Gallium(III) and indium(III) octaethylporphyrin dimeric complexes with a single μ-hydroxo bridge: Synthesis, structure and stability in anion-containing organic media

Article abstract of DOI:10.1016/S0020-1693(03)00267-6

The synthesis and single-crystal X-ray structures of the hydroxo-bridged complexes (μ-hydroxo)-bis(octaethylporphinato)gallium(III)perchlorate {[Ga(OEP)]₂OH}ClO₄ and (μ-hydroxo)- bis(octaethylporphinato)indium(III)tetrakis[3,5-bis-(trifluoromethyl)phenyl] borate {[In(OEP)]₂OH}TFPB are reported. These complexes are prepared by the titration of monomeric metalloporphyrin species in dichloromethane with diluted perchloric acid or by the addition of stoichiometric amounts of the tetraphenylborate derivative salt. The structures show that complexes of two metalloporphyrins are joined by a single protonated metal-oxygen-metal bridge with a nearly 150° bridge angle. The porphyrin rings of the dimers form dihedral angles of 15° Ga(III) and 23° In(III). In contrast to previously reported analogous dimeric Mn(III) and Fe(III) structures, the porphyrin rings of the present dimers are twisted by a much greater torsion angle of nearly 22°. In dichloromethane, high stability of the dimers is observed in the presence of perchlorate, but dissociation of the dimer species to monomers is found with increasing concentrations of halogen anions. This corresponds well with the observed anion selectivities recently reported for both electrochemical and optical anion sensors prepared with the respective Ga(III) and In(III) octaethylporphyrins in polymeric films.

Full text of DOI:10.1016/S0020-1693(03)00267-6

Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
www.elsevier.com/locate/ica
Gallium(III) and indium(III) octaethylporphyrin dimeric complexes
with a single m-hydroxo bridge: synthesis, structure and stability in
anion-containing organic media
Pawe l G. Parzuchowski a,b, Jeff W. Kampf a, Ewa Roz´niecka b,
Yevgeniy Kondratenko a, Elzbieta Malinowska b, Mark E. Meyerhoff a,*
˙
a Department of Chemistry, The University of Michigan, Ann Arbor, MI 48109-1055, USA
b Department of Chemistry, Warsaw University of Technology, 00-664 Warsaw, Poland
Received 11 April 2003; accepted 19 April 2003
Abstract
The synthesis and single-crystal X-ray structures of the hydroxo-bridged complexes (m-hydroxo)-bis(octaethylporphinato)-
gallium(III)perchlorate {[Ga(OEP)]2OH}ClO4 and (m-hydroxo)-bis(octaethylporphinato)indium(III)tetrakis[3,5-bis-(trifluoro-
methyl)phenyl]borate {[In(OEP)]2OH}TFPB are reported. These complexes are prepared by the titration of monomeric
metalloporphyrin species in dichloromethane with diluted perchloric acid or by the addition of stoichiometric amounts of the
tetraphenylborate derivative salt. The structures show that complexes of two metalloporphyrins are joined by a single protonated
metalÃ
/
oxygenÃmetal bridge with a nearly 1508 bridge angle. The porphyrin rings of the dimers form dihedral angles of 158 Ga(III)
/
and 238 In(III). In contrast to previously reported analogous dimeric Mn(III) and Fe(III) structures, the porphyrin rings of the
present dimers are twisted by a much greater torsion angle of nearly 228. In dichloromethane, high stability of the dimers is observed
in the presence of perchlorate, but dissociation of the dimer species to monomers is found with increasing concentrations of halogen
anions. This corresponds well with the observed anion selectivities recently reported for both electrochemical and optical anion
sensors prepared with the respective Ga(III) and In(III) octaethylporphyrins in polymeric films.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Porphyrin dimer; Metalloporphyrin; X-ray structures; Anion-selective sensors
1. Introduction
can exhibit unique anion selectivity patterns when
employed to fabricate sensors that function either by
an electrochemical (potentiometric) or optical transduc-
tion mode. Indeed, Ru(II) [2], Co(III) [3,4], Ga(III) [4],
Zr(IV) [5], In(III) [4,6,7], Th(III) [8], Mn(III) [9], Sn(IV)
In recent years, significant effort has been placed on
the development and study of new host molecules that
display selective binding recognition of anionic species
[1]. One objective of such work is to employ these host
compounds to prepare either electrochemical or optical
sensors that provide analytically useful anion responses
[1]. Among a wide range of host molecules examined to
date, it has been repeatedly demonstrated that polymeric
membranes/films doped with various metalloporphyrins
[10,11] and OÄ/Mo(V) [12] porphyrin-based sensors have
all been found to exhibit useful selectivities for a range
of anions including thiocyanate (Ru(II)), thiocyanate/
nitrite (Co(III)), fluoride (Ga(III) and Zr(IV)), chloride
(In(III) and Th(III)), acetate (Mn(III)) and salicylate
(Sn(IV) and OÄ/Mo(V)). In general, selectivity for one
anion over others is governed by the strength of anion
binding as an axial ligand to the metal ion center of the
metalloporphyrin within the organic polymeric phase of
the sensor [3].
