Preparation and structure of three solvatomorphs of the polymer [Co(dbm)2(4ptz)]n: Spin canting depending on the supramolecular organization

Article abstract of DOI:10.1021/ic7004979

The syntheses and X-ray structures of three isomeric 1D coordination polymers are reported. The complex [Co-(dbm)₂(MeOH)₂] (1) was used as a precursor in these reactions. The preparation and structure of 1 is also presented; this mononuclear complex is in the cis configuration because this allows the formation of a network of intermolecular hydrogen bonds in the solid state. Reaction of 1 with 2,4,6-tris-(4-pyridyl)-1,3,5-triazine (4ptz) yields the polymers [Co(dbm)₂(4ptz)]_n·nTHF (2a), [Co(dbm)₂(4ptz)]_n·0.75nTHF·0.5nEt ₂O (2b), and [Co(dbm)₂(4ptz)]_n-3nDMF (2c) in the form of zigzag chains, instead of the expected honeycomb architectures. This is because of the establishment of extended π-π stacking throughout these solids, which could not have occurred otherwise. Compounds 2a, 2b, and 2c are solvatomorphs, and formation of either one of them depends on the exact conditions of crystallization, which lead to significant differences in the supramolecular organization of the chains. Bulk magnetic measurements on 2a reveal weak antiferromagnetic exchange within the chains and small ordering throughout the solid that results in the manifestation of the phenomenon of spin canting, whereas for 2c the different supramolecular organization causes the antiferromagnetic exchange not to result in spin canting.

Full text of DOI:10.1021/ic7004979

Inorg. Chem. 2007, 46, 7154−7162
Preparation and Structure of Three Solvatomorphs of the Polymer
[Co(dbm)2(4ptz)]n: Spin Canting Depending on the Supramolecular
Organization
Leon´ı A. Barrios, Joan Ribas, and Guillem Arom´ı*
UniVersitat de Barcelona, Departament de Qu´ımica Inorga`nica, Diagonal 647,
08028 Barcelona, Spain
Jordi Ribas-Arin˜o
UniVersitat de Barcelona, Departament de Qu´ımica F´ısica and CERQT, Diagonal 647,
08028 Barcelona, Spain
Patrick Gamez
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden UniVersity, P. O. Box 9502,
2300 RA Leiden, The Netherlands
Olivier Roubeau
UniVersite´ de Bordeaux - CNRS CRPP, 115 aV. Dr A. Schweitzer, 33600 Pessac, France
Simon J. Teat
CCLRC Daresbury Laboratory, Warrington, Cheshire, UK WA4 4AD and AdVance Light Source,
Lawrence Berkeley Lab, 1 Cyclotron Rd, MS2-400, Berkeley, California 94720
Received March 14, 2007
The syntheses and X-ray structures of three isomeric 1D coordination polymers are reported. The complex [Co-
(dbm)2(MeOH)2] (1) was used as a precursor in these reactions. The preparation and structure of 1 is also presented;
this mononuclear complex is in the cis configuration because this allows the formation of a network of intermolecular
hydrogen bonds in the solid state. Reaction of 1 with 2,4,6-tris-(4-pyridyl)-1,3,5-triazine (4ptz) yields the polymers
[Co(dbm)2(4ptz)]n‚nTHF (2a), [Co(dbm)2(4ptz)]n‚0.75nTHF‚0.5nEt2O (2b), and [Co(dbm)2(4ptz)]n‚3nDMF (2c) in the
form of zigzag chains, instead of the expected honeycomb architectures. This is because of the establishment of
extended π−π stacking throughout these solids, which could not have occurred otherwise. Compounds 2a, 2b,
and 2c are solvatomorphs, and formation of either one of them depends on the exact conditions of crystallization,
which lead to significant differences in the supramolecular organization of the chains. Bulk magnetic measurements
on 2a reveal weak antiferromagnetic exchange within the chains and small ordering throughout the solid that
results in the manifestation of the phenomenon of spin canting, whereas for 2c the different supramolecular
organization causes the antiferromagnetic exchange not to result in spin canting.
Introduction
architecture”.1 Since the mid-1990s, research in coordination
chemistry has been influenced strongly by the development
of metallo-supramolecular chemistry,2 which involves the
design and preparation of intricate polymetallic coordination
Self-assembly has been defined as “the process by which
specific components spontaneously assemble in a highly
selectiVe fashion into a well-defined, discrete supramolecular
(1) Lehn, J.-M. Supramolecular Chemistry; VCH Publishers: New York,
1995.
(2) Steel, P. J. Acc. Chem. Res. 2005, 38, 243-250.
* To whom correspondence should be addressed. E-mail:
guillem.aromi@qi.ub.es.
7154 Inorganic Chemistry, Vol. 46, No. 17, 2007
10.1021/ic7004979 CCC: $37.00
© 2007 American Chemical Society
Published on Web 07/27/2007

SolWatomorphs of the Polymer [Co(dbm)2(4ptz)]n
Scheme 1. 4ptz Ligand
of cobalt(II), as possible 180° connecting nodes, was explored
here in order to construct extended paramagnetic frameworks
expected to form honeycomb arrangements. A requirement
for such an organization is that the coordination positions
of the metal, other than the axial ones, remain blocked by
other co-ligands. This type of arrangement built from 4ptz
has one precedent where the metallic linear links are formed
by strongly antiferromagnetically coupled, thus quasi-dia-
magnetic, [Cu2] acetate-bridged dimers.16
aggregates with specific structures or functions.3 Along these
lines, the creation of supramolecular networks can be
accomplished by the judicious combinations of organic
ligands and metals,4 thus exploiting the ability of metal-
ligand coordination bonds to provide simple and controlled
routes to 1D, 2D, or 3D metal-organic frameworks (MOFs),5
which constitute an exotic class of coordination polymers
and may exhibit unique properties.6-8 The bottom-up as-
sembly of MOFs from metal ions and organic linkers is
among the cornerstones of crystal engineering. In this
context, the final architecture might exhibit additional levels
of supramolecular organization, by exploiting other weak
interactions such as hydrogen bonding or π-π interactions,
among others. We have been interested in the preparation
of novel MOFs with relevance in the area of molecular
magnetism. One of our goals is that of organizing magnetic
nodes within coordination polymers with predetermined
structures in order to gain control of the magnetic properties
of the final material.
