MnII/CoII-terephthalate frameworks containing dipyridine coligands: Syntheses, crystal structures, magnetic behaviors, and thermal studies

Article abstract of DOI:10.1002/ejic.200500258

Three new metal-organic hybrid polymeric networks of Co^II and Mn^II with the molecular formulae [Co(bpp)(tp)(H₂O) ₂] (1), [Mn(bpds)(tp)(H₂O)₂]·(bpds) (2), and [Mn(4,4′-bipy)-(H₂O)₄]·(tp) (3) (bpp = 4,4′-trimethylenedipyridine; bpds = 4,4′-bipyridyl disulfide; 4,4′-bipy = 4,4′-dipyridyl; tp = terephthalate) have been synthesized and characterized by single-crystal X-ray diffraction studies, low temperature (300-2 K) magnetic measurements, and thermal behaviors. The structure determination of complexes 1 and 2 reveals a parallel interpenetrated structure of 2D layers with (4,4) topology, with metal ions at the nodes connected through tp and N,N-donor coligands. The octahedral N₂O ₄ chromophore surrounding the metal ion results from trans located tp oxygens, two water molecules, and two nitrogen donors of the co-ligands in the cis position. The presence of uncoordinated bpds between the interpenetrated layers leads to the formation of a wafer-like structure for 2. In complex 3, however, manganese(II) ions bridged by 4,4′-bipy and coordinated by four water molecules give rise to a 1D polymeric chain. The adjoining chains encapsulate terephthalate anions (tp) to give a 3D structure through H-bonding. Low-temperature magnetic data indicate weak antiferromagnetic coupling in complexes 1 and 2. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500258

FULL PAPER
MnII/CoII-Terephthalate Frameworks Containing Dipyridine Coligands:
Syntheses, Crystal Structures, Magnetic Behaviors, and Thermal Studies
Subal Chandra Manna,[a] Sanjit Konar,[a] Ennio Zangrando,[b] Ken-ichi Okamoto,[c]
Joan Ribas,*[d] and Nirmalendu Ray Chaudhuri*[a]
Keywords: Manganese() / Cobalt() / Crystal structure / Magnetic behavior / Supramolecular chemistry
Three new metal–organic hybrid polymeric networks of CoII
and MnII with the molecular formulae [Co(bpp)(tp)(H2O)2]
(1), [Mn(bpds)(tp)(H2O)2]·(bpds) (2), and [Mn(4,4Ј-bipy)-
(H2O)4]·(tp) (3) (bpp = 4,4Ј-trimethylenedipyridine; bpds =
gens, two water molecules, and two nitrogen donors of the
co-ligands in the cis position. The presence of uncoordinated
bpds between the interpenetrated layers leads to the forma-
tion of a wafer-like structure for 2. In complex 3, however,
manganese(II) ions bridged by 4,4Ј-bipy and coordinated by
four water molecules give rise to a 1D polymeric chain. The
adjoining chains encapsulate terephthalate anions (tp) to
give a 3D structure through H-bonding. Low-temperature
magnetic data indicate weak antiferromagnetic coupling in
complexes 1 and 2.
4,4Ј-bipyridyl disulfide; 4,4Ј-bipy
= 4,4Ј-dipyridyl; tp =
terephthalate) have been synthesized and characterized by
single-crystal X-ray diffraction studies, low temperature
(300–2 K) magnetic measurements, and thermal behaviors.
The structure determination of complexes 1 and 2 reveals a
parallel interpenetrated structure of 2D layers with (4,4) top-
ology, with metal ions at the nodes connected through tp and
N,N-donor coligands. The octahedral N2O4 chromophore
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
surrounding the metal ion results from trans located tp oxy- Germany, 2005)
use of (a) anionic bridging ligands, which, in addition, can
Introduction
partially or fully counterbalance the charge of the metal
centers, (b) anionic as well as neutral spacers to increase
the possibility of enhancing the dimension of molecular
materials, and (c) only neutral spacers, where charges of
the metal centers are counterbalanced by noncoordinating
anions.
