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Template effect using aroylhydrazone ligand: Synthesis, crystal structure and magnetic properties of a novel ferromagnetically coupled heptanuclear nickel(II) cluster with a vertex-shared dicubane structure
Inorganica Chimica Acta 455 (2017) 231–234
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Research paper
Template effect using aroylhydrazone ligand: Synthesis, crystal structure and magnetic properties of a novel ferromagnetically coupled heptanuclear nickel(II) cluster with a vertex-shared dicubane structure Samir Mameri Laboratoire de Chimie Moléculaire, UMR CNRS 7509, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
a r t i c l e
i n f o
Article history: Received 31 August 2016 Received in revised form 24 October 2016 Accepted 11 November 2016 Available online 12 November 2016 Keywords: Template effect Crystal structure Magnetic properties Coordination cluster Aroylhydrazone Nickel(II) Cubanes
a b s t r a c t The reaction of aroylhydrazone ligand H2L with Ni(II) metal ions afforded, upon crystallization under aerobic conditions, a novel heptanuclear Ni(II) cluster without this ligand (template effect of aroylhydrazone ligand). The heptanuclear [NiII7] compound 1 displays a metallic core which can be presented as a vertexshared dicubane structure. Noteworthy, (i) this ligand is used for the first time in coordination chemistry, and (ii) this cluster does represent the first example in Nickel chemistry that possesses this topology with a structure not supported by any organic bridging ligand. Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of magnetic bistability in dodecamanganese acetate [1,2], scientific interest in molecular clusters containing magnetic transition-metal ions has soared. Among the diverse reasons for this are the search for models of metal-containing biological sites [3], and new high-spin clusters and single-molecule magnets [4,5]. There continues to be a need for new synthetic methods to such molecules. One fertile approach is to use chelates containing good bridging groups that can foster formation of polynuclear products. However, the design and synthesis of molecular materials with predictable magnetic properties continues to remain a challenging task, because the structural factors that govern exchange coupling between paramagnetic centres are complex and elusive. Thus, new ligands are needed to provide us with the opportunity to attain new structural types and spin topologies. Conventional stepwise covalent construction face limitations. Indeed, coordinative processes that take place in solution always accompany with great complication, which hampers the designable synthesis of such compounds. However, the utilization
E-mail address: [email protected] http://dx.doi.org/10.1016/j.ica.2016.11.011 0020-1693/Ó 2016 Elsevier B.V. All rights reserved.
of supramolecular methods, e.g. hydrogen-bonding, metalmediated aggregation via reversible metal-ligand interactions, and template effects, can result in spectacular supramolecular structures. As part of our investigations on polynuclear systems exhibiting SMM properties, one approach is to prepare new open-chain compartmentalized ligands with the aim of capturing different types of paramagnetic centres to produce magnetically interesting systems in which their interconnection would be potentially left to the appreciation of the bridging ligands [6,7]. In particular, metal complexes of aroylhydrazone ligands have remained an attractive area of research for coordination chemists and structural chemists because of their versatile coordination chemistry and capability to generate varied molecular architecture and coordination geometry [8]. In this paper we wish to report the synthesis, crystal structure, and magnetic properties of an unexpected heptanuclear [NiII7(l3-OH)8(DMF)20(ClO4)6] coordination compound based on aroylhydrazone ligand H2L (Scheme 1). It is worth noting that (i) this ligand (although herein acting as template agent) is used for the first time in coordination chemistry, and (ii) this coordination compound represents the first example in Nickel chemistry that possesses this topology with a structure not supported by any organic ligand.
232
S. Mameri / Inorganica Chimica Acta 455 (2017) 231–234 Table 1 Crystal data and structure refinement summary for compounds 1.
Scheme 1. Chemical structure of 2-hydroxy-N0 -(4-methylpentan-2-ylidene)benzohydrazide (H2L ligand).