Results and Discussion
Synthesis. To find a suitable source of octahedral cobalt-
(II) with four equatorial positions occupied by chelating
ligands, and with two labile axial ligands, we decided to
prepare complex [Co(dbm)2(MeOH)2] (1). This complex was
thus expected to act as a linear building block within
supramolecular arrangements where it would be incorporated
by the coordination of external ligands at the axial positions,
while keeping the equatorial plane saturated by the chelating
dbm- donors. The mononuclear compound is not described
in the literature, although the electrochemical synthesis of
the corresponding EtOH analogue has been reported.17
Complex 1 could be conveniently prepared from the very
clean reaction (eq 1) of dibenzoylmethane (Hdbm) with
Co(AcO)2 in MeOH, from where the product precipitates in
Co(AcO)2 + 2Hdbm + 2MeOH + [Co(dbm)2(MeOH)2] +
For some time, we have been exploring the coordination
chemistry of triazine-based ligands with various paramagnetic
metals and have synthesized an important number of discrete
or extended polynuclear arrays with unprecedented topologies
and unusual magnetic properties.9-11 We have now turned
our attention to the trigonal ligand 2,4,6-tris-(4-pyridyl)-1,3,5-
triazine (4ptz, Scheme 1) as a tridentate coordination node
imposing a directionality of 120°. This ligand has been
previously employed in the preparation of very interesting
MOFs, involving non-paramagnetic metallic ions for the most
part, aimed at fulfilling various roles such as host-guest
functions.12-15 The reactivity of 4ptz with simple complexes
2AcOH (1)
crystalline and pure form and in high yield, as previously
observed for other similar compounds with the same
environment.18 Surprisingly, however, the crystal structure
of (1) revealed (below) the configuration in this complex to
be cis instead of trans. Nevertheless, the configuration
observed in subsequent products obtained from the reactions
of 1 with 4ptz ligands was always trans, proving cobalt(II)
to be labile toward the rearrangement of the dbm ligands.
Indeed, one of the goals in exploring the reactivity of
[Co(dbm)2(MeOH)2] (1) with the polyfunctional ligand 4ptz
was to investigate the possibility of the formation of a
honeycomb 2D extended array, as expected from the
combination of a trigonal knot (4ptz) and a potential linear
linker such as 1. Thus, complex 1 was allowed to react with
4ptz in THF solution in a 3:2 molar ratio, with the aim of
replacing the axial groups on the metal with nitrogen donors
of the multidentate ligand. To facilitate this, the process was
conducted at the temperature of reflux, because the nitrogen-
containing ligand is scarcely soluble in most solvents. At
the end of the reaction, contrary to what was expected for
the formation of a polymeric compound, no precipitate of a
cobalt complex was obtained. Orange-red crystals could be
obtained from Et2O layers of the reaction system, which,
(3) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629-1658.
(4) Gamez, P.; Reedijk, J. Eur. J. Inorg. Chem. 2006, 29-42.
(5) Khlobystov, A. N.; Blake, A. J.; Champness, N. R.; Lemenovskii, D.
A.; Majouga, A. G.; Zyk, N. V.; Schroder, M. Coord. Chem. ReV.
2001, 222, 155-192.
(6) Chen, B. L.; Liang, C. D.; Yang, J.; Contreras, D. S.; Clancy, Y. L.;
Lobkovsky, E. B.; Yaghi, O. M.; Dai, S. Angew. Chem., Int. Ed. 2006,
45, 1390-1393.
(7) Halder, G. J.; Kepert, C. J.; Moubaraki, B.; Murray, K. S.; Cashion,
J. D. Science 2002, 298, 1762-1765.
(8) Wu, C. D.; Hu, A.; Zhang, L.; Lin, W. B. J. Am. Chem. Soc. 2005,
127, 8940-8941.
(9) Quesada, M.; de Hoog, P.; Gamez, P.; Roubeau, O.; Aromi, G.;
Donnadieu, B.; Massera, C.; Lutz, M.; Spek, A. L.; Reedijk, J. Eur.
J. Inorg. Chem. 2006, 1353-1361.
(10) Gamez, P.; de Hoog, P.; Roubeau, O.; Lutz, M.; Driessen, W. L.;
Spek, A. L.; Reedijk, J. Chem. Commun. 2002, 1488-1489.
(11) Quesada, M.; de la Pen˜a-O’Shea, V. A.; Arom´ı, G.; Geremia, S.;
Massera, M.; Roubeau, R.; Gamez, P.; Reedijk, J. AdV. Mater. 2007,
19, 1397-1402.
(15) Biradha, K.; Fujita, M. Angew. Chem., Int. Ed. 2002, 41, 3392-3395.
(16) Batten, S. R.; Hoskins, B. F.; Moubaraki, B.; Murray, K. S.; Robson,
R. Chem. Commun. 2000, 1095-1096.
(17) Kostyuk, N. N.; Shirokii, V. L.; Vinokurov, I. I.; Dik, T. A.; Umreiko,
D. S.; Erdman, A. A. Zh. Neorg. Khim. 1992, 37, 68-71.
(18) Arom´ı, G.; Boldron, C.; Gamez, P.; Roubeau, O.; Kooijman, H.; Spek,
A. L.; Stoeckli-Evans, H.; Ribas, J.; Reedijk, J. Dalton Trans. 2004,
3586-3592.
(12) Halder, G. J.; Neville, S. M.; Kepert, C. J. Cryst. Eng. Comm. 2005,
7, 266-268.
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259.
(14) Dybtsev, D. N.; Chun, H.; Kim, K. Chem. Commun. 2004, 1594-
1595.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7155

Barrios et al.
instead of the expected honeycomb 2D array, were found
by X-ray diffraction (XRD) (below) to correspond to the
linear complex [Co(dbm)2(4ptz)]n‚nTHF (2a), where one of
the pyridyl rings of 4ptz was not engaged in coordination.
The reason for the formation of 2a instead of the coordina-
tively saturated complex predicted is to be found in the
stabilization energy gained by the interactions between chains
of 2a observed in the solid state (below), which could not
have taken place if the hexagonal network had formed. The
same reaction performed in CHCl3, on the other hand,
produced significant amounts of an orange precipitate that
was soluble in THF. Layers of this solution with Et2O led
to the formation of red crystals of a compound (2b) that
turned out to be a solvatomorph19 of 2a (below), displaying
only very small conformational differences with the latter.