The construction of one- to three-dimensional functional
metal-organic hybrid materials of paramagnetic metal ions
is of great interest as their intriguing network topologies
lead to potential applications,[1] for example in electrical,
conductivity, magnetism, host–guest chemistry, ion ex-
change, catalysis, nanotechnology, fluorescence, nonlinear
optics, etc. Research in this field has been carried out by a
number of eminent groups, in particular those of Rao,[2]
Yaghi,[3] Fujita,[4] Zaworotko,[5] etc. The availability of new
polyfunctional ligands, as well as the discovery of alterna-
tive synthetic procedures, has led to the syntheses of unique
and novel metal–organic frameworks (MOFs) that suggest
routes for chemists and physicists to pursue in search of
such materials. A literature survey shows that the most
commonly used strategies for the synthesis of MOFs are the
Recently, we have reported the synthesis of some struc-
turally and magnetically interesting MOFs using strategy
(a), such as [Ni3(fum)2(µ3-OH)2(H2O)4]n·2nH2O,[6] [Cu(µ-
fum)(NH3)2]n·2nH2O,[7] [Mn(mal)(H2O)2]n,[8] and [Co(H2O)4-
(fum)]n·nH2O,[9] where fumarate (fum) and malonate (mal)
dicarboxylates act as anionic bridging ligands only. We have
also reported MOFs obtained through strategies (b), where
dicarboxylates are used in combination with neutral spa-
cers, such as [{Cu3(mal)2(bpe)3(H2O)2}(NO3)2(H2O)2]n,[10]
[Cu2(fum)2(4,4Ј-bipy)]n·0.5nH2O,[11] [Mn2(mal)2(4,4Ј-bipy)-
(H2O)2]n,[8] [Cu4(mal)4(urotropin)]·7H2O and [Co2(mal)2-
(urotropin)]·2H2O,[12] and [Ni3(maleate)2(bpe)4(H2O)4]-
(NO3)2·H2O, [Mn(adipate)(bpe)],[13] [Ni(fum)(bpe)], and
[Ni(fum)(bpp)(H2O)][14] [bpe = 1,2-(bispyridine)ethane, bpp
= 1,3-bis(4-pyridyl)propane], and (c), where noncoordi-
nated dicarboxylates counterbalance the charge of the me-
tal ions, as in [Co(H2O)4(4,4Ј-bipy)]n(fum)n·4nH2O[9] and
[a] Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science,
Kolkata-700032, India
Fax: +91-33-2473-2805
E-mail: icnrc@iacs.res.in
[b] Dipartimento di Scienze Chimiche, University of Trieste,
34127 Trieste, Italy
[c] Department of Chemistry, University of Tsukuba,
Tsukuba, Ibaraki 305, Japan
2–
[{Mn(bpe)(H2O)4}(C4O4)·4.5H2O] (C4O4 = acetylene di-
[d] Departament de Química Inorgánica, Universitat de Barcelona,
Diagonal 647, 08028 Barcelona, Spain
E-mail: joan.ribas@qi.ub.es
carboxylate).[15] Thus, depending on the metal ion and di-
carboxylate or dicarboxylate/neutral bipyridine spacer, se-
veral MOFs with novel structural diversity and interesting
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
4646
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200500258
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MnII/CoII-Terephthalate Frameworks using Dipyridine Coligands
FULL PAPER
magnetic properties have been reported. This has prompted
us to synthesize new MOFs using a well-known but less-
Results and Discussion
documented dicarboxylate anion − terephthalate − in com- Description of the Structures
bination with other neutral bipyridines. The choice of
Complex 1
terephthalate arises as it possesses versatile coordination
modes (Scheme 1) and has the ability to form large and
tightly bound metal cluster aggregates with specific and di-
rectional hydrogen bonds in building the molecular archi-
tecture,[16] as well as to undergo π–π stacking due to the
presence of aryl rings (Scheme 2).
The crystal structure of complex 1 consists of 2D corru-
gated layers of square meshes of composition [Co(tp)(bpp)-
(H2O)2]n, as depicted in Figure 1. The cobalt ions, with oc-
tahedral coordination geometry, occupy the 4-connecting
nodes while bridging tp and bpp ligands give rise to a
square grid of equal sides (11.486×11.486 Å). Intranet hy-
drogen bonds reinforce the overall structure [O(1w)–O(4) =
2.66; O(2w)–O(6) = 2.64 Å]. The N2O4 chromophore about
the cobalt() center involves trans located tp oxygens and
two water molecules, with two bpp nitrogen donors in the
cis positions. The coordination bond lengths cover the
range 2.106(2) Å [Co–O(1w)] to 2.140(2) Å [Co–N(2)]
(Table 1). The bpp ligand exhibits a TG conformation[17]
with torsion angles of –174.5(3)° and 73.4(4)° about the
propyl chain. A careful analysis of the crystal structure
shows parallel interpenetrated layers,[18,19] as illustrated in
Figure 2, where weak π–π tp ring interactions are evident
(distance between centroids = 3.807 Å). The spacing be-
tween the mean planes through the cobalt atoms of each
sheet is 2.381 Å. Both the layers involved in interpen-
etration (A and B are structurally equal) are linked to the
adjacent sheet to form a concatenated -AB-BA-AB- struc-
ture, where hyphens indicate H-bonds involving the water
molecule O(1w) and the tp oxygen O(6) (O···O = 2.76 Å).