* Corresponding author. Tel.: ꢀ
4865.
/
1-734-763 5916; fax: ꢀ1-734-647
/
E-mail address: mmeyerho@umich.edu (M.E. Meyerhoff).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00267-6

P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ
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313
303
In the case of potentiometric anion-selective mem-
brane electrodes formulated with gallium(III), indiu-
m(III) and tin(IV) porphyrins in polymeric membranes,
it was discovered that unusual super-Nernstian re-
other bridging ligands for a (m-hydroxo)diiron(III)
complex was described as unprecedented. Since then,
two other structures for manganese(III) octaethyl- and
tetraphenylporphyrins have been published [18,19]
showing an analogous single m-hydroxo bridging group.
In one report [19], it was suggested that similar
structures for Ga(III) and In(III) porphyrins would be
forthcoming, but to our knowledge, there has been no
published data of these structures to date. Some further
indirect evidence regarding dimeric structures of Ga(III)
porphyrin complexes was obtained recently by electro-
spray mass spectrometry [20]. Indeed, the authors were
able to observe ions at m/z 1219 which were attributed
to the dimeric {[Ga(OEP)]2OH}ꢀ species.
sponses (slopes greater than ꢂ
observed toward target anions. This behavior has been
ascribed to a novel dimerꢁmonomer equilibrium of the
/
59 mV per decade) are
/
metalloporphyrins species within the organic membrane
phases of the sensors when in contact with an aqueous
test solution containing anions [13]. Based on UVꢁVis
/
spectra of the same metalloporphyrin-doped polymeric
films used to fabricate the devices, it has been suggested
that the equilibrium that occurs involves spontaneous
formation of m-hydroxy-bridged metalloporphyrins in
the organic polymer films, resulting from the addition of
lipophilic anion sites in the form of tetraphenylborate
derivatives. Such derivatives are typically added to
membranes to enhance anion selectivity in potentio-
metric anion sensors where the ionophore in the
membrane functions as a charged carrier [13,14]. In
membranes containing certain metalloporphyrins, the
tetraphenylborate derivative can also apparently help
stabilize the positively charged dimeric species between
two metalloporphyrins in the absence of appreciable
levels of anions in bathing aqueous test solution [15].
Upon addition of increasing concentrations of anions to
the aqueous sample phase that can ligate to the
metalloporphyrins, the dimers within the organic mem-
brane are converted to monomers, with a corresponding
large bathochromic shift in the observed Soret band as
Herein, we report the preparation and X-ray struc-
tures of the (m-hydroxo)-bis(octaethylporphinato)galliu-
m(III)perchlorate {[Ga(OEP)]2OH}ClO4 and (m-
hydroxo)-bis(octaethylporphinato)indium(III)tetra-
kis[3,5-bis-(trifluoromethyl)phenyl]borate {[In(OE-
P)]2OH}TFPB. We further illustrate via UVꢁVis
/
spectroscopy how certain anions added to a pure
organic-phase solution of these dimeric species can
break the dimers into corresponding monomers.
2. Experimental
2.1. General
H2(OEP) was purchased from MidCentury Chemicals
(Posen, IL), and indium(III) and gallium(III) chlorides
were purchased from Aldrich (St. Louis, MO). All the
solvents (Fisher, Chicago, IL) were distilled prior use.
1H NMR spectra were obtained on Varian 300 or 400
detected by UVꢁVis spectra of the films. Indeed, this
/
process is fully reversible when the anion concentration
in the test solution is decreased [13] and this chemistry
has formed the basis for a new chloride-selective optical
sensor using plasticized poly(vinyl chloride) films doped
with In(III) octaethylporphyrin (OEP) [6]. The overall
advantages and disadvantages of dimer formation in
potentiometric anion-selective sensors have been dis-
cussed in detail in a recent report [15].
The primary objective of this work is to confirm that
m-hydroxy-bridged dimers of In(III) and Ga(III) por-
phyrins can in fact be isolated, and their crystal
structures obtained. Moreover, preparation of these
dimers allows for simple pure organic phase experiments
that can illustrate how different anions interact and shift
MHz spectrometer in CDCl3. UVꢁVis spectra were
/
recorded using a Beckman DU 640B spectrophot-
ometer.
2.2. Synthetic procedures
2.2.1. Gallium(III) and indium(III) octaethylporphyrin
chlorides
Ga(OEP)Cl (1a) and In(OEP)Cl (1b) were synthesized
according to previously published procedures [21] by
refluxing of parent ligand with appropriate metal salt
the dimerꢁmonomer equilibrium in favor of monomer.
