Solvent-Dependent Self-Assembly of an Oxalato-Based Three

(2) The general use of preformed metal complexes as metalloligands(3) is an illustrative example of the so-called rational self-assembly methods. It a...
0 downloads 3 Views 1MB Size
Download PDF
Communication pubs.acs.org/IC

Solvent-Dependent Self-Assembly of an Oxalato-Based ThreeDimensional Magnet Exhibiting a Novel Architecture Marta Mon,† Thais Grancha,† Michel Verdaguer,‡ Cyrille Train,§ Donatella Armentano,*,⊥ and Emilio Pardo*,† †

Departament de Química Inorgànica, Instituto de Ciencia Molecular, Universitat de València, 46980 Paterna, València, Spain Institut Parisien de Chimie Moléculaire, Université Pierre et Marie Curie-Paris 6, UMR CNRS 8232, 75252 Paris Cedex 05, France § Laboratoire National des Champs Magnétiques Intenses, Université Grenoble-Alpes, UPR CNRS 3228, B.P. 166, 38042 Grenoble Cedex 9, France ⊥ Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, 87036 Rende, Cosenza, Italy ‡

S Supporting Information *

In this work, we report the synthesis, crystal structure, and spectroscopic and magnetic properties of a new bimetallic 3D CP of the formula (Me4N)6{Mn3[Cr(ox)3]4·6CH3OH (1). Despite the existence of a good number of publications reporting bimetallic oxalate-based 2D and 3D CPs,6,7 we show that it is still possible to discover novel architectures such as the binodal (3,4) network found in 1. Moreover, 1 shows a long-range ferromagnetic ordering with the highest critical temperature (TC) ever observed in a manganese−chromium oxalate based CP.6,7a−d Large purple parallelepipeds of 1, suitable for single-crystal Xray diffraction, were grown by slow diffusion of pure methanolic solutions containing the preformed (Me4N)3[Cr(ox)3]·3H2O and Mn(NO3)2·4H2O (see the Supporting Information). Instead, when a mixed H2O/MeOH (1:1 volume ratio) solution under the same reaction conditions was used, a chain compound of the formula Me4N[Mn(H2O)3Cr(ox)3]·H2O (2) was obtained.4b Hence, the solvent plays a key role in the molecular assembly process that leads to the formation of 1 and 2. This is tentatively attributed to the change in the solvent polarity that modifies the hydrogen bonding and coordinating ability of the reactants. In particular, it is well-known that supramolecular interactions, such as hydrogen bonds between the water molecules and free carbonyl groups from oxalate, are enhanced in aqueous solution and favor a partial occupation of the coordination sphere of the metal ions by water molecules in 2 (Figure S1).4b Compound 1 crystallizes in the polar R3c space group of the trigonal system (Table S1). The structure of 1 consists of an anionic 3D network, {MnII3[CrIII(ox)3]4}6−, and tetramethylammonium countercations, which are hosted in the channels running along the [001] direction, together with disordered crystallization methanol solvent molecules (Figures 1, 2, and S2 and S3). Within the anionic oxalate-bridged framework of 1, each CrIII ion is surrounded by three MnII ions, while each MnII ion is surrounded by four CrIII ions, accounting for the final 4:3 Cr/Mn stoichiometry (Figure 1). Overall, the different connectivities of the CrIII and MnII ions in 1, acting as tri- and tetraconnectors,

ABSTRACT: The old but evergreen family of bimetallic oxalates still offers innovative and interesting results. When (Me4N)3[Cr(ox)3]·3H2O is reacted with MnII ions in a nonaqueous solvent, a novel three-dimensional magnet of the formula [N(CH3)4]6[Mn3Cr4(ox)12]·6CH3OH is obtained instead of the one-dimensional compound obtained in water. This new material exhibits an unprecedented stoichiometry with a binodal (3,4) net topology and the highest critical temperature (TC = 7 K) observed so far in a manganese−chromium oxalate based magnet.

