region for [FeII(T-p-
OMePP)] displays commensurate spectral changes with
increasing HS- concentrations. The Q-band region starts
with a broad peak at ∼543 nm with two shoulders to the
red. The shoulders gradually grow into resolved peaks at
584 and 628 nm at the highest HS-/Fe ratios with
intermediate peaks seen at 576 and 617 nm at a HS-/Fe
ratio of near 2.5. The initial peak at 543 nm decreases in
intensity and shifts slightly to the red. The spectral
changes over the lower and higher HS- concentration
ranges are shown as panels B and C, respectively, in
Figure 3. These spectral changes clearly demonstrate that
the reaction of [FeII(T-p-OMePP)] with HS- leads to
more than one new species. The two species are most
probably identified as [FeII(T-p-OMePP)(SH)]- and
[FeII(T-p-OMePP)(SH)2)]2-, as shown in the following
equations.
Figure 2. Negative-ion-mode mass spectrum of [Na(222)][Fe(OEP)-
(SH)] with overlays of calculated m/z, z =1, for the four most abundant
isotopic variantsof[Fe(OEP)(SH)]- (red) and [Fe(OEP)(Cl)]- (blue). Bar
heights are proportional to their calculated relative occurrence.
K1
-
½FeIIðT-p-OMePPÞꢁ þ HS-
s
½FeIIðT-p-OMePPÞðSHÞꢁ
F
s
R
K2
-
½FeIIðT-p-OMePPÞðSHÞꢁ þ HS-
s
F
s
R
2 -
½FeIIðT-p-OMePPÞðSHÞ2ꢁ
Formation constants were calculated using least-squares
fits for the spectral data;44 the data are summarized in
Table 2.
The reaction of [FeII(OEP)] with HS- gave equally
complex spectra (shown in the top panel of Figure 4) and
point to the formation of the same species as in the T-p-
OMePP system. The broad Soret peak of [FeII(OEP)] at
384 nm splits into two sharper peaks as the HS-/Fe ratio
is increased from 0.0 to 1.5. Upon further ligand addition,
the two Soret peaks at 384 and 410 nm coalesce into a
single peak at 397 nm, which intensifies slightly at the
highest HS- levels. Further, a shoulder on the high-
wavelength side of the Soret peak in the initial spectrum
becomes gradually more prominent with increasing [HS-
] until in the limiting spectrum (HS-/Fe ratio at 9.6) it is a
nearly resolved peak at ∼439 nm. The Q-band region
again shows commensurate changes with increasing HS-
additions. The Q-band region in [FeII(OEP)] has two
peaks at 529 and 562 nm. The lower-energy band inten-
sifies to a maximum at a HS-/Fe ratio of 1.5; the further
addition of HS- causes the two peaks to gradually
coalesce into a single peak at 554 nm at the highest
concentrations of HS-. The spectral changes over the
lower and higher HS- concentration ranges are shown as
panels B and C, respectively, in Figure 4. Formation
Figure 3. UV-vis molar absorptivity plots of chlorobenzene solutions
of [Fe(T-p-OMePP)] with varied HS-/Fe ratios. The concentration of
[Fe(T-p-OMePP)] ranged from 0.085 to 0.073 mM, with the concentra-
tion of HS- adjusted according to the ratios reported in the figure.
A decrease in the [Fe(T-p-OMePP)] concentration is due to dilution
incurred upon ligand addition. Panel A shows a selection of spectral
traces from the complete range of HS-/Fe ratios explored, panel B results
from the lower HS- concentrations, and panel C results from the highest
HS- concentrations. Note that, for reasons of clarity, the concentration
color codingis distinct in eachpanel. From500to700 nm, plots are shown
at both regular scale and magnified 5ꢀ.
(44) Legget, D. J. SQUAD: Stability Quotients from Absorbance Data.
In Computational Methods for the Determination of Formation Constants;
Legget, D. J., Ed.; Modern Inorganic Chemistry Series; Plenum Press: New York,
1996; pp 159-217.
species. The complex changes are illustrated in the top
panel (A) of Figure 3. The Soret peak at 420 nm in the
initial spectrum has a modest shoulder at 444 nm. This

1022 Inorganic Chemistry, Vol. 49, No. 3, 2010
Pavlik et al.
