Sterically-induced synthesis of 3d–4f one-dimensional compounds: A new route towards 3d–4f single chain magnets

Inorganica Chimica Acta 361 (2008) 3997–4003

Contents lists available at ScienceDirect

Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica

Sterically-induced synthesis of 3d–4f one-dimensional compounds: A new route towards 3d–4f single chain magnets G. Calvez a, K. Bernot a,b, O. Guillou a,*, C. Daiguebonne a, A. Caneschi b,*, N. Mahé a a b

Sciences Chimiques de Rennes, Equipe ‘‘Matériaux Inorganiques: Chimie Douce et Réactivité”, UMR CNRS-INSA 6226, INSA, 20 Avenue des buttes de Coësmes, 35043 Rennes, France Laboratory of Molecular Magnetism, Dipartimento di Chimica di Firenze, Polo Scientifico, Via della Lastruccia, 3, 50019 Sesto Fiorentino, Italy

a r t i c l e

i n f o

Article history: Received 4 February 2008 Accepted 10 March 2008 Available online 15 March 2008 Dedicated to Dante Gatteschi Keywords: Crystal structure Coordination chemistry Molecular magnetism

a b s t r a c t Hexanuclear lanthanide complexes have been used as molecular precursors to built 3d–4f molecular chains. These complexes were originally targeted as building blocks for the synthesis of lanthanides-containing coordination polymers but reacting them with the 3d molecular precursor [Cu(opba)]2 lead to Ln(III)–Cu(II) hetero-bimetallic chains with general formula [Ln(NO3)(DMSO)2Cu(opba)(DMSO)2]1 with Ln = Gd–Er. The reaction mechanism can be explained by a sterically-induced reaction where the attack of the [Cu(opba)]2 moiety is driven by the hexanuclear lanthanide clusters geometry. Static magnetic properties of the Gd- and Dy-based chains have been investigated as well as the dynamic magnetic properties of the Dy-containing compound. These studies confirmed that this chemical strategy can possibly yield to 3d–4f single chain magnets. Ó 2008 Elsevier B.V. All rights reserved.

1. Introduction The synthesis and physico-chemical study of magnets is a very active research field [1]. Traditional magnets are quite common nowadays and in the search for miniaturization and integration new fields of investigation have been opened. Recently, coordination chemists in association with magnetochemists have succeeded in providing new advances in the field. In fact, magnetic nanoclusters characterized by a large easy axis magnetic anisotropy have been found to behave as tiny magnets at low temperature showing bistability and the associated magnetic hysteresis. Molecular nanomagnetism, and in particular the field of single molecule magnets (S.M.M.) has thus become a new investigation area [2]. This has represented a significant innovation in magnetism because magnetic hysteresis was previously considered a cooperative phenomenon. In the last 10 years many efforts have been devoted on one side to understand the magnetic behaviour of such compounds, and on the other, to synthesize new molecular materials, in particular with the aim to increase the temperature at which the memory effect is observable. With this last goal in mind the interest has been extended to molecular materials comprising anisotropic units arranged in one dimensional structures, called single chain magnets (S.C.M.) by analogy with the previously mentioned S.M.M. [3]. * Corresponding authors. E-mail address: [email protected] (O. Guillou). 0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2008.03.040

Although outstanding progresses were made in understanding the phenomena responsible for the magnetic behavior of SMMs and SCMs [4], the potentially exploitable dynamic properties of such materials have remained confined to very low temperatures. The chemists have thus explored alternatives routes to high temperature molecular nanomagnets. A possibility was to extend the synthetic strategy by using highly anisotropic spin carriers as building blocks. Orbitally degenerate ions are thus good candidates and lanthanides trivalent cations are now used to build magnetic edifices [5]. However the huge magnetic anisotropy of the lanthanide ions has to be combined with organic radical or with 3d metal ions in order to provide strong intra-cluster/chain magnetic interaction required for the observation of SMM or SCM behaviour. Different organic ligands have been used in the past to built 3d building blocks but one of the most used is certainly the opba4 (opba = orthophenylenebisoxamato) ligand. This ligand belongs to a family of organic ligands (R-pba) intensively studied in molecular magnetism that has been exploited for building binuclear [6] and trinuclear [7] compounds. Alternating ferromagnetic chains were also obtained [8], some of them with relevant Tc [9]. The R-pba derivatives possess two different chelating sites, two external bis-chelating sites made of an oxalate bridge; and one tetra-chelating site consisting in two amines and two carbonyl groups. This latter is highly favoured from the thermodynamic point of view, and stable precursors made of Mn, Cu and Zn are generally used [10]. The most known complexes based on the opba4 ligand are

3998

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003

Fig. 1. Left: [Cu(opba)]2 monomeric complex. right: Projection views of the ladder-like compound Gd2[Cu(opba)]3(DMSO)6(H2O)  (H2O).