Presumably, these differences are caused by slight changes
in solvents of crystallization, because compound 2b appears
in the crystal as [Co(dbm)2(4ptz)]n‚0.75nTHF‚0.5nEt2O. A
third isomorph, [Co(dbm)2(4ptz)]n‚3nDMF (2c), was isolated
as crystals directly from the reaction mixture, when the latter
was performed in dimethylformamide (DMF). Compound
2c again displays small differences from the supramolecular
organization, which turned out to vary the magnetic proper-
ties significantly (below).
Description of the Structures. The structure of com-
pounds 1, 2a, 2b, and 2c are presented in Figures 1-4.
Crystallographic data for all of the complexes are collected
in Table 1, whereas selected interatomic distances and angles
are in Tables 2, 3, and 4 and in the caption of Figure 1.
[Co(dbm)2(MeOH)2] (1). The structure of 1 (Figure 1) is
described as a mononuclear molecule comprising one
pseudo-octahedral cobalt(II) ion chelated by two dbm-
ligands and two solvent MeOH molecules. Interatomic
distances and angles featured by 1 are within normal ranges
(caption of Figure 1). Surprisingly, these ligands are featured
in cis configuration rather than trans. Of all of the mono-
nuclear cobalt complexes containing only two 1,3-diketonate
ligands (124 hits of the CCDC, version 5.27, Aug 2006), 51
are in cis configuration, of which the majority possess a third
chelating ligand, the latter thus precluding the occurrence
of the trans form. In fact, only about 15% of compounds of
the type [Co(1,3-diketone)2(L)2] (L ) monodentate ligand)
are cis, and in these cases, there is usually a cause favoring
this. In complex 1, the reason for the rare cis conformation
is the presence of self-complementary hydrogen bonding
between molecules (Figure 1, bottom), where each MeOH
ligand acts as a donor of a hydrogen bond to the oxygen
atom of a dbm ligand from a neigbouring complex. Each
molecule thus establishes a total of four such interactions,
twice as a donor and twice as an acceptor, with two other
molecules located on opposite sides, thereby forming chains
of hydrogen-bonded complexes. The same situation was
observed for a previously reported complex with a thienyl,
trifluoromethyl-based 1,3-diketonate,20 as is for the nickel
analogue of 1 [Ni(dbm)2(MeOH)2].21 Besides this network
of hydrogen bonds, no other intermolecular interactions other
Figure 1. ORTEP representation (top) at the 50% probability level of
complex [Co(dbm)2(MeOH)2] (1). Unique atoms of the central chromophore
are labeled. Only hydrogen atoms of the OH groups of the methanol ligands
are shown. Selected bond distances (Å) and angles (°): Co(1)-O(1),
2.0589(14); Co(1)-O(2), 2.0242(14); Co(1)-O(3); 2.1134(14); O(1)-Co-
(1)-O(2), 89.20(5); O(1)-Co(1)-O(3), 91.83(5); O(1)-Co(1)-O(1)a,
90.43(5); O(1)-Co(1)-O(2)a, 88.85(5); O(1)-Co(1)-O(3)a, 177.72(5);
O(2)-Co(1)-O(3), 90.84(5); O(2)-Co(1)-O(1)a, 88.85(5); O(2)-Co(1)-
O(2)a, 177.22(6); O(2)-Co(1)-O(3)a, 91.19(5); O(3)-Co(1)-O(1)a,
177.72(5); O(3)-Co(1)-O(2)a, 91.19(5); O(3)-Co(1)-O(3)a, 85.92(5). ‘a’
1
represents the [1 - x, y,
/ - z] symmetry operation. Representation
2
(bottom) of two molecules of 1, emphasizing the self-complementary
hydrogen bonding existing within chains of molecules in the crystal ([-O-
H‚‚‚O-], 2.799).
than weak van der Waals contacts occur within the crystal
of complex 1.
[Co(dbm)2(4ptz)]n‚nTHF (2a). Compound 2a is described
as a linear coordination polymer resulting from the infinite
succession of cobalt(II) ions and 4ptz ligands (part A of
Figure 2). The metals constitute connection knots of 180°
because their equatorial positions are saturated by two
chelating dibenzoyl donors per center. The polydentate 4ptz
ligands bridge pairs of metals through two of its pyridyl
moieties, the third one remaining uncoordinated. The result-
ing system is therefore disposed in a zigzag configuration,
with the uncoordinated pyridyl rings of the triazine-based
ligands oriented outward. This favors the interdigitation of
adjacent chains, allowing the establishment of a network of
(20) Pretorius, J. A.; Boeyens, J. C. A. J. Inorg. Nucl. Chem. 1978, 40,
1519-1528.
(21) Suzuki, H.; Matsumura, S.; Satoh, Y.; Sogoh, K.; Yasuda, H. React.
Funct. Polym. 2004, 59, 253-266.
(19) Chopra, D.; Row, T. N. G. Cryst. Growth Des. 2006, 6, 1267-1270.
7156 Inorganic Chemistry, Vol. 46, No. 17, 2007

SolWatomorphs of the Polymer [Co(dbm)2(4ptz)]n
additional π-π stacking connections involving these rings.
Therefore, it is very clear that the energy gain resulting from
the interaction between 4ptz ligands is the main reason for
the supramolecular disposition of the system in the solid state.
The metals within the chains are separated by 13.143 Å,
whereas the cobalt(II) ions of different chains can be as close
as 8.632 Å.
Polymeric, structurally characterized complexes with the
ligand 4-ptz as a µ bridge are very scarce in the literature.22,23
The vast majority of coordination compounds made with this
ligand have it in the µ3 mode, either as infinite arrays or as
discrete, supramolecular architectures.12-15
[Co(dbm)2(4ptz)]n‚0.75nTHF‚0.5nEt2O (2b). The struc-
ture of 2b (part B of Figure 2) reveals that the composition
of this compound only differs from 2a in the solvents of
crystallization. Thus, 2b also consists of a 1D polymer with
alternating cobalt(II) ions and µ-4ptz ligands in zigzag form,
with the metals in the same coordination environment as in
2a. However, in this compound there is one solvent site
occupied by a molecule of THF with 50% occupancy,
whereas a nearby site is occupied partially by either one
molecule of Et2O or one molecule of THF with 50 and 25%
occupancies, respectively. These solvents occupy approxi-
mately the same position within the asymmetric unit as the
THF molecule in 2a; however, the differences cause a
significant change in the supramolecular organization of the
polymer in the crystal (Figures 3 and 4). Thus, whereas each
chain is also interacting with two other chains on opposite
sides through π-π stacking of the 4ptz ligands (part B of
Figure 4), the zigzag ribbons do not describe a sinusoidal
conformation but show a rather flat disposition (part B′ of
Figure 4). Thus, the adjacent interacting chains are located
on top of each other and mutually shifted, describing infinite
sheets in the form of a staircase (part C of Figure 4). The
change in the spatial arrangement of the polymers cause the
4ptz-4ptz interactions to occur in a slightly different manner.