T

he synthesis of new two- (2D) or three-dimensional (3D) coordination polymers (CPs)1 draws much attention from scientists working in different fields such as coordination chemistry, crystal engineering, and materials chemistry.1 The interest in CPs of high dimensionality is associated with both structural and functional versatility.2 The general use of preformed metal complexes as metalloligands3 is an illustrative example of the so-called rational self-assembly methods. It allows for a somehow better control of both the structure and properties of the final CP, although the sensitivity to numerous parameters (solvent, temperature, counterions, etc.) leaves an open door toward structural variability. Among the wide variety of organic ligands used to build up high-dimensional CPs, the oxalate ligand (C2O42− = ox) merits special attention because of its large variety of coordination modes4 and its efficiency in transmitting the exchange magnetic coupling between neighboring metal centers.5 A careful look at the literature shows that the combination of tris(oxalate)metalate(III) complexes together with a MII ion in the presence of the appropriate templating countercation can lead to a wide range of bimetallic 2D and 3D CPs with different architectures and thrilling functionalities,2b as exemplified by the pioneering work of Okawa,6a Decurtins,6b,c and Coronado.6d,e Among other functions, they include chirality,6f slow magnetic relaxation,6g second harmonic generation,6h spin-crossover behavior,6i ferroelectricity,6j proton6k,l and electrical6m conductivity, and magnetic ordering.6a−e,7 © XXXX American Chemical Society

Received: May 24, 2016

A

DOI: 10.1021/acs.inorgchem.6b01256 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

through the oxalate bridge are in the range 5.550(2)−5.674(2) Å (Figures 1 and S4). The anionic heterobimetallic open framework of 1 shows receptor-type properties toward the Me4N+ cations through multiple and weak O(ox)···H−C host−guest interactions (Figures 2 and S5). Even if it was not possible to find a reasonable model for the disordered MeOH molecules (see the Supporting Information), structural analysis revealed an estimated volume of accessible solvent voids of 3500.2 Å3, which represents up to 25.0% of the total unit cell volume (13997.0 Å3). This feature should likely account for the cocrystallized methanol molecules embedded inside the rings, in good agreement with elemental analysis for 1. The solvent content of 1 was confirmed by thermogravimetric analysis (Figure S6). Moreover, the powder X-ray diffraction pattern of a polycrystalline sample of 1 is consistent with the calculated one (Figure S7), confirming the purity of the bulk material. Figure 3a shows the thermal dependence of χMT for 1, with χM being the molar magnetic susceptibility per Mn3Cr4 unit and T

Figure 1. View of a fragment of the anionic network of 1. Cr and Mn atoms are depicted as green and blue spheres, respectively, whereas ligands are represented by sticks.

Figure 2. View along the c crystallographic axis of the bimetallic network of 1 showing the channels occupied by the tetramethylammonium cations (yellow spheres).

respectively, yield an unprecedented binodal (3,4) net with (63)(63·83) topology (Figure S2). The CrIII ions are sixcoordinated by three bis(bidentate) oxalate bridging ligands in a trigonally distorted CrO6 octahedron [with an average Cr−O bond distance of 1.978(4) Å]. The MnII ions are eightcoordinated to four oxalate bridges from different [CrIII(ox)3]3− entities in a distorted MnO8 square antiprism (Figure S3). Such a high coordination number for the MnII environment in 1 is rare for first-row transition-metal ions.6k,l,7e,8 In fact, in the wide family of oxalate-bridged manganese−chromium CPs, the eightcoordination of the MnII ion is a key parameter in the observation of the original stoichiometries and topologies.6k,l In 1, the Mn−O bond lengths cover a wide range of values with three short [2.177(5)−2.249(5) Å], two intermediate [2.305(4)−2.374(4) Å], two long [2.412(5)−2.414(5) Å], and one very long [2.662(5) Å] distances. This situation contrasts to that observed in previously reported oxalate-bridged manganese−chromium CPs,6k,l where the MnO8 geometry is slightly less distorted, with bond lengths varying in the ranges 2.22−2.53 and 2.25−2.43 Å, respectively. Finally, the values of the Cr···Mn separations

Figure 3. (a) Temperature dependence of χMT for 1 under an applied dc field of 100 G (T < 50 K) and 1 T (T ≥ 50 K). The inset shows the field dependence of M at 2.0 K. (b) FCM (●) and ZFCM (○) for 1 measured upon cooling and warming, respectively, within a field of 50 G. The inset shows the temperature dependence of χM″ at 100 (green), 1000 (red) and 10000 (blue) Hz.

the temperature. At room temperature, the χMT value is 21.13 cm3 mol−1 K, which is slightly above that expected for the sum of three high-spin MnII ions (SMn = 5/2) and four CrIII ions (SCr = 3 /2), χMT = 20.59 cm3 mol−1 K.5 Upon cooling, χMT increases smoothly until ca. 15 K and then rises abruptly to reach a sharp maximum at about 7.0 K. Overall, the observed magnetic behavior is in agreement with a moderate intramolecular ferromagnetic coupling between the high-spin MnII ions and the CrIII ions through the oxalate bridge, as was previously documented.5 B

DOI: 10.1021/acs.inorgchem.6b01256 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

(France). M.M. and T.G. thank the MINECO and the Universitat de València for predoctoral contracts. Thanks are extended to the Ramón y Cajal Program and the “Ayudas Fundación BBVA a Investigadores y Creadores Culturales” (to E.P.).