As shown in Figure 3, these interactions contribute to the
enhancement of molecular dimensionality. It is worthwhile
to note that the aqua ligand O(1w) forms intra- and inter-
layer H-bonds and presents a shorter coordination distance
in comparison to Co–O(2w) [2.106(2) vs. 2.132(2) Å]. The
tp carboxylates are rather tilted from a coplanar conforma-
tion and form dihedral angles of 26.0(2)° and 37.6(2)° with
the aromatic ring as a subtle balance to favor the intranet
Scheme 1.
Scheme 2.
Herein we report the syntheses, crystal structures, low-
temperature magnetic studies, and thermal behaviors of
three novel MnII/CoII-terephthalate frameworks containing
dipyridyl coligands, namely [Co(bpp)(tp)(H2O)2] (1),
[Mn(bpds)(tp)(H2O)2]·(bpds) (2), and [Mn(4,4Ј-bipy)(H2O)4]·
(tp) (3) (tp = terephthalate; bpp = 4,4Ј-trimethylenedipyr-
idine; bpds = 4,4Ј-bipyridyl disulfide; 4,4Ј-bipy = 4,4Ј-di-
pyridyl). Complexes 1 and 2 show unexpected 2D parallel
interpenetrated structural motifs, whereas in complex 3 the
use of linear 4,4Ј-bipy spacers gives rise to 1D coordination
polymers with encapsulated tp anions. The low-temperature
magnetic data of complexes 1 and 2 show weak antiferro-
magnetic coupling. Complex 1 exhibits thermally induced
reversible octahedral (pink) h tetrahedral (blue) thermo-
chromism upon dehydration/rehydration.
Figure 1. View down axis c of the 2D sheet of complex 1 with
relevant atom labeling scheme about the Co atom.
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H-bonding (Figure 1) and, at the same time, the stacking
between phenyl rings of the interpenetrated nets (Figure 2).
Table 1. Selected bond lengths [Å] and angles [°] for complexes 1–3.
1
Co–O(1w)
Co–O(2w)
Co–O(3)
2.106(2)
2.132(2)
2.127(2)
95.02(7)
88.89(6)
86.93(6)
179.68(6)
89.48(7)
84.33(7)
89.47(7)
85.20(7)
Co–O(5)
Co–N(1)
Co–N(2)
2.127(2)
2.136(2)
2.140(2)
175.45(7)
172.19(6)
91.36(7)
96.43(7)
92.84(7)
90.13(7)
90.30(8)
125.03(19)
125.12(19)
O(1w)–Co–O(2w)
O(1w)–Co–O(3)
O(1w)–Co–O(5)
O(1w)–Co–N(1)
O(1w)–Co–N(2)
O(2w)–Co–O(3)
O(2w)–Co–O(5)
O(2w)–Co–N(1)
O(2w)–Co–N(2)
O(3)–Co–O(5)
O(3)–Co–N(1)
O(3)–Co–N(2)
O(5)–Co–N(1)
O(5)–Co–N(2)
N(1)–Co–N(2)
O(4)–C(14)–O(3)
O(6)–C(21)–O(5)
2[a]
Figure 3. Interpenetrated sheets (each pair indicated in black and
gray) concatenated by H-bonds (dotted lines) in complex 1.