/
and sodium acetate in dry acetic acid. NMR and UVꢁ
/
There are many literature reports describing the
structures of bridged dimeric porphyrin species. For
example, numerous iron(III), manganese(IV) and ruthe-
nium(IV) oxo-bridged X-ray structures have been pub-
lished [16]. The first example of a new class of bridged
metal(III) porphyrin complexes with a single hydroxo
bridge was reported by Scheidt et al. [17]. They
presented an X-ray structure that revealed a single
bridging group and a single counteranion for two
iron(III) octaethylporphyrin units. The lack of any
Vis data matched those published previously [21,22].
2.2.2. Ga(OEP)OH (2a) and In(OEP)OH (2b)
The solutions of metalloporphyrins 1 were dissolved
in dichloromethane and washed three times with 2 N
KOH and then three times with water. The organic
phases were then separated and dried with Na2SO4. The
products were crystallized from hexanes and dried under
vacuum.

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P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
2.2.3. {[Ga(OEP)]2OH}ClO4 (3a)
A solution of monomer 2a (62 mg) in 5 ml of
Table 1
Crystal data and structure refinement for {[In(OEP)]2OH}TFPB and
{[Ga(OEP)]2OH}ClO4×H2O
/
dichloromethane was placed in a closed vial. The UVꢁ
/
Vis spectrum was obtained (350ꢁ430 nm). The absorp-
tion band for the monomer appears with a lmax at 400
nm. Small amounts of freshly prepared 15 mM HClO4
/
{[In(OEP)]2OH}TFPB
{[Ga(OEP)]2OH}ClO4×
/
H2O
Empirical for- C104H102BF24In2N8O
mula
Formula weight 2176.39
C72H91ClGa2N8O6
(0.1ꢁ
/
0.3 ml) were added. After each addition, the
Vis spectrum
sample was shaken for 5 min and a UVꢁ
/
1339.42
158(2)
was recorded again. Disappearance of the 400 nm band
was observed. The dimer band appeared at 380 nm. The
reaction was completed when the 400 nm band totally
disappeared. The organic phase was then separated and
dried with Na2SO4. Crystalline product was obtained
from a dichloromethane/hexane mixture. Proton NMR
in chloroform solvent was employed to further confirm
the formation of the new dimer complex.
Temperature
(K)
123(2)
˚
Wavelength (A) 0.71073
Crystal system, tetragonal, P4/ncc
space group
0.71073
triclinic, P1
¯
Unit cell di-
mensions
˚
a (A)
˚
33.2941(16)
33.2941(16)
18.0579(12)
90
13.707(5)
13.762(5)
18.379(7)
72.781(6)
85.930(6)
89.784(6)
3303(2)
b (A)
˚
c (A)
1H NMR (400 MHz, CDCl3) d (ppm): 9.37 (s, 4H,
a (8)
b (8)
g (8)
CH Ä
/
), 4.21ꢁ
/
4.12 (m, 8H, CH2), 4.08ꢁ
/
3.98 (m, 8H,
90
90
CH2), 1.71 (t, 24H, CH3, Jꢃ
/7.65 Hz), 1.50 (s, H2O).
3
˚
Volume (A ) 20017.1(19)
Calculated den- 8, 1.444
2, 1.347
2.2.4. {[In(OEP)]2OH}TFPB (3b)
sity, Z
(g cmꢂ3
A solution of monomer 2b (4.41 mg) in 6 ml of
dichloromethane was shaken overnight with 3 mg of
potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]bo-
)
Absorption
coefficient
0.558
8872
0.915
1412
(mmꢂ1
F(000)
)
rate in 3 ml of 0.4 M NaOHaq. The UVꢁVis spectrum
/
confirmed disappearance of the monomer band at 400
nm. The organic phase was separated and dried with
Na2SO4. Crystalline product was obtained from a
dichloromethane/hexane mixture. Proton NMR in
chloroform solvent was again used to further confirm
that the product had a different spectrum from the
starting monomer In(OEP) species.
Crystal size
(mm3)
0.41ꢄ
/
0.14ꢄ
/
0.13
0.22ꢄ
/
0.22ꢄ0.20
/
Theta range for 2.74ꢁ
/28.76
1.55ꢁ24.41
/
data collection
(8)
Limiting indices
ꢂ/
315
/
h 5
/
31, ꢂ/445
/
ꢂ
/
155
k 516, ꢂ
31503
/
h 5
/
15, ꢂ
/
155
/
k 544, ꢂ
/
/245/l 5/24
/
/215
/l 5
/21
Reflections col- 263900
lected
1H NMR (400 MHz, CDCl3) d (ppm): 9.64 (s, 4H,
CH Ä
4.14 (m, 8H, CH2), 4.06ꢁ
24H, CH3, Jꢃ7.74 Hz), 1.56 (s, H2O).