The observed ferromagnetic behavior is further confirmed by the M versus H plot (with M being the molar magnetization per Mn3Cr4 unit and H the applied direct-current magnetic field) at 2.0 K (inset of Figure 3a). The isothermal magnetization curve of 1 exhibits a very fast saturation, typical of a long-range ferromagnetic ordering, with the maximum M value of 26.8 Nβ at 7.0 T being close to that expected (M = 27 Nβ).5 Finally, no hysteresis can be observed for 1 because it behaves as a soft magnet.6,7 The divergence of the field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves at 7.0 K (Figure 3b) suggests the onset of a long-range ferromagnetic transition, which is ultimately confirmed by the sharp frequency-independent maxima at 7.0 K in the χ″M versus T plots (inset of Figure 3b). Interestingly, although this ferromagnetic ordering has already been observed in other oxalate-based 2D and 3D manganese− chromium compounds, 1 exhibits a Curie temperature (TC ≈ 7.0 K) not only higher than that seen in other 3D manganese− chromium frameworks presenting large oxalate O−Mn distances and low-symmetry MnII ions (TC ≈ 3.0−4.0 K)6e,k,7d but also higher than those presented by the regular oxalato-based 2D manganese−chromium compounds (TC ≈ 6 K).6a,c,d This can be tentatively related to the fact that 1 exhibits the highest connectivity among all of the reported manganese−chromium networks. In conclusion, we report the novel oxalate-based 3D magnet 1, of the formula [N(CH3)4]6[Mn3Cr4(ox)12]·6CH3OH, constructed by following a well-known metalloligand design strategy that relies on the use of the [CrIII(ox)3]3− complex as a ligand toward MnII ions in the presence of tetramethylammonium organic cations in a nonaqueous solvent. When the polarity of the solvent is changed, the coordination bonds are favored over hydrogen bonds during the self-assembly process, leading to the formation of a 3D coordination network originally in both stoichiometry and topology. In this network, the oxalate-bridged chains previously observed in 2 are further linked by newly formed oxalate bridges. Following its increased connectivity, this new high-dimensional open-framework magnet possesses the highest TC reported so far for oxalate-bridged manganese(II)− chromium(III) magnets.

■

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01256. Experimental preparation and characterization of 1, Table S1, and Figures S1−S7 (PDF) CCDC 1480930 (CIF)