Mn–O(2)
Mn–O(1w)
2.131(2)
2.204(3)
Mn–N(1)
2.309(3)
O(2)–Mn–O(2Ј)
O(2)–Mn–O(1w)
O(2)–Mn–O(1wЈ)
O(2)–Mn–N(1)
O(2)–Mn–N(1Ј)
176.02(14)
88.29(10)
88.91(10)
88.63(10)
94.03(10)
O(1w)-Mn–O(1wЈ) 90.68(16)
O(1w)–Mn–N(1Ј) 176.41(11)
Complex 2
O(1w)–Mn–N(1)
N(1)–Mn–N(1Ј)
O(3)–C(1)–O(2)
86.64(11)
96.14(15)
124.8(3)
Complex
2
contains
a
2D
undulating
[Mn(tp)(bpds)(H2O)2]n sheet (Figure 4), extending in the ab
plane, where octahedral manganese ions occupy the 4-con-
necting nodes of the square grid, which has equal sides of
11.425 Å. The square grid is strengthened by hydrogen
bonds involving the aqua ligand and the adjacent carboxyl-
ate oxygen [O(1w)–O(3Ј) = 2.71 Å]. The manganese() ion
is positioned on a twofold axis with trans located tp oxy-
gens, with the coordination geometry being completed by
two water molecules and two bpds N donors in the cis posi-
tion. The Mn–O(2), Mn–O(1w), and Mn–N(1) bond
lengths are 2.131(2), 2.204(3), and 2.309(3) Å, respectively
(Table 1). The 2D layers reveal a parallel interpenetration
with a topology closely comparable to that observed in
complex 1 (Figure 5). The entangled layers in the present
arrangement seem more tightly connected, with the mean
planes through the metals being separated by 2.228 Å and
the π-stacking of tp rings being more efficient (centroid-to-
centroid distance = 3.568 Å). The conformation assumed
by the tp is also very similar to that found in the cobalt
complex, with angles between the carboxylate groups and
aromatic ring of 26.3(3)°. However, compared with complex
1, the main difference emerges from the presence of uncoor-
dinated bpds between the interpenetrated layers. This pecu-
liar feature leads to the formation of a wafer-like structure,
where the bidentate bpds ligands are linked to water mole-
cules through hydrogen bonds (N···O = 2.840 Å;L N···HO
= 158.9°). A view of the crystal packing is given in Figure 6.
An estimation of the torsion angles around the disulfide
bonds in a series of coordination polymers indicates rigidity
in the bpds ligands [C–S–S–C angles between 83.8(6)° and
95.5(8)°],[20] regardless of the different coordination envi-
ronment. The present value for the coordinated bpds ligand
falls in the range reported (92.5°), while it is 102.7° in free
bpds. Correspondingly, the N···N distance is longer in the
3[b]
Mn–O(1w)
Mn–O(2w)
O(1w)–Mn–O(1wЈ) 169.87(9)
O(1w)–Mn–O(2w) 94.25(7)
O(1wЈ)–Mn–O(2w) 86.52(7)
2.208(2)
2.188(2)
Mn–N(1)
Mn–N(2)
2.210(2)
2.269(3)
O(2w)-Mn–O(2wЈ) 171.29(9)
O(2w)–Mn–N(1)
O(2w)–Mn–N(2)
N(1)–Mn–N(2)
O(3)–C(7)–O(3ЈЈ)
85.65(4)
94.35(4)
180.0
O(1w)–Mn–N(1)
O(1w)–Mn–N(2)
95.06(4)
84.94(4)
124.5(3)
O(4)–C(12)–O(4ЈЈ) 124.8(3)
[a] Symmetry code: (Ј) –x + 1/4, –y + 1/4, z. [b] Symmetry code:
(Ј) –x + 1/2, y, –z + 3/2; (ЈЈ) –x + 1/2, y, –z + 1/2.
Figure 2. Parallel interpenetration of 2D sheets in complex 1 (coor-
dinated water oxygens not shown for sake of clarity).
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MnII/CoII-Terephthalate Frameworks using Dipyridine Coligands
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Figure 4. 2D sheet of complex 2 with relevant atom labeling scheme
about the Mn ion located on a twofold axes (primed atoms at –x
+ 1/4, –y + 1/4, z).
Figure 6. Crystal packing (view along axis b) of complex 2 with
uncoordinated bpds ligands sandwitched between the parallel inter-
penetrated layers and connected through H-bonds (dotted lines) to
coordinated water molecules. The larger circles indicate Mn ions.
lengths and bond angles is given in Table 1. The MnN2O4
chromophore presents a slightly distorted octahedral coor-
dination geometry, with the equatorial oxygens showing a
tetrahedral distortion ( 0.18 Å). The Mn–O(1w) and Mn–
O(2w) distances are 2.208(2) and 2.188(2) Å, respectively;
the nitrogen bipy donors N(1) and N(2) occupy the trans
axial positions with Mn–N(1) and Mn–N(2) distances of
2.210(2), 2.269(3) Å, respectively. The rings of the 4,4Ј-bipy
ligand are not coplanar, but are tilted by about 20°. The
terephthalate dianions are also located on twofold axes and
are sandwiched by 4,4Ј-bipy ligands of contiguous poly-
meric chains to give rise to a three-dimensional structure
through a H-bonding scheme with the water molecules. In
fact, O2w is involved in H-bonding with the sandwiched tp
anions (O3 and O4 at 2.74 Å, mean value), while O1w is
connected to O4 at a longer distance (2.90 Å) and also a
symmetry-related O3 of a side-located tp at 2.71 Å (not
shown in Figure 7).
