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Journal of Molecular Structure 825 (2006) 60–69

2,2 0-Oxydiacetato-bridged complexes containing Sm(III)and bivalent cations. Synthesis, structure, magnetic properties

and chemical speciation

J. Torres a, F. Peluffo a, S. Domınguez b, A. Mederos b, J.M. Arrieta c, J. Castiglioni d,F. Lloret e, C. Kremer a,*

a Departamento Estrella Campos, Quımica Inorganica, Facultad de Quımica, CC 1157, Montevideo, Uruguayb Departamento de Quımica Inorganica, Universidad de La Laguna, Tenerife, Spain

c Departamento de Quımica Inorganica, Universidad del Paıs Vasco – EHU, Bilbao, Spaind LAFIDESU, DETEMA, Facultad de Quımica, CC 1157, Montevideo, Uruguay

e Departamento de Quımica Inorganica, Universidad de Valencia, Spain

Received 24 February 2006; received in revised form 31 March 2006; accepted 31 March 2006Available online 5 June 2006

Abstract

Heterometallic compounds containing Sm(III), bivalent cations M (M = Cu, Ni, Co, Mn, Ca, Mg), and 2 0,2 0-oxydiacetate (oda) asconnecting ligand have been prepared and characterized. The complexes can be formulated as [Sm2M3(oda)6] Æ xH2O. The structure of[Sm2Cu3(oda)6(H2O)6] shows the presence of the Sm(III) coordinated by six carboxy and three ether oxygen atoms, and the Cu(II) cationbonded to four carboxy oxygens and two molecules of water. An open 3D framework is observed, containing large hexagonal channels.At room temperature, the polynuclear complexes behave as built by magnetically isolated paramagnetic ions, but at low temperatures,very weak antiferromagnetic interactions M – M are predominant. The chemical systems were also investigated in solution (25.0 �C,I = 0.5 M Me4NCl) by potentiometry. The same kind of polynuclear species have been found.� 2006 Elsevier B.V. All rights reserved.

Keywords: Lanthanide; 2,20-Oxydiacetate; Polynuclear complexes; Carboxylato bridge

1. Introduction

During the last ten years, heterobimetallic complexescontaining Cu(II) and lanthanide ions (Ln) bridged by car-boxylic acids have been reported and studied [1–13]. Otherexamples, though scarce, include analogous complexescontaining other metals instead of copper [14–16]. In suchcompounds, metal ions are connected by carboxylatobridges resulting in different structural architectures, fromdiscrete bimetallic complexes to extended 3D arrays.Besides the fascinating structural diversities, these com-

0022-2860/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2006.03.103

* Corresponding author. Tel: +598 2 9249739; fax: +598 2 9241906.E-mail address: ckremer@fq.edu.uy (C. Kremer).

pounds show potential applications in different fields. Theyare appropriate models to study the nature of magneticinteractions between lanthanides and d-transition metalions, and they could be useful materials in separation,catalysis, gas storage and molecular recognition [17–19].A very recent and excellent review accounts for this kindof polynuclear complexes [20].

Among the potential carboxylato bridges, oda (2,2 0-oxy-diacetate) has proved to bridge Ln(III) and Cu(II) with theformation of very interesting structures [1–7]. In these struc-tures, the Ln metal ion is nine coordinated, being surroundedby nine oxygen atoms from three oda ligands. Copper atomsare six coordinated by six oxygen atoms, four from[Ln(oda)3] units (through a l-COO bridge), and two fromwater molecules. The structures [Ln2Cu3(oda)6] Æ 3H2O

J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69 61

(Ln = Gd, Nd), [Ln2Cu3(oda)6(H2O)6] Æ 12H2O (Ln = Dy,Ho, Y, Gd, Eu, Nd, Pr), [Ln2Cu3(oda)6(H2O)6] (Ln = Nd,Er, Yb), and [Ln2Cu3(l2-H2O)(oda)6(H2O)3] Æ 3H2O(Ln = La, Ce) have been reported. Analogous complexeswith Sm, Tb, Tm and Lu have not been studied. The mostinteresting point in the structures is the formation of a 3Dnetwork containing large hexagonal channels of nearly 6Adiameter. The channels contain the lattice water molecules.This type of structures is very interesting for manyapplications. As catalysts for example, they can provideappropriate binding and activation of the reactingmolecules, as well as stabilization of reaction intermediatesand transition states.

Up to now, the studies on these heteropolynuclearcomplexes have been mostly focused on lanthanide-copper compounds at solid state. No reports can befound on the possibility to prepare analogous complexeswith other M(II) transition metals. Moreover, it wouldbe very interesting to know if such polynuclear speciescan also exist in aqueous solution. If so, the complexeswould be potential homogeneous catalysts for manyprocesses.