3d–4f spin ladders involving CuII or ZnII cations as 3d ion [11] (see Fig. 1). As this ligand is able to mediate quite strong magnetic interaction between the central metal ion and the externally coordinated cations, it is a very good candidate for building 3d–4f molecular chains. Unfortunately direct reaction of lanthanides precursors on CuII-R-pba derivatives does not lead to a chain but always to the previously cited spin ladders. On the other hand, for several years, some of us are currently working in the field of hetero-polynuclear lanthanide complexes synthesis with the aim of designing highly porous materials where poly-nuclear complexes would act as metallic centres. This strategy has been successfully applied in later years for 3d-metal ions and very promising materials involving zinc tetra-nuclear complexes have been obtained [12]. In order to synthesise poly-nuclear lanthanide complexes that could be used as a molecular precursors for new highly porous coordination polymers we have thus developed and rationalized a synthetic route [13]. This one, based on a subtle balance between various experimental parameters, has been described some years ago [14]. The obtained complexes have general formula [Ln6O(OH)8(NO3)6(H2O)12](NO3)2  5H2O where Ln = Nd–Yb (see Fig. 2). They can be thermally dehydrated leading to anhydrous [Ln6O(OH)8(NO3)6](NO3)2 complexes which are rather stable in anhydrous solvents. Our synthetic approach consists in substituting the nitrato groups by bidentate ligands. The main problem encountered here is to find the good operating conditions for substituting the nitrate without destroying the hexanuclear complex. Indeed the hexanuclear complex has often been destroyed during tentative syntheses. However, the coordination polymers finally obtained were original and different from those obtained by reactions involving a simple lanthanide salt [15]. This can be understood by considering the different accessibility of lanthanide ions when they are involved in a hexanuclear complex or not. Actually, due to the inner character of their valence orbitals, lanthanide ions can be compared to rigid spheres and present no structuring effect and the spatial distribution of the

Fig. 2. View of the hexanuclear entity [Er6(l6-O)(l3-OH)8(NO3)6(H2O)12]2+.

ligands is mainly driven by steric effects [16]. On the opposite, when the lanthanide ion belongs to a hexanuclear complex it can only interact along one direction with the ligand. Furthermore the most interesting feature was the presence, in the obtained compound, of a remaining nitrate coordinated to the lanthanide ion in a bidentate fashion. In fact, by using the previously described copper-based opba4 derivative as bidentate ligand; this sterically-driven coordination mechanism provide a mono-dimensional compound that may be a benchmark for a new route toward 3d–4f based single chain magnets as schematized in Fig. 3. We wish to report here our first attempt along this line.

3999

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003

Fig. 3. Scheme of the synthetic strategy used to synthesized the chain compound.