/
), 7.76 (bs, 4H, borate), 7.56 (s, 2H, borate), 4.23ꢁ
/
Unique reflec- 12770 (Rint
tions
ꢃ
/
0.0907)
10839 (Rint
ꢃ
/
0.0862)
/3.97 (m, 8H, CH2), 1.69 (t,
Completeness
Absorption
correction
to thetaꢃ
semi-empirical from
equivalents
/
28.76 (98.0%) to thetaꢃ
/24.41 (99.7%)
/
semi-empirical from
equivalents
0.868 and 0.700
Max. and min. 0.9310 and 0.8036
transmission
3. X-ray structure determinations
3.1. {[Ga(OEP)]2OH}ClO4×H2O (3a)
Refinement
method
Full-matrix least-squares Full-matrix least-squares
on F2
on F2
10839/0/821
/
Data/restraints/ 12770/0/505
parameters
Purple plates of 3a were crystallized from dichlor-
omethane/hexane at room temperature. A crystal of
Goodness-of-fit 1.091
on F2
1.006
Final R indices R1ꢃ
[Iꢀ2s(I)] 0.1556
R1ꢃ0.0935, wR2ꢃ
0.1657
0.721 and ꢂ
/
0.0638, wR2ꢃ
/
R1ꢃ
0.0861
R1ꢃ0.1333, wR2ꢃ
0.0954
0.763 and ꢂ
/
0.0528, wR2ꢃ
/
dimensions 0.22 mmꢄ
mounted on a standard Bruker SMART CCD-based
/
0.22 mmꢄ0.20 mm was
/
/
R indices (all
data)
/
/
/
/
X-ray diffractometer equipped with a normal focus Mo-
˚
target X-ray tube (lꢃ0.71073 A) operated at 2000 W
/
Largest diff.
peak and hole
/0.787
/0.680
power (50 kV, 40 mA). The X-ray intensities were
measured at 158(2) K; the detector was placed at a
distance of 4.959 cm from the crystal. A total of 2232
frames were collected with a scan width of 0.38 in v and
phi with an exposure time of 30 s per frame. The frames
were integrated with the Bruker SAINT software
package with a narrow frame algorithm [23]. The
integration of the data yielded a total of 31 503
ꢂ3
˚
(e A
)
reflections to a maximum 2u value of 48.88 of which
10 839 were independent and 5268 were greater than
2s(I). The final cell constants (Table 1) were based on
the xyz centroids of 4063 reflections above 10s(I).

P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ
/
313
305
Analysis of the data showed negligible decay during
data collection; the data were processed with SADABS
and corrected for absorption [24]. The structure was
solved and refined with the Bruker SHELXTL (version
4. Determination of the dimer and monomer contents in
the organic solution upon addition of tetrabutylammonium
anion salts
¯
5.10) software package, using the space group P1 with
4.1. {[Ga(OEP)]2OH}ClO4
Zꢃ
/
2 for the formula C72H89N8O5ClGa2×
/
H2O [25]. All
Appropriate amounts of a concentrated solution of 3a
in dichloromethane (0.3 mM) were placed in 10 ml
volumetric flasks together with required amounts of a
stock solution of tetrabutylammonium salt to yield mole
ratios ranging from 0 to 1.25. The flasks were diluted to
mark with dichloromethane and mixed thoroughly.
non-hydrogen atoms were refined anisotropically with
the hydrogen atoms placed in idealized positions. Full-
matrix least-squares refinement based on F2 converged
at R1ꢃ
/
0.0528 and wR2ꢃ
/
0.0861 (based on I ꢀ2s(I)),
/
R1ꢃ0.1333 and wR2ꢃ0.0954 for all data. Additional
details are presented in Table 1 and are given as
/
/
UVꢁVis spectra were recorded for each mixture using
/
supporting information in a CIF file.
a 10-mm path-length quartz cell.
4.2. {[In(OEP)]2OH}TFPB
3.2. {[In(OEP)]2OH}TFPB (3b)
Seven and one-half mg of 3b was dissolved in 25 ml of
chloroform. The 0.3 ml aliquots of the above solution
were placed in vials containing dry tetrabutylammonium
salts in molar ratios ranging from 0 to 1.25 relative to
the dimer. The exact amounts of tetrabutylammonium
salts were initially placed into the vials via solutions, and
then evaporated to dryness. The final solutions were
shaken and spectra measured in 0.1-mm path-length
quartz cells.
Purple needles of 3b were grown by diffusing hexane
into a dichloromethane/toluene solution at 25 8C. A
crystal of dimensions 0.41 mmꢄ
/
0.14 mmꢄ0.13 mm
/
was cut from a larger needle and mounted on a standard
Bruker SMART CCD-based X-ray diffractometer
equipped with a LT-2 low-temperature device and
˚
0.71073 A)
normal focus Mo-target X-ray tube (lꢃ
/
operated at 2000 W power (50 kV, 40 mA). The X-ray
intensities were measured at 133(2) K; the detector was
placed at a distance of 4.954 cm from the crystal. A total
of 3030 frames were collected with a scan width of 0.38
in v and phi with an exposure time of 90 s per frame.
The frames were integrated with the Bruker SAINT
software package with a narrow frame algorithm [26].
The integration of the data yielded a total of 263 900
reflections to a maximum 2u value of 57.98 of which
12 770 were independent and 8779 were greater than
2s(I). The final cell constants (Table 1) were based on
the xyz centroids of 6962 reflections above 10s(I).