Figure 5. View of parallel interpenetration of 2D sheets (ab plane)
in complex 2. The larger circles represent Mn ions (coordinated
water oxygens not shown for sake of clarity).
latter (8.494 vs. 8.029 Å), a conformation that appears to
assist the N–OH2 hydrogen bond.
As a comparison, in the 1D polymer [Mn(bpds)(F6-
acac)2],[21] (F6-acac = hexafluoroacetylacetonate), which
represents the only known example of manganese() ions
bridged by a bpds ligand, longer Mn–N distances of
2.282 Å are found, with the metals separated by 11.785 Å.
The 4,4Ј-bipy ligand spans the metal ions at a distance
correspondening to the length of the crystallographic b axis,
namely 11.565 Å (Figure 7), while the shortest interchain
Mn···Mn separation in the 3D architecture is 6.562 Å. The
orientations (dihedral angles) taken up by carboxylate
groups with respect to the phenyl ring are 4.86(5)° and
Complex 3
The Mn(H2O)4 units in complex 3 are bridged by 4,4Ј- 22.03(6)°, which is assumed to favor the H-bonding.
bipy ligands to give a 1D coordination polymeric array The overall structure presents structural features com-
along the crystallographic b direction, with metals located parable to those observed in the analogous Mn polymeric
on twofold axes. A drawing of the packing with the atom derivative with croconate (C5O5)2– dianions.[22] However,
labeling scheme is shown in Figure 7; a selection of bond accounting for the smaller dimensions of (C5O5)2– (with re-
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J. Ribas, N. Ray Chaudhuri et al.
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teraction, respectively. E1/k, the effect of spin-orbit coupling
and site distortion, is of the order of +100 K.[28,29] Excellent
results have been reported in one- and two-dimensional co-
balt() complexes.[28]
The χMT vs. T plot for 1 (χM is the molar magnetic
susceptibility for one CoII ion) is shown in Figure 8. A χMT
value of 3.27 cm3 mol–1 K at 300 K is a typical value for the
CoII system.[30,31] Upon decreasing the temperature, the
χMT values decrease continuously to 1.91 cm3 mol–1 K at
2 K. To calculate an estimated J value we used the Rueff
expression, which suitable for any temperature greater than
the possible Tc.[28] The fit values obtained with this pro-
cedure are: A + B = 3.5 cm3 mol–1 K, in agreement with
those given in the literature.[28] The E1/k value of 69.09 K
is of the same magnitude as those reported by Rueff et al.
for several one- and two-dimensional cobalt() complex-
es.[30b] As for the value found for the antiferromagnetic ex-
change interaction, it is very weak (E2/k = 0.21 K), corre-
sponding to J = –0.42 K (ca. –0.3 cm–1), according to the
Ising chain approximation, χMT = exp(J/2kT) (Figure 8).
The reduced magnetization curve, M/Nβ, at 2 K tends to
2.35 Nβ at 5 T, a typical value for isolated or quasi-isolated
cobalt() ions (Figure 8 inset).
Figure 7. Crystal packing of complex 3 viewed down the c axis
showing the terephthalate anions encapsulated between the -
Mn(H2O)4-(4,4Ј-bipy)- polymers [dotted lines indicate H-bonds,
symmetry operation: (Ј) –x + 1/2, y, –z + 3/2; (ЈЈ) –x + 1/2, y, –z +
1/2].
spect to tp) in the latter, an additional water molecule was
detected in the lattice in order to favor the H-bonding inter-
actions.
Magnetic Properties
Although the crystal nets consist of a two-dimensional
structure with terephthalate and bpp or bpds as bridging
ligands in complexes 1 and 2, respectively, we assumed the
possible couplings between the long amines bpp and bpds
to be zero. With this hypothesis, the magnetic data can be
interpreted as being derived from a pseudo-one-dimen-
sional structure formed by cobalt() and manganese() ions
(for 1 and 2, respectively) linked by terephthalate at a long
distance. For complex 3, the terephthalate dianion remains
encapsulated and the manganese ions are bridged by long
4,4Ј-bipy ligands (Mn···Mn = 11.565 Å). Such a type of
bridging ligand usually gives negligible antiferromagnetic
interactions,[23] therefore we did not study the magnetic be-
havior.
Complex 1
Figure 8. Plot of χMT vs. T for complex 1 (solid line represents
the best fit using the Rueff formula). Inset: plot of the reduced
magnetization (M/Nβ) vs. H at 2 K for complex 1.