Table 2. Formation Constants and Derived λmax (log ε) Values for Hydrosulfide Porphyrinate Complexes
Soreta
Q banda
complex
stability constant
[Fe(OEP)(SH)]-
5.0 ( 0.2b
10.4 ( 0.2c
4.7 ( 0.4b
8.7 ( 0.4c
4.6 ( 0.7b
9.2 ( 0.4c
380 (4.84)
397 (4.89)
428 (4.81)
418 (4.98)
421 (5.36)
416 (4.90)
416 (5.03)
528 (4.07)
552 (4.17)
543 (4.07)
585 (4.03)
542 (4.38)
584 (4.12)
562 (4.21)
[Fe(OEP)(SH)2]2-
[Fe(T-p-OMePP)(SH)]-
[Fe(T-p-OMePP)(SH)2]2-
[Fe(TMP)(SH)]-
447 (5.10)
459 (4.69)
446 (5.10)
452 (4.73)
613 (3.55)
627 (4.10)
610 (3.76)
627 (4.06)
656 (3.64)
[Fe(TMP)(SH)2]2-
a nm. b log K1, K1 = [Fe(Por)(SH)-]/[Fe(Por)][SH-]. c log β2, β2 = [Fe(Por)(SH)22-]/[Fe(Por)][SH-]2.
Figure 5. UV-vis molar absorptivity plots of chlorobenzene solutions
of [Fe(TMP)] with varied Fe/1-MeIm/HS- ratios. The concentration of
[Fe(TMP)] ranged from 0.069 to 0.053 mM, while 1-MeIm ranged from
0.36 to 0.28 mM and HS- was adjusted according to the ratios reported in
the figure. The decrease in the [Fe(TMP)] concentration is due to dilution
incurred upon ligand addition. From 500 to 700 nm, plots are shown at
both regular scale and magnified 5ꢀ.
was reacted with increasing levels of HS-, a large increase of
the Soret band is observed as the HS-/Fe ratio is increased
from 0.0 to 1.2, followed by a rapid decrease as the HS-/Fe
ratio is increased from 1.2 to 4.7. The limiting spectrum
shown in Figure 5 is strikingly similar to the limiting
spectrum from the reaction of [FeII(TMP)] with HS-
(Figure S4 in the Supporting Information), consistent with
a common final species. We suggest that the species respon-
sible for the intense Soret peak at the HS-/Fe ratio of 1.2 is
[FeII(TMP)(SH)(1-MeIm)]- and that further additions of
HS- results in the formation of [FeII(TMP)(SH)2]2-
.
Figure 4. UV-vis molar absorptivity plots of chlorobenzene solutions
of [Fe(OEP)] with varied HS-/Fe ratios. The concentration of [Fe(OEP)]
ranged from 0.113 to 0.088 mM, with the concentration of HS- adjusted
according to the ratios reported in the figure. The decrease in the
[Fe(OEP)] concentration is due to dilution incurred upon ligand addition.
Panel A shows a selection of spectral traces from the complete range of
HS-/Fe ratios explored, panel B results from the lower HS- concentra-
tions, andpanel C resultsfromthe highestHS- concentrations. Note that,
for reasons of clarity, the concentration color coding is distinct in each
panel. From 500 to 700 nm, plots are shown at both regular scale and
magnified 5ꢀ.
Synthesis. The strong evidence for the existence of
[FeII(Por)(SH)]- and [FeII(Por)(SH)2]2- led us to attempt
their synthesis for further characterization. Crystalliza-
tion experiments with the OEP and T-p-OMePP deriva-
tives yielded crystals of the five-coordinate species,
[Na(222)][FeII(Por)(SH)], with the HS-/Fe ratio ranging
from 1.2 to 2.0 in the crystallizing solvent. Crystallization
from solutions with the HS-/Fe ratio of 5.0, near the
solubility-imposed maximum, again yields the five-coor-
dinate species. The lower solubility of the five-coordinate
species, and/or instability of the doubly charged bis-HS-
adduct, may preclude isolation of [FeII(Por)(SH)2]2- as a
solid. Similar results were obtained for bulk prepara-
tions where only the five-coordinate species were ob-
tained. All attempts to prepare mixed-ligand species were
unsuccessful.
constants were again calculated using least-squares fits
for the spectral data, and values are summarized in
Table 2. The spectral changes observed during the reac-
tion of [FeII(TMP)] with HS- (given in Figure S4 of the
Supporting Information) are quite similar to those of
[FeII(T-p-OMePP)], with only small differences in the
wavelength maxima and relative intensities, as shown in
Table 2.