Analysis of the data showed negligible decay during
data collection; the data were processed with SADABS
and corrected for absorption [24]. The structure was
solved and refined with the Bruker SHELXTL (version
5.10) software package, using the space group P4/ncc
5. Results and discussion
5.1. Syntheses
Compounds 1a and 1b were synthesized according to
the previously published procedures [21] as summarized
in Section 2. The products were chromatographed on
activated neutral alumina (Brockmann I, Â150 mesh)
/
with chloroform as the mobile phase. If necessary, the
chromatography was repeated. The final metallopor-
phyrin products were crystallized from chloroform/
hexane mixtures. The OH forms of the respective
metalloporphyrins were obtained by simply shaking an
organic-phase solution of the metalloporphyrin chlor-
ides 1 with a 2 N aqueous solution of KOH to exchange
chloride with hydroxide.
The dimers 3 were prepared via two different routes
(Fig. 1). The Ga(III) dimer compound, 3a, was formed
from 2a by shaking a dichloromethane solution of this
species with increasing amounts of a diluted water
with Zꢃ
/
8 for the formula C104H102BF24N8OIn2×
/(sol-
vent) [25]. All non-hydrogen atoms were refined aniso-
tropically with the hydrogen atoms placed in a mixture
of idealized and refined positions. The compound
crystallizes on a twofold rotation axis in the crystal
lattice. The lattice has two voids, which contain a
mixture of disordered solvent and borate anions. These
were modeled by use of the PLATON/SQUEEZE
routine [27]. Full details are given in the associated
CIF file. Full-matrix least-squares refinement based on
solution of perchloric acid. During this process, UVꢁ
/
Vis spectra were monitored. Crystals were ultimately
obtained by slow diffusion of excess hexane into chloro-
form solution of 3a.
F2 converged at R1ꢃ
on I ꢀ2s(I)), R1ꢃ0.0935 and wR2ꢃ
data. Additional details are presented in Table 1 and are
/
0.0638 and wR2ꢃ
/
0.1556 (based
The dimer of the In(OEP), 3b, could not be synthe-
/
/
/0.1657 for all
sized in the same way. The UVꢁVis spectra did not
/
show any significant change in absorption in the range
of 390 nm when perchloric acid was added to a solution
given as supporting information as a CIF file.

306
P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
Fig. 1. Metalloporphyrin dimer formation in the presence of lipophilic anion. Mꢃ
/
Ga (2a and 3a) or In (2b and 3b), Aꢂ ꢃ
perchlorate (3a) or
/
tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate (3b).
of 2b. There was some shift in the monomer absorption
band (from 400 to 405 nm), but no evidence of dimer
formation via generation of a new Soret band blue
shifted from the monomer (as observed for Ga(OEP)
and previously for the corresponding Fe(OEP) and
Mn(OEP) dimeric species). The desired In porphyrin
dimer 3b was instead synthesized by mixing 2b with
potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]bo-
rate with a mole ratio 2:1. Addition of the 0.4 M
the plane of the Ga(1)Ã
/
O(1)Ã
/
Ga(2) bonds. The two
porphyrin macrocycles are not parallel but rather form a
dihedral angle of 158. The closest distance of two
porphyrin macrocycles measured between C(9) and
˚
C(40) was found to be 3.43 A. The two porphyrin
macrocycles are not located directly one above the
other. The average measured NÃ
sion angle is 22.238.
Figs. and show ORTEP diagrams of
/
Ga(1)Ã
/
G(2)ÃN? tor-
/
4
5
NaOH was necessary to shift the monomerꢁ
/
dimer
{[In(OEP)]2OH}ꢀ cation. Fig. 5 illustrates the number-
ing scheme for the top porphyrin of the dimer. The
numbering scheme for the bottom porphyrin is the same
and is not shown.
equilibrium toward the dimer within the dichloro-
methane solution. This mixture was shaken for several
hours and crystals were ultimately obtained by slow
diffusion of hexane into organic solution of the dimer.
In contrast to gallium dimer structure, the indium one
is quite regular. The distances between In atoms and
˚
hydroxy bridge oxygen are equal and longer (2.119 A)
than in other similar structures (see Tables 3 and 4). The
6. X-ray structures
In(1)Ã
/
OÃIn(1)#1 angle is found to be 144.458, the
/
smallest value among the analogous dimeric structures
reported to date (see Table 4). Both indium atoms are
located the same distance from the plane of the
Figs.
2
and
3
are ORTEP diagrams of the
{[Ga(OEP)]2OH}ꢀ cation. Fig. 3 also illustrates the
labeling scheme used in Table 2 for non-hydrogen
atoms. Selected bond distances and bond angles are
provided in Table 2.
˚
macrocycle by 0.42 A. The hydrogen atom adjacent to
O(1) is positioned in the plane of the In(1)Ã
/
O(1)Ã
/
In(1)#1 bonds. The two porphyrin macrocycles are
again not parallel but form a dihedral angle of 238.
