Coordination capabilities of a novel organic polychlorotriphenylmethyl monosulfonate radical

Article abstract of DOI:10.1021/ic060182j

The treatment of α-H-p-H-PTM (PTM = polychlorotriphenylmethane) with oleum 65% followed by deprotonation and oxidation leads to the isolation of a novel pure organic radical PTMSO₃H·3H₂O·0. 5hexane (2). The X-ray diffraction of 2 reveals a layered structure with disordered H₂O molecules between facing sulfonic acid groups. We have explored the coordination abilities of the sulfonate derivative using different metals. The treatment of 2 with mild bases yields the sulfonate radical PTMSO₃Na·H₂O (3). On the other hand, the new compound [Cu(Py)₂(H₂O)₄]-(PTMSO ₃)₂·2H₂O·2EtOH (4) has been crystallized using Cu^II as the metallic counterion in the presence of pyridine. The structure reveals a solvent-separated ion-pair-type compound, with no direct coordination of the metal ion with the sulfonate group, and the formation of organic layers between layers of transition metal complexes. This situation has been overcome by favoring the stabilization of the sulfonate group over the Cu^II center by changing the pyridine ligand to cyclam. This has led to compound [Cu(cyclam)](PTMSO₃)₂·6EtOH (5a), in which the sulfonate group acts as a monodentate axial ligand for the Cu^II center. We have observed a single-to-single crystal rearrangement from 5a to [Cu(cyclam)](PTMSO₃)₂ (5b) because of the loss of the solvent of crystallization, without significant modification of the metal coordination environment. All species have been structurally and magnetically characterized, and the magnetic coupling between the organic radicals and the metal paramagnetic centers is discussed.

Full text of DOI:10.1021/ic060182j

Inorg. Chem. 2006, 45, 5383−5392
Coordination Capabilities of a Novel Organic Polychlorotriphenylmethyl
Monosulfonate Radical
Xavi Ribas,†,‡ Daniel Maspoch,†,# Klaus Wurst,§ Jaume Veciana,*,† and Concepcio´ Rovira*,†
Departament de Nanocie`ncia Molecular i Materials Orga`nics, Institut de Cie`ncia de Materials de
Barcelona, CSIC, Campus de la UAB, E-08193 Bellaterra, Spain, and Institut fu¨r Allgemeine
Anorganische und Theoretische Chemie, UniVersitat Innsbruck, Innrain 52a, Innsbruck, Austria
Received February 1, 2006
The treatment of
R
-H-p-H-PTM (PTM
)
polychlorotriphenylmethane) with oleum 65% followed by deprotonation
3H2O 0.5hexane (2). The X-ray
and oxidation leads to the isolation of a novel pure organic radical PTMSO3H
‚
‚
diffraction of 2 reveals a layered structure with disordered H2O molecules between facing sulfonic acid groups. We
have explored the coordination abilities of the sulfonate derivative using different metals. The treatment of 2 with
mild bases yields the sulfonate radical PTMSO3Na
‚H2O (3). On the other hand, the new compound [Cu(py)2(H2O)4]-
(PTMSO3)2 2H2O
‚
‚
2EtOH (4) has been crystallized using CuII as the metallic counterion in the presence of pyridine.
The structure reveals a solvent-separated ion-pair-type compound, with no direct coordination of the metal ion with
the sulfonate group, and the formation of organic layers between layers of transition metal complexes. This situation
has been overcome by favoring the stabilization of the sulfonate group over the CuII center by changing the pyridine
ligand to cyclam. This has led to compound [Cu(cyclam)](PTMSO3)2‚6EtOH (5a), in which the sulfonate group acts
as a monodentate axial ligand for the CuII center. We have observed a single-to-single crystal rearrangement from
5a to [Cu(cyclam)](PTMSO3)2 (5b) because of the loss of the solvent of crystallization, without significant modification
of the metal coordination environment. All species have been structurally and magnetically characterized, and the
magnetic coupling between the organic radicals and the metal paramagnetic centers is discussed.
Introduction
coordinating groups of the organic moieties account for the
crystal engineering of the metal-organic polymers synthe-
sized so far.2 A step forward has been the incorporation of
persistent stable organic radicals embedded in the coordina-
tion polymers in a manner such that the unpaired spins can
magnetically interact.3,4 Our group has recently reported
several para- and meta-substituted polychlorotriphenylmethyl
radicals (PTM)5 with different numbers of carboxylic acid
groups (n ) 1-6)6-8 that have been used as magnetically
active building blocks for the synthesis of multifunctional
materials. Exhaustive structural and magnetic studies have
The search of materials exhibiting multiple functionalities
has been the focus of intensive investigation in the molecular
materials community. The combination of different physical
properties in the same material and the observation of multi-
stabilities simultaneously in different physical channels is a
crucial step toward the design of new electronic, magnetic,
or optical devices.1 One of the extensively used approaches
to synthesize functional materials is the metal-organic
strategy for obtaining coordination polymers which incor-
porate open-shell transition metals. The precise control of
the coordination geometry of the transition metal and the
(2) (a) Janiak, C. Dalton Trans. 2003, 14, 2781-2804. (b) Braga, D. Chem.
Commun. 2003, 22, 2751-2754. (c) Eddaoudi, M.; Moler, D. B.; Li,
H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem.
Res. 2001, 34, 319-330.
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R.; Venturi, G.; Vindigni, A.; Rettori, A.; Pini, M. G.; Novak, M. A.
Angew. Chem., Int. Ed. 2001, 40, 1760-1763. (b) Vaz, M. G. F.;
Pinehiro, L. M. M.; Stumpf, H. O.; Alcantara, A. F. C.; Goleen, S.;
Ouahab, L.; Cador, O.; Mathonie`re, C.; Kahn, O. Chem.sEur. J. 1999,
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2842-2848.
* To whom correspondence should be addressed. E-mail: cun@icmab.es
(C.R.); vecianaj@icmab.es (J.V.).
† Institut de Cie`ncia de Materials de Barcelona.
§ Universitat Innsbruck.
‡ Current Address: Departament de Qu´ımica, Universitat de Girona,
Campus Montilivi, E-17071 Girona, Spain.
# Current Address: Institute for Nanotechnology, Northwestern Univer-
sity, 2145 Sheridan Road, Evanston, IL 60208.
(1) Itkis, M. E.; Chi, X.; Cordes, A. W.; Haddon, R. C. Science 2002,
296, 1443-1445.