2. Results and discussion 2.1. Synthesis of the ligand and complexes Aroylhydrazone ligand H2L can be easily prepared in quantitative yield, using the single MW synthesis developed by Barros’ group [9]. The literature documents no example of this ligand in the construction of coordination compounds. The complexes described in this work were obtained upon reaction of H2L ligand with a base (Et3N) and Ni(ClO4)6H2O in DMF mixture, under aerobic conditions, and crystallized by slow diffusion of Et2O to the mother liquor at room temperature [10]. Various reaction conditions such as reaction components, stoichiometry, concentration, reaction time, pH and temperature were investigated, and we report here the optimum conditions that we have established. It is also worth noting that since the stirring of Ni(ClO4)6H2O salts in DMF solutions have not afforded any structural motif, it can be claimed that H2L notably acts as a template in the construction of this novel heptanuclear Ni(II) cluster. 2.2. Crystal structure of the heptanuclear [Ni7] [11] X-ray structure determination of 1 revealed a heptanuclear Ni (II) coordination cluster (Fig. 1) which crystallizes in the monoclinic C2/c space group. Crystal data and refinement details of the structure determination for 1 are listed in Table 1.
Compound
12DMF
Empirical formula Formula weight Temperature/K Crystal system Space group a/Å b/Å c/Å a/° b/° c/° Volume/Å3 Z qcalcg/cm3 l/mm1 F(0 0 0) Crystal size/mm3 Radiation 2H range for data collection/° Index ranges Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit on F2 Final R indexes [I P 2r (I)] Final R indexes [all data] Largest diff. peak/hole/e Å3
C60H148Cl6N20Ni7O52 2605.65 173 monoclinic C2/c 21.9453(12) 23.2318(9) 23.5694(13) 90.00 104.245(6) 90.00 11646.9(10) 4 1.486 1.337 5448.0 0.34 0.14 0.1 Mo Ka (k = 0.71073) 5.74–58.42 29 6 h 6 17, 23 6 k 6 29, 30 6 l 6 24 23,173 13,117 [Rint = 0.0308, Rsigma = 0.0584] 13,117/4/692 1.038 R1 = 0.0498, wR2 = 0.1122 R1 = 0.0789, wR2 = 0.1311 0.50/0.52
Notably, no molecules of H2L are present in the complex, as the main core consists entirely of the Ni metal centres, dimethylformamide (DMF) solvent molecules and bridging l3-OH groups. The structure contains a central Ni atom (Ni4) which is located to an inversion centre and linked to the remaining crystallographically independent metal centres (Ni1, Ni2, Ni3) through three O atoms from the l3-OH groups (O2, O3, O4). These bridging groups link two peripheral Ni atoms with the central Ni atom, while a fourth l3-OH group bridges the three peripheral metal centres through the O1 oxygen atom. Additionally, each of these peripheral metal centres also coordinate to three O atoms of DMF solvent molecules. As a result, all Ni atoms do possess a distorted octahedral geometry. Ni1, Ni2 and Ni3 centres have similar coordination, where the basal plane of each octahedron consists of two DMF oxygen atoms and two bridging O atoms from l3-OH groups. The apical positions are occupied by one DMF oxygen atom and one bridging O atom. In the case of Ni4, all positions are occupied by bridging O atoms. Two dimethylformamide solvent molecules are also present in the crystal lattice, as well as six perchlorate anions which complete the charge balance. No hydrogen bonds or other supramolecular interactions are observed within the structure. Selected interatomic bond distances and angles are given in Table 2. From topological point of view, the metallic core of cluster 1 can be presented as a vertex-shared dicubane structure and enumerated as 3,6M7-2 (Fig. 2) [12]. Although fused cubanes are less rare for other transition metals such as iron [13], literature survey indicates that compound 1 represents the fourth example in Nickel chemistry that possess this topology [14–16] and notably the first example whose structure is not supported by any organic ligand. 2.3. Magnetic studies [17]