With this in mind, we decided to investigate the Sm(III)-oda-M(II) (M = Cu, Mn, Ni, Fe, Co, Ca, Zn, Cd, Be, Mg,Pb) and Sm(III)-oda-VO2+ systems, both at solid state andin solution. Samarium has not been previously studied, nei-ther in solution nor at solid state, and provides a newexample to further investigate this interesting series. Chem-ical speciation of these systems at 25.0 �C, I = 0.5 MMe4NCl is reported for the first time. In addition, a fewsystems containing M 0(III) cations (M 0 = Fe, Al) areincluded in this work. We also report susceptibility mea-surements of the magnetically relevant heteropolynuclearspecies.

2. Experimental

2.1. Materials and methods

All common laboratory chemicals were reagent grade,purchased from commercial sources and used withoutfurther purification. Sm(NO3)3 Æ 6H2O, SmCl3 Æ 6H2O,BeSO4 Æ 4H2O, CaCl2 Æ 2H2O, MgCl2 Æ 6H2O, MnCl2 Æ4H2O, NiCl2 Æ 6H2O, ZnCl2, CdCl2 Æ 2.5H2O, CoCl2 Æ6H2O, Cu(NO3)2 Æ 3H2O, CuCl2 Æ 2H2O, Pb(NO3)2,FeSO4 Æ 7H2O, FeCl3 Æ 6H2O, Al(NO3)3 Æ 9H2O, and anaqueous commercial 48% solution of VOCl2, were usedas metal sources. 2,2 0-Oxydiacetic acid solutions wereprepared by weighing the Fluka reagent.

The infrared spectra, as KBr pellets, were obtained froma Bomen MB 102 FT-IR spectrophotometer. Elementalanalysis (C, H) was performed on a Carlo Erba EA 1108instrument. Thermal analysis was performed on a Shimad-zu TGA-50 instrument with a TA 50I interface, using aplatinum cell and nitrogen atmosphere. Experimental con-ditions were 0.5 �C min�1 temperature ramp rate and50 mL min�1 nitrogen flow rate.

2.2. Synthesis of the complexes

2.2.1. Synthesis of [Sm2 Cu3(oda)6] Æ 18H2O(1)

Cu(NO3)2 Æ 3H2O (0.36 g, 1.5 mmol) andSm(NO3)3 Æ 6H2O (0.44 g, 1.0 mmol) were dissolved in10 mL of water. 2,2 0-Oxydiacetic acid (0.40 g, 3.0 mmol)was dissolved in another 10 mL water, and the pH valuewas adjusted to 7.0 with ammonium hydroxide. Both solu-tions were mixed, and a clear blue solution was obtained.After a few minutes a microcrystalline pale blue solid wasobtained, and separated by filtration, washed with water(3 · 2 mL), and dried with acetone (2 · 2 mL) and diethyle-ther (3 · 2 mL). The mother liquour was allowed to evapo-rate slowly for 4–5 days in order to obtain suitable crystalsfor X-ray diffraction. Yield 60–70%. Anal. Calc. forC24H60O48Cu3Sm2: C, 17.9; H, 3.8. Found: C, 19.8; H,4.2%. IR peaks associated to the oda ligand appear at:1605, 1439, and 1124 cm�1. The TGA diagram shows aweight loss of 19.6% in the range 50–100 �C which corre-sponds to the loss of all water molecules, calc. 20.2%.Decomposition point, 216 �C.

2.2.2. Synthesis of [Sm2Ni3 (oda)6] Æ 18H2O(2)

Ni(NO3)2 Æ 6H2O (0.44 g, 1.5 mmol) andSm(NO3)3 Æ 6H2O (0.44 g, 1.0 mmol) were dissolved in10 mL of water. 2,2 0-Oxydiacetic acid (0.40 g, 3.0 mmol)was dissolved in another 10 mL water, and the pH valuewas adjusted to 7.0 with ammonium hydroxide. Both solu-tions were mixed, and a clear green solution was obtained.The solution was allowed to evaporate slowly at room tem-perature for 4–5 days. A pale green solid was filtered,washed with water (3 · 2 mL), and dried with acetone(2 · 2 mL) and diethylether (3 · 2 mL). Yield 35–40%.Anal. Calc. for C24H60O48Ni3Sm2: C, 18.1; H, 3.8. Found:C, 18.0; H, 4.0%. IR peaks associated to the oda ligandappear at: 1618, 1438, and 1125 cm�1. The TGA diagramshows a weight loss of 20.4% in the range 50–220 �C whichcorresponds to the loss of all water molecules, calc. 20.3%.Decomposition point, 296 �C.

2.2.3. Synthesis of [Sm2 Co3(oda)6] Æ 18H2O(3)

This compound was obtained as 2, starting fromCo(NO3)2 Æ 6H2O (0.44 g, 1.5 mmol). A microcrystallinepink solid was collected after 4–5 days. Yield 40–45%.Anal. Calc. for C24H60O48Co3Sm2: C, 18.1; H, 3.8.Found: C, 17.9; H, 4.1%. IR peaks associated to theoda ligand appear at: 1608, 1438, and 1125 cm�1. TheTGA diagram shows a weight loss of 20.5% in the range50–160 �C which corresponds to the loss of all water mol-ecules, calc. 20.4%. Decomposition point, 237 �C.