2. Experimental 2.1. Synthesis of [Ln(NO3)(DMSO)2Cu(opba)(DMSO)2]1 with Ln = Gd–Er Anhydrous hexanuclear lanthanide complexes with general formula Ln6O(OH)8(NO3)6  2NO3 with Ln = Gd–Er have been used as starting materials. They have been obtained thanks to established procedures [17]. The copper(II) precursor Na2[Cu(opba)]  3H2O was prepared as already described [18]. On one hand 0.25 mmol of [Ln6O(OH)8(NO3)6]  2(NO3) were dissolved in 5 mL of DMSO. On the other hand 0.25 mmol of Na2[Cu(opba)]  3 H2O were dissolved in 30 mL of DMSO. The two solutions were then mixed and the resulting mixture was allowed to evaporate slowly at 70 °C in air. After a week small crystals appeared. They were filtered off, washed with ethoxyethyl, and dried in air. Single crystals suitable for crystal structure characterization have been obtained for the Er-containing compound. Anal. Calc. for [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1: Er, 19.6; Cu, 7.5; N, 4.9; O, 24.4; S, 15.0; C, 25.3; H, 3.3. Found: Er, 19.5; Cu, 7.6; N, 5.2; O, 24.4; S, 14.8; C, 25.2; H, 3.4%. Anal. Calc. for [Gd(NO3)(DMSO)2Cu(opba)(DMSO)2]1: Gd, 18.6; Cu, 7.5; N, 5.0; O, 24.7; S, 15.1; C, 25.6; H, 3.3. Found: Gd, 18.7; Cu, 7.6; N, 5.0; O, 24.8; S, 15.2; C, 25.76; H, 3.2%. Anal. Calc. for [Dy(NO3)(DMSO)2Cu(opba)(DMSO)2]1: Dy, 19.1; Cu, 7.5; N, 5.0; O, 24.5; S, 15.2; C, 25.6; H, 3.3. Found: Dy, 19.0; Cu, 7.4; N, 4.9; O, 24.7; S, 15.3; C, 25.5; H, 3.4%. 2.2. X-ray structure determination A single crystal of [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1 was sealed in a glass capillary for X-ray single crystal data collection. The crystal was mounted on a Nonius Kappa CCD diffractometer at room temperature with Mo Ka radiation (k = 0.71073 Å). Preliminary cell constants were determined from reflections obtained on 10 frames (1°u rotation per frame). For the data collection, a crystal-to-detector distance of 45.0 mm has been used and data collection strategy (determination and optimization of the detector and goniometer positions) has been performed with the help of the COLLECT program [19] to measure Bragg reflections of the asymmetric triclinic basal unit cell. The reflections have been indexed, Lorentz-polarization corrected and then integrated by the DENZO program of the KAPPA CCD software package [20]. Structure determination has been performed with the solving programs SIR97 [21]and SHELXL97 [22], that revealed all the nonhydrogen atoms. All metallic and sulfur atoms of the molecular ladder-like entity were refined anisotropically using the SHELXL pro-

gram. The other atoms were refined isotropically. Hydrogen atoms have not been localized. Crystal data and structure refinement of the Er(III) containing compound are listed in Table 1. The characterization of the other compounds has been assumed on the basis of comparisons between their experimental powder X-ray diffraction diagrams and the calculated one from the crystal structure. The calculated XRD diagram has been performed using POWDERCELL [23] software and compared with experimental one using WINPLOTR [24] software. 2.3. X-ray powder diffraction The X-ray powder diffraction diagrams have been collected using a Panalyticals X’Pert Pro diffractometer with an X’celerator detector. The recording conditions were 40 kV, 40 mA for Cu Ka (k = 1.542Å), the diagrams were recorded in h/h mode in 60 min

Table 1 Experimental data for the X-ray diffraction study of [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1 Molecular formula Formula weight (g mol1) Crystal dimensions (mm) Temperature (K) Crystal system Space group a (Å) b (Å) c (Å) V (Å3) Z Dcalc (g cm3) F(0 0 0) l (cm1) Radiation, k (Å) h k l Range

h Range (°) Data collected Observed data (F obs P 2rðF 2obs ÞÞ Parameters refined Ra (%) Rwb (%) Goodness-of-fit Final shift/error Residual density (e Å3)

ErCuN3O13S4C18H28 853.5 0.095  0.090  0.085 298(2) orthorhombic Pcmn (No. 62) 10.0031(2) 14.0175(3) 21.3811(3) 2998.02(10) 8 1.828 1576 4.7400 monochromated Mo Ka (0.71073) 12 6 h 6 12; 18 6 k 6 18; 27 6 l 6 27 1.00 6 h 6 27.48 3578 2813 215 4.67 6.48 1.049 0.000 0.242 (in the vicinity of Cu)

w ¼ 1=½r2 ðF 2o Þ þ ð0:0713  PÞ2 þ 9:6319  P where P ¼ ðF 2o þ 2  F 2c Þ=3. P P a R1 = kFoj  jFck/ jFoj. hP .P i1=2 b wR2 ¼ wðF 2o  F 2c Þ2 . wF 4o

4000

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003

between 5° and 75° (8378 measurements) with a step size of 0.0084° in 2h and a scan time of 50 s. 2.4. Magnetic measurements The dc-magnetic susceptibility measurements were performed with a Cryogenic S600 SQUID magnetometer between 2 and 300 K in an applied magnetic field of 1000 Oe for temperatures in the range 2–50 K and 10 kOe for temperatures between 50 and 300 K. Samples were measured as pellets and corrected for the diamagnetic contribution as calculated with Pascal’s constants. The ac-magnetic susceptibility measurements were performed on the same samples using a homemade ac-probe operating in the range 100–25 000 Hz [25].

two oxygen atoms and two nitrogen atoms belonging to the (opba) entity in a square planar fashion and by two oxygen atoms in apical positions from two coordinated DMSO molecules thus forming a distorted octahedral. There are no crystallization molecules in the crystalline framework. The crystal packing of this compound can be described as the juxtaposition of the chain like molecular motifs as can be seen in Fig. 5. The shortest intra-chain intermetallic distance (Er–Cu) is roughly 5.655 Å. The coordinated DMSO molecules point toward the inter-chain space along the ~ b axis while coordinated nitrato groups point toward the inter-chain space along the ~ a axis. The inter-chain space is thus filled by the non-coordinated part of the DMSO molecules. The shortest inter-chain intermetallic contact (Cu–Cu) is roughly 8.014 Å. The shortest inter-chain Er–Er contact is 8.786Å and Er–Cu is 8.898 Å.