Fig. 1. Structure of compound 1. For clarity, H atoms, counter-ions and lattice solvent molecules are omitted. Identification of the atoms: Ni green, O red, N blue, C black. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The actual heptanuclear core of 1 represents corner-shared double cubanes. [Ni7] cluster 1 may be viewed as the condensation of two [Ni4] groups sharing one nickel(II) ion. Despite the tendency of Ni(II) containing clusters to couple ferromagnetically, comparatively few heptanuclear structures are known. Most of the previously reported heptanuclear clusters show low symmetry,
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S. Mameri / Inorganica Chimica Acta 455 (2017) 231–234 Table 2 Selected bond distances (Å) and angles (°) for 12DMF. Ni1AO1 Ni1AO2 Ni1AO4 Ni1AO5 Ni1AO6 Ni1AO7 Ni2AO1 Ni2AO2 Ni2AO3 Ni2AO8 Ni2AO9 Ni2AO10 Ni3AO1 Ni3AO3 Ni3AO4 Ni3AO11 a
2.063(2) 2.020(2) 2.014(2) 2.075(3) 2.096(2) 2.066(2) 2.084(2) 2.027(2) 2.019(2) 2.049(2) 2.099(2) 2.079(2) 2.066(2) 2.025(2) 2.029(2) 2.043(2)
Ni3AO12 Ni3AO13 Ni4AO2a Ni4AO2 Ni4AO3 Ni4AO3a Ni4AO4 Ni4AO4a Ni1AO1ANi2 Ni1AO1ANi3 Ni1AO2ANi2 Ni1AO2ANi4 Ni1AO4ANi3 Ni1AO4ANi4 Ni2AO1ANi3 Ni2AO2ANi4
2.059(3) 2.086(2) 2.053(2) 2.053(2) 2.047(2) 2.047(2) 2.036(2) 2.036(2) 97.77(10) 96.33(9) 101.08(10) 96.23(9) 99.08(9) 96.93(9) 96.82(9) 94.58(8)
Ni2AO3ANi3 Ni2AO3ANi4 Ni3AO3ANi4 Ni3AO4ANi4 Ni1ANi2 Ni1ANi3 Ni1ANi4 Ni2ANi3 Ni2ANi4 Ni3ANi4
100.26(10) 94.97(8) 96.16(9) 96.37(9) 3.1243(6) 3.0762(6) 3.0319(5) 3.1038(6) 2.9977(4) 3.0299(4)
1/2-X, 3/2-Y, 1-Z.
Fig. 2. Topological representation 3,6M7-2 of heptanuclear [NiII7] cluster 1.
showing a variety of vertex- and edge-sharing of the NiX6 coordination polyhedra [12]. The magnetic studies on 1 show dominant ferromagnetic interactions between the nickel(II) ions, in agreement with the structural feature. Because of unavailability of a simulation program, the theoretical simulation of experimental data was not possible. Such core has been found in hydroxo and alkoxo clusters (Co [18], Ni [12,14], Cu [7], Zn [19], Cd [20], Ca [21]) and in the case of Ni(II) and Co(II) the clusters do exhibit dominant ferromagnetic behavior [22,23]. Direct-current (dc) magnetic susceptibility studies of 1 were performed under an applied magnetic field of 1000 Oe in the 300–4.0 K temperature range (Fig. 3). The value of vT at 300 K of 11.7 cm3 K mol1 is larger than expected for seven isolated NiII ions with g = 2.0 (7.0 cm3 mol1 K) which can be due to the ferromagnetic interactions between nickel ions, together with the contribution of a bigger value of g factor which is usually larger than 2.0 for NiII ion. The compound shows a stable increase of the vT product on decreasing the temperature from 300 to 4 K, reaching a value for vT of 36.7 cm3 K mol1 at 4 K, suggesting that ferromagnetic interactions between paramagnetic centres are present in this molecule. The maximal value of vT 36.7 cm3 mol1 K at low temperature as well the magnetization measurements (Fig. 3, inset) suggest the presence of S = 7 (g 2.3) as the ground state. All the experimental data notably indicate the occurrence of an overall ferromagnetic interaction in complex 1.
Fig. 3. vT and v versus T plots for cluster 1. Inset: Magnetization M vs applied field H at 4.0 K.