In this case, the triazine rings are almost perfectly staggered
(part B of Figure 3), forming quasi-ideal Piedfort pairs,24,25
the distance between the centroids of the interacting triazine
rings being 3.366 Å. The separation between adjacent metals
within the chains is 13.292 Å, whereas the smallest interchain
distance between two metals is 10.589 Å.
Figure 2. ORTEP representation at the 50% probability level of
compounds [Co(dbm)2(4ptz)]n‚nTHF (2a, A), [Co(dbm)2(4ptz)]n‚0.75nTHF‚
0.5nEt2O (2b, B), and [Co(dbm)2(4ptz)]n‚3nDMF (2c, C). Hydrogen atoms
are not shown for clarity. The amount of crystallization solvent per cobalt
ion is shown.
π-π interactions. Thus, each 4ptz ligand interacts with an
equivalent partner located in front and slightly shifted, in
such a way that the projection of one triazine nitrogen atom
in one ligand falls near the center of the triazine ring opposite
to it (part A of Figure 3). The distance between this nitrogen
atom and the centroid of the triazine ring in front of it is
3.477 Å. The strain of the supramolecular organization in
2a causes the 4ptz ligands to be significantly curved, instead
of planar (part A of Figure 3, bottom), helping the chains to
describe a sinusoidal line when observed from the side and
along the zigzag plane (part A′ Figure 4). In these waves,
the heterocyclic ligands lie at the maxima and minima of
amplitude. Thus, each chain interacts with two parallel chains
located on each side of the zigzag through two infinite
sequences of 4ptz-4ptz interactions. Because each chain
(wave) runs in opposite phase to the adjacent chain (Figure
4A′), the π-π interactions occur between ligands located
on points of opposite amplitude, thus, the interacting chains
describe infinite sheets that are parallel to the zigzag planes
(parts A and A′′ of Figures 4). The space between sheets is
efficiently occupied by the phenyl rings of the dbm- ligands
and the molecules of tetrahydrofuran (THF). There are no
[Co(dbm)2(4ptz)]n‚3nDMF (2c). Coordination complex
2c (part C of Figure 2) shares the same composition as 2a
and 2b, except for the solvents of crystallization, which now
consist of three full molecules of DMF per asymmetric unit.
These molecules are located in three well-defined areas
within the unit cell but each of them displays more than one
disordered orientation, as inferred by the inspection of part
C of Figure 2. The new solvent composition results again in
a different structural disposition of the zigzag polymers
(22) Rarig, R. S.; Zubieta, J. J. Chem. Soc., Dalton Trans. 2001, 3446-
3452.
(23) Cotton, F. A.; Lin, C.; Murillo, C. A. J. Chem. Soc., Dalton Trans.
2001, 499-501.
(24) Piedfort pairs are pairs of 1,3,5-trisubstituted aromatic rings stacked
in a perfectly staggered manner.
(25) Jessiman, A. S.; Macnicol, D. D.; Mallinson, P. R.; Vallance, I. J.
Chem. Soc., Chem. Commun. 1990, 1619-1621.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7157

Barrios et al.
Figure 3. Two 4ptz ligands from adjacent chains of 2a (A), 2b (B), and 2c (C) and the cobalt ions bound to them, emphasizing the π-π stacking
interactions existing between them. (Top) Top view. (Bottom) Side view.
throughout the lattice. In 2c, each polymer interacts by
interdigitation of the 4ptz ligands with two other equivalent
polymers, one below and one above, as in 2b. However, in
the present compound, the ribbons are shifted with respect
to each other along the 1D direction, by a distance of
approximately the width of the triazine ring (∼2.3 Å). Thus,
the pairs of interacting 4ptz moieties do not project their
triazine rings exactly on top of each other but in a shifted
manner so that one triazine ring projects just next to the other
(part C of Figure 3 and part C of Figure 4). The distance
between the closest atoms from different triazine rings is
3.404 Å. The metals within the ribbons are located 13.280
Å apart, whereas the shortest Co‚‚‚Co vector between chains
is 9.979 Å long.
Molecular Mechanics Calculations. The structures of
compounds 2a, 2b, and 2c were surprising because it was
expected that the most-favored outcome of the reactions
leading to them would be the result of the maximum
occupancy of the coordination sites of the 4ptz ligand. It
was assumed that this would produce a 2D honeycomb
architecture with fused hexagons featuring 4ptz ligands at
the common edges and cobalt(II) knots on the sides (Figure
5), whereas the actual structure was completely different.