3. Results and discussion 3.2. Magnetic measurements 3.1. Crystal structure The crystal structure of compound [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1 consists of hetero-bimetallic Er(III)–Cu(II) chains spreading along the ~ c axis (Fig. 4). As expected the starting hexanuclear complex has been destroyed and a remaining bidentate nitrato group is bound to the Er(III) ion. Therefore, the lanthanide ion is eight-coordinated by four oxygen atoms from the [Cu(opba)]2 entities, two oxygen atoms from coordinated DMSO molecules and two oxygen atoms from the nitrato group thus forming a distorted bicapped trigonal prism. The Cu(II) ion is six coordinated by

We focused our analysis on the gadolinium (1) and dysprosium (2) derivatives since: (i) in case of relevant magnetic coupling in the material, the nature and magnitude of the CuII–GdIII exchange interaction can be easily determined, since GdIII, with a 8S7/2 ground term, has no orbital contribution to the magnetic moment and the Heisenberg–Dirac–Van Vleck Hamiltonian can be employed (ii) dysprosium(III) is expected to bring a strong anisotropy to the magnetic moment and, consequently, one important condition to eventually observe the slow relaxation of the magnetization is fulfilled.

Fig. 4. Projection view of an extended asymmetric unit along with the labelling scheme of compound [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1.

Fig. 5. Projection view along the ~ a (left), ~ b (middle) and ~ c axis (right) of compound [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1.

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003

Fig. 6. Thermal variation of the vMT product in the temperature range 2–300 K for the GdIII (circles) and the DyIII derivative (lozenges). Empty symbols are recorded in an external field of 0.1 kOe, half-filled in 1 kOe and full-filled in 10 kOe.

4001

Fig. 7. Experimental thermal variation of 1/vM for the GdIII derivative and Curie– Weiss fit of the high-temperature region (15–300 K). In inset: experimental (circles) and calculated from the Brillouin function (full black line) magnetization of the GdIII derivative in field range 0–60 kOe. Lozenges represent the experimental magnetization of the DyIII based derivative.

3.3. Static magnetic properties The vMT versus T curves were recorded for both compounds and are reported in Fig. 6. The GdIII derivative, 1, shows a room temperature vMT value of 8.35 emu K mol1 in agreement with the expected value for an S = 7/2 plus an S = 1/2. On cooling the curves are almost flat down to 10 K. The vMT value then increases abruptly to reach 9.95 emu K mol1at 2 K. The DyIII based compound, 2, has a room temperature vMT value of 14.38 emu K mol1 in agreement with the expected value for a DyIII of configuration 6H15/2 plus an S = 1/2 (14.54 emu K mol1). The curve is almost flat down to 160 K when it starts to decrease first slowly, then more rapidly below 50 K. It reaches a rounded minimum at 10.2 K (12.27 emu K mol1). Below this temperature a very sharp increase is visible down to 2 K. No plateau is displayed for this temperature and the value of the vMT product is 15.28 emu K mol1. These two curves are very similar, the only difference residing in the high temperature decrease of the DyIII based compounds, but this is only a consequence of the depopulation of the stark sub levels and do not involve any type of magnetic interaction. Moreover this phenomenon hampers the observation of an eventual magnetic exchange interaction between the CuII and the DyIII ions. Thus both the GdIII and DyIII based chain show an increase of the vMT value at low temperature that can be associated with a weak ferromagnetic interaction in the material. Hence, if the inverse of the susceptibility, measured on this first one is plotted against the temperature and fit the curve in the high temperature region, we obtain a Curie–Weiss temperature of h = 1.2 ± 0.2 K (see Fig. 7). The M versus H curves are also depicted in Fig. 7, together with the Brillouin simulation. On both sample the M versus H curves are linear only at very low field. This justifies the three different fields used to measure the vMT versus T curve (Fig. 6). The value of the magnetization curves increases rapidly with the field. Above 10 kOe the two curves increase more slightly but without reaching the saturation. At 60 kOe the GdIII and DyIII-based compounds display a magnetization value of about 40 000 emu mol 1 and 35 000 emu mol1, respectively. M versus H curves have also been recorded thanks to a VSM apparatus and no opening of hysteresis is visible down to 1.6 K. The magnetization of the GdIII derivative has to be compared to the one simulated using the Brillouin function, for a spin S = 7/2 plus an S = 1/2. The magnetization curve is slightly higher the simulated one for low fields, and above for field larger than 5 kOe. This is an evidence for the presence of two interactions in the material, a ferromagnetic and an antiferromagnetic one.

