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Inclusion of organic pyridin-3-onate anions by sheets of hydroxo-bridged Cu(II) dimeric complexes
Sonia Iglesias, Oscar Castillo, Antonio Luque *, Pascual Roman
Departamento de Quımica Inorganica, Universidad del Paıs Vasco, Apartado 644, E-48080 Bilbao, Spain
Received 30 October 2002; accepted 20 January 2003
Abstract
A pillared layered compound [Cu2(m-OH)2(phen)2(H2O)2][Cu2(m-OH)2(HCO3)2(phen)2](3-pyO)2 �/10H2O (1) [phen�/1,10-phenan-
throline, 3-pyOH�/3-hydroxypyridine] has been prepared and characterized by X-ray diffraction analysis, thermoanalytical
techniques and variable-temperature susceptibility measurements. The compound crystallizes in the triclinic group P1 with cell
parameters: a�/11.499(2), b�/11.600(2), c�/13.374(3) A, a�/71.88(2)8, b�/78.25(2)8, g�/71.36(2)8. Two different centrosymmetric
dimers coexist in the crystal structure, one of them is neutral and the other one is a cation. In both dimeric entities the Cu(II) atoms
show distorted square-pyramidal environments with the basal plane formed by the two nitrogen atoms of the phenantroline ligand
and the oxygen atoms of two bridging hydroxyl groups. The apical positions are filled by the oxygen atom from a water molecule
(cationic dimer) or from a monodentate hydrogencarbonato ligand (neutral dimer). The dimers interact by means of hydrogen
bonds and offset face-to-face aromatic interactions to form cationic layers. The pyridin-3-onate anions and the crystallization water
molecules occupy the space between the layers and cross-link the nearest-neighbour layer by means of hydrogen bonds to afford a
three-dimensional structure. Variable temperature measurements show a ferromagnetic intradimer interaction with a J value of �/
125.5 cm�1.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Copper complexes; Hydroxo complexes; Intercalation compound; Magnetic properties
1. Introduction
Crystal engineering of organized metal-organic su-
pramolecular architectures has evolved rather rapidly in
recent years because of their intrinsic aesthetic appeal
and potentially exploitable properties in areas such as
inclusion or intercalation system for ion- or molecule-
exchange, adsorption, shape-selective catalysis, non-
linear optical and magnetic materials [1�/4]. Most often,
interestingly one-, two- and three-dimensional coordi-
nation polymers have been made by employing the
covalent linkages provided by suitable bridging ligands.
In addition, there have been studies that utilise non-
covalent linkages such as hydrogen bonding [5,6] and
aryl�/aryl stacking interactions [7] to increase the
dimensionality of metal complex frameworks in order
to generate three-dimensional compounds with novel
properties. Thus, one of the strategies for the rational
synthesis of crystalline metal assemblies is to utilise the
hydrogen bonding and/or p�/p stacking capability of the
ligands in addition to their coordination ability. By
utilising these ideas, several compounds with layer or
chain structure have been synthesised intercalating small
organic molecules having multihydrogen bonding sites.
We describe herein a new metal-organic assembled
compound [Cu2(m-OH)2(phen)2(H2O)2][Cu2(m-OH)2(H-
CO3)2(phen)2](3-pyO)2 �/10H2O (1) which is constructed
from doubly aromatic stacking and hydrogen bond-
supported layers of di-m-hydroxo dimeric complexes and
pyridin-3-onate anions. These charged organic mole-
cules are introduced between the cationic layers and
joined to them by means of hydrogen bonding and
electrostatic interactions. In addition to the crystal
* Corresponding author. Tel.: �/34-946-012 701; fax: �/34-944-648
500.
E-mail address: qipluara@lg.ehu.es (A. Luque).
Inorganica Chimica Acta 349 (2003) 273�/278
www.elsevier.com/locate/ica
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00085-9
structure, magnetic and thermal properties are also
described.