■

REFERENCES

(1) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460− 1494. (2) (a) Maspoch, D.; Ruiz-Molina, D.; Veciana, J. Chem. Soc. Rev. 2007, 36, 770−818. (b) Clemente-León, M.; Coronado, E.; Martí-Gastaldo, C.; Romero, F. M. Chem. Soc. Rev. 2011, 40, 473. (c) Grancha, T.; Ferrando-Soria, J.; Castellano, M.; Julve, M.; Pasán, J.; Armentano, D.; Pardo, E. Chem. Commun. 2014, 50, 7569−7585. (3) Dul, M.-C.; Pardo, E.; Lescouëzec, R.; Journaux, Y.; FerrandoSoria, J.; Ruiz-García, R.; Cano, J.; Julve, M.; Lloret, F.; Cangussu, D.; Pereira, C. L. M.; Stumpf, H. O.; Pasán, J.; Ruiz-Pérez, C. Coord. Chem. Rev. 2010, 254, 2281−2296. (4) (a) Scott, K. L.; Wieghardt, K.; Sykes, A. G. Inorg. Chem. 1973, 12, 655−663. (b) Pardo, E.; Train, C.; Boubekeur, K.; Gontard, G.; Cano, J.; Lloret, F.; Nakatani, K.; Verdaguer, M. Inorg. Chem. 2012, 51, 11582− 11593. (5) Pardo, E.; Train, C.; Lescouëzec, R.; Boubekeur, K.; Ruiz, E.; Lloret, F.; Verdaguer, M. Dalton Trans. 2010, 39, 4951−4958. (6) (a) Tamaki, H.; Zhong, Z. J.; Matsumoto, N.; Kida, S.; Koikawa, M.; Achiwa, N.; Hashimoto, Y.; Okawa, H. J. Am. Chem. Soc. 1992, 114, 6974−6979. (b) Decurtins, S.; Schmalle, H. W.; Schneuwly, P.; Oswald, H. R. Inorg. Chem. 1993, 32, 1888−1892. (c) Pellaux, R.; Schmalle, H. W.; Huber, R.; Fischer, P.; Hauss, T.; Ouladdiaf, B.; Decurtins, S. Inorg. Chem. 1997, 36, 2301−2308. (d) Clemente-León, M.; Coronado, E.; Galán-Mascarós, J.-R.; Gómez-García, C. J. Chem. Commun. 1997, 1727−1728. (e) Coronado, E.; Galán-Mascarós, J. R.; Gómez-García, C. J.; Martínez-Agudo, J. M. Inorg. Chem. 2001, 40, 113−120. (f) Gruselle, M.; Train, C.; Boubekeur, K.; Gredin, P.; Ovanesyan, N. Coord. Chem. Rev. 2006, 250, 2491−2500. (g) Clemente-León, M.; Coronado, E.; Gómez-García, C. J.; López-Jordà, M.; Camón, A.; Repollés, A.; Luis, F. Chem. - Eur. J. 2014, 20, 1669−1676. (h) Train, C.; Nuida, T.; Gheorghe, R.; Gruselle, M.; Ohkoshi, S. J. Am. Chem. Soc. 2009, 131, 16838−16843. (i) Clemente-León, M.; Coronado, E.; López-Jordà, M.; Desplanches, C.; Asthana, S.; Wang, H.; Létard, J.-F. Chem. Sci. 2011, 2, 1121. (j) Pardo, E.; Train, C.; Liu, H.; Chamoreau, L.-M.; Dkhil, B.; Boubekeur, K.; Lloret, F.; Nakatani, K.; Tokoro, H.; Ohkoshi, S.; Verdaguer, M. Angew. Chem., Int. Ed. 2012, 51, 8356−8360. (k) Pardo, E.; Train, C.; Gontard, G.; Boubekeur, K.; Fabelo, O.; Liu, H.; Dkhil, B.; Lloret, F.; Nakagawa, K.; Tokoro, H.; Ohkoshi, S.; Verdaguer, M. J. Am. Chem. Soc. 2011, 133, 15328−15331. (l) Maxim, C.; Ferlay, S.; Tokoro, H.; Ohkoshi, S.-I.; Train, C. Chem. Commun. 2014, 50, 5629−5632. (m) Coronado, E.; Galán-Mascarós, J. R.; Gómez-García, C. J.; Laukhin, V. Nature 2000, 408, 447−449. (7) (a) Carling, S. G.; Mathonière, C.; Day, P.; Malik, K. M. A.; Coles, S. J.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1996, 1839−1843. (b) Mathonière, C.; Nuttall, C. J.; Carling, S. G.; Day, P. Inorg. Chem. 1996, 35, 1201−1206. (c) Coronado, E.; Galán-Mascarós, J.-R.; GómezGarcía, C.-J.; Ensling, J.; Gütlich, P. Chem. - Eur. J. 2000, 6, 552−563. (d) Ballester, G.; Coronado, E.; Gimenez-Saiz, C.; Romero, F. M. Angew. Chem., Int. Ed. 2001, 40, 792−795. (e) Armentano, D.; De Munno, G.; Mastropietro, T. F.; Julve, M.; Lloret, F. Chem. Commun. 2004, 1160− 1161. (f) Armentano, D.; De Munno, G.; Mastropietro, T. F.; Julve, M.; Lloret, F. J. Am. Chem. Soc. 2005, 127, 10778−10779. (g) CorellaOchoa, M. N.; Benet-Buchholz, J.; Martínez-Belmonte, M.; GalánMascarós, J. R. Inorg. Chem. 2015, 54, 4678−4687. (8) (a) Rochon, F. D.; Melanson, R.; Andruh, M. Inorg. Chem. 1996, 35, 6086−6092. (b) Desjardins, S. R.; Wilcox, D. E.; Musselman, R. L.; Solomon, E. I. Inorg. Chem. 1987, 26, 288−300.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (D.A.). *E-mail: [email protected] (E.P.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the MINECO (Spain; Projects CTQ2013-46362-P and CTQ2013-44844-P and Excellence Unit “Maria de Maeztu” MDM-2015-0538), the Ministero dell’Istruzione, dell’Università e della Ricerca (Italy), and CNRS C

DOI: 10.1021/acs.inorgchem.6b01256 Inorg. Chem. XXXX, XXX, XXX−XXX