Based on X-ray analysis, the coordination heptanuclear core of 1 represents corner-shared double cubanes of Ni4 in which the bridging function between Ni ions are oxygen atoms in which the NiAOANi angles and NiAO distances are similar (Table 2). The average values for the NiAOANi angles in [Ni7] cluster is ca. 97°. According to magneto-structural correlation of cubanes Ni4 alcoxo-bridged clusters [21], this angle matches well with the presence of ferromagnetic interactions between the Ni(II) paramagnetic centres with theoretical value of exchange parameters equal to +8.0 cm1. The experimental values of magnetization at 7.0 T and temperature 4.0 K (Fig. 3, inset) are in agreement with a S = 7 ground state, M = 16.7 Nb against the expected value of 14 Nb for g = 2. Assuming that only the spin ground state S = 7 of the molecule is significantly populated, the magnetization data make us to conclude that the g can have values P 2.3.
3. Conclusions In conclusion, our discovery of coordination compound 1 has revealed the first example of heptanuclear Ni(II) cluster whose
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structure is not supported by any organic ligand. Magnetic measurements on isolated single crystals have interestingly revealed 1 to be in a high symmetry dicubane motif. Magnetically, cluster 1 appears to behave as expected with a ferromagnetic interaction within the Ni(II) ions, yielding a S = 7 ground state.
[11]
Acknowledgments This work was supported by the Centre National de la Recherche Scientifique (CNRS). The author acknowledge the Institute für Anorganische Chemie (KIT, Karlsruhe, GERMANY) for provision of instrumentation on the SQUID. Dr. George E. Kostakis (University of Sussex, UK) is gratefully thanked for the scientific discussions.
[12]
[13]
References [1] R. Sessoli, H.-L. Tsai, A.R. Shake, S. Wang, J.B. Vincent, K. Folting, D. Gatteschi, G. Christou, D.N. Hendrickson, J. Am. Chem. Soc. 115 (1993) 1804. [2] R. Sessoli, D. Gatteschi, A. Caneschi, M.A. Novak, Nature 365 (1993) 141. [3] (a) A. Caneschi, F. Ferraro, D. Gatteschi, M.C. Melandri, P. Rey, R. Sessoli, Angew. Chem. Int. Ed. 28 (1989) 1365; (b) T.G. Carrell, A.M. Tyryshkin, G.C. Dismukes, J. Biol. Inorg. Chem. 7 (2002) 2; (c) A. Mishra, W. Wernsdorfer, K.A. Abboud, G. Christou, Chem. Commun. 54 (2005). [4] A.L. Barra, A. Caneschi, A. Cornia, F. Fabrizi de Biani, D. Gatteschi, C. Sangregorio, R. Sessoli, L. Sorace, J. Am. Chem. Soc. 121 (1999) 5302–5310; . For reviews, see:(a) G. Christou, D. Gatteschi, D.N. Hendrickson, R. Sessoli, MRS Bull. 25 (2000) 66; (b) G. Aromi, E.K. Brechin, Struct. Bonding 122 (2006) 1. [5] G. Christou, Polyhedron 24 (2005) 2065; M. Mannini, F. Pineider, P. Sainctavit, C. Danieli, E. Otero, C. Sciancalepore, A.M. Talarico, M.-A. Arrio, A. Cornia, D. Gatteschi, R. Sessoli, Nat. Mater. 8 (2009) 194; M. Mannini, F. Pineider, C. Danieli, F. Totti, L. Sorace, Ph. Sainctavit, M.-A. Arrio, E. Otero, L. Joly, J.C. Cezar, A. Cornia, R. Sessoli, Nature 468 (2010) 417; J.A.J. Burgess, L. Malavolti, V. Lanzilotto, M. Mannini, S. Yan, S. Ninova, F. Totti, S. Rolf-Pissarczyk, A. Cornia, R. Sessoli, S. Loth, Nat. Commun. 