10.1021/ic060182j CCC: $33.50
Published on Web 06/15/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 14, 2006 5383

Ribas et al.
been performed on discrete copper(II) complexes bearing two
axially coordinated PTMMC (monocarboxylated para-
substituted PTM radical), showing three unpaired antiferro-
magnetically coupled (2J/KB ) -30 to -50 K) spins.9
Furthermore, via the use of crystal engineering strategies on
different PTM derivatives, a metal-organic nanoporous
structure combining CuII ions and the PTMTC radical
(tricarboxylated para-substituted PTM radical) was synthe-
sized and described as a magnetic sponge with bulk magnetic
ordering and with promising potential for application as a
magnetic sensor.10
It is in this context that we decided to explore the
substitution of the carboxylic functional group (-COOH)
by a sulfonic group (-SO3H) in the PTM radicals to
investigate its potential use as a magnetically active building
block for metal-organic coordination compounds. Herein,
we report the synthesis of the PTM-SO3H radical and the
coordinative possibilities of the deprotonated sulfonic group
in its use as a magnetically active organic ligand. Although
the sulfonate anion is generally considered to be a poor
ligand,11 with many examples of weakly interacting or
noninteracting sulfonates found in the literature,12 there is
an increasing interest in the exploration of the sulfonate group
as an efficient ligand for metals to form metal-organic
layered structures,13 as an analogy to the metal-phosphonate
structures.14 In general, the sulfonate group cannot displace
H2O molecules from the primary coordination sphere of the
metal. However, alkali ions, large alkaline earth ions, and
Ag(I) ions have been shown to be exceptions to the general
trend.13 The difference seems to rely on the nonpreferences
for a coordination number or geometry. Indeed, the coopera-
tive interactions in the formation of extended structures such
as AgPhSO3, AgOTs, and Ag(4-pyridinesulfonate) were
reported to be responsible for the robustness of these
structures, with thermal stabilities higher than 300 °C.15 The
cooperative interactions have been attributed to the spherical
trioxy anionic sulfonate groups because they allow multiple
connectivities to the metal centers.16 With these bibliographic
precedents, we have explored, for the first time, the
coordination capabilities of a stable organic radical bearing
a sulfonate group, and two examples with a nonparamagnetic
alkaline metal ion and a paramagnetic transition metal ion
such as CuII are presented. In the latter compound, we will
demonstrate that a solvent-separated ion pair (SSIP) situation
in the structure precludes magnetic communication between
the two distinct magnetic centers. We will also show that it
is possible to force direct coordination of the sulfonate group
to the copper center and discuss the magnetic consequences.
Experimental Section
Materials. Solvents of reagent grade quality supplied by SDS
were dried before use with a standard method and stored under
Ar. Reagents were obtained commercially from Aldrich and used
without further purification.
Elemental analyses were performed by SA-UAB (Servei
d’Ana`lisi-Universitat Auto`noma de Barcelona). UV-vis-NIR
spectra were recorded on a Varian Cary 5 spectrophotometer. IR
spectra were obtained on a Perkin-Elmer Spectrum One spectro-
photometer using KBr pellets. Cyclic voltammetry experiments were
carried out at room temperature with an EG&G (PAR263A)
potentiostat-galvanostat in a normal three-electrode cell (Ag/Ag+
reference) with Pt wires as working and auxiliary electrodes.
Distilled and argon-degassed methanol or acetonitrile were used
as solvents with 0.1 M (nBu4N)+PF6- as supporting electrolyte (scan
rate ) 100 mV s-1). Thermogravimetric analyses were performed
under argon with a high sensitivity Perkin-Elmer TGA7 balance.
(4) (a) Minguet, M.; Luneau, D.; Lhotel, E.; Vincent Villar, Paulsen, C.;
Amabilino, D. B.; Veciana, J. Angew. Chem., Int. Ed. 2002, 41, 586-
589. (b) Vostrikova, K. E.; Luneau, D.; Wernsdorfer, W.; Rey, P.;
Verdaguer, M. J. Am. Chem. Soc. 2000, 122, 718-719. (c) Oshio,
H.; Ito, T. Coord. Chem. ReV. 2000, 198, 329-346. (d) Marvilliers,
A.; Pei, Y.; Cano, J.; Vostrikova, K. E.; Paulsen, C.; Rivie`re, E.;
Audie`re, J.-P.; Mallah, T. Chem. Commun. 1999, 1951-1952. (e)
Field, L. M.; Lahti, P. M.; Palacio, F. Chem. Commun. 2002, 636-
637. (f) Stroh, G.; Turek, P.; Rabu, P.; Ziessel, R. Inorg. Chem. 2001,
21, 5334-5342. (g) Min, K. S.; Rhinegold, A. L.; Miller, J. S. Inorg.
Chem. 2005, 44, 8433-8441.
(5) Ballester, M. Acc. Chem. Res. 1985, 12, 380-387.
(6) (a) Maspoch, D.; Gerbier, P.; Catala, L.; Vidal-Gancedo, J.; Wurst,
K.; Rovira, C.; Veciana, J. Chem.sEur. J. 2002, 8, 3635-3645. (b)
Roques, N.; Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.;
Tejada, J.; Rovira, C.; Veciana, J. Chem. Commun. 2005, 4801-4803.
(c) Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Tejada,
J.; Rovira, C.; Veciana, J. C. R. Chem. 2005, 8, 1213.
(7) Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Wurst, K.; Tejada, J.;
Rovira, C.; Veciana, J. J. Am. Chem. Soc. 2004, 126, 730-731.
(8) Maspoch, D.; Domingo, N.; Ruiz-Molina, D.; Vaughan, G.; Wurst,
K.; Tejada, J.; Rovira, C.; Veciana, J. Angew. Chem., Int. Ed. 2004,
43, 1828-1832.
(9) (a) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Rovira, C.; Veciana, J.
Dalton Trans. 2004, 1073-1082. (b) Maspoch, D.; Ruiz-Molina, D.;
Wurst, K.; Rovira, C.; Veciana, J. Chem. Commun. 2004, 1164-1165.
(c) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Rovira, C.; Veciana, J.
Chem. Commun. 2002, 2958-2959.
X-ray powder diffraction studies were performed in the Serveis
Cient´ıfico-Te`cnics de la UB. The polycrystalline samples were
gently ground and placed in Lindemann capillary tubes of 0.2 mm
of diameter. A Debye-Scherrer geometry diffractometer INEL
CPS-120 (radius ) 250 mm) was used. The radiation used was Cu
KR1 (λ ) 1.540598 Å), with a working power of 40 KV (30 mA).
The detector was sensitive to 120° position, with 4096 measure
channels. The equipment contents a Germanium(111) flat primary
monochromator and a reflector mirror from OSMIC Gutman Optics
(13B-413). The beam height was 2-3 mm for all samples, and its
width was 0.1 mm. Calibration was performed using Na2Ca2Al2F13
(NAC) as an external reference (cubic function SPLINE). Linear-
ization was done with the PEAKOC software (from INEL). Typical
measurement times were about 3 h.
(10) Maspoch, D.; Ruiz-Molina, D.; Wurst, K.; Domingo, N.; Cavallini,
M.; Biscarini, F.; Tejada, J.; Rovira, C.; Veciana, J. Nature Mater.
2003, 2, 190-195.
(11) Davies, J. A.; Hockensmith, C. A.; Kukushkin, V. Y.; Kukushkin, Y.
N. Synthetic Coordination Chemistry: Principles and Practice; World
Scientific: London, 1996; p 58.
(12) (a) Lawrence, G. A. Chem. ReV. 1986, 86, 17-33. (b) Smith, G.;
Cloutt, B. A.; Lynch, D. E.; Byriel, K. A.; Kennard, C. H. L. Inorg.