2.2.4. Synthesis of [Sm2 Mn3(oda)6] Æ 9H2O(4)

This compound was obtained as 2, starting fromMn(NO3)2 Æ 4H2O (0.38 g, 1.5 mmol). Cubic pale yellowcrystals were collected after 4–5 days. Yield 40–45%. Anal.Calc. for C24H42O39Mn3Sm2: C, 20.3; H, 3.0. Found: C,20.2; H, 3.1%. IR peaks associated to the oda ligand

Table 1Crystallographic data for compound 1

Empirical formula C24H49O42.5Cu3Sm2

Formula weight 1508.95Crystal system HexagonalSpace group P6/mcca (A) 14.983(1)b (A) 14.983(1)c (A) 14.865(1)a (�) 90b (�) 90c (�) 120V (A3) 2890.0(3)Z 2Dcalc (g cm�3) 1.734l (Mo Ka) (mm�1) 3.185F (000) 1488Crystal dimensions (mm) 0.18 · 0.14 · 0.07Theta range for data collection (�) 3.14 � 37.89Limiting indices �17 6 h 6 24, �25 6 k 6 7,

�18 6 l 6 23Reflections (collected/ unique, (Rint)) 2514/1508 (0.0569)Completeness to theta = 37.89� 0.932R1

a, wR2b [F2 > 2r(F2)] 0.0482, 0.01812

Goodness-of-fit on F2 0.990Largest diff. peak and hole (e A�3) 1.23 and �1.383

a R1 ¼PjjF oj � jF cjj=

PjF cj.

b wR2 ¼ fP½wðF 2

o � F 2cÞ2�=

P½wðF 2

oÞ2g1=2.

62 J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69

appear at: 1608, 1438, and 1120 cm�1. The TGA diagramshows a weight loss of 11.5% in the range 50–240 �C whichcorresponds to the loss of all water molecules, calc. 11.6%.Decomposition point, 310 �C.

2.2.5. Synthesis of [Sm2 Ca3(oda)6] Æ 10H2O(5)Pale yellow crystals of this compound were obtained

as 2, starting from CaCl2 Æ 2H2O (0.22 g, 1.5 mmol).Yield 15–25%. Anal. Calc. for C24H44O40Ca3Sm2: C,20.7; H, 3.2. Found: C, 20.8; H, 3.2%. IR peaks associ-ated to the oda ligand appear at: 1616, 1438, and1124 cm�1. The TGA diagram shows a weight loss of12.8% in the range 160–220 �C which corresponds tothe loss of all water molecules, calc. 12.9%. Decomposi-tion point, 210 �C.

2.2.6. Synthesis of [Sm2 Mg3(oda)6] Æ 9H2O(6)

Pale yellow crystals of this compound were obtained as2, starting from MgCl2 Æ 6H2O (0.31 g, 1.5 mmol). Yield15–25%. Anal. Calc. for C24H42O39Mg3Sm2: C, 21.7; H,3.2. Found: C, 22.2; H, 4.6%. IR peaks associated to theoda ligand appear at: 1621, 1436, and 1122 cm�1. TheTGA diagram shows a weight loss of 11.6% in the range80–160 �C which corresponds to the loss of all water mol-ecules, calc. 12.2%. Decomposition point, 165 �C.

2.3. X-Ray data collection and refinement

X-ray data collection for 1 was performed at roomtemperature (293(2) K) with a Xcalibur diffractometer(graphite monochromated Mo Ka radiation (k =0.71073 A)) equipped with a Sapphire-II CCD cameraas an area detector. The data reduction was done withthe CrysAlis RED program [21]. Neither absorption norextinction corrections were applied. Relevant crystallo-graphic data are shown in Table 1. The structure wassolved by direct methods locating most non-hydrogenatoms. It was completed by successive difference Fouriermaps. Refinement was anisotropic for non-hydrogenatoms. The hydrogen atoms of the organic ligands werecalculated at idealized positions with fixed distances, andrefined with isotropic displacement parameters related tothe equivalent isotropic displacement parameter of theatom to which it is bonded. The structure determinationwas achieved using SHELXS [22] and refinement wasdone using SHELXL programs included in the SHELX-97 package [23].

2.4. Magnetic measurements

Magnetic susceptibility measurements (2.0–300 K) werecarried out with a Quantum Design SQUID magnetometerunder an applied magnetic field of 1T at high temperature(T > 20 K) and 250 G at low temperature (T < 20 K) toavoid any problem of magnetic saturation. The correctionsfor the diamagnetism were estimated from Pascal constants[24].