This, in a way, could be taken as another argument in favor
of a previously reported and rather provocative thought
stating that “One of the continuing scandals in the physical
sciences is that it remains in general impossible to predict
the structure of eVen the simplest crystalline solids from
knowledge of their chemical composition”.26 In this case,
however, the composition of the expected product was also
different from that which was finally isolated. It is very likely
that the preference for linear chains (above) with one free
coordination site on each 4ptz ligand is explained by the
establishment of a network of π-π interactions through
interdigitation of these zigzag chains. The formation of a
2D honeycomb would prevent these interactions from taking
place. To eliminate the hypothesis that there are steric reasons
for the lack of formation of the 2D network, we performed
molecular mechanics calculations. These were done with the
program Gaussian 03, using the universal force field.27 The
results showed the hypothetical hexagonal polygon to be
stable; therefore, there is not a steric reason for the prevention
of its formation, thereby reinforcing the idea that the stacking
interactions between the heterocycles are highly responsible
for the supramolecular organization of compounds 2a, 2b,
and 2c. It is interesting to point out here that a recent report
just appeared describing a coordination system that organizes
as honeycombs at the supramolecular level, thanks to the
establishment of π-π interactions between the large-surface
aromatic ligands composing it.28
Magnetic Properties. One of the driving forces for
producing the assemblies reported here is the preparation of
new magnetic materials. A study of the bulk magnetic
properties was performed on complexes 2a and 2c. The
interpretation of the magnetic behavior of octahedral cobalt-
(II) complexes is complicated by the spin-orbit coupling
of the 4T1g ground state.29 Calculation of exchange parameters
can be done only for dinuclear complexes,30,31 whereas full
diagonalization methods allow for the determination of J
values for simple polynuclear systems in the low-temperature
1
regions (where the effective spin S′ is /2).32 Complexes 2a
and 2c are composed of 1D chains, and these can usually be
considered as a succession of anisotropic S ) 1/2 pseudo spins
of Ising type for their modeling.33 Likewise, these systems
are amenable to a phenomenological treatment (below).34
Bulk magnetization measurements of [Co(dbm)2(4ptz)]n‚
nTHF (2a) and [Co(dbm)2(4ptz)]n‚3nDMF (2c) were per-
formed in the 2-300 K range under a field of 5000 G and
represented in the form of øMT versus T plots (Figures 6
and 7), where øM is the molar paramagnetic susceptibility
per cobalt(II). The øMT values at 300 K are (in the 2a/2c
(27) Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A.; Skiff,
W. M. J. Am. Chem. Soc. 1992, 114, 10024-10035.
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Applications; Wiley-VCH: New York, 2000.
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(32) Borra´s-Almenar, J. J.; Clemente-Juan, J. M.; Coronado, E.; Tsukerblat,
B. S. Inorg. Chem. 1999, 38, 6081-6088.
(33) Angelov, S.; Drillon, M.; Zhecheva, E.; Stoyanova, R.; Belaiche, M.;
Derory, A.; Herr, A. Inorg. Chem. 1992, 31, 1514-1517.
(34) Rueff, J. M.; Masciocchi, N.; Rabu, P.; Sironi, A.; Skoulios, A. Eur.
J. Inorg. Chem. 2001, 2843-2848.
(26) Maddox, J. Nature 1988, 335, 201.
7158 Inorganic Chemistry, Vol. 46, No. 17, 2007

SolWatomorphs of the Polymer [Co(dbm)2(4ptz)]n
In this equation, A + B is equivalent to the Curie constant,
C, whereas E1 and E2 represent the energies of the spin-
orbit coupling and the exchange interaction, respectively.
Excellent fits were obtained for both complexes with the
following parameters (keeping the 2a/2c format); A + B )
3.7/3.6 cm3mol-1K, just above the range typically encoun-
tered for octahedral cobalt(II) ions (C ) ∼2.8-3.4 cm3 mol-1
K),34,36 E1/k ) 103.9/86.3 cm-1, of the same order as
previously reported for analogous systems,34,36 and for E2/k
) 0.9/0.5 cm-1 (i.e., J ) -1.8/-1.0 cm-1, using the
Hamiltonian of the type H ) -JSiSj for the magnetic
exchange). A temperature-independent paramagnetism value
of 1.8 × 10-3 cm3 mol-1 was employed for these fits, as is
commonly done for octahedral cobalt(II) systems.37 A small
intrachain exchange interaction is not unexpected, given the
extended nature of the bridge, formed by three heterocycles
separated by single bonds. The reduced magnetization curve
at 2 K, M/Nâ versus H/T tends to 2.5/2.2 µB at 2 T (not
shown), in good agreement with the values reported in the
literature.34 More interesting about these compounds was the
investigation into the possible magnetic exchange in two or
three dimensions that could result from the supramolecular
organization of the system in the solid state. This conjecture
was investigated by examining the susceptibility of both
compounds at various, lower magnetic fields or through ac
measurements. Thus, when smaller magnetic fields were
applied (20, 50, 100, 300, and 1000 G), øMT versus T plots
were obtained for compound 2a that varied significantly with
the magnitude of this field (Figure 6, inset). These plots were
superimposable down to around 20 K and showed a moderate
increase in the øMT value upon further cooling to reach
maxima that were higher as the field became smaller. This
is indicative of weak ferromagnetic ordering within the 3D
network, which, in a system composed of antiferromagnetic
chains, may originate as a result of the phenomenon of spin
canting. This was further supported by results from ac
measurements, which revealed øM′′ signals (øM′′ is the out-
of-phase component of øM) with maxima near 8 K, which
were independent of the frequency used in the experiment
(Figure S1 in the Supporting Information). Because the
interactions within the 3D network leading to this canting
are weak, the maxima of øMT versus T do not reach very
high values (4.13 cm3 mol-1 K under 20 G). The fact that
the M/Nâ versus H/T curve does not increase rapidly at low
fields corroborates that 2a is not a ferromagnetic ordered
solid. Moreover, no hysteresis response of the magnetization
was observed at 2 K. The phenomenon of canting, which
arises from single-ion magnetic anisotropy and/or antisym-
metric interactions is relatively common, although the
reported species with cobalt(II) are quite scarce. Some of
them include the classical M[CoCl3]n 1D systems,38 a linear
azido derivative,39 or the hexameric complex (K2[CoO3-
PCH2N(CH2CO2)2])6, the first discrete molecular system
Figure 4. Stick representation of 2a (top), 2b (middle), and 2c (bottom)
emphasizing the supramolecular organization of the chains in the solid
state. The dbm- ligands and solvate molecules are not shown for
clarity, as well as the hydrogen atoms. (A, B, C) top view; (A′, B′, C′) side
view perpendicular to the chains; (A′′, B′′, C′′) side view parallel to the
chains.
format) 3.7/3.4 cm3 mol-1 K, and these continuously decrease
to 1.8/1.6 cm3 mol-1 K at 2 K. Spin-orbit coupling causes
the observed 300 K øMT value to be higher than expected
for an isolated S ) 3/2 system (1.87 cm3 mol-1 K) as well as
its decrease upon cooling.29,35 Values on the high end or
above the range of 2.75-3.4 cm3 mol-1 K indicate very little
deviation from ideal octahedral geometry. An estimation of
the exchange interaction within such a 1D system can be
obtained by using a two-exponential phenomenological
equation (eq 2).34
(36) Rueff, J. M.; Masciocchi, N.; Rabu, P.; Sironi, A.; Skoulios, A.