Chem. 1998, 37, 3236-3242. (c) Dalrymple, A. A.; Shimizu, G. K.
H. Chem. Commun. 2002, 2224-2225.
(13) Cote´, A. P.; Shimizu, G. K. H. Coord. Chem ReV. 2003, 245, 49-64.
(14) (a) Kaschak, D. M.; Johnson, S. A.; Hooks, D. E.; Kim, H.-N.; Ward,
M. D.; Mallouk, T. E. J. Am. Chem. Soc. 1998, 120, 10887-10894.
(b) Clearfield, A. Prog. Inorg. Chem. 1998, 47, 371-510.
(15) (a) Shimizu, G. K. H.; Enright, G. D.; Ratcliffe, C. I.; Rego, G. S.;
Reid, J. L.; Ripmeester, J. A. Chem. Mater. 1998, 10, 3282-3283.
(b) Shimizu, G. K. H.; Enright, G. D.; Ratcliffe, C. I.; Preston, K. F.;
Reid, J. L.; Ripmeester, J. A. Chem. Commun. 1999, 1485-1486. (c)
May, L. J.; Shimizu, G. K. H. Chem. Mater. 2005, 17, 217-220.
(16) Ma¨kinen, S. K.; Melcer, N. J.; Parvez, M.; Shimizu, G. K. H. Chem.s
Eur. J. 2001, 7, 5176-5182.
5384 Inorganic Chemistry, Vol. 45, No. 14, 2006

Polychlorotriphenylmethyl Monosulfonate Radical
The synthesis of the R-H-p-H-PTM precursor was performed
according to the procedure described in the literature.17
1 mL of ethanol was added dropwise to a solution of 3.8 mg (0.016
mmol) of Cu(NO3)2‚3H2O in a mixture of 5 mL of ethanol, 0.5
mL of H2O, and 3 drops of pyridine (large excess). Immediately
after the addition, the solution was filtered and left to stand at room
temperature for several days, until the appearance of 24 mg (0.012
mmol) of red-block crystals corresponding to compound 4. MW:
1995.17 g/mol. Yield: 78%. IR (KBr pellet): ν 3435, 1656, 1609,
1449, 1336, 1305, 1256, 1212, 1115, 1060, 1017, 874, 817, 697,
669, 602, 515 cm-1. Anal. Calcd (%) for C52Cl28S2N2H34O14Cu:
C, 30.75; S, 3.16; H, 1.69; N, 1.38. Found: C, 30.50; S, 3.10; H,
1.75; N, 1.45. EPR (on solid, 298 K): g1 ) 2.0060 (∆Hpp ) 35
G), g2 ) 2.265. EPR (on solid, 120 K): g1 ) 2.0097 (∆Hpp ) 42
G), g2 ) 2.2418.
r-H-PTMSO3H (1). A solution of 1.8 g (2.48 mmol) of R-H-
p-H-PTM in 40 mL of 65% oleum was heated at 95 °C with stirring
for 60 h. The reaction mixture was cooled to room temperature
and poured over ice (150 mL). The solid precipitate was filtered,
rinsed with H2O, and dissolved in 100 mL of CHCl3. The addition
of a saturated solution of NaHCO3 (100 mL) allowed the sulfonate
sodium salt to dissolve in the aqueous fraction. The latter was
acidified with concentrated aqueous HCl until a permanent acid
pH and extracted with CHCl3 (3 × 200 mL). The latter solution
was dried with anhydrous Na2SO4, filtered, and evaporated. The
solid was purified by column chromatography (silica gel/acetone).
The product was decolored by dissolving it in 50 mL of CHCl3
and left over active carbon for 3 days, followed by a second
purification by column chromatography. The aliquots of the product
were evaporated giving 1.05 g (1.30 mmol) of R-H-PTMSO3H (1).
MW: 806.62 g/mol. Yield: 53%.
PTMSO3H‚3H2O‚0.5hexane (2). To a solution of 100 mg (0.124
mmol) of R-H-PTMSO3H (1) in 10 mL of freshly distilled DMSO,
0.5 g (0.0125 mol) of smashed NaOH was added. The suspension
was placed in an automatic shaker during 24 h in a dark room.
The intense red solution was then filtered, and 37 mg (0.146 mmol)
of resublimated I2 were added; the mixture was shaken and left for
1 h. Twenty milliliters of a solution of aqueous NaHSO3 (3.9%)
were added, followed by acidification with concentrated HCl until
a permanent acidic pH. The compound was extracted with CHCl3,
dried with anhydrous Na2SO4, and evaporated. The dark-red powder
was chromatographied in column with silica gel and eluted with
acetone. The product was redissolved in CHCl3 and recolumnated
in the same conditions yielding 85 mg (0.011 mmol) of a dark-red
powder corresponding to 2. MW: 805.62 g/mol. Yield: 85%.
Compound 2 was recrystallized from CHCl3/n-hexane producing
block-shaped crystals of PTMSO3H‚3H2O‚0.5hexane (2).
[Cu(cyclam)](PTMSO3)2‚6EtOH (5a) and [Cu(cyclam)](PT-
MSO3)2 (5b). Fifty-two milligrams (0.063 mmol) of PTMSO3Na
radical (3) dissolved in 20 mL of ethanol was placed at the bottom
of a glass tube. A solution of 7.6 mg (0.031 mmol) of Cu(NO3)2‚
6H2O and 6.3 mg of cyclam (1,4,8,11-tetraazacyclotetradecane) in
20 mL of ethanol was then carefully added. The self-diffusion of
both solutions resulted in the precipitation of 20 mg (0.011 mmol)
of red crystals after 4 days, corresponding to compound 5a. The
crystals lost all the solvent of crystallization after removal from
the mother liquor, suffering a crystal-to-crystal reorganization
resulting in compound 5b (see text). MW (5b): 1873.11 g/mol.
Yield (5b): 35%. IR (KBr pellet): ν 3436, 3196, 2923, 2849, 1631,
1458, 1429, 1137, 1306, 1213, 1114, 1058, 817, 670, 601, 514 cm-1
.
Anal Calcd (%) for C48Cl28S2N4H24O6Cu: C, 30.78; S, 3.52; H,
1.29; N, 2.99. Found: C, 30.64; S, 3.65; H, 1.10; N, 2.86. EPR
(on solid, 298 K): g1 ) 2.0199 (∆Hpp ) 11.4 G), g2 ) 2.0670.
EPR (on solid, 120 K): g1 ) 2.0206 (∆Hpp ) 12.9 G), g2 ) 2.0681.
Compound 5a has been characterized by X-ray diffraction studies
on one crystal in mother liquor.
Crystallographic Determination. Crystals for X-ray determi-
nation (see Supporting Information) were grown by hexane diffusion
into a CHCl3 solution of compound 2 and from direct synthesis in
ethanol for compounds 4 and 5a. The structure of compound 5b
was obtained from the measurement of the 5a crystal mounted in
a capillary after evaporation of the ethanol molecules of crystal-
lization. Crystal data was collected on a Nonius Kappa CCD
diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.71073 Å) at 233(3) K for 2 and 4 and 290(2) K for 5a/5b.