2.5. Potentiometric measurements

Solutions of the metals were standardized according tostandard techniques [25–27]. Solutions were freed ofcarbon dioxide by Ar bubbling. The standard HCl solutionwas prepared from Merck standard ampoules. The titrantsolution (0.1 M solution of Me4N(OH) in 0.5 M Me4NCl)was prepared by dissolving Me4N(OH) Æ 5H2O (Fluka),and standardized with potassium biphthalate.

The protonation constants of the ligand, oda, weredetermined through three potentiometric titrations (ca.150 experimental points each) in the concentrationrange 10–20 mM, covering pH values between 2 and11. Similarly, hydrolysis constants of Be(II), Al(III)and VO2+ under the conditions of the study weredetermined by titrations of solutions containing onlythe cations. Pb(II) hydrolysis was studied in 0.5 MNaNO3 to avoid PbCl2 precipitation. pH valuesbetween 2 and those causing precipitation of the corre-sponding hydroxide, and concentrations between 2 and20 mM were covered. In our calculations, the modeland the values of the stability constants for the hydro-lysis of iron(III), proposed by Daniele et al. [28], havebeen taken into account. Fe(II) and Sm(III) hydrolysisparameters have been taken from our previouslyreported values [29,30].

The behavior of oda in the presence of M(II) ions wasanalyzed through at least three potentiometric titrations(ca. 150 experimental points each) for each metal ion, atconcentrations ranging from 0.5 to 15 mM, and oda:M(II)molar ratios 1:1 to 5:1. For other metal systems, i.e., those

J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69 63

containing Sm(III), Fe(III), Al(III) and VO2+, complexa-tion was studied analogously.

Then, the formation of mixed species was tested by atleast three other potentiometric titrations with oda:metalion:Sm molar ratios between 2:1:1 and 6:3:2, and differenttotal concentrations of the components.

In all cases, the solutions were poured into a 50 mLtitration cell. After thermal equilibrium was reached,hydrogen ion concentrations were determined in succes-sive readings, each performed after a small incrementaladdition of standard 0.1 M Me4N(OH) solution (carriedout with the help of a Crison 2031 piston buret). Electro-motive force values were recorded with the help of aRadiometer 85 pH meter, using a glass electrode and acalomel reference electrode. The ionic strength was keptconstant throughout the titrations by using solutionscontaining 0.5 M Me4NCl and relatively low concentra-tions of the metal ions. Pre-saturated argon (free ofCO2) was bubbled through the solutions during titrationsto eliminate the effect of atmospheric carbon dioxide,and the temperature was kept at 25.0 (±0.1) �C. The cellconstants E�, and the liquid junction potentials weredetermined according to the methods of Biedermannand Sillen [31] and Liberti and Light [32]. Data wereanalyzed using the HYPERQUAD program [33], andspecies distribution diagrams were produced using theHySS program [34]. The fit of the values predicted bythe model to the experimental data was estimated onthe basis of the parameter r, corresponding to the scaledsum of square differences between predicted and experi-mental values.

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

30 112

Tempe

Wei

ght v

aria

tion

(mg)

62.0

Fig. 1. TGA diagram of compound 2 (under nitrogen atmosphere). The first m6H2O. Dashed line represents the first derivative.

3. Results and discussion

3.1. Synthesis and characterization

The direct reaction of oda in aqueous neutral solutionwith the stoichiometric amount of M(II) salts (M = Cu,Ni, Co, Mn, Ca, Mg) and Sm(III) led to the formation ofcomplexes with formula [Sm2M3(oda)6] Æ x H2O (x = 18 forM = Cu, Ni, Co, x = 10 for Ca, and x = 9 for M = Mn,Mg). This composition is supported by the elemental analy-sis and TGA determinations. Thermal analyses showed massloss even at low temperatures as 50 �C, suggesting the pres-ence of weakly bonded water molecules. This characteristicis especially remarkable in compound 1, and seems to beresponsible for the slight disagreement in the elemental anal-ysis results. In fact, when solids are stored is a desiccator oversilica, the TGA showed that, at least, two water moleculesare not present anymore. For compounds 2, 3, and 4, the lossof mass involved a well defined two-steps process (Fig. 1).The first corresponds to crystallization water (12 moleculesfor 2 at 62 �C, 12 molecules for 3 at 80 �C, and 3 moleculesfor 4 at 100 �C). The second loss of weight corresponds tocoordinated water molecules (6 for complexes 2 – 4 at 202,220, and 210 �C, respectively). Hence, they can be formulat-ed as [Sm2M3(oda)6(H2O)6] Æ x 0H2O (x 0 = 12 for M = Ni,Co, and x 0 = 3 for M = Mn). The presence of six coordinat-ed water molecules is also in agreement with the structure of1, described in the next section. Only one process of loss ofwater can be observed for the other compounds, correspond-ing to all water molecules. At higher temperatures decompo-sition of the solid occurs.