The spectral changes observed in the reaction of [FeII-
(TMP)(1-MeIm)2] with HS- also indicate the formation of
a new species. When a solution of [FeII(TMP)(1-MeIm)2]
Attempts to prepare iron(III) species also were not
successful; the HS- ligand reduced all iron(III) porphyr-
inates used. In our attempts to prepare [FeIII(Por)(SH)]

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1023
species, we reacted [Fe(Por)(OClO3)], Por=OEP or T-p-
OMePP, with NaHS in chlorobenzene in the presence of
(222) to aid in the solubilization of NaHS. In all cases,
mixtures of [Fe(Por)(SH)]- and [Fe(Por)(SH)2]2- were
obtained. Spectra obtained from these synthetic proce-
dures were similar to those obtained from the reaction of
[FeII(Por)] with HS-, as shown in Figure S7 in the
Supporting Information. This is in contrast to the earlier
report of the preparation of the low-spin iron(III) deri-
vative [Fe(T-p-OMePP)(SH)].29 A certain ambiguity is
associated with this complex because no direct evidence
for the hydrogen atom of HS- was obtained nor was an
Fe-S stretch observed. However, the physical properties
of [Fe(T-p-OMePP)(SH)] were consistent with an axially
symmetric low-spin iron(III) species and include
€
Mossbauer, EPR, NMR, and magnetic susceptibilities.
€
Figure 6. Mossbauer spectrum of [Na(222)][Fe(OEP)(SH)] 0.5C6H6 at
3
The low-spin state seems unexpected. A reduction, but a
rather slow reduction, of [FeIII(T-p-OMePP)(SH)] on
standing in a toluene or benzene solution was noted. It
is possible that environmental factors play a significant
role in this reduction. The apparent ease of reduction of
iron(III) porphyrinates to iron(II) in reactions with hy-
drosulfide leads us to believe that the stability of the
reported sulfide-bound iron(III) heme proteins results
either from a specialized (low-polarity) protein environ-
ment or from the protein allowing only limited access to
the binding site, which deters reduction at low concentra-
tions of sulfide species.
25 K with a magnetic field of 500 G. The experimental data and
deconvolution of the spectrum into two equal-area doublets are shown.
€
Table 3. Mossbauer Parameters for [Na(222)][Fe(OEP)(SH)] 0.5C6H6
3
a
a
δFe
iron site
ΔEQ
Γb
Tc
a
a
a
a
b
b
b
b
2.81
2.86
2.62
2.62
2.14
2.13
2.13
2.09
0.95
0.96
0.90
0.92
0.89
0.90
0.93
0.89
0.66
0.68
0.58
0.52
0.36
0.37
0.37
0.38
25
50
100
200
25
50
100
200
Far-IR spectra gave νFe-S=344 cm-1 in [Na(222)][Fe-
(OEP)(SH)]; the peak shifted to 340 cm-1 in the 57Fe
isotopomer, confirming the participation of iron in the
vibration. The analogous peak in [Na(222)][Fe(T-p-
OMePP)(SH)] was found at 337 cm-1. Exposure of the
original pellet to air for 24 h led to the disappearance of
the 344 cm-1 Fe-S peak. The IR stretch of the SH group
was not observed for either porphyrin complex; the band
is typically weak but has been previously reported at
2550 cm-1 for [Fe(SH)2(dmpe)2].36 The electrospray mass
spectrum, described earlier, clearly demonstrates that the
axial ligand is not chloride, a common possible impurity
in the iron(II) systems.
a mm/s. b fwhm, mm/s. c K.
consistent with iron(III) species. Table 4 compares the
€
Mossbauer parameters of iron sites “a” and “b” with
other high-spin iron(II) porphyrinates, four-coordinate
iron(II) species, and some iron(III) compounds.46-56 The
most comparable species are those with axial thiolates as
the ligand; [FeII(TpivPP)(SC2H5)]- has ΔEQ=2.18 mm/s
and δFe =0.83 mm/s and [FeII(TpivPP)(SC6HF4)]- has
ΔEQ = 2.38 mm/s and δFe = 0.83 mm/s. Other iron(II)
compounds, with nitrogen or oxygen as anionic axial
ligands, have slightly higher δFe values but signifi-
cantly larger ΔEQ values; some representative examples
are [Fe(TPP)(2-MeIm-)]- with ΔEQ = 3.60 mm/s and
€
Mossbauer Spectra. Mossbauer spectra for
€
[Na(222)][FeII(OEP)(SH)] 0.5C6H6 were collected bet-
3
ween 25 and 200 K in a 500 G magnetic field. The spectra
consist of two peaks that broaden with decreased tem-
perature. Shoulders are clearly evident in the 25 K
spectrum consistent with two quadrupole doublets, as
shown in Figure 6. The data can be fit to four, equal area,
overlapped Lorentzian lines for each temperature; values
of the fits are provided in Table 3. The two quadrupole
doublets are designated as “a” and “b”. At 25 K, the
quadrupole splitting (ΔEQ) values are 2.81 and 2.14 mm/s
with corresponding isomer shifts (δFe) of 0.95 and
0.89 mm/s. Some temperature dependence was observed;
ΔEQ values are 2.62 and 2.09 mm/s with corresponding
(46) Nasri, H.; Fischer, J.; Weiss, R.; Bill, E.; Trautwein, A. J. Am. Chem.