Intensities were integrated using DENZO and scaled with
SCALEPACK. Several scans in the φ and ω directions were made
to increase the number of redundant reflections, which were
averaged in the refinement cycles. This procedure replaces an
empirical absorption correction. The structure was solved with direct
methods (SHELXS86) and refined against F2 (SHELX97).18
Hydrogen atoms at the carbon atoms were added geometrically and
refined using a riding model. Hydrogen atoms at the disordered
solvent H2O and hexane molecules were omitted for 2 and found
and refined with bond restraints for the H2O and ethanol molecules
of 4. All non-hydrogen atoms were refined with anisotropic
displacement parameters.
UV-vis (THF): λmax (ꢀ) 285 (6500), 368 (16 800), 385 (32 600),
505 (1000), 565 nm (920 cm-1
M
-1). IR (KBr pellet): ν 2928,
2223, 1508, 1337, 1307, 1258, 1200, 1132, 1117, 1060, 818, 739,
713,695, 671, 659, 602, 515 cm-1. Anal. Calcd (%) for C19Cl14-
SO3H‚2H2O: C, 27.11; S, 3.80; H, 0.60; Cl, 58.98. Found: C,
26.91; S, 3.74; H, 0.56; Cl, 59.30. CV (in CH2Cl2): E1/2 (vs Ag/
AgCl) -0.13 V. EPR (CH3CN/toluene 1/1): g ) 2.0023 (∆Hpp
)
4.0 G), no half-field signal.
PTMSO3Na‚H2O (3). Fifty milligrams (0.0621 mmol) of the
PTMSO3H radical (2) was dissolved in 20 mL of THF, and an
excess NaHCO3 (20 mL of a saturated solution) was added to
produce a precipitate that was filtered and dried under vacuum.
The solid obtained was recrystallized from a mixture of THF and
hexane yielding 45 mg (0.053 mmol) of red plate-shaped crystals
of the PTMSO3Na‚H2O radical salt (3). MW: 845.61 g/mol.
Yield: 86%. UV-vis (THF): λmax (ꢀ) 269 (sh, 13 800), 386
(27 200), 425 (sh, 2500), 510 (sh, 860), 566 nm (800 cm-1 M -1).
IR (KBr pellet): ν 2926, 2856, 1510,1337, 1307, 1255, 1224, 1117,
1065, 818, 713, 671, 603, 515 cm-1. Anal. Calcd (%) for C19Cl14-
SO3Na‚1H2O: C, 26.99; S, 3.79; H, 0.24. Found: C, 27.36; S, 3.90;
H, 0.48. CV (in CH2Cl2/THF 99/1): E1/2 (vs Ag/AgCl) -0.16 V.
EPR (CH3CN/toluene 1/1): g ) 2.0020 (∆Hpp ) 1.0 G), no half-
field signal. EPR (on oriented single crystal): gmin ) 2.0014 (∆Hpp
) 8.9 G), gmax ) 2.0022 (∆Hpp ) 2.86 G).
The quality of the crystals will be reflected by their diffraction
power and mosaicities, whereas small crystals, disordered parts in
the unit cell, and high crystal mosaicities often reduce the diffraction
power. For a good measurement with our Nonius KappaCCD, we
need crystals with a mosaicity of 0.4-0.6 and a size of around 0.2
× 0.2 × 0.2 mm3, whereas the size depends more precisely on the
number the heavy atoms and the size of the unit cell. These criteria
[Cu(py)2(H2O)4](PTMSO3)2‚2H2O‚2EtOH (4). Twenty-five
milligrams (0.031 mmol) of PTMSO3H radical (2) dissolved in
(17) Ballester, M.; Riera, J.; Castanyer, J.; Rovira, C.; Armet, O. Synthesis
1986, 64-66.
(18) Sheldrick, G. M. SHELXL97: Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 45, No. 14, 2006 5385

Ribas et al.
Table 1. Crystal Data and Structure Refinement of Compounds 2, 4, 5a, and 5b
2
4
5a
5b
formula
fw
cryst system
space group
a (Å)
C22H14Cl14O6S
902.69
monoclinic
P21/c
25.3000(10)
15.3074(6)
18.6765(7)
90
99.957(2)
90
C52H34Cl28CuN2O14S2
2031.07
triclinic
P1h
8.7847(3)
8.8026(2)
24.6455(8)
84.876(2)
87.119(2)
82.879(2)
1882.05(10)
1
C60H60Cl28CuN4O12S2
2149.38
triclinic
P1h
8.760(3)
15.449(6)
16.617(5)
84.77(2)
83.07(2)
82.44(1)
2206.5(13)
1
C48H24Cl28CuN4O6S2
1872.97
triclinic
P1h
8.730(2)
8.775(2)
22.060(6)
95.95(2)
94.83(2)
95.92(2)
1664.1(7)
1
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
7124.0(5)
8
1.683
Dc (g cm-3
T )K)
)
1.792
233(2)
1.618
290(2)
1.869
290(2)
233(2)
λ(Mo KR) (Å)
0.71073
1.177
21.00
25 957
7582
0.71073
1.400
24.99
7381
5456
0.71073
1.198
17.50
4691
2683
0.71073
1.566
17.50
3435
2048
µ (mm-1
)
2θ max (deg)
reflns collected
independent reflns
(Rint ) 0.0772)
(Rint ) 0.0233)
(Rint ) 0.0984)
Rint ) 0.0600
params
743
477
348
283
GOF on F2
1.033
0.0687/0.1670
1.079
0.0400/0.0882
1.055
0.0932/0.1761
1.114
0.0986/0.1885
a
R/Rw
a R ) ∑|Fo - Fc|/∑Fo and Rw ) {∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2 where w ) 1/[σ2(Fo2 + (aP)2 + bP], P ) (Fo + 2Fc )/3, and the a and b are constants
2
2
2
2
given in the Supporting Information.
Scheme 1
are fulfilled only for 4 with size of 0.4 × 0.2 × 0.1 mm3 and a
mosaicity of 0.6. The diffraction power of 2, with size of 0.4 ×
0.2 × 0.02 mm3 and mosaicity of 0.8, is more reduced by the crystal
size, and visible reflections on the frames could be seen only to a
2Φ value of 38°. The measurements of 5a and 5b were difficult
because the crystals immediately lose solvent ethanol, and therefore,
the 5a crystals were placed in a glass-capillary with mother liqueur.
The crystal size of 5a was only 0.2 × 0.07 × 0.03 mm3 and the
mosaicty of 1.9 is extremely high, therefore reflections on the frames
were seen only to a 2Φ value of 28°. Because of the fewer
reflections, carbon atoms could only be refined with isotropic
displacement parameters. After two weeks, the mother liqueur was
reduced by about the half because of a leak in the capillary, and
the same crystal was remeasured with a mosacity of 2.5 and the
lattice constants of 5b.
modulation amplitude was kept well below the line width and the
microwave power well below saturation.