196 279

rature (˚C)

202.4

ass loss (62.0 �C) corresponds to 12H2O, and the second one (202.4 �C) to

C2

O2

C1

C2

O1

C1

O1

O1

O1OW

O2

C1

C1

O2

C2O2

CuO3

C2

C2

O2

OWO1C1

O1

Sm

O3C1

C2

O1

O3

C1O2

O2

O2

C2

C2

C2

C1

O2

O1

C1

O1

Fig. 2. View of the structure of [Sm2Cu3(oda)6(H2O)6] with atomlabelling. Thermal ellipsoids are drawn at 30% probability level, and allhydrogen atoms have been omitted for clarity.

64 J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69

IR spectra were almost identical for all metal ions sug-gesting very similar structures. It is noticeable the shift ofmCOO (1724, 1419 cm�1) of the free ligand to ca. 1608 and1438 cm�1. Besides, upon complexation, mCOC of1149 cm�1 for the free ligand shifted to ca. 1125 cm�1.

3.2. Description of the structure of

[Sm2Cu3(oda)6(H2O)6] Æ 6.5H2O(1)

Selected bond lengths and angles for 1 are summarizedin Table 2. As shown in Fig. 2, each Sm3+ is tridentatelychelated by three oda ligands, forming the building block[Sm(oda)3]3�. The coordination geometry of the samariumatom can be described as a distorted tricapped trigonalprism. The six carboxylate oxygen atoms form a trigonalprism (Sm–O distance 2.427(3) A) with three ether oxygenatoms as capping ones at a longer distance, 2.514(4) A.Each building block is connected to six Cu atoms via singlesyn-anti l-carboxylato-O,O 0 bridges. Sm–Cu distancethrough this bridge is 5.703 A. Copper atoms are six-coor-dinated. They are surrounded by four carboxylato oxygenatoms (Cu–O distance 1.957(3) A), which define a perfectequatorial plane and two water molecules at longer dis-tances (Cu–O distance 2.509(4) A). Thus, Cu2+ exhibitsan elongated octahedral geometry. The coordination poly-hedrons of both ions are shown in Figure S1 (Supplemen-tary Material).

The formation of l-carboxylato bridges in the threedirections yields a 3D network structure. Samariumbuilding blocks create a 2D hexagonal pattern (Fig. 3)repeated along the z axis. As in the case of analogousstructures [1–7], hexagonal channels are formed. Thediameter of these channels in 1 is nearly 10.9 A.

The number of crystallization water molecules found inthe measured single crystal is not coincident with thatdetermined in the bulk solid (see Experimental). The pres-ence of very weakly bound water molecules (as reflected inthe TGA profiles) would account for this fact.

3.3. Magnetic properties

The magnetic properties of compounds 1–4, in the formof vMT vs. T (vMT being the magnetic susceptibility perSm2M3 unit), are shown in Fig. 4. At room temperature,

Table 2Selected bond lengths (A) and angles (�) for compound 1

Bond lengths Angles

Sm–O(2) 2.427(3) O(2)–Sm–O(3)Sm–O(3) 2.514(4) O(2)i–Sm–O(3)Cu–O(1) 1.957(3) O(2)–Sm–O(2)ii

Cu–O(W) 2.509(4) O(2)i–Sm–O(2)ii

C(1)–O(1) 1.246(4) O(2)ii–Sm–O(2)iii

C(1)–O(2) 1.251(5) O(2)iii–Sm–O(3)C(2)–O(3) 1.388(4) O(3)ii–Sm–O(3)C(1)–C(2) 1.505(6)

Symmetry codes: (i) 1 � y, 1 � x, 0.5 � z; (ii) 1 � y, x � y, z; (iii) 1 � x + y, y

all of them present the expected values of vMT for magnet-ically isolated paramagnetic ions, i.e., 2.0, 4.1, 10.0 and13.0 cm3 mol�1 K, respectively. With the exception of 3

(Sm-Co complex), the vMT values decrease linearly withT up to about 100 K. Then, they decrease rapidly to get0.75, 2.25, 4.6 and 11.2 cm3 mol�1 K at 2 K for 1–4,respectively.

The Sm(III) ion presents a 6H ground term which issplitt by spin-orbit coupling into six levels, the energy beingincreased from 6H5/2 to 6H15/2. The spin-orbit parameter isaround 200–250 cm�1 [18]. So, the first excited state, 6H7/2,will be significantly populated at room temperature andabove. In the free-ion approximation, the expression ofthe magnetic susceptibility, taking into account the sixstates arising from 6H, is given in equation A1 (Appendix).From this expression, vMT decreases as T decreases, andtends to a limit value of 0.09 cm3 mol�1 K, as T fi 0. Thisvalue can be smaller due to the ligand field effect, whichpartially splits the 6H5/2 ground state. The total multipletwidth of such splitting is of a few tens of wavenumbers[18]. However, this effect is not important in describingthe magnetic properties of the compounds because of thevery low value of vMT at low T for the free ion(vMT 6 0.09 cm3mol�1 K).