4
Considering the spin-orbit coupling due to the T1g
ground state for octahedral CoII complexes,[24] precise cal-
culations to derive the J parameter from experimental data
in all the temperature range are not possible except for di-
nuclear[25] or small polynuclear complexes.[26] One-dimen-
sional systems of CoII are frequently associated with aniso-
tropic Ising systems, and they can be fitted in the low-tem-
perature zone by assuming again an effective spin, SЈ, of
½.[27] More recently, Rueff et al.[28] have proposed a phe-
nomenological approach for some low-dimensional CoII
systems that allows an estimation of the strength of the
antiferromagnetic exchange interactions. They postulated
the phenomenological equation:
Complex 2
The χMT vs. T plot is given in Figure 9 for one manga-
nese() ion. The χMT values start at 4.35 cm3 mol–1 K, cor-
responding to the value for one isolated manganese() ion
(with g Ϸ 2.00). This value decreases smoothly to close to
4.0 cm3 mol–1 K at 2 K. Such behavior is typical for a very
weak antiferromagnetic coupling between manganese()
ions in the chain. The magnetism of this kind of one-dimen-
sional MnII system has been studied theoretically mainly by
Fisher by assuming an infinite number of classical spins (S
= 5/2).[32] The best-fit parameters were: J = –0.045 0.01, g
= 2.00 0.004, and R = 4.1×10–3 (R is the agreement factor
AχMT = A exp(–E1/kT) + B exp(–E2/kT)
where A + B is the Curie constant [approx. 2.8– defined as Σi[(χMT)obs – (χMT)calc]2/Σi[(χMT)obs]).[33] The g
3.4 cm3 mol–1 K for octahedral cobalt() ions], and E1 and value agrees perfectly with that expected for a manganese()
E2 represent the “activation energies” corresponding to the ion (S = 5/2, g = 2.00). The reduced magnetization (Fig-
spin-orbit coupling and the antiferromagnetic exchange in- ure 9, inset) is also indicative of a very weak antiferromag-
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MnII/CoII-Terephthalate Frameworks using Dipyridine Coligands
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netic coupling. The experimental values tend to 4.8 Nβ and bonding. It should be noted that after dehydration the net-
practically follow the Brillouin formula at 2 K for S = 5/2 work in 2 collapses as the terephthalate carboxylate fails to
and g = 2.0.
function here as a chelate to attain octahedral geometry,
which is a requirement for the existence of MnII in the poly-
meric networks according to the crystal structure (Fig-
ure 4).
Complex 3 is thermally stable up to 100 °C, a lower tem-
perature than that of 2. It undergoes dehydration in two
steps that overlap each other and is fully dehydrated at
150 °C. The dehydrated species collapses immediately upon
further heating as the manganese centers fail to attain the
required geometry after removal of their water molecules.
Conclusions
We have reported the syntheses, crystal structures, low-
temperature magnetic studies, and thermal behaviors of
three metal–organic hybrid polymeric networks. The tp and
bipyridine ligands in complexes 1 and 2, respectively, take
part in formation of a covalently bonded 2D parallel inter-
penetrated polymeric architecture, whereas in complex 3 the
tp anions are encapsulated by 1D Mn(4,4Ј-bipy) chains.
The presence of uncoordinated bpds ligands in 2 between
the interpenetrated layers leads to formation of a wafer-
like structure where bpds is anchored to coordinated water
molecules through H-bonds. All these crystal structures
contain extensive H-bonding between the water molecules
and the tp oxygens, which increases the dimensionality of
the architectures to 3D. As a consequence, in order to favor
H-bonding connections the tp carboxylate groups show dif-
ferent conformations, as indicated by the dihedral angles of
the carboxylates with respect to the phenyl ring. These are
about 30° in complexes 1 and 2, and quite different in 3
(about 5° and 22°). The variable-temperature magnetic data
reveal weak antiferromagnetic coupling for 1 and 2.
Figure 9. Plot of χMT vs. T for complex 2 (solid line represents the
best fit). Inset: plot of the reduced magnetization, M/Nβ (solid line
indicates the Brillouin formula for S = 5/2 and g = 2.0).