The static magnetic susceptibilities of polycrystalline randomly
oriented samples of 2, 3, 4 and 5b were measured in the temperature
range of 2-300 K with a Quantum Design MPMSXL supercon-
ducting SQUID magnetometer operating at a magnetic field strength
of 0.5 T. The paramagnetic susceptibility was calculated with a
diamagnetic correction estimated from tabulated Pascal constants.
Results and Discussion
Synthesis of PTMSO3H‚3H2O‚0.5hexane (2). Radical
PTMSO3H was synthesized by a two-step procedure starting
from p-H-polychlorotriphenylmethane (R-H-p-H-PTM),17 as
shown in Scheme 1. The introduction of the sulfonic group
at the para position of one of the phenyl rings bearing the
p-H atom was achieved by dissolving R-H-p-H-PTM in 65%
oleum and heating the mixture at 90 °C for 90 h. Successive
acid and basic extractions afforded compound R-H-PTMSO3H
(1) in moderate yield. The PTMSO3H radical was formed
by oxidation of the corresponding anion previously obtained
by deprotonation of the R-H precursor (Scheme 1). The target
compound PTMSO3H radical was isolated as a crystalline
material in good yield. Recrystallization of the red crystalline
material in CHCl3/n-hexane yielded red block-shaped crystals
suitable for single-crystal X-ray diffraction. The compound
Further details of the crystal structure determinations are given
in Table 1. Graphical representations were prepared using the
Mercury 1.4 (CCDC) program.
Magnetic Measurements. EPR spectra of 2-4 and 5b were
obtained in a conventional X-band spectrometer (Bruker ESP 300
E) equipped with a microwave bridge ER041XK, a rectangular
cavity operating in T102 mode, a field controller ER 032M system,
and a Oxford ESR-900 cryostat, which enabled measurements in
the temperature range of 110-350K. The temperature was moni-
tored by a Au (0.07 at % Fe)-chromel thermocouple placed close
to the sample. The measurements were performed on a bulk poly-
crystalline sample, placed inside a quartz tube, and in solution. The
5386 Inorganic Chemistry, Vol. 45, No. 14, 2006

Polychlorotriphenylmethyl Monosulfonate Radical
Figure 3. Structure of [Cu(py)2(H2O)4](PTMSO3)2‚2H2O‚2EtOH (4)
(representative atoms labeled).
Figure 1. Asymmetric unit of the radical PTMSO3H‚3H2O‚0.5hexane (2)
structure (representative atoms labeled).
PTMSO3Na‚H2O (3). The synthesis of this alkaline salt
was easily achieved by the deprotonation of the PTMSO3H
radical (2) with a mild base (NaHCO3). The recrystallization
of the resulting red powder in THF/hexane produced red
plate-shaped crystals that could not be properly resolved by
X-ray diffraction because of the low quality of crystals.20
This low-quality structural determination precludes the
correct assignment of the electron densities found between
the sulfonate groups: it is probably a mixture of Na ions
and H2O molecules.
[Cu(py)2(H2O)4](PTMSO3)2‚2H2O‚2EtOH (4). The syn-
thesis of this compound was achieved by the diffusion of a
solution of an excess of pyridine in ethanol to an ethanolic
solution of the PTMSO3H radical (2) and CuII(NO3)2‚6H2O.
The pyridine acted at the same time as a base to deprotonate
the sulfonic acid to the sulfonate group and as a ligand for
the CuII dication. This strategy resembled the one used for
the synthesis of a metal-organic porous compound named
MOROF-1.10 The choice of nitrate as a counteranion for the
copper source was made because of its low coordinative
abilities to exclude it as a competitor of the sulfonate group
in the possible formation of the complex.
Figure 2. Ellipsoid (50%) mode representation of the crystal packing of
PTMSO3H‚3H2O‚0.5hexane (2).
Compound 4 crystallizes as red prismatic crystals in the
triclinic system, space group P1h (Table 1). The asymmetric
unit contains one copper atom located on a symmetric center
with formula PTMSO3H‚3H2O‚0.5hexane (2) crystallizes in
the monoclinic system, space group P21/c (Table 1 and Table
S1, see Supporting Information). The asymmetric unit
contains two different PTMSO3H radicals, six H2O molecules
disordered in different positions with occupancies from 0.67
to 0.33, and one n-hexane molecule with high mobility
(Figure 1). The sulfonic oxygen atoms present a high
connectivity with the O atoms of the H2O molecules, but
the disorder in the water positions precludes a detailed
description. The crystal packing of 2 shows an alternated
layered polar-apolar structure along the a direction, with a
2D network of water-sulfonic interactions as the polar layer
and a 2D layer formed by the organic chlorinated part of
the PTMSO3H molecules as the apolar counterpart, with one
molecule of n-hexane embedded in the interface of both
layers (Figure 2). The apolar layer is stabilized by multiple
Cl‚‚‚Cl contacts,19 a supramolecular motif commonly ob-
served in PTM-type compounds.
-
and one molecule of PTMSO3 , one coordinated pyridine,
two coordinated H2O molecules, and one H2O and EtOH
molecules of crystallization in general positions (Figure 3).
-
The structure of 4, with a stoichiometry of two PTMSO3
molecules per copper ion, reveals that there is no direct
coordination of the sulfonate group with the CuII cation; thus
it acts as a counteranion of the CuII dication. Indeed, the
metal ion shows a hexacoordination to two pyridine and two
H2O molecules in the equatorial plane and to two additional
H2O molecules in the axial positions. In contrast with the
structure of 3, no disorder is found on the O atoms of the
sulfonate groups. This allows one to clearly determine the
strong H-bonding network between the sulfonate groups,
H2O, and ethanol molecules of the structure. The three O
atoms of each sulfonate group show two H-bonds with the
(20) The diffraction image of 3 was similar to 2, in the sense that almost
the same crystal cell was obtained showing an alternated layered
polar-apolar structure as in 2. But in this case, the quality reduction
comes more from the mosaicity of 1.4 than from the size of 0.45 ×
0.35 × 0.1 mm3. Three further crystals of 3 were examined, but all
had higher mosaicities.
(19) For a study of Cl‚‚‚Cl contacts, see: (a) Sarma, J. A. R. P.; Desiraju,
G. R. Acc. Chem. Res. 1986, 19, 222. (b) Desiraju, G. R.; Parthasa-
rathy, R. J. Am. Chem. Soc. 1989, 111, 8725-8726.
Inorganic Chemistry, Vol. 45, No. 14, 2006 5387

Ribas et al.
Figure 5. Structure of (a) [Cu(cyclam)](PTMSO3)2‚6EtOH (5a) and (b)
[Cu(cyclam)](PTMSO3)2 (5b). Only representative atoms are labeled.
ligand (to form the cationic complex [Cu(cyclam)]2+) into
an ethanolic solution of the PTMSO3Na radical (3).
Compound 5a crystallizes as red plate-shaped crystals in
the triclinic system, space group P1h (Table 1). The asym-
metric unit contains one molecule of PTMSO3 , half
Figure 4. Crystal packing of [Cu(py)2(H2O)4](PTMSO3)2‚2H2O‚2EtOH
(4) (copper coordination environment and sulfonate groups depicted in the
space-filling mode).