2. Experimental
2.1. Synthesis
All chemicals are reagent grade and used as received
without further purification. An aqueous solution (30
ml) of Cu(NO3)2 �/3H2O (0.246 g, 1.0 mmol) and 1,10-
phenanthroline (0.198 g, 1.0 mmol) was added dropwise
and slowly to a vigorously stirred solution of 3-hydro-
xypyridine (0.190 g, 2.0 mmol) and K2CO3 (0.276 g, 2.0
mmol) in water (30 ml). Prismatic blue crystals began to
form at ambient temperature within 1 week. Yield: 75�/
80% (based on metal). Anal . Found: C, 46.0; H, 4.6; Cu,
16.3; N, 8.9. Calc. for C60H70Cu4N10O24: C, 45.9; H,
4.5; Cu, 16.2; N, 8.9%. Main IR features (cm�1, KBr
pellet): 3420s, 3200s for [n (O�/H)]; 3080s for [n(C�/H)];
1645sh, 1625sh for [d (O�/H)]; 1610m, 1590m, 1570m for
[nas(C�/N)�/nas(C�/C)]; 1400m, 1385m, 1340m for
[ns(CO2)]; 1245m, 1225m, 1140m, 1105w, 1100w for
[dip(C�/H)]; 1040w for [ns(C�/O)]; 875m, 835s, 815w for[d (CO2)]; 780w, 720s, 680w, 645m, 560w for [dop(C�/H)];
470w, 430w for [nas(Cu�/O)].
2.2. Physical measurements
Elemental analyses (C, H, N) were performed on aPerkin�/Elmer CHN-2400 analyser. Metal content was
determined by absorption spectrometry. IR spectra of
the KBr discs were recorded on a Nicolet 740 FT-IR.
Magnetic susceptibility measurements were carried out
on polycrystalline samples with a Quantum Design
SQUID susceptometer operating at 1000 and 5000 G.
Thermal analysis (TG/DTG/DTA) were carried out with
a TA Instruments SDT 2960 thermal analyser in asynthetic air atmosphere (heating rate: 58 min�1).
2.3. Crystal structure determination and refinement
Data collection for compound 1 was carried out at
293(2) K on an Enraf�/Nonius CAD4 diffractometerwith graphite-monochromated Mo Ka radiation (l�/
0.71073 A). Crystallographic data are given in Table 1.
Absorption correction was not applied. The crystal
structure was solved by using the SIR-92 program [8]
and refined by full-matrix least-squares on F2 including
all reflections (SHELXL-93) [9]. All non-hydrogen atoms
were anisotropically refined, except those belonging to
the crystallization water molecules. All the hydrogenatoms were located in the Fourier difference maps.
However, they were not refined. Hydrogen atoms of
crystallization water molecules are not located.
3. Results and discussion
The assembled structure of compound 1 consists of
uncoordinated water molecules, layers constructed from
centrosymmetric hydroxo-bridged Cu(II) dimers and
organic pyridin-3-onate anions which are introduced
between the layers. An ORTEP drawing of the asym-
metric unit and the symmetry-related fragments for 1 is
shown in Fig. 1, and selected bond distances angles are
listed in Table 2.
There are two centrosymmetric dimeric complexes in
the layer, one of them is neutral and the other one is a
cation. The geometries around the metal ions are similar
to each other: a distorted square-pyramidal polyhedron
[CuN2O3] with the basal plane comprised of two
nitrogen atoms from the 1,10-phenanthroline ligands
[Cu�/N: 2.022(5)�/2.038(5) A] and the oxygen atoms of
two bridging hydroxo groups [Cu�/O: 1.935(5)�/1.953(5)
A]. The four equatorial atoms at each Cu(II) atom are
practically coplanar [maximum deviation from the least-
squares planes is 0.09 A for N18], but the copper atoms
are displaced 0.204(2) A [Cu1, neutral] and 0.183(2) A
[Cu2, cation] out of this plane towards the apical
positions which are occupied by a non-protonated
oxygen atom of a hydrogencarbonato ligand [Cu1�/O4:
2.201(5) A] (neutral entity) and the oxygen atom of a
Table 1
Crystal data and structure refinement parameters for [Cu2(m-
OH)2(phen)2(H2O)2][Cu2(m-OH)2(HCO3)2(phen)2](3-pyO)2 �/10H2O
(1) a
Empirical formula C60H70Cu4N10O24
Formula weight 1569.46
Space group /P1
a (A) 11.499(2)
b (A) 11.600(2)
c (A) 13.374(3)
a (8) 71.88(2)
b (8) 78.25(2)
g (8) 71.36(2)
V (A3) 1595.7(6)
Z 1
Dobs (g cm�3) 1.62(1)
Dcalc (g cm�3) 1.633
m (mm�1) 1.406
Crystal size (mm) 0.30�/0.30�/0.25
Max. u (8) 30
Reflections collected 9883
Independent reflections 9290
Data, restrains, parameters 9290, 0, 417
Reflections with I ]/2s (I ) 5248
Final R1, wR2 indices [I ]/2s (I )] 0.0668, 0.1458
All data 0.1495, 0.1813
Goodness-of-fit S on F2 1.008
Largest difference peak, hole (e A�3) 1.219, �/0.762
a R1�/a (jjFoj�/jFcjj)/a jFoj, wR2�/[a w (Fo2�/Fc
2)2/a w (Fo2)2]1/2;
S�/[a w (Fo2�/Fc
2)2/(n�/p )]1/2; w�/1/s2(Fo2)�/(0.1894P )2 with P�/
(jFoj2�/2jFcj2)/3, where n is the number of observed reflections and p
is the number of parameters refined.