Chem.sEur. J. 2002, 8, 1813-1820.
(37) Boca, R. Struct. Bonding 2006, 117, 1-264.
(38) Carlin, R. L. Magnetochemistry; Springer: Berlin, Germany, 1986.
(39) Hong, C. S.; Koo, J. E.; Son, S. K.; Lee, Y. S.; Kim, Y. S.; Do, Y.
Chem.sEur. J. 2001, 7, 4243-4252.
(35) Telfer, S. G.; Sato, T.; Kuroda, R.; Lefebvre, J.; Leznoff, D. B. Inorg.
Chem. 2004, 43, 421-429.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7159

Barrios et al.
Table 1. Crystallographic Parameters of Complexes 1, 2a, 2b, and 2c
1
2a
2b
2c
formula
fw (g mol-1
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C32H30CoO6
569.49
monoclinic
C2/c
16.9583(8)
16.3460(7)
10.3880(6)
90.00
108.779(2)
90.00
C52H42CoN6O5
889.85
triclinic
C53H45CoN6O5.25
908.91
C57H55CoN9O7
1037.03
triclinic
)
monoclinic
P21/n (no. 14)
10.5892(8)
26.548(2)
17.186 (1)
90.00
104.898(2)
90.00
4668.8(6)
4
P1h (no. 2)
12.1547(5)
13.4488(5)
15.7972(7)
71.850(2)
71.099(2)
70.895(2)
2246.7(2)
2
P1h (no. 2)
13.8982(11)
14.1768(11)
15.0948(11)
94.089(2)
101.607(2)
112.116(2)
2663.3(4)
2
2726.3(2)
4
1.388
Z
F
calcd (g cm-3
)
1.315
150(2)
1.293
150(2)
1.293
150(2)
T (°C)
150(2)
cryst shape
color
needle
orange
block
red
parallelepiped
red
block
red
dimensions (mm)
unique data
0.40 × 0.08 × 0.08
0.27 × 0.12 × 0.12
0.30 × 0.30 × 0.17
0.06 × 0.03 × 0.01
3981
8741
9430
13 573
unique data
2956
7365
8374
10 580
with I > 2σ(I)
R1, wR2a
0.0410, 0.0988
0.0457, 0.1178
0.0659, 0.1824
0.0552, 0.1531
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [(∑w(Fo - Fc )2 /∑wFo )]1/2
.
2
2
4
Table 2. Selected Interatomic Distances (Angstroms) and Angles for
Complex 2aa,b
Table 3. Selected Interatomic Distances (Angstroms) and Angles for
Complex 2ba,b
Co(1)-O(24)
2.0339(14)
2.0263(14)
2.2131(19)
2.0339(14)
2.0263(14)
2.2131(18)
2.0360(16)
2.0347(16)
2.1603(17)
2.0360(16)
2.0347(16)
2.1603(17)
13.1427(6)
91.12(6)
89.52(6)
180.0
88.88(6)
90.48(6)
84.54(6)
88.88(6)
180.0
95.46(6)
90.48(6)
95.46(6)
180.0000
90.44(6)
91.32(6)
180.0
Co(1)-O(24)
2.026(2)
2.0287(18)
2.025(2)
2.0227(19)
2.189(2)
2.214(2)
13.2920
89.08(7)
178.71(8)
91.49(8)
94.15(8)
83.58(8)
90.79(8)
179.42(8)
89.20(8)
91.73(8)
88.64(8)
84.57(8)
97.71(8)
90.65(8)
88.44(8)
177.53(8)
Co(1)-O(28)
Co(1)-O(28)b
Co(1)-N(1)
Co(1)-O(41)b
Co(1)-O(24)a
Co(1)-O(45)
Co(1)-O(28)a
Co(1)-N(1)
Co(1)-N(1)a
Co(1)-N(13)b
Co(2)-O(41)
Co(1)‚‚‚Co(1)b
Co(2)-O(45)
O(24)-Co(1)-O(28)
O(24)-Co(1)-O(41)
O(24)-Co(1)-O(45)
O(24)-Co(1)-N(1)
O(24)-Co(1)-N(13)b
O(28)-Co(1)-O(41)
O(28)-Co(1)-O(45)
O(28)-Co(1)-N(1)
O(28)-Co(1)-N(13)b
O(41)-Co(1)-O(45)
O(41)-Co(1)-N(1)
O(41)-Co(1)-N(13)b
O(45)-Co(1)-N(1)
O(45)-Co(1)-N(13)b
N(1)-Co(1)-N(13)b
Co(2)-N(13)
Co(2)-O(41)b
Co(2)-O(45)b
Co(2)-N(13)b
Co(1)‚‚‚Co(2)
O(24)-Co(1)-O(28)
O(24)-Co(1)-N(1)
O(24)-Co(1)-O(24)a
O(24)-Co(1)-O(28)a
O(24)-Co(1)-N(1)a
O(28)-Co(1)-N(1)
O(28)-Co(1)-O(24)a
O(28)-Co(1)-O(28)a
O(28)-Co(1)-N(1)a
N(1)-Co(1)-O(24)a
N(1)-Co(1)-O(28)a
N(1)-Co(1)-N(1)a
O(41)-Co(2)-O(45)
O(41)-Co(2)-N(13)
O(41)-Co(2)-O(41)b
O(41)-Co(2)-O(45)b
O(41)-Co(2)-N(13)b
O(45)-Co(2)-N(13)
O(45)-Co(2)-O(41)b
O(45)-Co(2)-O(45)b
O(45)-Co(2)-N(13)b
N(13)-Co(2)-O(41)b
N(13)-Co(2)-O(45)b
N(13)-Co(2)-N(13)b
a ‘a’ represents the [-x, 1 - y, 1 - z] symmetry operation. b ‘b’
represents the [3/2 - x, /2 + x, /2 - x] symmetry operation.
1
1
with the anisotropy of the cobalt(II) ions, leads to the
generation of a net magnetization within the chain as a result
of the antiferromagnetic ordering (Scheme 2). According to
this, compound 2c should not exhibit the phenomenon of
canting, because the 1D ribbons in this compound are almost
straight and not undulated (part C′ of Figure 4′). Indeed, the
øMT versus T plots at different fields for 2c are all
superimposable, revealing the absence of canting. Likewise,
this polymer showed no øM′′ signals in the ac magnetic
measurements. This study demonstrates that solvents of
crystallization may influence the supramolecular organization
of MOFs, to the point of significantly changing their
magnetic response.