-
molecule of cyclam, and three EtOH molecules of crystal-
lization (the latter shows a 1:1 disorder) in general positions
(Figure 5a). Finally, the copper atom is located on a
symmetric center. The structure of 5a, with a stoichiometry
H2O molecules directly coordinated to a copper center, two
other H-bonds with H2O molecules of crystallization, and
one additional H-bond with an ethanol molecule of crystal-
lization (Table S1, see Supporting Information). An ad-
ditional H-bond exists between each ethanol molecule and
one H2O molecule axially coordinated to the copper atom,
and there is also another H-bond between each H2O molecule
of crystallization and one of the equatorially coordinated H2O
molecules. Overall, this leads to a complex supramolecular
-
of two PTMSO3 molecules per copper ion, reveals a η1-
monodentate coordination of the sulfonate group with the
copper cation through one O atom. The copper center shows
an axially elongated octahedral geometry with four N atoms
(cyclam ligand) placed in the equatorial plane and two O
-
atoms from the PTMSO3 radical anions in axial positions
-
organization in which each PTMSO3 unit participates in
(Table S1, see Supporting Information).
the formation of one R6 (16), one R3 (10), and one R2 (8)
6
4
2
The 3D crystal packing is determined by two major
cyclic hydrogen-bonded motifs (Figure S1, see Supporting
Information). Simultaneously, each CuII complex contributes
to the formation of two of each one. Additionally, a torsion
of 55.4° is observed for the pyridine planes with respect to
the equatorial plane around the copper center that may be
related to the supramolecular π‚‚‚H-C interaction with the
methyl group of the ethanol molecule of crystallization
(pyridine centroid‚‚‚H26B-C26 distance of 3.106 Å).
The crystal packing of 4 reveals the formation of alternat-
ing organic/inorganic 2D layers (Figure 4). Each organic
layer is built up by the interaction of the chlorinated organic
part of the PTMSO3- molecules in the c direction, whereas
the inorganic layer is formed by Cu complex molecules along
the c axis. Thus, the layers are connected by an intricate
network of strong H-bonds but with no direct coordination
of the charge-carrier atoms (i.e., the sulfonate group and the
copper center). The latter allows defining this structure as
an example of a solvent-separated ion pair (SSIP).
supramolecular interactions. First, multiple Cl‚‚‚Cl contacts
between PTMSO3 anions of different complex molecules
-
exist along the ab plane. The structure is further stabilized
by a H-bond network, extended along the ab plane, between
ethanol molecules placed in the voids left by the rectangular
organization built up through Cl‚‚‚Cl contacts from different
complex molecules. The H-bonding network propagates
along the b axis because of the interaction of ethanol
molecules with the ligand molecule and also with the
noncoordinating O atoms of the sulfonate groups (Figure 6).
All of this together leads to a 2D alternated organic/inorganic
layered structure, in which the monodentate coordination of
the sulfonate groups to the copper center is responsible for
the connection of the organic and inorganic layers.
[Cu(cyclam)](PTMSO3)2 (5b). Compound 5b is obtained
after the evacuation of all the ethanol molecules of crystal-
lization from the as-synthesized compound 5a. This is
achieved simply by removal of the crystals from the mother
liquor and exposure to the air. The structure of 5b was
obtained from the same crystal of 5a after a crystal-to-crystal
[Cu(cyclam)](PTMSO3)2‚6EtOH (5a). The synthesis of
this compound was achieved by diffusing a previously pre-
pared ethanolic solution of CuII(NO3)2‚6H2O and the cyclam
5388 Inorganic Chemistry, Vol. 45, No. 14, 2006

Polychlorotriphenylmethyl Monosulfonate Radical
Figure 6. Crystal packing of [Cu(cyclam)](PTMSO3)2‚6EtOH (5a) (copper
coordination environment depicted in the space-filling mode).
transformation10,21 because of the evacuation of ethanol
molecules of crystallization. Compound 5b crystallizes in
the triclinic system, space group P1h (Table 1). The asym-
metric unit is very similar to that of 5a and contains one
Figure 7. Crystal packing of [Cu(cyclam)](PTMSO3)2 (5b) (copper
coordination environment depicted in the space-filling mode).
inorganic layer is substituted by charge-assisted H-bonded
disordered H2O molecules). The main difference between
compounds 3, 4, and 5 is the ability of the sulfonate group
to be coordinated to the metal center. Despite having a
nonreliable structure for 3, the complete chemical and
spectroscopic characterization ensures the presence of Na
-
PTMSO3 anion and one-half of a cyclam molecule in
general positions, and the copper atom is in a symmetry
center. The η1-coordination mode of the sulfonate group is
almost identical to the one described for 5a (Figure 5b and
Table S1, see Supporting Information).
-
atoms that are coordinated to the -RSO3 group, possibly
The crystal packing is dominated by Cl‚‚‚Cl contacts
between the PTMSO3- radicals, Cl‚‚‚H-C contacts between
anion moieties and the aliphatic backbone of cyclam, and
π‚‚‚H-C interactions between the aromatic rings of the anion
and the aliphatic backbone of the ligand. Overall, this
compound can be described as a 2D alternating organic/
inorganic layered structure, with the layers extending along
the ab plane (Figure 7). The major difference with respect
to 5a comes from the reorganization of the complex
molecules because of the instability of the structure of 5a
after removal of the ethanol molecules. Basically, the Cl‚‚
‚Cl interactions of 5a are not sufficient to support the voids
left by the solvent. Thus, the reorganization results in the
more compact structure of 5b, visualized with a 25% reduc-
tion of the cell volume (Table 1). The sulfonate group in 5b
only plays the role of an axial monodentate ligand and does
not participate in any other intermolecular interaction.
Structural Comparison. All studied compounds show a
2D alternated organic/inorganic layered structure. The or-
ganic layer is built up by the interaction of the chlorinated
together with H2O molecules. On the contrary, no direct
coordination of the sulfonate group to the CuII dication is
found in 4. The poor coordinating ability of the sulfonate
group is well-known, but several groups have faced the
challenge of controlling the coordination possibilities of the
sulfonate group, and several examples, ranging from direct
coordination to the metal to solvent-separated ion pair
compounds, are well described. Shimizu and co-workers have
determined that sulfonate ions do not efficiently displace
solvent from the primary coordination sphere of most metal
ions under hydrous conditions, except in the case of alkaline,
larger alkaline earth ions, and silver(I) ions.13 For the latter
metals, a very rich variability on the coordination modes is
described. Also Kennedy and co-workers have shown a clear
trend of the degree of coordination and connectivity of the
sulfonate group to the s-block metals as a function of the
electronegativity of the metal, in a family of sulfonated azo
dyes.22 Thus, structures without direct sulfonate-metal
coordination (type I) are found when the s-block metal ion
has a Pauli electronegativity higher than 1.29. On the other
hand, structures with simple -RSO3-M bonds (type II) are
found with s-block metals with electronegativities in the
range of 1.2-0.88. Finally, structures showing high con-
nectivity between the -RSO3- group and the metal ion (type
III) are found when the Pauli electronegativities are below
0.88. The sodium compound 3 described in this work should
be a type III structure since Na has a Pauli electronegativity
-
organic part of the PTMSO3 molecules, whereas the
inorganic layer is formed by the metal complex (with the
exception of the pure organic compound 2, where the
(21) (a) Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K. J. J. Am. Chem.