S. Iglesias et al. / Inorganica Chimica Acta 349 (2003) 273�/278274
water molecule [Cu2�/O3w: 2.212(6) A] (cation). The
Cu� � �Cu distance within the dinuclear units are 2.894(1)
[Cu1] and 2.884(1) A [Cu2]; while the Cu�/O�/Cu angle
are 95.8(2) and 96.3(2)8, respectively. Both dimeric
entities show a chair conformation with dihedral angles
of 17.7(2) and 14.9(2)8 between the 1,10-phenanthroline
ligand and the strictly planar Cu2O2 core. The shift of
the hydroxide bridged hydrogen atom respect to the
Cu2O2 core for the cationic dimer [H2�/O2� � �O2b:
41(2)8] is smaller than that found for the neutral entity
[H1�/O1� � �O1a: 61(2)8] in which the hydroxide groups
are involved in an intramolecular hydrogen bonds
(Table 3) with the non-protonated oxygen atom of the
carbonato ligand [O1� � �O5a: 2.756(8) A].
The dimeric entities form sheets which are spreading
out along the ac -plane (Fig. 2) and supported by both
the off-set face-to-face interactions between the aro-
matic rings of 1,10-phenanthroline ligands from adja-
cent complexes [nearest neighbour C(114)�/N(28)
distance: 3.41(1) A] and hydrogen bonds involving the
coordination water molecule and the oxygen atoms of
the hydrogencarbonato ligand. There are not any direct
interaction between the sheets.
The oxygen atoms of the apical ligands project
forward to the outside of the layer to create channels
along the b -direction. Planar pyridin-3-onate anions are
included in the channels and serve as pillars to link
adjacent sheets to afford an extended 3D network. This
is achieved through two kinds of hydrogen bond
occurring between the organic anion and the complexes.
The coordinated water molecule of the cationic dimer is
hydrogen bonding donor attached to the pyridinic
nitrogen atom on the organic anion and the exocyclic
O� atom stablishes a hydrogen bond with the proto-
nated oxygen atom of a HCO3� coordinated anion
belonging to the adjacent sheet. As expected for negative
Fig. 1. An ORTEP drawing of the two dimeric entities and the organic anion showing the hydrogen bonding contacts.