Soc. 1987, 109, 2549.
(47) Schappacher, M.; Weiss, R. R.; Montiel-Montoya, R.; Gonser, U.;
Bill, E.; Trautwein, A. Inorg. Chim. Acta 1983, 78, L9.
(48) Hu, C.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. J. Am. Chem. Soc.
2005, 127, 15018.
(49) Shaevitz, B. A.; Lang, G.; Reed, C. A. Inorg. Chem. 1988, 27, 4607.
(50) Bominaar, E. L.; Ding, X.; Gismelseed, A.; Bill, E.; Winkler, H.;
Trautwein, A. X.; Nasri, H.; Fisher, J.; Weiss, R. Inorg. Chem. 1992, 31,
1845.
(51) Collman, J. P.; Hoard, L.; Kim, N.; Lang, G.; Reed, C. A. J. Am.
Chem. Soc. 1975, 97, 2676.
(52) Hu, C.; Noll, B. C.; Schulz, C. E.; Scheidt, W. R. Inorg. Chem. 2007,
46, 619.
(53) Strauss, S. H.; Silver, M. E.; Long, K. M.; Thompson, R. G.;
Hudgens, R. A.; Spartalian, K.; Ibers, J. A. J. Am. Chem. Soc. 1985, 207,
4207.
(54) Maricondi, C.; Straub, D. K.; Epstein, L. M. J. Am. Chem. Soc. 1972,
94, 4157.
δ
Fe values of 0.92 and 0.89 mm/s at 200 K.
The observed ΔEQ and δFe values are strongly consis-
tent with known high-spin iron(II) porphyrin com-
plexes.45 Isomer shift values are far too large to be
(55) Moss, T. H.; Bearden, A. J.; Caughey, W. S. J. Chem. Phys. 1969, 51,
2624.
(56) Tang, S. C.; Koch, S.; Papaefthymiou, G. C.; Foner, S.; Frankel, R.
B.; Ibers, J. A.; Holm, R. H. J. Am. Chem. Soc. 1976, 98, 2414.
€
(45) Debrunner, P. G. Mossbauer Spectroscopy of Iron Porphyrins. In
Iron Porphyrins; Lever, A. B. P., Gray, H. B., Eds.; VCH Publishers Inc.:
New York, 1983; Chapter 2, Part 3.

1024 Inorganic Chemistry, Vol. 49, No. 3, 2010
Pavlik et al.
the table are other [FeII(Por)X] complexes with singly
charged anionic ligands63,64 and related [FeIII(Por)(SR)]
complexes.66,67
€
Table 4. Mossbauer Parameters for Relevant Iron(II) and -(III) Porphyrinates
a
a
complex
ΔEQ
δFe
Γb
Tc
ref
The atom displacements of the iron and the core atoms
from the 24-atom and 4-nitrogen-atom mean planes of
[FeII(OEP)(SH)]- are given in Figures 7 (anion 1) and S5
in the Supporting Information (anion 2). Also displayed
on these formal diagrams are the averaged values of the
bond distance and angle in each of the cores; the agree-
ment between the two cores is very good. The iron atom
displacements from the four-nitrogen planes (ΔN4) of
Iron(II) Complexes
[Fe(OEP)(SH)]-, site “a”
[Fe(OEP)(SH)]-, site “b”
[Fe(TpivPP)(SC2H5)]-
[Fe(TpivPP)(SC6HF4)]-
[Fe(TpivPP)(Cl)]-
2.82
2.13
0.95
0.89
0.83
0.83
1.01
1.03
1.05
1.03
1.06
1.00
1.00
0.52
0.57
0.62
0.66
25
25
4.2
4.2
77
4.2
4.2
4.2
4.2
4.2
4.2
4.2
twd
twd
48
47
47
49
50
46
46
48
48
51
52
53
0.36
0.30
0.32
0.31
0.25
0.30
0.40
0.38
0.29
0.33
þ2.18e
2.38
4.36
[Fe(TPP)(OC6H5]-
[Fe(TpivPP)(O2CCH3)]-
[Fe(TpivPP)(OCH3)]-
[Fe(TpivPP)(OC6H5]-
[Fe(OEP)(2-MeIm-)]-
[Fe(TPP)(2-MeIm-)]-
[Fe(TPP)] (I42d)
