Note

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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