This has to be related with the structure of the compound. The GdIII–CuII magnetic exchange interaction in similar environment is reported to be ferromagnetic [11]. Consequently it is reasonable to suppose that the same conclusion can be made here. Concerning the antiferromagnetic interaction, the special disposition of the chain is likely to give rise to such inter-chain interaction. First of all, the DMSO molecules are creating through the hydrogen atoms of their terminal group an hydrogen bonded network. It connects the DMSO molecules linked to a CuII atom with the one linked to another CuII atom belonging to another chain. Moreover the aromatic rings of the opba4 ligand gives rise to p–p stacking interactions that are likely to be antiferromagnetic. Consequently we cannot exclude that the Curie–Weiss temperature extracted before is contaminated by a small AF contribution. Finally, extending this considerations to the DyIII-based compound, it has been shown on the spin ladder derivatives that the nature of the magnetic exchange interaction between the Gd and Dy-based compounds are identical and we expect a comparable trend here [10]. 3.4. Dynamic magnetic properties ac magnetic measurements were performed on the DyIII derivative in absence of external field. On both in and out-of-phase signals small frequency dependence is visible below 5 K. Even if low, the v00M =v0M ratio is enough to be out of the region of the noise of the ac-probe. The frequency dependence is visible on all the frequencies in the range 100–25 000 Hz (Fig. 8.)

Fig. 8. Temperature dependence of thein phase and out-of-phase susceptibility for the DyIII derivative in the 100–25 000 Hz frequency range (color mapping from red (100 Hz) to blue (25 000 Hz)). In inset a zoom on the out-of-phase susceptibility.

4002

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003

However, no Arrhenius or Argand plot can be extracted from this measurement, since neither the v00M versus T nor the v0M versus frequency curves display peaks. Hence no further analysis of this data has been made. As a last statement, this compound does not present any field dependence of the v00M signal. Recently some of us reported a similar compound (3) [26] where the [Ni(bpca)]2 ligand was used as 3d building block to form 3d–4f chains. In this compound a very weak v00M =v00M ratio was observed, highlighting poor dynamic properties. The chains 1 and 2, reported here, can be considered as a further enhancement of the magnetic properties of 3 since, even if the compounds are similar, the ferromagnetic interaction is bigger here than the one reported for 3. The reason resides in the choice of the bridging ligand. On a first approximation the two 3d building blocks used here are quite similar since the [Ni(bpca)]2 and the [Cu(opba)]2 are both bis bidentate ligands. But one can find however some differences between those two entities: (i) the distances between the LnIII cation and the inner 3d ion is bigger when using [Ni(bpca)]2 than [Cu(opba)]2 (5.86 Å and 5.65 Å, respectively). (ii) the [Cu(opba)]2 involve oxalate claws to coordinate the lanthanide, which are known to transmit extremely well the magnetic interactions [10]. In comparison the [Ni(bpca)]2 used in 3 is known to be less efficient. (iii) The compound 3 reproduce the unfavorable geometric arrangement illustrated by some of us on DyIII–MII–DyIII trimeric species (4) [27] where lanthanides bind