The closest distance of the two porphyrin macrocycles
measured between C(5) and C(6)#1 was found to be
As can be seen in Fig. 2, the most striking feature of
the {[Ga(OEP)]2OH}ꢀ cation is the presence of a water
molecule coordinated to the Ga(1) atom. The
Ga(1)Á Á ÁO(2) interactions causes some irregularities in
the structure of the dimer 3a. The distances of Ga(1) and
˚
3.76 A. Similar to the gallium structure above, the two
In porphyrin macrocycles are not located directly above
˚
Ga(2) to O(1) are not equal and they differ by 0.1 A
which is a large value given other X-ray structures of
each other. The average measured NÃ
/
In(1)Ã
/
In(1)#1ÃN?
/
torsion angle is 22.858.
this type (see Tables 2 and 4). The Ga(1)Ã
/
(OH)Ã/Ga(2)
angle is 151.968. The Ga(1) atom is located almost in the
plane of the macrocycle. The distance of the Ga(1)
coordinates from average plane formed by N(1) to N(4)
7. NMR analysis
˚
atoms is only 0.09 A. The Ga(2) coordinates indicate
that it is out of the average (N5) to N(8) plane by 0.36
˚
A. The hydrogen atom adjacent to the O(1) is located in
1
Fig. 6 shows the H NMR spectra of the monomeric
and dimeric forms of Ga(III) and In(III) metallopor-

P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ
/
313
307
Fig. 2. Edge-view ORTEP diagram of the cation of {[Ga(OEP)]2OH}ꢀ
ellipsoids are drawn at the 50% probability level. Porphyrin hydrogen atoms are omitted for clarity.
×
/
H2O with the Ga(1)Ã
/
O(H)ÃGa(2) bridge in the plane of the paper. Thermal
/
phyrins. Formation of a dimer causes a large shift of
resonances originating from the porphyrin ring CHÄ
protons towards higher fields. The shift is larger in
case of the gallium compound 3a than for the indium
dimer 3b. Chemical shifts of methylene groups remain
unaffected by dimer formation in both cases; however,
/
Fig. 3. Top-view ORTEP diagram of the cation of {[Ga(OEP)]2OH}ꢀ with the Ga(1)Á Á ÁGa(2) axis perpendicular to the plane of the paper. Thermal
ellipsoids are drawn at the 50% probability level.

308
P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
Table 2
the presence of water. It is believed that water is
necessary for the formation of dimeric structures [28],
˚
Selected bond lengths (A) and angles (8) for {[Ga(OEP)]2OH}ClO4×
H2O
/
since no dimer was observed by UVꢁVis in polymeric
/
films under dry-box conditions. In addition, as shown in
Fig. 2, the X-ray structure of 3a indicates a presence of
one molecule of water per each gallium octaethylpor-
phyrin dimer. Crystals of 3b may also contain water,
since the lattice has two voids, in which a mixture of
disordered solvent and borate anions likely exist.
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
/
O(1)
N(3)
N(4)
N(2)
N(1)
O(2)
1.995(3)
2.019(4)
2.029(4)
2.029(4)
2.040(4)
2.213(3)
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
/
O(1)
N(6)
N(5)
N(7)
N(8)
1.895(3)
2.028(4)
2.034(4)
2.041(4)
2.041(4)
/
/
/
/
/
/
/
/
/
O(1)Ã
O(1)Ã
N(3)Ã
O(1)Ã
N(3)Ã
N(4)Ã
O(1)Ã
N(3)Ã
N(4)Ã
N(2)Ã
O(1)Ã
N(3)Ã
N(4)Ã
N(2)Ã
N(1)Ã
/
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
Ga(1)Ã
/
N(3)
97.71(14) O(1)Ã
92.15(14) O(1)Ã
89.87(15) N(6)Ã
92.09(13) O(1)Ã
90.38(15) N(6)Ã
175.68(16) N(5)Ã
87.84(14) O(1)Ã
174.44(17) N(6)Ã
89.94(15) N(5)Ã
89.39(15) N(7)Ã
176.65(11) Ga(2)Ã
/
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
Ga(2)Ã
O(1)Ã
/
N(6)
106.49(14)
99.93(14)
88.77(15)
98.04(13)
87.97(16)
161.93(15)
95.88(13)
157.61(15)
88.22(15)
88.06(16)
151.98(16)
/
/N(4)
/
/N(5)
/
/
N(4)
/
/
N(5)
8. UV
/
Vis analysis
/
/N(2)
/
/N(7)
ꢁ
/
/
N(2)
/
/
N(7)
N(7)
/
/
N(2)
/
/
Compounds 2 and 3 exhibit lmax of the Soret bands in
/
/N(1)
/
/N(8)
the region between 370 and 420 nm. Monomerꢁ
/
dimer
transition causes a large hypsochromic shift in the lmax,
/
/
N(1)
N(1)
N(1)
/
/
N(8)
N(8)
N(8)
/
/
/
/
which is analytically useful for anion and neutral species
detection [4,6,28]. The lmax for monomeric metallopor-
phyrins in organic solvents ranges from 401 to 410 nm
depending on the metal, anion coordinated and solvent
/
/
/
/
/
/O(2)
/
/Ga(1)
/
/
O(2)
O(2)
O(2)
O(2)
85.56(14)
88.53(14)
87.19(13)
88.88(14)
/
/
/
/
used. For example, in chloroform, lmax In(OEP)Cl
ꢃ406
/
/
/
nm and lmax In(OEP)F 404 nm. The values for dimers
ꢃ
/
are consistent. The lmax for the Ga(III) porphyrin dimer
is 379 nm, the In dimer has a lmax at 387 nm.