The small antiferromagnetic J values for 1 and 2 may be
interpreted as being due to the terephthalate bridging li-
gand. When the coordination mode is that shown in
Scheme 1A (complexes 1 and 2), the terephthalate bridging
ligand shows a very small antiferromagnetic coupling for
M = MnII, CoII, NiII, and CuII.[33] To the best of our
knowledge, only two Mn complexes with this kind of
coordination have
[{Mn(dca)(terpy)(MeOH)}2(µ-ta)][34] and [Mn2(phen)4-
(H2O)2(µ-ta)](ClO4)2.[35] The calculated
values of
been reported to
date
−
J
–0.06 cm–1 and –0.065 cm–1, respectively, are in good agree-
ment with that found in complex 2. All these very weak J
values are in accordance with the MO calculations made by
Cano et al.,[35] which show that a terephthalate bridge is
not a suitable bridging unit to mediate significant exchange
coupling.
Experimental Section
Materials: High purity 4,4Ј-trimethylenedipyridine (98%), 4,4Ј-bi-
pyridyl disulfide (Aldrithiol-4; 98%), 4,4Ј-dipyridyl (98%), diso-
dium terephthalate (96%), and manganese() chloride tetrahydrate
(98%) were purchased from the Aldrich Chemical Co. Inc. and
were used. All other chemicals were of AR grade.
Thermal Studies
The pink complex 1 starts to lose its coordinated water
molecules, upon heating, at around 125 °C and becomes de-
hydrated at 190 °C, yielding the species [Co(bpp)(tp)] (1a,
blue), which reverts to 1 in a humid atmosphere (relative
humidity of ca. 60%) at ambient temperature. This dehy-
dration-rehydration process involves an octahedral h tetra-
hedral transformation of CoII that shows thermochromism,
as evidenced from the solid state electronic spectra [(19455,
ca. 16666, and 8510 cm–1 for 1) and (19300, 17985, 14000–
15500, and 8802 cm–1 for 1a; Figure S1)] and room tem-
perature magnetic measurements [µeff for 1 (see magnetic
properties) and for 1a 4.82 µB (at 300 K)].
Physical Measurements: Elemental analyses (carbon, hydrogen, and
nitrogen) were performed with a Perkin–Elmer 240C elemental an-
alyzer. IR spectra were measured as KBr pellets on a Nicolet 520
FTIR spectrometer. Magnetic measurements were carried out with
polycrystalline samples (20–30 mg) by the Servei de Magnetoquím-
ica, Universitat de Barcelona, with a Quantum Design MPMS
SQUID magnetometer operating at a magnetic field of 0.1 T, in
the temperature range 2–300 K. The diamagnetic corrections were
evaluated from Pascal’s constants. Thermogravimetric analyses
were carried out with a Mettler Toledo Star system. The UV/Vis
reflectance spectra were recorded between 300–1400 nm with a Hit-
achi U-3501 spectrophotometer at room temperature in the solid
state.
Complex 2 starts to lose water molecules, upon heating,
at 110 °C and shows continuous decomposition with con-
comitant formation of an intermediate species. The initial
temperature of dehydration suggests the presence of coordi-
Crystallographic Data Collection and Refinement: Crystal data and
nated water molecules as well as their involvement in H- details of data collections and refinements for the structures re-
Eur. J. Inorg. Chem. 2005, 4646–4654
www.eurjic.org © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4651

J. Ribas, N. Ray Chaudhuri et al.
FULL PAPER
ported are summarized in Table 2. Diffraction data for all com-
plexes were carried out on a Rigaku Mercury CCD area detector
using graphite-monochromated Mo-Kα radiation. Cell refinement,
indexing, and scaling of the data sets were carried out using the
Crystal package.[36] All the structures were solved with SIR97[37]
and subsequent Fourier analyses[38] and refined by the full-matrix
least-squares method based on F2 with all observed reflections.[38]
Most of the water hydrogens detected in the difference Fourier map
were restrained with a fixed O–H bond length (0.85 Å). All the
calculations were performed using the WinGX System, Ver
1.64.05.[39]
terephthalate (1 mmol, 0.210 g) and stirred for 20 min. Then, a
methanolic solution (5 mL) of bpds (1 mmol, 0.220 g) was poured
slowly into it and the resulting mixture was refluxed for 4 h. It was
then allowed to cool and filtered. The filtrate was kept in a CaCl2
desiccator and shiny, yellowish single crystals suitable for X-ray
determination were obtained after a few days. Yield: 0.500 g (72%).
C28H24MnN4O6S4 (695.70): calcd. C 48.30, H 3.45, N 8.05; found
C 48.29, H 3.45, N 8.04. IR: ν = 3500–3090 (s), 3008 (w), 2904 (w),
˜
1579 (vs), 1566 (vs), 1379 (s), 1319 (w), 1222 (vw), 815 (w), 758
(w), 704 (w) cm–1.