Table 2
Selected bond lengths (A) and angles (8) for compound 1 a
Neutral dimer
Bond lengths
Cu(1)�/O(1) 1.945(5) Cu(1)�/N(18) 2.022(5)
Cu(1)�/O(1a) 1.953(5) Cu(1)�/O(4) 2.201(5)
Cu(1)�/N(11) 2.038(5) Cu(1)� � �Cu(1a) 2.894(1)
Bond angles
O(1)�/Cu(1)�/O(1a) 84.2(2) N(18)�/Cu(1)�/N(11) 81.5(2)
O(1)�/Cu(1)�/N(18) 97.5(2) O(1)�/Cu(1)�/O(4) 98.8(2)
O(1a)�/Cu(1)�/N(18) 170.5(2) O(1a)�/Cu(1)�/O(4) 97.5(2)
O(1)�/Cu(1)�/N(11) 166.2(2) N(18)�/Cu(1)�/O(4) 91.5(2)
O(1a)�/Cu(1)�/N(11) 94.7(2) N(11)�/Cu(1)�/O(4) 95.0(2)
Cu(1)�/O(1)�/Cu(1a) 95.8(2)
Cationic complex
Bond lengths
Cu(2)�/O(2) 1.935(5) Cu(2)�/N(28) 2.025(5)
Cu(2)�/O(2b) 1.938(4) Cu(2)�/O(3w) 2.212(6)
Cu(2)�/N(21) 2.022(5) Cu(2)� � �Cu(2b) 2.884(1)
Bond angles
O(2)�/Cu(2)�/O(2b) 83.7(2) N(21)�/Cu(2)�/N(28) 81.7(2)
O(2)�/Cu(2)�/N(21) 168.7(2) O(2)�/Cu(2)�/O(3w) 94.8(2)
O(2b)�/Cu(2)�/N(21) 95.7(2) O(2b)�/Cu(2)�/O(3w) 96.4(2)
O(2)�/Cu(2)�/N(28) 96.8(2) N(21)�/Cu(2)�/O(3w) 96.5(2)
O(2b)�/Cu(2)�/N(28) 170.0(2) N(28)�/Cu(2)�/O(3w) 93.6(2)
Cu(2)�/O(2)�/Cu(2b) 96.3(2)
a Symmetry codes: (a) �/x , �/y , �/z ; (b) �/1�/x , �/y , �/1�/z .
Table 3
Hydrogen bonds (A, 8) in compound 1 a
D�/H� � �A D�/H H� � �A D� � �A D�/H� � �A
O1�/H1� � �O5a (intra) 0.78 2.06 2.756(8) 150
O2�/H2� � �O6b 0.84 2.10 2.876(9) 154
O6�/H6� � �O37c 0.82 1.72 2.512(9) 161
O3w�/H3A� � �N31d 0.79 1.99 2.761(9) 164
O3w�/H3B� � �O5e 0.82 1.86 2.662(9) 164
a Symmetry codes: (a) �/x , �/y , �/z ; (b) �/1�/x , y , z ; (c) 1�/x , 1�/
y , �/z ; (d) �/1�/x , y , �/1�/z ; (e) �/x , �/y , �/1�/z .
S. Iglesias et al. / Inorganica Chimica Acta 349 (2003) 273�/278 275
charge assisted hydrogen bonding, the distances of this
last one are in the range of strong hydrogen bonds. The
dihedral angle between the planar anions and the ac -
plane is 738. The crystal architecture of compound 1
resembles the framework of a building, the sheets would
be the floors and the pyridin-3-onate anions serve as
pillars. This crystal building is similar to that found for
the compounds {(pyOH2)2[M(CA)2(H2O)2]}n (M�/
Cu2�, Co2�; CA�/chloranilate dianion; pyOH2�/n-
hydroxipyridinium cation (n�/3, 4) [10] in which planar
pyOH2� cations are perpendicular included between
anionic layers of chloroanilato mononuclear complexes
supported by both the stacking and the hydrogen
bonding interactions.
The organic anions in 1 are parallel stacked along the
b -axis but no face-to-face or edge-to-edge interactions
between their aromatic rings have been found. The
crystallization water molecules are inserted between the
sheets and the pyridin-3-onate anions, and they are
linked together and to the oxygen atoms of the complex
sheets and the pyO� counterion by means of an
extensive network of hydrogen bonds. The thermal
degradation of the title compound in synthetic air
atmosphere shows that the crystallization water mole-
cules are released in an endothermic process in the
temperature range 55�/110 8C (exp. weight lost 11.38%,
calc. 11.47%). Immediately, the compound undergoes a
progressive loss of mass between 110 and 175 8Cattributable to the lost of the coordination water
molecule (exp. 2.39%, calc. 2.29%). The total degrada-
tion of the anhydrous compound yields CuO above
430 8C (exp. 80.34%, calc. 79.73%).
Fig. 2. (a) Layer of dimeric complex entities, linked by stacking aromatic�/aromatic interactions (double dashed lines) and hydrogen bonds (dotted
lines). (b) Packing diagram of compound 1 viewed along the crystallographic c axis. (c) Packing diagram of compound 1 viewed along the
crystallographic a axis.