The experimental susceptibility data corresponding tothe high temperature region (T P 100 K) were fitted bymeans of the independent contributions of the ions:

62.54(7) O(1)iv–Cu–O(1) 89.14(13)138.32(7) O(1)iv–Cu–O(1)v 90.86(13)81.52(7) O(1)–Cu–O(1)v 180.00(13)83.36(7) O(W)–Cu–O(W)vi 180.00(16)

125.11(5) O(W)–Cu–O(1) 84.33(8)73.39(4) O(W)–Cu–O(1)vi 95.67(8)

120.02(11) O(1)–C(1)–O(2) 126.5(4)

, 0.5 � z; (iv) x, y, �z; (v) 1 � x, �y, �z; (vi) 1 � x, �y, z.

Fig. 3. Packing view of [Sm2Cu3(oda)6(H2O)6] showing the 3D columnar structure generated and the channels along the crystallographic c axis. H atomsand crystallization water molecules are omitted for clarity.

Fig. 4. Thermal variation of the vMT product for compounds 1 (a), 2 (b), 3 (c) and 4 (d): (o) experimental data; (- - -) best fit curve considering no magneticinteraction; (—-) best fit curve considering antiferromagnetic interaction (see text).

J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69 65

66 J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69

vM ¼ 2vMðSm3þÞ þ 3vMðM2þÞ; ð1Þwhere vM(Sm3+) is given in Appendix (Eq. A.1), and

vMðM2þÞ ¼ Nb2g2

3kTSðS þ 1Þ; ð2Þ

(S = 1/2 for Cu(II), 1 for Ni(II), and 5/2 for Mn(II)). Incontrast to these metal ions, the Co(II) ion in octahedralgeometry presents a first-order orbital momentum, and

Table 3Best fit data on vMT values for compounds 1 – 4

Compound k(Sm3+) /cm�1 gM �h/K �J 0/cm�1 b

1 221.2 2.08 2.13 1.482 223.6 2.12 1.06 0.283 220.0 a 0.21 0.034 230.3 2.0 0.37 0.02

a The analysis of the Co(II) ion was done taking into account the spin-orbit coupling, k, in Oh symmetry. The data obtained in this way were:kCo(II) = �128 cm�1 and A = 1.35 (see text).

b Calculated from the expression J 0 = 3kh/ZS(S + 1), with Z = 4.

Table 4Protonation constants of the ligand oda, hydrolysis of metal cations, and th(except for Pb(II) hydrolysis, I = 0.5 M NaNO3)

Equilibrium

oda

L2� + H+M HL�

L2� + 2H+M H2L

log bq�r

b1–1 b1–2 b1–3 b2–1

Cation hydrolysis

VO2+ �5.27(8)Al(III) �9.9(1) �14.12(3)Pb(II) �6.9(1)Fe(II) �6.74Be(II) �11.8(1) �3.001(4Fe(III) �2.8 �5.8Sm(III) �6.7

Cation log bqpr

b111 b110 b11�1 b120 b12�1

M-oda species

Be2+ 2.24(1)Mg2+ 4.95(3) 1.48(2)Ca2+ 5.13(4) 2.82(2)VO2+ 7.6(1) 5.6(1) 7.2(1) 1.3(1)Mn2+ 2.16(5)Fe2+ 4.34(8) 2.01(1)Co2+ 2.15(1)Ni2+ 4.86(3) 2.42(1)Cu2+ 5.67(2) 3.46(1) �1.14(2)Zn2+ 4.67(5) 3.13(1)Cd2+ 2.14(1)Pb2+ 6.54(1) 4.21(1) 6.0(1)Al3+ 5.14(6) 2.79(2) �1.47(3)Fe3+ 4.64(5) 1.92(9) 8.33(4)Sm3+ 5.64(1) 9.62(2)

so, we have used Eq. (A.2) (Appendix) which accountsfor the orbitally degenerated 4T1g ground state.

The magnetic behavior under this approach (absence ofany magnetic interaction) is depicted in Fig. 4 as dashedlines. Below 100 K (50 K for 3) the vMT values decreasemore rapidly, indicating the occurrence of antiferromag-netic interactions between the paramagnetic centres. Wehave used a Weiss constant, h, with the form of (T�h) toaccount for this antiferromagnetic interaction. The corre-sponding fit in the whole range of temperature is given assolid lines in Fig. 4. The best-fit data for compounds 1–4

are depicted in Table 3. Usual values of k and g forSm3+ and the other d-metal ions were obtained. In the caseof compound 3, the values of k = �128 cm�1 and A = 1.35(the crystal field parameters) are very close to thoseobserved for other Co(II) complexes [35].