þ4.01e
þ4.25e
3.67
˚
0.55 and 0.52 A for 1 and 2, respectively, are consistent
˚
3.90
with the iron(II) anionic complexes, notably 0.53 A of
þ3.71e
þ3.60e
1.51
II
[FeII(TPP)(Cl)]-,59 0.49 A of [Fe (TpivPP)(Br)]-,60 and
˚
II
0.52 A of [Fe (TPP)(SC2H5)] .
- 61
˚
NRf
[Fe(TPP)] (P1)
[Fe(OEP)]
2.21
1.71
NRf
NRf
20
4.2
Interestingly, the porphyrin core conformations of
anions 1 and 2 of [FeII(OEP)(SH)]- have some substan-
tial differences. The plots of the iron atom displacements
from the two mean planes of Figures 7 and S5 in the
Supporting Information clearly show that both anions
have domed cores but otherwise differ in the patterns of
atom displacements. Clearly additional, but distinct, dis-
tortions from nonplanarity are present in the two anions.
The differences for the two anions in the asymmetric unit
occur despite identical composition in a common lattice.
The different types of distortions have been categorized as
ruffling, doming, saddling, waving, and propellering and
may be simultaneously present in a porphyrin core to
varying degrees.68,69 The deformations can be differen-
tiated using the normal-coordinate structural decomposi-
tion (NSD) procedure, a method to calculate the
contribution from each type of distortion.70 The results
from the NSD analysis for the two [FeII(OEP)(SH)]-
anions along with a number of additional high-spin
iron(II) porphyrinates coordinated by an anionic axial
ligand are presented in Table 6. The table makes clear
that, although both [FeII(OEP)(SH)]- anions have a
substantial doming component, the differing distortion
is that the anion core of 1 has a ruffling component,
whereas the anion core of 2 has a large saddling compo-
nent. The overall difference in the core conformations
probably leads to the modest difference in the Fe-Np
bond distances.
Iron(III) Complexes
[Fe(TPP)(Cl)]
[Fe(TPP)(Br)]
[Fe(OEP)(SC6H5)]
0.46
0.72
0.31
0.41
0.45
0.49
NRf
NRf
NRf
4.2
4.2
4.2
54
54
56
a mm/s. b fwhm, mm/s. c K. d This work. e Sign of ΔEQ experimentally
defined. f Not reported.
δFe=1.00 mm/s and [Fe(TPP)(OC6H5)]- with ΔEQ=4.01
mm/s and δFe = 1.03 mm/s. Four-coordinate iron(II)
compounds have significantly lower δFe values, 0.52
and 0.62 mm/s for [Fe(TPP)] and [Fe(OEP)], respectively.
€
Possible reasons for the appearance of two Mossbauer
distinguishable sites in crystalline [Na(222)][FeII(OEP)-
(SH)] 0.5C6H6 will be discussed subsequently.
3
Structures of the [FeII(Por)(SH)]- Anions. The asym-
metric unit of crystalline [Na(222)][FeII(OEP)(SH)] 0.5-
3
C6H6 contains two square-pyramidal anions with hydro-
sulfide as the axial anionic ligand, as shown in in Figures 1
and S1 in the Supporting Information. The two anions
will be referred to as anion 1 and anion 2. The two
porphyrin moieties do have some small, but significant,
differences in their coordination geometry. The average
Fe-Np distances are consistent with high-spin iron(II)
˚
˚
complexes: 2.1192(13) A for anion 1 and 2.1081(14) A for
anion 2.57,58 The Fe-S distances of 2.3929(5) and
2.3830(5) A for 1 and 2, respectively, are reasonable,
˚
II
- 59
˚
longer than the 2.340(5) A Fe-Cl of [Fe (TPP)(Cl)]
€
As has been noted previously, the Mossbauer spectrum
II
of crystalline [Na(222)][FeII(OEP)(SH)] 0.5C6H6 dis-
˚
and shorter than the 2.434(2) A Fe-Br of [Fe (Tpiv-
3
PP)(Br)]-.60 Known iron(II) thiolate values: 2.360(2) A in
˚
played two overlapping quadrupole doublets. The most
likely explanation for the two signals is that the confor-
mational differences are driving modest differences in the
electronic distribution that is revealed in the quadrupole
splitting values. Although we have no way of unambigu-
ously associating a particular conformation with the
quadrupole splitting, we think that the anion with its
slightly longer Fe-Np bond distances is to be associated
[FeII(TPP)(SC2H5)]- 61 and 2.324(2) A in [Fe (TpivPP)-
II
˚
(SC2H5)]- 62 are slightly shorter than the Fe-SH values.
These data are summarized in Table 5. Also included in
(57) Scheidt, W. R.; Reed, C. A. Chem. Rev. 1981, 81, 543.
(58) Scheidt, W. R. Systematics of Porphyrins and Metalloporphyrins. In
The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, CA, 2000; Vol. 3, pp 72-73.