[Mn(4,4Ј-bipy)(H2O)4]·(tp) (3): This complex was synthesized fol-
lowing the procedure adopted for complex 2 using 4,4Ј-bipy
(1 mmol, 0.156 g) instead of bpds. Colorless crystals of 3 suitable
for X-ray diffraction were obtained from the CaCl2 desiccator after
a few days. Yield: 0.313 g (70%). C18H20MnN2O8 (447.30): calcd.
CCDC-262151 to -262153 (for 1–3, respectively) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
C 48.29, H 4.47, N 6.26; found C 48.28, H 4.48, N 6.27. IR: ν =
˜
3500–3020 (s, v br.), 1656 (vw), 1610 (s), 1559 (vs), 1419 (vw), 1368
Table 2. Crystallographic data and details of structure refinements
for complexes 1–3.
(vs), 1067 (vw), 807 (w), 752 (w), 632 (vw) cm–1.
Supporting Information: A table containing H-bonding parameters,
the thermogravimetric curves of complexes 1, 2, and 3, and the
solid-state electronic spectra for complexes 1 and 1a, see also foot-
note on the first page of this article.
1
2
3
Empirical formula
Mr [gmol–1
Crystal system
Space group
a [Å]
C21H22CoN2O6 C28H24MnN4O6S4 C18H20MnN2O8
]
457.35
monoclinic
C2/c
16.883(7)
15.579(6)
18.317(8)
123.778(3)
4004.3(29)
8
1.517
0.899
1896
27.48
695.70
orthorhombic
Fddd
15.635(7)
16.663(8)
45.74(2)
90.00
11916.2(95)
16
1.551
0.773
5712
27.48
49378
3696
0.079
2125
447.30
monoclinic
P2/n
6.995(4)
11.565(6)
11.420(6)
101.824(6)
904.2(8)
2
1.643
0.782
462
27.48
Acknowledgments
b [Å]
c [Å]
β [°]
Volume [Å3]
Z
N. R. C. thanks Council of Scientific and Industrial Research, New
Delhi, and J. R. thanks the Spanish Goverment (BQU2003/00539)
for financial support.
Dcalcd. [gcm–3
]
µ (Mo-Kα) [mm–1
F(000)
]
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θmax [°]
Reflection collected 32844
14916
2165
0.038
Unique reflections
Rint
Observed reflec-
tions I Ͼ 2σ(I)
4735
0.035
3643
1625
Parameters refined 287
Goodness of fit (F2) 1.087
201
1.058
0.0517
0.0983
0.381, –0.337
152
1.019
0.0350
0.0684
0.282, –0.295
[a]
R1 [I Ͼ 2σ(I)]
0.0397
0.0798
0.264, –0.232
[a]
wR2
∆ρ [eÅ–3
]
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = [Σw(Fo – Fc ) /Σw(Fo2)2]1/2
.
2
2 2
[Co(bpp)(tp)(H2O)2] (1): A methanolic solution (5 mL) of bpp
(1 mmol, 0.198 g) was added dropwise to a methanolic solution
(5 mL) of Co(NO3)2·6H2O (1 mmol, 0.291 g) with constant stir-
ring. An aqueous solution (10 mL) of disodium terephthalate
(1 mmol, 0.210 g) was added to the resulting light-pink reaction
mixture and stirred for 1 h. A deep-pink complex separated out.
Single crystals suitable for X-ray analysis were obtained by diffus-
ing a methanolic solution (10 mL) of bpp into an aqueous (10 mL)
layer containing Co(NO3)2·6H2O and disodium terephthalate (1:1)
in a tube. The deep-pink crystals deposited at the junction of the
two layers after a few days. Yield: 0.320 g (70%). C21H22CoN2O6
(457.35): calcd. C 55.10, H 4.81, N 6.12; found C 55.18, H 4.80, N
6.16. IR: ν = 3604 (vs), 3256 (s), 3071 (w), 2943 (s), 2872 (vw),
1615 (vs), 1546 (vs), 1501 (w), 1380 (s) 1018 (w), 795 (s), 757 (s),
˜
510 (w) cm–1.
[Mn(bpds)(tp)(H2O)2]·(bpds) (2): A methanolic solution (10 mL) of
manganese() chloride tetrahydrate (1 mmol, 0.197 g) was allowed
to react with an aqueous solution (10 mL) of disodium
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 4646–4654

MnII/CoII-Terephthalate Frameworks using Dipyridine Coligands
FULL PAPER
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