trough [M(bpca)]2 building blocks have their easy axes almost orthogonal, leading to a drastic diminution of the dynamic magnetic properties of the complexes. On the contrary in 1 and 2 the easy axes of the lanthanides are almost parallel since they are linked by a glide plane. This is thus the ideal arrangement for a non-cancellation of the high anisotropy of the lanthanide (see Fig. 9). (iv) The isolation of the chains is higher in 1 and 2 than in 3 since the ligand used can give rise to fewer p–p interactions and hydrogen bonds. All the statements detailed above significantly increase the ratio between the intra and inter-chain magnetic exchange interaction in 2 and may be the reason why its v00M =v0M ratio is considerably higher than in 3. Nevertheless, given the high Curie–Weiss constant extracted for the GdIII derivative (1), one should expect more spectacular dynamic properties for 2. In fact, when looking at the crystal packing of the compound, it is quite hard to consider the chains as magnetically isolated (see Fig. 5). The metal–metal distances are quite high but the presence and most importantly the arrangement of the DMSO molecules is a major problem here. It may create a hydrogen bond network, principally in the ab and bc planes, that is able to mediate inter-chain magnetic interaction that hampers the magnetic slow relaxation of the chains. 4. Conclusion We describe here an original route toward new coordination compounds by using hexanuclear lanthanides complexes as molecular precursors. Their geometry and rather good stability in anhydrous solvents allows a sterically-induced degradation of these entities when reacted with the [Cu(opba)]2 3d precursor. This reaction leads to infinite 3d–4f molecular chains in which the 3d–4f magnetic exchange interaction is relevant. The GdIII and DyIII derivatives display static magnetic properties quite appealing, confirming the good choice of the ligand when compared to similar compounds. Moreover, the use of this ligand optimizes the geometrical arrangement of the DyIII ions along the chain that is known to favour the dynamic magnetic processes. Nevertheless, inter-chain magnetic interactions are still relevant here and the DyIII-based chain does not behave as a SCM. However, the use of bulkier ligands, based on already known substituted R-opba entities [10] should enhance the magnetic insulation of the chains and allow for synthesizing 3d–4f single chain magnets. 5. Supplementary material CCDC 674672 contains the supplementary crystallographic data for [Er(NO3)(DMSO)2Cu(opba)(DMSO)2]1. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Acknowledgments The Center of Crystallography of the ‘‘Université de Rennes” is acknowledged for its recording of the crystallographic data. We acknowledge the financial support from Italian MURST (FIRB and PRIN grants), from the EC through the Human Potential Program RTN-QUELMOLNA (MRTN-CT-2003-504880), from the NE-MAGMANET (NMP3-CT-2005-515767) and of Ente Cassa di Risparmio di Firenze. References

Fig. 9. Schematic representation of the backbone of 2 (top), 3 (middle) and 4 (bottom picture), where the coordinating planes are highlighted, illustrating the orientation of the coordination polyhedron of the lanthanides. 2 and 3 are polymeric compounds whereas 4 is a trimeric finite entity.

[1] (a) O. Kahn, Molecular Magnetism, VCH, New York, 1993; (b) D. Gatteschi, J. Villain, R. Sessoli, Molecular Nanomagnets, Oxford University Press, Oxford, UK, 2006.