S. Iglesias et al. / Inorganica Chimica Acta 349 (2003) 273�/278276
Variable temperature magnetic susceptibility mea-
surements (2.0�/300 K) were carried out on a powdered
sample of the complex taken from the same uniform
batches used for structural determination. The measure-ments were repeated several times and with different
magnetic fields, and all give the same results. The xMT
(xM being the molar magnetic susceptibility per di-
nuclear entitiy) versus T curve is plotted in Fig. 3. At
300 K the xMT starts at a value of about 0.88 cm3 K
mol�1 and increases to 1.13 cm3 K mol�1 at about 30 K
after which it decreases slightly to 1.11 cm3 K mol�1 at
2 K. This curve is as expected for a dominantferromagnetic coupling with weak intermolecular anti-
ferromagnetic interactions and/or zero-field splitting of
the triplet ground state which would account for the
decrease of xMT at T B/8 K.
In the crystal structure we can distinguish two
different dimeric entities; however, taking into account
the slight differences between them, a similar value of
the exchange coupling constant can be assumed. Theexperimental data were fitted to a modified Bleaney�/
Bowers expression [11]
xM�2Ng2b2
k(T �U)[3 � exp(�J=kT)];
where N , g , b , k and T have their usual meanings. A
Weiss constant (U ) was introduced into the temperatureterm to account for both intermolecular effects and
zero-field splitting. The fit was accomplished by mini-
misation of R�/ai [(xMT )obs(i)�/(xMT )calc(i)]2/ai [(xM-
T )obs(i)]2 by least-squares procedure. The best-fitted
parameters obtained were J�/125.5 cm�1, g�/2.14,
U�/�/0.06 K and R�/4.4�/10�5. All of our attempts
to modelize the magnetic behaviour with two different
intradimer exchange coupling parameters led to very
similar values of the exchange parameters.
Hydroxo- and alcoxo-bridged dinuclear compoundsof transition metals have received much attention
because of their different magnetic properties [4,12�/
15]. One of the most extensively studied families is
that of di-m-hydroxo-bridged Cu(II) binuclear com-
plexes for which a classical correlation between the
Cu�/O�/Cu bond angle (8 ) and the experimental ex-
change constant (J ) (J�/�/74.538�/7270 cm�1) indi-
cates that those complexes are antiferromagnetic for8�/988, but ferromagnetic for smaller angles [16]. The
sign of the exchange parameter for 1 is in agreement
with this correlation [8 values are 95.8(2) and 96.3(2)8,for neutral and cationic entities, respectively]. However,
recently advanced theoretical calculations using differ-
ent density functional methods have demonstrated that
another structural parameters such as small variances in
the Cu�/O(bridge) distances, the out of plane displace-ment of the hydroxo hydrogen atom, the non-planarity
of the Cu2O2 core, and the distance from copper atom to
the basal plane can play an important role on the fine
tuning of the exchange coupling [17�/19].
4. Conclusions
In this paper a novel hydroxo-bridged Cu(II) com-
pound with the organic pyridin-3-onate anion has been
characterized from magnetic, structural and thermalpoints of view. The crystal structure analysis shows the
coexistence of neutral and cationic hydroxo-bridged
Cu(II), held together by means of non-covalent interac-
tions to form sheets. The organic pyridin-3-onate anions
and the crystallization water molecules are inserted
between the sheets and stabilize the crystal structure
by means of hydrogen bonds. The magnetic studies
reveal the occurrence of intradimer ferromagnetic inter-actions, which are in agreement with the Cu�/O�/Cu
angle values below 988.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 194632. Copies of this
information may be obtained free of charge from TheDirector, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: �/44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk/conts/
retrieving.html).
Fig. 3. Thermal dependence of xMT for title compound: (k)
experimental data; (*/) best theoretical fit (see text). The inset shows
the field dependence of the magnetisation at 2 K: (k) experimental
data; (*/) a guide to the eye.
S. Iglesias et al. / Inorganica Chimica Acta 349 (2003) 273�/278 277
Acknowledgements
This work has been carried out with the financial
support of the Universidad del Paıs Vasco/EuskalHerriko Unibertsitatea (UPV/EHU) (Project UPV/
EHU 169.310-EA-8057/2000). We thank F. Lloret for
his assistance with susceptibility measurements.
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