89.56(6)
88.68(6)
91.82(7)
89.56(6)
180.0000
88.18(7)
88.68(6)
88.18(6)
180.0
a ‘a’ represents the [-x, 1 - y, 1 - z] symmetry operation. b ‘b’
represents the [3/2 - x, /2 + x, /2 - x] symmetry operation.
1
1
displaying this property at the solid state.40 The canting in
compound 2a may be caused by the sinusoidal disposition
of the chains of [-Co-4ptz-Co-4ptz-], which, together
Experimental Section
Syntheses. All of the reactions were performed in air and using
solvents and reagents as received.
(40) Gutschke, S. O. H.; Price, D. J.; Powell, A. K.; Wood, P. T. Angew.
Chem., Int. Ed. 1999, 38, 1088-1090.
7160 Inorganic Chemistry, Vol. 46, No. 17, 2007

SolWatomorphs of the Polymer [Co(dbm)2(4ptz)]n
Scheme 2. Representation of the Sinusoidal [-Co-4ptz-Co-4ptz-]
Chain of 2a and the Possible Orientation of the Cobalt(II)
Spin-Moments as a Result of the Antiferromagnetic Ordering of These
and the Anisotropy of the Metal, to Yield a Nonzero Net Magnetization
within the Chain
A mixture of 4-cyanopyridine (10 g, 96 mmol), 18-crown-6 (1 g,
3.8 mmol), potassium hydroxide (225 mg, 4.0 mmol), and decalin
(10 mL) was stirred at near 200 °C for about 3 h. The system turned
into a dark-brown solution upon warming. The solvents were
distilled under a vacuum, and the residue, which consisted of a
dark paste, was washed with warm pyridine and then with Et2O.
The product was obtained as pinkish crystals. The yield was 40%.
[Co(dbm)2(MeOH)2] (1). A yellow solution of dibenzoyl-
methane (Hdbm) (1.31 g, 5.3 mmol) in MeOH (80 mL) was added
to a stirred magenta solution of Co(AcO)2‚4H2O (0.73 g, 2.9 mmol)
in MeOH (20 mL). The solution turned red-orange and an orange
solid precipitated immediately. The mixture was kept undisturbed
for 2 h at 4 °C, and then an orange product was collected by
filtration, washed twice with Et2O (2 × 5 mL) after keeping the
mother liquor, and dried in air. The yield was 62%. Anal. Calcd
(Found) for 1: C, 67.49 (67.17); H, 5.31 (5.04). Crystals suitable
for X-ray crystallography were obtained from the mother liquor,
after further slow evaporation. IR (cm-1): 524.35 (m), 625.59 (m),
685.84 (m), 715.38 (m), 749.20 (m), 787.07 (w), 940.49 (w), 1023.06
(m), 1156.71 (w), 1230.15 (m), 1309.96 (m), 1395.66 (Vs), 1453.53
(s), 1479.17 (s), 1523.04 (Vs), 1547.79 (s), 1594.23 (m).
Figure 5. Representation of a structure with a hexagonal arrangement as
calculated by molecular mechanics, showing that this architecture would
be stable from the steric and electronic points of view.
[Co(dbm)2(4ptz)]n‚nTHF (2a). Solid 4ptz (25 mg, 1.6 mmol)
was added to a stirred orange solution of complex 1 (69 mg, 2.4
mmol) in tetrahydrofuran (THF) (25 mL). The orange mixture was
brought to reflux, and the heating was maintained for 24 h, during
which, the color turned to red-orange. After this, the resulting
solution was allowed to cool to room temperature and was layered
with Et2O. After a few days, red, well-shaped crystals had formed
on the walls of the tube. The yield was 60%. Anal. Calcd (Found)
for 2a: C, 70.19 (69.97); H, 4.76 (4.58); N, 9.44 (9.65). IR (cm-1):
721.56 (w), 804.48 (w), 1062.58 (w), 1311.04 (w), 1371.95 (m),
1409.98 (m), 1456.79 (s), 1477.51 (m), 1520.59 (Vs), 1549.22 (m),
1593.32 (m), 1616.63 (m).
Figure 6. Plot of øMT versus T per ion of cobalt(II) for [Co(dbm)2(4ptz)]n‚
nTHF (2a) at a constant field of 5000 G. The solid line is a fit to the
experimental data. The inset shows analogous plots of øMT versus T at
various fields.
[Co(dbm)2(4ptz)]n‚0.75nTHF‚0.5nEt2O (2b). Solid 4ptz (25
mg, 1.6 mmol) was added to a stirred orange solution of complex
1 (69 mg, 2.4 mmol) in CHCl3 (25 mL). The mixture was stirred
for 48 h, after which the color turned to red-orange, and an orange
precipitate had formed. The solid was collected by filtration and
washed three times with Et2O (3 × 5 mL). The orange solid was
stirred with THF (10 mL) and layered with Et2O. After a week,
well-shaped red crystals had formed on the walls of the tubes, and
a white microcrystalline product was found in suspension. The red
crystals could be easily separated from the white material after
successive washings with Et2O. The yield was 20%. Anal. Calcd
(Found) for 2b (-0.5nEt2O): C, 70.26 (70.10); H, 4.62 (4.76); N,
9.64 (9.40). IR (cm-1): 690.96 (w), 722.83 (w), 802.30 (w), 1062.34
(w), 1312.10 (w), 1373.24 (m), 1412.05 (m), 1456.96 (m), 1478.08
(m), 1517.23 (Vs), 1549.32 (s), 1593.12 (m).
Figure 7. Plot of øMT versus T per ion of cobalt(II) for [Co(dbm)2(4ptz)]n‚
3nDMF (2c) at a constant field of 5000 G. The solid line is a fit to the
experimental data.
[Co(dbm)2(4ptz)]n‚3nDMF (2c). Solid 4ptz (25 mg, 1.6 mmol)
was mixed with complex 1 (69 mg, 2.4 mmol) in DMF (30 mL) to
yield a red-orange solution. The mixture was stirred for 2 h and
øMT ) A exp(-E1/kT) + B exp(-E2/kT)
(2)
2,4,6-Tris-(4-pyridyl)-1,3,5-triazine (4ptz). This ligand was
prepared through a slight modification of a published procedure.41
(41) Anderson, H. L.; Anderson, S.; Sanders, J. K. M. J. Chem. Soc., Perkin
Trans. 1995, 2231-2245.