G. Calvez et al. / Inorganica Chimica Acta 361 (2008) 3997–4003 [2] (a) G. Christou, D. Gatteschi, D.N. Hendrickson, R. Sessoli, MRS Bull. 25 (2000) 66; (b) D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268; (c) L. Thomas, F. Lionti, R. Ballou, D. Gatteschi, R. Sessoli, B. Barbara, Nature 383 (1996) 145; (d) J.R. Friedman, M.P. Sarachik, J. Tejada, R. Ziolo, Phys. Rev. Lett. 76 (1996) 3830; (e) W. Wernsdorfer, R. Sessoli, Science 284 (1999) 133; (f) S. Hill, R.S. Edwards, N. Aliaga-Alcalde, G. Christou, Science 302 (2003) 1015; (g) R. Sessoli, D. Gatteschi, A. Caneschi, M.A. Novak, Nature 365 (1993) 141. [3] (a) R. Clerac, H. Miyasaka, M. Yamashita, C. Coulon, J. Am. Chem. Soc. 124 (2002) 12837; (b) C. Coulon, H. Miyasaka, R. Clerac, Structure and Bonding, vol. 122, Springer, Berlin, 2006. p. 163. [4] (a) R. Lescouezec, J. Vaissermann, C. Ruiz-Perez, F. Lloret, R. Carrasco, M. Julve, M. Verdaguer, Y. Dromzee, D. Gatteschi, W. Wernsdorfer, Angew. Chem., Int. Ed. 42 (2003) 1483; (b) E. Pardo, R. Ruiz-Garcia, F. Lloret, J. Faus, M. Julve, Y. Journaux, F. Delgado, C. Ruiz-Perez, Adv. Mater. 16 (2004) 1597; (c) L.M. Toma, R. Lescouezec, J. Pasan, C. Ruiz-Perez, J. Vaissermann, J. Cano, R. Carrasco, W. Wernsdorfer, F. Lloret, M. Julve, J. Am. Chem. Soc. 128 (2006) 4842; (d) H. Miyasaka, R. Clerac, K. Mizushima, K. Sugiura, M. Yamashita, W. Wernsdorfer, C. Coulon, Inorg. Chem. 42 (2003) 8203; (e) H. Miyasaka, T. Madanbashi, K. Sugimoto, Y. Nakazawa, W. Wernsdorfer, K. Sugiura, M. Yamashita, C. Coulon, R. Clerac, Chem.-Eur. J. 12 (2006) 7029; (f) L. Lecren, W. Wernsdorfer, Y.G. Li, A. Vindigni, H. Miyasaka, R. Clerac, J. Am. Chem. Soc. 129 (2007) 5045; (g) L. Bogani, C. Sangregorio, R. Sessoli, D. Gatteschi, Angew. Chem., Int. Ed. 44 (2005) 5817; (h) K. Bernot, L. Bogani, A. Caneschi, D. Gatteschi, R. Sessoli, J. Am. Chem. Soc. 128 (2006) 7947; (i) K. Bernot, L. Bogani, R. Sessoli, D. Gatteschi, Inorg. Chim. Acta 360 (2007) 3807; (j) J.-P. Costes, J.-M. Clemente-Juan, F. Dahan, J. Milon, Inorg. Chem. 43 (2004) 8200; (k) T.-F. Liu, D. Fu, S. Gao, Y.-Z. Zhang, H.-L. Sun, G. Su, Y.-J. Liu, J. Am. Chem. Soc. 125 (2003) 13976; (l) T. Kajiwara, M. Nakano, Y. Kaneko, S. Takaishi, T. Ito, M. Yamashita, A. Igashira-Kamiyama, H. Nojiri, Y. Ono, N. Kojima, J. Am. Chem. Soc. 127 (2005) 10150; (m) M. Balanda, M. Rams, S.-K. Nayak, Z. Tomkowicz, W. Haase, K. Tomala, J.-V. Yakhmi, Phys. Rev. B 74 (2006) 224421; (n) Y.-L. Bai, J. Tao, W. Wernsdorfer, O. Sato, R.-B. Huang, L.-S. Zheng, J. Am. Chem. Soc. 128 (2006) 16428; (o) A. Caneschi, D. Gatteschi, N. Lalioti, C. Sangregorio, R. Sessoli, G. Venturi, A. Vindigni, A. Rettori, M.-G. Pini, M.-A. Novak, Angew. Chem., Int. Ed. 40 (2001) 1760. [5] D. Gatteschi, C. Benelli, Chem. Rev. 102 (6) (2002) 2369. [6] (a) J.-P. Costes, F. Dahan, A. Dupuis, J.-P. Laurent, Inorg. Chem. 35 (1996) 2400; (b) J.-P. Costes, F. Dahan, A. Dupuis, J.-P. Laurent, Inorg. Chem. 36 (1997) 3429; (c) J.-P. Costes, A. Dupuis, J.-P. Laurent, J. Chem. Soc., Dalton Trans. (1998) 735; (d) L. Ramade, O. Kahn, Y. Jeannin, F. Robert, Inorg. Chem. 36 (1997) 930; (e) M. Sakamoto, Y. Kitakami, H. Sakiyama, Y. Nishida, Y. Fukuda, M. Sakai, Y. Sadaoka, A. Matsumoto, H. Okawa, Polyhedron 16 (1997) 3345. [7] (a) A. Bencini, C. Benelli, A. Caneschi, A., Carlin, R.L. Dei, A. Gatteschi, D.,J. Am. Chem. Soc. 107 (1985) 8128.; (b) A. Bencini, C. Benelli, A. Caneschi, A. Dei, D. Gatteschi, J. Magn. Mater. Mater. 54–57 (1986) 1485;

[8]

[9] [10]

[11]

[12]

[13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]