Due to the extremely weak magnetic interactionsbetween f and d orbitals (SmIII–MII), the magnetic interac-tions between second neighbors (MII–MII) are generallystronger [36]. Neglecting the magnetic interactions SmIII–

e formation constants for M-oda complexes, 25.0 �C, I = 0.5 M Me4NCl

log K r

3.811(5) 1.66.515(9)

b2–2 b3–3 b6–8 r

�7.55(5) 1.93.60.3Ref. [29]

) �8.831(9) �27.53(4) 0.2�2.9 Ref. [28]

Ref. [30]

b121 b12�2 b130 b31�3 b222 r

�6.49(2) 1.31.82.4

9.0(1) 2.512.6(1) 2.3

0.711.7(1) 1.8

1.62.00.81.71.01.3

10.87(6) �0.33(8) 1.811.8(2) 0.7

J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69 67

MII, and using the weak field approximation, an exchangeparameter, J 0, between divalent transition metal ions (MII–MII) can be calculated through Eq. (3):

J 0 ¼ 3khzSðS þ 1Þ ; ð3Þ

where z = 4 (number of MII nearest neighbors) in all cases.The absolute values of J 0 decrease from CuII–CuII to MnII–MnII, indicating that the superexchange pathway carboxy-lato-Sm-carboxylato is operative. In the case that the mag-netic interaction were dipolar in nature, the J 0 values wouldincrease as S is larger.

3.4. Chemical speciation in aqueous solution

The obtained data of protonation constants of theligand are depicted in Table 4. Results are in line with thosepreviously reported [37–39].

2 4 6 8 10pH

0

20

40

60

80

100

% fo

rmat

ion

rela

tive

to L

2 4 6 8 10pH

0

20

40

60

80

100

% fo

rmat

ion

rela

tive

to L

L

NiL

HL

H2L

L

PbL2

PbL

HL

H2L

PbHL

a

b

SmL3

SmL2

L

HL

H2L

SmL

c

2 4 6 8 10pH

0

20

40

60

80

100

% fo

rmat

ion

rela

tive

to L

Fig. 5. Species distribution diagram for the Ni(II)-oda (a), Pb(II)-oda (b),and Sm(III)-oda systems (c). In all cases, [oda] = 30 mM, [M] = 10 mM,T = 25.0 �C, and I = 0.5M Me4NCl. Charges of the species are omitted forclarity.

Table 4 shows formation constants of complexes of odawith M(II) and M(III) cations. Stable species were detectedfor all the studied metal ions. In particular, 1:1 species werealways present in the systems. For most +2 cations, MLspecies (L represents the fully deprotonated form of oda)are predominant. This is shown in Fig. 5a. Formationconstants of ML species are in line with previously report-ed data, when available [38–40]. Only in the case of Pb(II)(Fig. 5b), VO2+, and M3+ cations (Fig. 5c), species contain-ing 2:1 and 3:1 molar ratios (ligand to metal) are importantin the speciation. Be(II) exhibits the presence of[Be3(OH)3(oda)]+, a polynuclear species derived from thehydrolytic [Be3(OH)3]3+ which is predominant over pH 5.This kind of species have been found in many systems [41].

Heterobimetallic species are found (Table 5), if Sm,oda and a second metal are mixed in solution.[Sm2M3(oda)6(OH)3]3� is present for most systems con-taining M2+ cations, and represents the predominant spe-cies in solution (Fig. 6). It can be derived from theneutral less soluble species [Sm2M3(oda)6(H2O)6], isolatedat solid state. This neutral species was not detected insolution. Hydroxide groups in the hydroxylated speciesare probably coordinated to M, taking into accountthe presence of coordinated water into the crystal struc-ture. For Be(II), Ca(II), Mg(II), Mn(II), Fe(II), Pb(II),and Al(III), [SmM(oda)3(OH)]2� is also detected. Thisspecies, containing only one OH� group per mol, is pre-dominant in the case of Ca(II) and Mg(II). Be(II) alsoforms an hydroxylated species, [SmBeL3(OH)2]3�, whichis predominant in the systems, specially at pH valueshigher than 7.

Trivalent cations, Fe(III) and Al(III), like most +2 cat-ions, predominate as a 2:3:6 species, but in this case with ahigher degree of deprotonation. [Sm2Fe3(oda)6(OH)6]3�,and [Sm2Al3(oda)6(OH)5]2� are the predominant species.

Table 5Formation constants for Sm-M-oda complexes, 25.0 �C, I = 0.5MMe4NCl

[Sm2M3L6(OH)n] [Sm2M3L6] [SmML3(OH)n] [SmML3] r

Be2+ 34.23(6) 11.14(2) n = 1;6.11(3) n = 2

1.5

Mg2+ 10.49(3) n = 1 1.1Ca2+ 11.91(2) n = 1 0.8Mn2+ 24.6(1), n = 3 11.76(3) n = 1 2.0Fe2+ 24.1(1), n = 3 12.11(3) n = 1 2.5Co2+ 23.46(5) n = 3 2.6Ni2+ 22.80(6) n = 3 2.5Cu2+ 24.60(7) n = 3 2.0Zn2+ 24.35(5) n = 3 2.4Cd2+ 22.88(7) n = 3 2.0Pb2+ 28.71(7) n = 3 13.45(1), n = 1 1.0VO2+ 38.21(8) n = 1 2.5Fe3+ 36.67(3) n = 3;

28.31(5) n = 614.23(3) n = 2 18.91(4) 1.9

Al3+ 22.6(2) n = 3;14.57(5) n = 5

10.97(5) n = 1 1.7

Charges of the species are omitted for clarity. Tabulated values correspondto log of the overall formation constants.