Inorganic Chemistry, Vol. 46, No. 17, 2007 7161

Barrios et al.
was left to evaporate slowly. After three to four weeks, well-shaped
red crystals had formed that were collected by filtration. The yield
was 22%. Anal. Calcd (Found) for 2c: C, 66.02 (65.72); H, 5.35
(5.20).; N, 12.16 (11.96). IR (cm-1): 643.11 (w), 650.72 (w), 724.32
(w), 804.25 (w), 1062.17 (w), 1089.53 (w), 1222.91 (w), 1311.25
(w), 1372.92 (s), 1409.09 (s), 1457.89 (s), 1478.83 (m), 1517.16
(Vs), 1548.58 (Vs), 1592.43 (m), 1675.17 (s).
Physical Measurements. Field-cooled measurements of the
magnetization of a smoothly powdered microcrystalline sample of
2a were performed in the range of 2-300 K with a Quantum Design
MPMS-5XL SQUID magnetometer with an applied field of 5 kG.
Corrections for diamagnetic contributions of the sample holder to
the measured magnetization and of the sample to the magnetic
susceptibility were performed experimentally and by using Pascal’s
constants, respectively. Measurements were taken under an ac
magnetic field in the 2-40 K range at 1339 and 107 Hz frequencies.
IR spectra were recorded as KBr pellet samples on a Nicolet 5700
FTIR spectrometer. Elemental analyses were performed in-house
on a Perkin-Elmer Series II CHNS/O Analyzer 2400, at the Servei
de Microana`lisi of CSIC, Barcelona, Spain.
X-ray Crystallography. X-ray diffraction (XRD) data for
compound 1 were recorded on a Nonius Kappa CCD diffractometer
with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å).
DENZO-SMN was used for data integration, and SCALEPACK
corrected data was used for Lorentz-polarization effects.42 Measure-
ments on single crystals of 2a, 2b, and 2c were made using silicon-
(111) monochromated synchrotron radiation (λ ) 0.8457 Å) and a
Bruker APEXII CCD area-detector diffractometer, using standard
procedures and programs for Station 16.2 of Daresbury SRS. Data
were collected on a Bruker APEXII diffractometer using the APEX2
software. In all three cases, the crystals were mounted onto the
diffractometer at low temperature under nitrogen at ca. 150 K. The
structures were solved using direct methods with the SIR92 (1),43
SHELXTL (2a),44,45 or SIR97 (2b and 2c)46 programs. Further
refinements were done using the SHELXTL package. All of the
non-hydrogens were refined anisotropically with the exception of
disordered solvent areas in 2b and 2c; in the former, this area
contains one molecule of Et2O (50% occupancy) and two THF
molecules, which were disordered over two positions with 25 and
50% occupancies, respectively. Displacement parameters and 1,2/
1,3 distance restraints were used to model these solvent molecules.
A residual electron density peak remained in the refinement in the
disordered solvent area that could not be modeled reasonably.
Hydrogen atoms were placed geometrically on calculated positions
on their riding atom. (Uij ) 1.2 Ueq for the atom to which they
are bonded (1.5 for methyl)). For 2c, the non-hydrogen atoms not
refined anisotropically are those from solvents in disordered
positions with less that 50% occupancy. In this compound, the
hydrogen atoms placed in calculated positions were possible and
refined using a riding model. In the case of the disordered DMFs,
it was not possible to either place or find them in the difference
map, and they were omitted from the refinement. Geometrical and
displacement parameter restraints were used to model the disordered
DMF. Displacement parameter restraints were used in the modeling
of one of the phenyl rings, and even so, a couple of carbon atoms
have displacement parameter ratios max/min of around 5:1. Splitting
the cited was considered, but as no new chemical information would
result, they were left as they were.
Conclusions
Intermolecular hydrogen-bonding interactions are at the
root of the unexpected cis configuration displayed by the
complex [Co(dbm)2(MeOH)2] (1) in the solid state, as
revealed in this work by single-crystal X-ray crystallography.
This configuration rearranges into trans upon reaction with
the multidentate, radial 4ptz ligand. The resulting product
is a 1D polymer of the formula [Co(dbm)2(4ptz)]n, with a
zigzag arrangement instead of the expected honeycomb
organization, despite the fact that molecular mechanics
calculations demonstrate that such architecture would be
stable. The reason for the observed solid-state structure is
the establishment of a network of π-π stacking inter-
actions, which represent a higher energy gain than full
coordination of the 4ptz ligand. Three isomers of this
polymer have been prepared and characterized by single-
crystal XRD, which differ in the nature and position of
crystallization solvents and result in different relative dis-
positions of the 1D chains at the supramolecular level. A
study of the magnetic properties of two of the polymers
reveals that the supramolecular structure has a profound
impact on the magnetic properties of the solid. Thus, the
compound where the 1D chains exhibit a sinusoidal shape
(2a) shows the phenomenon of spin canting, presumably as
a consequence of the mutually tilted orientation of the cobalt-
(II) centers within the chains. If the chains are straight (2b
and 2c), the spin canting disappears. This opens the prospect
of exploiting derivatives of this new type of system for the
investigation of spin canting as a function of various subtle
structural factors.
Acknowledgment. This work was supported by Dutch
WFMO (Werkgroep Fundamenteel-Materialen Onderzoek),
CW (Foundation for the Chemical Sciences), and NWO
(Organization for the Scientific Research), the CNRS,
Bordeaux 1 university, and the Spanish Ministerio de Ciencia
y Tecnolog´ıa through a “Ramo´n y Cajal” contract. We
acknowledge the provision of time at the CCLRC Daresbury
Laboratory via support by the European Union.
(42) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276, 307.
(43) Altomare, A.; Cascarano, G. G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1993, 27, 435.
(44) Sheldrick, G. M.: University of Go¨ttingen, 1997.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(45) Sheldrick, G. M.: University of Go¨ttingen, 1997.
(46) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
IC7004979
7162 Inorganic Chemistry, Vol. 46, No. 17, 2007