(59) Hu, C.; Sulok, C. D.; Paulat, F.; Lehnert, N.; Zatsman, A. I.;
Hendrich, M. P.; Schulz, C. E.; Scheidt, W. R., manuscript in preparation.
(60) Nasri, H. Ph.D. Thesis, University of Louis Pasteur, Strasbourg,
France, 1987.
(61) Caron, C.; Mitschler, A.; Riviere, G.; Ricard, L.; Schappacher, M.;
Weiss, R. J. Am. Chem. Soc. 1979, 101, 7401.
(62) Schappacher, M.; Ricard, L.; Weiss, R. R.; Montiel-Montoya, R.;
Bill, E.; Trautwein, A. X. Inorg. Chem. 1989, 28, 4639.
(65) Tang, S. C.; Koch, S.; Papaefthymiou, G. C.; Foner, S.; Frankel, R.
B.; Ibers, J. A.; Holm, R. H. J. Am. Chem. Soc. 1976, 98, 2414.
(66) Miller, K. M.; Strouse, C. E. Acta Crystallogr., Sect. C 1984, C40,
1324.
(67) Miller, K. M.; Strouse, C. E. Inorg. Chem. 1984, 23, 2395.
(68) Scheidt, W. R.; Lee, Y. J. Recent Advances in the Stereochemistry of
Metallotetrapyrroles. Struct. Bonding (Berlin) 1987, 64, 1-70.
(69) Shelnutt, J. A.; Song, X.; Ma, J.; Jia, A.; Jentzen, W.; Medforth, C. J.
Chem. Soc. Rev. 1998, 27, 31.
(63) Nasri, H.; Ellison, M. K.; Shaevitz, B.; Gupta, G. P.; Scheidt, W. R.
Inorg. Chem. 2006, 45, 5284.
(64) Mandon, D.; Ott-Woelfel, F.; Fischer, J.; Weiss, R.; Bill, E.;
Trautwein, A. X. Inorg. Chem. 1979, 101, 2442.
(70) Sun, L.; Shelnutt, J. A. Program is available via the internet at http://
jasheln.unm.edu.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1025
˚
Table 5. Selected Distances (A) and Angles (deg) for Iron(II) Porphyrinates with Anionic Ligands
ÆFe-Npæa,b
Fe-Lb
Fe-S-Rc
ΔN4
ref
b,d
complex
Iron(II) Complexes
[Fe(OEP)(SH)]-, Fe(1)
[Fe(OEP)(SH)]-, Fe(2)
[Fe(TpOMePP)(SH)]-
[Fe(TPP)(SC2H5)]-
[Fe(TpivPP)(SC2H5)]-
[Fe(TpivPP)(OC6H5)]-
[Fe(TpivPP)(O2CCH3)]-
[Fe(TpivPP)(NO3)]-
[Fe(TpivPP) (2-MeIm-)]-
[Fe(TPP)(Cl)]-
2.1192(13)
2.1081(14)
2.108(5)
2.096(4)
2.074(10)
2.114(2)
2.107(2)
2.070(16)
2.11(2)
2.1161(11)
2.108(15)
2.094(3)
2.079(2)
2.3929(5)
2.3830(5)
2.3887(13)
2.360(2)
2.324(2)
1.937(4)
2.034(3)
2.069(4)
2.002(15)
2.3400(5)
2.301(2)
2.434(3)
2.712(1)
98.5(10)e
100.2(15)e
106.(2)e
0.55
0.52
0.52
0.52
0.44
0.56
0.55
0.42
0.52
0.56
0.53
0.49
0.40
tw
tw
tw
61
62
46
46
63
64
59
47
60
60
106.64
[Fe(TpivPP)(Cl)]-
[Fe(TpivPP)(Br)]-
[Fe(TpivPP)(I)]-
Iron(III) Complexes
[Fe(T-p-OMePP)(SH)]f
[Fe(Proto IX DME)(SC6H4NO2)]
[Fe(OEP)(SC6H5)]
2.0155(19)
2.064(18)
2.057(6)
2.2928(27)
2.324(2)
2.299(3)
2.298(5)
NA
0.33
0.43
0.47
0.40
29
65
66
67
100.4(2)
102.5(3)
103.7
[Fe(TPP)(SC6HF4)]
2.058(2)
a Average Fe-Np distance. b A. c deg. d Iron displacement from the four-nitrogen plane. e R = H. f Low spin.
˚
properties of the two anions. Significant differences
are not apparent (see Figure S2 in the Supporting
Information).
Table 6 also gives the results of the NSD analysis for a
number of additional high-spin iron(II) porphyrinates
with anionic axial ligands. All of these anionic species are
seen to display significant core doming; moreover, all
have at least one other significant core distortion mode.