Table 3
˚
Selected bond lengths (A) and angles (8) for {[In(OEP)]2OH}TFPB
9. Dissociation of the dimers in organic phase
In(1)Ã
In(1)Ã
In(1)Ã
In(1)Ã
/
O(1)
N(2)
N(4)
N(1)
2.1193(12) In(1)Ã
/
N(3)
2.144(4)
0.84(2)
2.1193(12)
/
2.129(3)
2.134(3)
2.136(3)
O(1)Ã
O(1)Ã
/
H(1)
In(1)#1
a
It was shown previously [6,13,28] that in an organic
polymeric phase, dimers 3 break in the presence of
selected anions or neutral species added to the surround-
ing aqueous phase (or gas phase). The same process
occurs in pure organic phase as tetrabutylammonium
anion salts are added to either methylene chloride or
chloroform solutions of the isolated dimeric species.
Indeed, Fig. 7 illustrates the generic chemistry that takes
place within an organic phase upon addition of tetra-
butylammonium salts for which the counteranion is a
reasonably strong ligand with the metal ion center of the
metalloporphyrin that forms the dimer.
/
/
/
O(1)Ã
O(1)Ã
N(2)Ã
O(1)Ã
N(2)Ã
N(4)Ã
O(1)Ã
/
In(1)Ã
In(1)Ã
In(1)Ã
In(1)Ã
In(1)Ã
In(1)Ã
In(1)Ã
/
N(2) 105.62(13) N(2)Ã
N(4)
97.14(13) N(4)Ã
N(4) 157.21(14) N(1)Ã
N(1) 104.43(11) H(1)Ã
/
In(1)Ã
In(1)Ã
In(1)Ã
O(1)Ã
O(1)Ã
87.52(13) In(1)#1Ã
98.14(11)
/
N(3)
N(3)
N(3)
In(1)#1 a
87.48(13)
88.04(14)
157.37(14)
107.77(10)
107.77(10)
144.5(2)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
N(1)
88.07(13) H(1)Ã
/
/
In(1)
/
/
N(1)
/
O(1)Ã
In(1) a
/
/
/N(3)
a
Symmetry transformations used to generate equivalent atom #1:
yꢀ1, ꢂxꢀ1, ꢂzꢀ1/2.
ꢂ/
/
/
/
/
/
In the case of the In(III) dimer, to obtain stable
solutions of this species, it is necessary to work with
Table 4
Comparison of the various {[M(OEP)]2OH}ꢀ structures
total dimer concentration that is ꢀ
concentrations, it was found that the UVꢁ
/
100 mM. At lower
Metal (M)
MÃ(OH) distance (A)
Mn [18] Fe [17] Ga
In
/
Vis band
˚
/
2.024
1.998
1.924
1.952
1.995
1.895
2.119
2.119
corresponding to the dimeric structure decreases, and
the monomer band increases, over relatively short
periods of time (e.g., 10 min). This necessitates using
very short path-length cells to record the change in the
spectrum of the In(III) dimer, as the mole ratio of anion
added to dimer is increased. Fig. 8 shows an example of
the spectral changes observed when increasing mole
ratios of tetrabutylammonium chloride are added to a
chloroform solution of {[In(OEP)]2OH}TFPB. It can be
seen that the intensity of the absorption bands at 387
and 406 nm strongly depend on the amount of tetra-
butylammonium chloride in the solution, with an
MÃ
/
OÃ
/
M angle (8)
152.73 146.22 151.96 144.45
22.9
Average NÃ
/
MÃM?Ã
/
/
N? torsion
4.3
8.6
22.2
angle (8)
Dihedral angle a (8)
12.7
19.9
15.0
23.0
a
The angle between the two porphyrin mean planes.
the gallium compound exhibits higher multiplicity of the
signals. The methyl group resonances are shifted slightly
toward a higher field. All the spectra were run in dry
chloroform. The spectra of the dimers, however, show

P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ
/
313
309
Fig. 4. Edge-view ORTEP diagram of the cation of {[In(OEP)]2OH}ꢀ with the In(1)Ã
ellipsoids are drawn at the 50% probability level. Porphyrin hydrogen atoms are omitted for clarity.