Soc. 2004, 126, 3817-3828. (b) Kumar Maji, T.; Uemura, K.; Chang,
H.-C.; Matsuda, R.; Kitagawa, S. Angew. Chem., Int. Ed. 2004, 43,
3269-3272. (c) Uemura, K.; Kitagawa, S.; Kondo, M.; Fukui, K.;
Kitaura, R.; Chang, H.-C.; Mizutani, T. Chem.sEur. J. 2002, 8, 3587-
3600. (d) Biradha, K.; Fujita, M. Angew. Chem., Int. Ed. 2002, 41,
3392-3395. (e) Biradha, K.; Hongo, Y.; Fujita, M. Angew. Chem.,
Int. Ed. 2002, 41, 3395-3398. (f) Suh, M. P.; Ko, J. W.; Choi, H. J.
J. Am. Chem. Soc. 2002, 124, 10976-10977.
(22) Kennedy, A. R.; Kirkhouse, J. B. A.; McCarney, K. M.; Puissegur,
O.; Smith, W. E.; Staunton, E.; Teat, S. J.; Cherryman, J. C.; James,
R. Chem.sEur. J. 2004, 10, 4606-4615.
Inorganic Chemistry, Vol. 45, No. 14, 2006 5389

Ribas et al.
Figure 8. Single-to-single crystal rearrangement after evacuation of EtOH molecules from 5a leading to 5b.
value of 0.869. However, the high connectivity of Na to the
-RSO3 group could not be demonstrated because of the
weight losses (Figure S3, see Supporting Information). The
first endothermic weight loss of 1.5% that can be assigned
to the removal of one solvent ethanol molecule (theoretical
value 2.3%) was observed between 70 and 95 °C. A second
consecutive and gradual weight loss of 4.2% was then
observed from 95 to 200 °C, which is attributed to the
departure of the remaining ethanol molecule and two H2O
solvent molecules (theoretical value 4.1%). Finally, an abrupt
weight loss attributed to decomposition was observed at 250
°C. Such a decomposition process was confirmed by infrared
spectra.
In a separate experiment, a crystalline sample of 4 was
heated in argon to 200 °C and then was studied by infrared
spectra and XRPD. The infrared spectra confirms the total
evacuation of the crystallization solvent molecules from the
hydrogen-bonded network of 4, and simultaneously, XRPD
studies confirmed that 4 remains crystalline and stable up
to 200 °C. Indeed, the XRPD pattern of the desolvated
sample shows that the positions and intensities of all lines
remain unchanged when compared with the theoretical
XRPD pattern obtained from the crystal structure (Figure
S4, see Supporting Information). This lets a potential
accessible void volume of 11%, which represents a volume
of 207.4 Å3 compared to the 1882.1 Å3 of the total cell
volume.26 The structural stability of desolvated 4 is remark-
able because it is a structure maintained by a second-sphere
coordination “soft” network.27 We believe that the stability
of 4 is directly related to the H-bond network described above
and especially to the simultaneous six-member rings between
two sulfonates of different layers through the copper-
coordinated H2O molecules. Also the multiple Cl‚‚‚Cl
contacts between the PTM derivatives within the organic
layer stabilize the structure up to 200 °C.
-
low quality of crystals, and the presence of water molecules
cannot be discarded.23 On the other hand, structure 4 is an
example of a type I solvent-separated ion pair, also in line
with both an electronegativity value for Cu of 1.9 and the
well-known poor coordination capability of the sulfonate
group toward transition metals.
However, very recent publications have shown that the
sulfonate group is capable of coordinating dicationic copper
if the ligands that complete the coordination of the metal
have suitably placed C-H bonds that can stabilize the
SO3-M bond as an axial coordination.24 To test this
-
possibility with the PTMSO3 radical anion, we chose the
square-planar [Cu(cyclam)]2+ cation with the aim that the
cyclam backbone will stabilize the axial coordination of the
sulfonate groups by H-bonding. The structural description
of compounds 5a and 5b is the successful result of the
strategy applied. The direct coordination of the sulfonate
group to the copper center in a η1-monodentate fashion in
5a and 5b is achieved because of the stabilization through
H-bonding of the noncoordinating O atoms and the C-H
and N-H residues of the ligand backbone.25 Thus, the
sulfonate group can now compete and displace the H2O
molecules from the coordination environment of the copper
center, in contrast to 4.
Thermal Stability Studies. Thermal stabilities of the
crystal structure of compounds 2, 3, and 4 were determined
by thermal gravimetric studies combined with infrared
spectra and X-ray powder diffraction (XRPD). Thermal
analysis of 2 and 3 shows no noticeable weight loss below
200 and 230 °C, respectively (Figure S2, see Supporting
Information), beyond which decomposition occurs as con-
firmed by infrared spectra. On the other hand, thermogravi-
metric analysis of a crystalline sample of 4 indicates three
Thermogravimetric studies were also performed with
compound 5b, showing no weight loss below 275 °C, at
which point the decomposition starts. As detailed above,
compound 5a undergoes a rapid transformation to 5b after
the removal of the ethanol molecules of crystallization, which
occurs at room temperature within a few seconds (Figure
8). The calculation of the void volume left by the evacuation
(23) Kennedy and co-workers also reported a few exceptions to their
classification (see ref 22), for example, an unexpected solvent-separated
ion pair in a sulfonate-sodium compound.
(24) (a) Cai, J.; Chen, C.-H.; Liao, C.-Z.; Yao, J.-H.; Hu, X.-P.; Chen,
X.-M. J. Chem. Soc., Dalton Trans. 2001, 1137-1142. (b) Mahmoud-
khani, A. H.; Cote´, A. P.; Shimizu, G. K. H. Chem. Commun. 2004,
2678-2679.
(26) Speak, A. L. PLATON; Utrecht University: Utrecht, The Netherlands,
(25) For H-bonding in organic sulfonates, see: Haynes, D. A.; Chrisholm,
J. A.; Jones, W.; Motherwell, W. D. S. CrystEngComm 2004, 6 (95),
584-588.
1998.
(27) Dalrymple, S. A.; Shimizu, G. K. H. Supramol. Chem. 2003, 15 (7-
8), 591-606.
5390 Inorganic Chemistry, Vol. 45, No. 14, 2006

Polychlorotriphenylmethyl Monosulfonate Radical
of the ethanol molecules in 5a (a void volume of 31%)26
suggests that the channels are too large and the structure is
not stable. Thus, a rearrangement toward the more compact
structure of 5b is favored, as confirmed by the XRPD pattern
of a microcrystalline sample of 5b that agrees with the
calculated pattern from its crystal structure.
Magnetic Properties. EPR measurements on PTMSO3H
(2) and PTMSO3Na (3) compounds in solution showed one
single line at g ) 2.0020 (∆Hpp ) 4 G) and 2.0023 (∆Hpp
) 1 G), respectively, with no signal at half field, denoting
that the organic radicals do not have noticeable interactions.