This is reflected in the large values of Doop (a measure of
the total displacements; Table 6). Note that none of these
complexes are derivatives with peripheral crowding de-
signed to induce significant nonplanar distortions. A
similar analysis has been done for high-spin iron(II)
porphyrinates with (neutral) imidazole as the axial li-
gand.71 These two systems provide some interesting
comparisons. Although the imidazole derivatives also
frequently display core doming, the magnitude is, on
3
average, only /4 that of the anionic species. Moreover,
the total distortion value Doop is also only about 60% in
the imidazole-ligated species. These differences are con-
sistent with the idea that there are two distinct S=2 states
for high-spin iron porphyrinate derivatives that are char-
acterized by, inter alia, apparent differences in the size of
the iron center.59
The X-ray structure of a second hydrosulfide deriva-
tive, [Fe(T-p-OMePP)(SH)]-, has also been determined.
The coordination geometry for this complex is similar to
that of its OEP analogue, with an Fe-S bond distance of
˚
2.3887(13) A and an average Fe-Np distance of 2.108(5)
Figure 7. Mean-plane diagrams for anion 1 of [Na(222)][Fe(OEP)-
(SH)] 0.5C6H6. The values of the atomic displacements from 24-atom
(top) and 4-nitrogen-atom (bottom) mean planes are given in units of 0.01
˚
A. Also entered on the diagrams are mean porphyrin core bond lengths in
angstroms and mean bond angles in degrees.
˚
A. Table 7 details the coordination site geometry, and
3
Table 5 compares the geometry of [Fe(T-p-OMePP)-
(SH)]- to those of the OEP analogue and related por-
phyrin complexes. The displacements of all porphyrinate
atoms from the 24-atom mean plane and the 4-nitrogen-
atom plane are presented in Figure S6 in the Supporting
Information. Although the porphyrin core is less domed
with the larger quadrupole doublet (“a”). This issue is
difficult to study because any rigorous evaluation
requires samples with identical composition but differing
core conformations. We carefully studied the crystal
packing pattern to see if differing environments of the
HS- ligand could be the cause of the differing physical
(71) See Table 3 of: Hu, C.; An, J.; Noll, B. C.; Schulz, C. E.; Scheidt, W.
R. Inorg. Chem. 2006, 45, 4177.

1026 Inorganic Chemistry, Vol. 49, No. 3, 2010
Pavlik et al.
˚
Table 6. Out-of-Plane Displacements (A) of the Minimal Basis for the X-ray Crystal Structures of Five-Coordinate High-Spin Iron(II) Porphyrinates
Δd
ref
a
b
c
porphyrin
Doop
δoop
sad
ruf
dom
wav(x)
wav(y)
pro
ΔN4
[Fe(OEP)(SH)]-, Fe(1)
[Fe(OEP)(SH)]-, Fe(2)
[Fe(T-p-OMePP)(SH)]-
[Fe(OEP)(2-MeIm-)]-
[Fe(TpivPP)(2-MeIm-)]-
[Fe(TpivPP)(NO3)]-
[Fe(TpivPP)(O2CCH3)]-
[Fe(TpivPP)(OC6H5)]-
[Fe(TpivPP)(SC2H5)]-
[Fe(TPP)(2-MeIm-)]-
[Fe(TPP)(Cl)]-
0.526
0.514
0.444
0.772
0.613
0.574
0.582
0.443
0.542
0.666
0.649
0.015
0.012
0.024
0.005
0.018
0.012
0.008
0.013
0.017
0.005
0.009
0.016
0.324
-0.316
-0.511
0.205
-0.081
-0.077
-0.058
0.228
-0.536
-0.335
-0.207
-0.001
0.090
0.497
0.420
0.528
0.505
0.387
0.396
0.080
-0.359
-0.481
-0.393
-0.203
-0.261
-0.365
-0.207
-0.277
-0.176
-0.290
-0.301
-0.398
0.019
-0.049
0.181
-0.014
0.041
0.122
-0.090
-0.012
0.033
0.006
-0.100
0.018
-0.242
-0.106
0.035
-0.003
-0.009
0.032
-0.012
-0.001
0.020
0.55
0.52
0.52
0.56
0.53
0.55
0.55
0.57
0.44
0.56
0.56
0.70
0.64
0.59
0.65
0.65
0.65
0.65
0.63
0.54
0.66
0.69
tw
tw
tw
48
64
63
50
46
62
48
59
0.109
-0.154
-0.012
0.028
0.049
0.003
-0.018
0.019
0.098
-0.005
-0.016
-0.013
a Observed total distortion. b Mean deviations. c Displacement of iron from the mean plane of the four pyrrole nitrogen atoms. d Displacement of iron
from the 24-atom mean plane.