/
O(H)ÃIn(1)#1 bridge in the plane of the paper. Thermal
/
increase in the monomer band as chloride:dimer ratio is
increased. It should be noted that no clear isosbestic
point in the spectra is observed because there are more
than two species in equilibrium with the dimer. Indeed,
upon addition of exogenous anions the dimer breaks to
form monomers with bound anion ligand, bound
hydroxide, and also some fraction of monomer where
the TFPB serves as a non-ligated counteranion species.
Fig. 5. Top-view ORTEP diagram of the cation of {[In(OEP)]2OH}ꢀ with the In(1)Á Á ÁIn(1)#1 axis perpendicular to the plane of the paper. Thermal
ellipsoids are drawn at the 50% probability level. Only labeling scheme for the ‘‘top porphyrin’’ is given for clarity.

310
P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
Fig. 6. 400 MHz 1H NMR spectra of the monomeric and dimeric forms of Ga(III) and In(III) metallooctaethylporphyrins.
Similar UVꢁ
/
Vis data, as shown in Fig. 8, were
tetrabutylammonium anion salts). Fig. 9 illustrates how
each of the halides are capable of effectively breaking
the m-hydroxo-bridged dimers for both the Ga(III) and
In(III) species, but perchlorate, even in excess mole ratio
recorded for both porphyrin dimers 3a and 3b, with
increasing mole ratios of five different anions: fluoride,
chloride, bromide, iodide and perchlorate (as added via
Fig. 7. Monomerꢁ
/
dimer equilibrium of 3 in the presence of tetrabutylammonium halide. Rꢂ ꢃ
Fꢀ, Clꢀ, Brꢀ, Iꢀ
/
perchlorate (3a), tetrakis[3,5-bis-(trifluoro-
methyl)phenyl]borate (3b). Aꢀ ꢃ
/
.

P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ
/
313
311
Fig. 8. Changes in the UVꢁ/Vis spectrum of {[In(OEP)]2OH}TFPB in the presence of tetrabutylammonium chloride in dichloromethane. Numbers
show the mole ratio between tetrabutylammonium chloride and the porphyrin dimer.
to the dimers, is not capable of breaking the dimer
structures. This is in good agreement with the selectivity
observed for potentiometric ion-selective membrane
electrodes formulated with Ga(III) and In(III) porphyr-
ins, which have been shown to spontaneously form
dimers within the organic membranes of the sensors
[4,6]. Indeed, such sensors display relatively high selec-
tivity for anions over perchlorate, even though perchlo-
rate has a much more favorable single anion partition
coefficient into the organic membranes of such devices
[1].
necessary to spontaneously form dimeric complexes in
organic polymeric films used for anion and gas-phase
amine sensing [28].
The stability of both complexes was tested in the
presence of tetrabutylammonium salts of selected an-
ions. These experiments showed high stability in the
presence of perchlorate ions and complete decomposi-
tion into monomers in the presence of halogen anions
when present at a mole ratio ]1.0.
/
11. Supplementary materials
10. Summary
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre. Copies of this information may be
obtained free of charge from The Director, CCDC
210716 for Gallium (OEP) 2OH dimer and CCDC
210717 for the Indium (OEP) 2OH dimer, 12 Union
The synthesis of the hydroxo-bridged complexes
H2O and {[In(OEP)]2OH}TFPB
{[Ga(OEP)]2OH}ClO4×
/
through two different routes is demonstrated. The
gallium dimer was synthesized by careful titration of
organic solution of metalloporphyrin with diluted per-
chloric acid. The indium compound can only be isolated
by the addition of stoichiometric amount of tetraphe-
nylborate derivative to an organic phase containing the
In(OEP) monomer at elevated pH. The X-ray structures
Road, Cambridge, CB2 1EZ, UK (fax: ꢀ44-1223-336-
/
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk). Complete crystallographic details
are available from attached CIF files.
for both complexes show presence of metalÃ
/
oxygenÃ
/
metal bridge with angles of 151.968 and 144.458,
respectively. Both structures show that the porphyrin
rings are twisted far more than previously reported Fe
Acknowledgements
and
Mn
hydoxo-bridged
structures.
H2O structure has one molecule
The
{[Ga(OEP)]2OH}ClO4×
/
We thank the National Institutes of Health for
supporting this work (EB 00784).
of water coordinated at metal ion, which supports
earlier experimental findings that contact with water is

312
P.G. Parzuchowski et al. / Inorganica Chimica Acta 355 (2003) 302ꢁ313
/
Fig. 9. Decrease in dimer bands at 379 nm (a) and 387 nm (b) for Ga(III) and In(III) porphyrin dimers, respectively, as a function of the mole ratio of
different anions added to organic-phase solutions of the dimers: (2) Fꢀ, (^) Clꢀ, (k) Brꢀ, (ꢀ) Iꢀ, (I) ClO4.
/
[8] E.D. Steinle, U. Schaller, M.E. Meyerhoff, Anal. Sci. 14 (1998)
79.
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