4003

(c) A. Bencini, C. Benelli, A. Caneschi, A. Dei, D. Gatteschi, Inorg. Chem. 25 (1986) 572; (d) G. Condorelli, I. Fragala, S. Guiffrida, A. Cassol, Z. Anorg, Allg. Chem. 412 (1975) 251. (a) Y. Pei, O. Kahn, J. Sletten, J.-P. Renard, R. Georges, J.-C. Gianduzzo, J. Curely, Q. Xu, Inorg. Chem. 27 (1988) 47; (b) O. Kahn, Y. Pei, M. Verdaguer, J.-P. Renard, J. Sletten, J. Am. Chem. Soc. 110 (1988) 782. K. Nakatani, J.-Y. Carriat, Y. Journaux, O. Kahn, F. Lloret, J.-P. Renard, Y. Pei, J. Sleten, M. Verdaguer, J. Am. Chem. Soc. 111 (1989) 5739. (a) R.-L. Oushoorn, Thèse de doctorat de l’Université Paris XI d’Orsay, 1995.; (b) M.-L. Kahn, Thèse de doctorat de l’Université de Bordeaux, 1999.; (c) M.-L. Kahn, C. Mathonière, O. Kahn, Inorg. Chem. 38 (1999) 3692; (d) M.-L. Kahn, M. Verelst, P. Lecante, C. Mathonière, O. Kahn, Eur. J. Inorg. Chem. (1999) 527; (e) M. Verelst, L. Sommier, P. Lecante, A. Mosset, O. Kahn, Chem. Mater. 10 (1998) 980; (f) A. van der Bilt, K.-O. Joung, R.-L. Carlin, L.J. de Jongh, Phys. Rev. B22 (1980) 1259; (g) B. Cervera, J.-L. Sanz, M.-J. Ibanez, G. Vila, F. Lloret, M. Julve, R. Ruiz, X. Ottenwaelder, A. Aukaloo, S. Poussereau, Y. Journaux, M.-C. Munoz, J. Chem. Soc., Dalton Trans. (1998) 781, and reference cited therein; (h) R. Ruiz, J. Faus, F. Lloret, M. Julve, Y. Journaux, Coordin. Chem. Rev. 195 (1999) 1069, and reference cited therein; (i) X. Ottenwaelder, Thèse de doctorat de l’Université de Paris XI, 2001. (a) O. Guillou, O. Kahn, R.-L. Oushoorn, K. Boubekeur, P. Batail, Inorg. Chim. Acta 119 (1992) 198, and reference cited therein; (b) A. Andruh, L. Ramade, E. Codjovi, O. Guillou, O. Kahn, J.-C. Trombe, J. Am. Chem. Soc. 115 (1993) 1822, and reference cited therein; (c) See for low T magnetic and specific heat studies: M. Evangelisti, Ph.D. thesis, Universiteit Leiden, 2001. M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, O.M. Yaghi, Science 295 (2002) 469; H.K. Chae, D.Y. Siberio-Perez, J. Kim, Y. Go, M. Eddaoudi, A.J. Matzger, M. O’Keeffe, O.M. Yaghi, Nature 427 (2004) 523. N. Mahé, O. Guillou, C. Daiguebonne, Y. Gérault, A. Caneschi, C. Sangregorio, J.-Y. Chane-Ching, P.E. Car, T. Roisnel, Inorg. Chem. 44 (2005) 7743. Z. Zak, P. Unfried, G. Giester, J. Alloy Compd. 205 (1994) 235; G. Giester, P. Unfried, Z. Zak, J. Alloy Compd. 257 (1997) 175. O. Guillou, C. Daiguebonne, G. Calvez, F. Le Dret, P.E. Car, J. Alloy Compd. (2007), doi:10.1016/j.jallcom.2007.04.198. C. Daiguebonne, O. Guillou, Y. Gérault, K. Boubekeur, Recent Res. Develop. Inorg. Chem. 2 (2000) 165. N. Mahé, O. Guillou, C. Daiguebonne, Y. Gérault, A. Caneschi, C. Sangregorio, J.-Y. Chane-Ching, P.E. Car, T. Roisnel, Inorg. Chem. 44 (2005) 7743. H. Stumph, Y. Pei, O. Kahn, L. Ouahab, F. Le Berre, E. Codjovi, Inorg. Chem. 32 (1993) 5687. Nonius COLLECT: KAPPACCD software; The Netherlands: Delft, 1998. Z. Otwinowski, W. Minor, Meth. Enzymol. (1997) 307. A. Altomare, M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 32 (1999) 115. G.M. Sheldrick, T.R. Schneider, Macromol. Crystallogr. B (1997) 319. W. Kraus, G. Nolze, J. Appl. Crystallogr. 29 (1996) 301. T. Roisnel, J. Rodriguez-Carjaval, Materials Science Forum, in: Proceedings of the Seventh European Powder Diffraction Conference (EPDIC 7), 2000, p. 118. S. Midollini, A. Orlandini, P. Rosa, L. Sorace, Inorg. Chem. 44 (2005) 2060. A.M. Madalan, K. Bernot, F. Pointillart, M. Andruh, A. Caneschi, Eur. J. Inorg. Chem. (2007) 5533. F. Pointillart, K. Bernot, R. Sessoli, D. Gatteschi, Chem.-Eur. J. 13 (2007) 1602.