3 5 7 9pH

0

20

40

60

80

100%

form

atio

n re

lativ

e to

Sm

Sm(OH)3(s)

[Sm2Cu3L6(OH)3]3-

3 5 7 9pH

0

20

40

60

80

100

% fo

rmat

ion

rela

tive

to C

u

[SmL2]-

[SmL3]3-

[SmL]+

[Sm2Cu3L6(OH)3]3-

[CuL(OH)]-

[Cu]2+

[Cu(HL)]+

[CuL]

a

b

Fig. 6. Species distribution diagram for the Sm–Cu–oda system. In bothfigures, [Sm] = 2mM, [Cu] = 3mM, [oda] = 6mM, T = 25.0 �C, andI = 0.5 M Me4NCl.

68 J. Torres et al. / Journal of Molecular Structure 825 (2006) 60–69

4. Concluding remarks

2,2 0-Oxydiacetate has proved to bridge Sm(III) and dif-ferent di and trivalent cations. The formation of speciescontaining [Sm2M3] units has been found at solid state,and, for the first time, in solution. The structure of the solidcompound [Sm2Cu3(oda)6(H2O)6] Æ 6.5H2O follows thosefound for Cu(II) and other lanthanide ions. The presenceof large channels in the 3D array was also found. Ourresults of the potentiometric experiments suggest that thesespecies are also present in solution, probably containingthis stable and particular arrangement. This result opensthe possibility to assay the compounds in many and newapplications.

Acknowledgement

This work was supported by Comision Sectorial deInvestigacion Cientıfica (CSIC, Uruguay), PEDECIBA(Uruguay), DINACYT (Uruguay) and Consejerıa deEducacion, Cultura y Deportes (Canary Islands Govern-ment, Spain, Grant PI2002/057). Financial aid fromthese organizations is gratefully thanked. The equipmentfor thermal analysis was kindly donated by the JapaneseGovernment.

Appendix A

A.1 The expression of the magnetic susceptibility forSm3+ (considering the six states arising from 6H) is [18]:

v ¼PJ¼15=2

J¼5=2 ð2J þ 1ÞvðJÞ exp½�EðJÞ=kT �PJ¼15=2J¼5=2 ð2J þ 1Þ exp½�EðJÞ=kT �

; ðA:1Þ

where v(J) and E(J) are given by:

vðJÞ ¼ Ng2Jb

2JðJ þ 1Þ3kT

þ 2Nb2ðgJ � 1ÞðgJ � 2Þ3k

EðJÞ ¼ k½JðJ þ 1Þ � 35=4�2

:

vmay be expanded as (equation A.1):

v ¼ Nb2

3kTxða1xþ b1 þ ða2xþ b2Þe�7x=2�

þða3xþ b3Þe�8x þ ða4xþ b4Þe�27x=2 þ ða5xþ b5Þe�20x

þða6xþ b6Þe�55x=2Þ��ð3þ 4e�7x=2 þ 5e�8x

þ6e�27x=2 þ 7e�20x þ 8e�55x=2Þ

with a1 = 2.143, a2 = 42.92, a3 = 283.7, a4 = 620.6,a5 = 1122, a6 = 1813, b1 = 7.347, b2 = 1.641,b3 = �0.6571, b4 = �1.9400, b5 = �2.835 and b6 = �3.556.

(A.2) Magnetic susceptibility for a Co(II) ion in octahe-dral symmetry [42]

vM ¼Nb2

kTYZ

ðA:2Þ

where

Y ¼ 7ð3� AÞ2

5þ 12ð2þ AÞ2

25Ax

þ 2ð11� 2AÞ2

45þ 176ðAþ 2Þ2

675Ax

$ %expð� 5Ax

2Þ

þ ðAþ 5Þ2

9� 20ðAþ 2Þ2

27Ax

$ %expð�4AxÞ

and

Z ¼ 3þ 2 expð� 5Ax2Þ þ expð�4AxÞ

being x = k/kT.

Appendix B. Supplementary data

Showing the coordination polyhedrons of Sm3+ andCu2+ ions in 1. Crystallographic data for structural analy-sis of compound 1 have been deposited with the CambridgeCrystallographic data centre, CCDC 275623. Copies of thisinformation may be obtained free of charge from theDirector CCDC, 12 Union Road, Cambridge, CB2-1EZ,UK (fax: + 44-1223-336033, e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk). Supplementary dataassociated with this article can be found, in the onlineversion, at doi:10.1016/j.molstruc.2006.03.103.

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