On the other hand, the EPR measurements on solid poly-
crystalline samples of the Cu-containing compounds 4 and
5b at room temperature showed a typical axial symmetry
signal for an elongated octahedral CuII center at room
temperature with g1 ) 2.0060(∆Hpp ) 35 G) and g2 ) 2.265
for 4 and g1 ) 2.0199 (∆Hpp ) 11.4 G) and g2 ) 2.0670 for
5b, with minor changes on the spectra at 120 K. The signal
of the organic radical (typically with g ) 2.0030) lies
eclipsed under the intense signal of the copper in 4 and 5b.
The magnetic properties of polycrystalline samples of 2,
3, 4, and 5b were measured on a SQUID magneto/
susceptometer in the temperature range of 1.8-300 K at a
constant magnetic field of 0.5 T. The temperature dependence
of the product of the molar susceptibility and temperature
(øT) for compounds 2, 3, and 4 can be found in the
Supporting Information (Figures S5-S10). Compounds 2 and
3 exhibit a typical paramagnetic behavior in the 10-300 K
temperature range, with øT product values that fully agree
with the theoretical value of 0.375 emu K-1 mol-1 and
expected for uncorrelated S ) 1/2 moieties. Similarly, the
øT product value for 4 also remains constant at 1.13 emu K
mol-1, which is in agreement with the theoretical value of
1.125 emu K-1 mol-1 expected for three uncorrelated S )
Figure 9. Temperature dependence of the product of the magnetic
susceptibility and the temperature for complex 5b. The solid line was
calculated for a linear three-spin model as described in the manuscript.
K, fixing g ) 2.04. From the comparison with the antifer-
romagnetic coupling constants found for similar systems
using the monocarboxylated PTM radical (2J/KB ) -30 to
-50 K),9a it can be deduced that the carboxylate group is a
better moiety than the sulfonate moiety in terms of magnetic
communication between the radical and the metal ion. The
qualitative analysis of the torsion angles of the sulfonate-
containing ring in 5b with respect to the corresponding
monocarboxylated PTM radical Cu complex9a does not reveal
a clear difference that could induce a high variation in the
spin density over the ligand groups responsible for this result.
Theoretical studies are needed to understand this point.
Nevertheless, it cannot be excluded that a η2-coordination
mode of the sulfonate group with respect to the metal may
enhance the magnetic interaction.
Summary
In summary, we have reported the synthesis of a novel
pure organic radical of the PTM family bearing one sulfonic
group, compound PTMSO3H‚3H2O‚0.5hexane (2). We have
explored for the first time the coordination capabilities of a
radical bearing a sulfonate group: one example with a
nonparamagnetic alkaline metal, compound PTMSO3Na‚H2O
(3), and one example with a paramagnetic transition metal
ion such as CuII, compound [Cu(py)2(H2O)4](PTMSO3)2‚
2H2O‚2EtOH (4). In the latter compound, we have shown
that a solvent-separated ion pair (SSIP) situation in the
structure precludes magnetic communication between the two
distinct magnetic centers. We have also demonstrated that
is possible to overcome this situation and force the direct
coordination of the sulfonate group to the copper center by
choosing a metal complex bearing a ligand suitable to
stabilize the axial coordination of the sulfonate moiety, as
occurs in compound [Cu(cyclam)](PTMSO3)2‚6EtOH (5a).
This compound readily losses the solvent molecules of
crystallization upon exposure to open air and rearranges to
compound [Cu(cyclam)](PTMSO3)2 (5b) in a single-to-
single-crystal transformation. The direct coordination of the
organic radical through the sulfonate group is reflected on
an enhanced antiferromagnetic coupling between the para-
-
1/2 moieties (two PTMSO3 radicals and one CuII ion).
Below 10 K, the øT product slightly decreases in accordance
with the presence of very weak intermolecular antiferro-
magnetic interactions. All magnetic behaviors were fitted to
the Curie-Weiss law between 1.8 and 300 K, with C ) 0.37,
0.37, and 1.12 emu K mol-1 and a Weiss constant of θ )
-0.7, -0.1, and -0.3 K for compounds 2, 3, and 4,
respectively.
Identical measurements performed in compound 5b show
the presence of stronger antiferromagnetic interactions result-
ing from the direct coordination of PTMSO3 moieties to CuII
ions (Figure 9). A øT value of 1.17 emu K mol-1 was
obtained at 300 K, which is close to the theoretical 1.15 emu
K mol-1 value expected for three isolated S ) 1/2 spins and
with a g factor of 2.04, as previously measured by EPR.
When the temperature is lowered, øMT remains constant
until 100 K, from which point it follows a continuous fall
down to 0.78 emu K mol-1 at 1.9 K. The resulting
experimental data was quantitatively analyzed on the basis
of a linear three-spin model, using the following effective
Hamiltonian, H ) -2J(SR1SM + SMSR2), modified to take
into account the presence of intermolecular interactions (θ)
in the molecular-field approximation.28 The resulting pa-
rameters for the best fit were 2J/kB ) -4.6 K and θ ) -0.1
(28) Ishimaru, Y.; Kitano, M.; Kumada, H.; Koga, N.; Iwamura, H. Inorg.
Chem. 1998, 37, 2273-2280.
Inorganic Chemistry, Vol. 45, No. 14, 2006 5391

Ribas et al.
magnetic centers. We believe that this study represents an
overview of the crystal engineering possibilities of the novel
sulfonate derivative PTM organic radical, in line with other
studies on the sulfonate group coordination, but focusing on
the introduction of magnetic functionality within the metal-
organic approach that yielded remarkable layered hybrid
organic-inorganic structures. We have been successful in
ions, and the design of new molecular multifunctional
magnetic materials via incorporation of more -SO3- moieties
in the PTM skeleton, is currently underway.
Acknowledgment. This work was supported by DGI,
Spain (Project MAT2003-04699) and DGR Catalonia (Project
2005SGR00362). D.M. is grateful to the Generalitat de
Catalunya for a postdoctoral grant. X.R. acknowledges a Juan
de la Cierva contract from MEC Spain.
-
the use of the radical PTMSO3 anion as building block in
metal-organic coordination compounds and have shown that
the antiferromagnetic coupling between the organic and CuII
open-shell species is significantly lower than that for the
monocarboxylated PTM derivatives. Theoretical studies will
be undertaken to compare the differences in spin density
between the carboxylate and sulfonate groups. Further
experimentation aimed at exploration of the additional
Supporting Information Available: X-ray crystallographic files
in CIF format for structures 2, 4, 5a, and 5b, table of selected bond
distances and angles for all compounds (Table S1), and com-
plemetary structural (Figure S1), thermogravimetric (Figure S2 and
S3), XRPD studies (Figure S4), and magnetic measurements for
compounds 2, 3, and 4 (Figure S5-S10). This material is available
free of charge via the Internet at http://pubs.acs.org.
-
coordination abilities of the PTM-SO3 radical, such as
different coordination modes or its reactivity with other metal
IC060182J
5392 Inorganic Chemistry, Vol. 45, No. 14, 2006