Table 7. Selected Bond Distances and Angles for [Na(222)][Fe(Por)(SH)]
sized, isolated, and characterized by single-crystal structure
€
determinations, IR and Mossbauer spectroscopy, and mass
Por
Fe-Na
Fe-Sa
S-Ha N-Fe-Nb Fe-S-Hb
spectrometry. The results from all analyses are consistent
with high-spin iron(II) with iron-bound sulfur. The physical
properties are most similar to those of other high-spin iron-
(II) porphyrinates with axial anionic ligands. Solution bind-
ing studies yield values for formation constants that are
comparable to those of imidazoles. Extinction coefficients
and peak maxima for hydrosulfidometalloporphyrin com-
plexes have been reported. Porphyrin core conformations for
the [Fe(Por)(SH)]- species were analyzed by NSD and
compared for all iron(II) species with anionic ligands. The
OEP complexes may display larger contributions from dom-
ing than those of related iron(II) species.
OEP, Fe(1) 2.1148(13) 2.3929(5) 1.31(2) 86.18(5)
98.8(12)
2.1172(13)
2.1219(13)
2.1231(13)
86.15(5)
86.35(5)
86.65(5)
OEP, Fe(2) 2.0976(13) 2.3830(5) 1.23(2) 87.50(5)
100.3(15)
2.1073(14)
2.1136(14)
2.1138(14)
86.00(5)
86.47(5)
86.32(5)
T-p-OMePP 2.105(3)
2.105(3)
2.108(3)
2.3887(13) 1.36(5) 86.61(12) 106.(2)
86.06(12)
86.19(12)
87.00(12)
2.116(3)
a
A. b deg.
˚
Acknowledgment. We thank Prof. Ken Olson, Indiana
University School of Medicine-South Bend, for early
discussions on the potential gasotransmitter H2S. We
acknowledge Dr. W. C. Boggess of the University of Notre
Dame for help with mass spectrometry. We thank the
National Institutes of Health for support of this research
under Grant GM-38401 and the NSF for X-ray instrumen-
tation support under Grant CHE-0443233.
than that in the OEP species, it is still strongly distorted,
as shown in Table 6, with unusually large wav(x,y)
components. A complete description of the treatment of
hydrogen atoms of the HS- ligand in the two complexes is
given in the Supporting Information. A comparison of
the Fe-S-H geometries with those of thiolates (Table 7)
shows strong similarities.
Summary
Supporting Information Available: Discussion of the hydro-
sulfide hydrogen atom assignment in the X-ray crystal struc-
tures, further validation of sulfur ligation, and experimental
details of UV-vis binding studies, ORTEP drawing of anion 2
of [Na(222)]Fe(OEP)(SH)] (Figure S1), plot of the asymmetric
This work clearly shows that HS-, the most abundant
form of H2S at physiological pH, can act as a good ligand in
iron porphyrinate systems and that the combination of heme
proteins and the HS- ligand could have a significant place in
heme biological systems. The observed reducing power of
HS- with isolatedhemesstrongly suggeststhathemeproteins
coordinating to sulfide ligands in the iron(III) oxidation state
either must have specialized (low-polarity) environments or
must allow only limited access to the HS-/S2- binding site.
There are no equivalent restrictions for the iron(II) species.
Solution UV-vis spectral investigations show stability for
three distinct iron(II) species [Fe(Por)(SH)]-, [Fe(Por)-
(SH)2]2-, and a mixed-ligand species [Fe(Por)(SH)(Im)]-.
The five-coordinate species, [Fe(Por)(SH)]-, are the first
hydrosulfidoiron(II) porphyrinate compounds to be synthe-
unit of the structure for [Na(222)]Fe(OEP)(SH)] 0.5C6H6
3
(Figure S2), thermal ellipsoid plot for [Fe(T-p-OMePP)(SH)]-
(Figure S3), UV-vis plot of the reactions of [FeII(TMP)] with
HS- (Figure S4), mean-plane diagrams for [Na(222)]Fe(OEP)-
(SH)] (Figure S5), mean-plane diagrams for [Fe(T-p-OMePP)-
(SH)]- (Figure S6), spectra detailing the reaction products with
SH- and FeIII (Figure S7), complete crystallographic informa-
tion for [Na(222)][Fe(OEP)(SH)] 0.5C6H6 (Tables S1-S6) and
3
that for Na(222)][Fe(T-p-OMePP)(SH)] C6H5Cl (Tables S7-
3
S12), and crystallographic data in CIF format. This mate-
rial is available free of charge via the Internet at http://pubs.
acs.org.