6 (2015). [6] See and references therein: (a) A.M. Ako, S.M. Alam, S. Mameri, Y. Lan, M. Stocker, P. Müller, C.E. Anson, M. Hibert, A.K. Powell, Eur. J. Inorg. Chem. 26 (2012) 4131; (b) S. Mameri, A.M. Ako, F. Yesil, M. Hibert, Y. Lan, C.E. Anson, A.K. Powell, Eur. J. Inorg. Chem. 26 (2014) 4326. [7] See and references therein: (a) A. Domingo, D. Specklin, V. Rosa, S. Mameri, V. Robert, R. Welter, Eur. J. Inorg. Chem. 15 (2014) 2552; (b) S. Mameri, D. Specklin, R. Welter, C. R. Chim. 18 (2015) 1370. [8] See for instance and references therein: S. Naskar, S. Naskar, R.J. Butcher, S.K. Chattopadhyay, Inorg. Chim. Acta 363 (2010) 3641. [9] M. Andrade, M.T. Barros, J. Comb. Chem. 12 (2010) 245. [10] Experimental procedure: Et3N (278 ll, 2 mmol) was added to a solution of H2L (260 mg, 1 mmol) in DMF (15 ml). Then, the resulting solution was stirred for 5 min at room temperature before Ni(ClO4)26(H2O) (730 mg, 2 mmol) was
[14] [15] [16] [17]
[18]
[19]
[20]
[21] [22] [23]
added. The resulting green solution was further stirred for 10 min at this temperature and filtrated. Notably, (i) big blue block shaped crystals identified as [Ni7] (1), and (ii) small blue needle shaped crystals identified as NiL2 (2) were obtained by slow diffusion of Et2O after a 10-day standing at room temperature. Single crystal X-ray diffraction measurements were performed at 173 K by using a Nonius Kappa CCD or a Bruker APEX-II CCD diffractometer with Mo-Ka radiation. The crystal structures were solved by direct methods and refined by employing full-matrix least-squares on F2 (SHELXL-97). All nonhydrogen atoms were refined anisotropically, and the hydrogen atoms of organic ligands were introduced by using a riding model (SHELXL-97). CCDC-1478902 (for 1) and -1478903 (for 2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. See for instance and references therein: (a) G. Luca, A. Andrea, C. Antonio, C. Fabretti, A. Caneschi, D. Gatteschi, Inorg. Chem. (1998) 3759; (b) G.E. Kostakis, V.A. Blatov, D.M. Proserpio, Dalton Trans. 41 (2012) 4634. S.W. Saalfrank, I. Bernt, E. Uller, F. Hampel, Angew. Chem., Int. Ed. 34 (1995) 2716; R. Bagai, M.R. Daniels, K.A. Abboud, G. Christou, Inorg. Chim. Acta 47 (2008) 3318. T.D. Keene, M.B. Hursthouse, D.J. Price, New J. Chem. 28 (2004) 558. S. Petit, P. Neugebauer, G. Pilet, G. Chastanet, A.-L. Barra, A.B. Antunes, W. Wernsdorfer, D. Luneau, Inorg. Chem. 51 (2012) 6645. X. Xu, S. Gou, W. Huang, Y. Ma, Y. Li, Eur. J. Inorg. Chem. (2003) 2054. Magnetic susceptibility data (4.0–300 K) were collected on powdered blue block shaped crystals using a SQUID magnetometer (Quantum Design MPMSXL), applying magnetic fields of 0.1 T. All the data were corrected for the contribution of the sample holder and the diamagnetism of the samples estimated from Pascal’s constants (see: a) P. Pascal, Ann. Chim. Phys. 19 (1910) 5; (b) O. Kahn, Molecular Magnetism, VCH Publishers, Inc., New York, Weinheim, Cambridge, 1993. (a) R.-K. Chiang, C.-C. Huang, C.-S. Wur, Inorg. Chem. 40 (2001) 3237; (b) Q. Chen, M.-H. Zeng, Y.-L. Zhou, H.-H. Zou, M. Kurmoo, Chem. Mater. 22 (2010) 2114. (a) J.A. Real, G. De Munno, R. Chiappetta, M. Julve, F. Lloret, Y. Journaux, J.-C. Colin, G. Blondin, Angew. Chem., Int. Ed. 33 (1994) 1184; (b) X. Xi, Y. Fang, T. Dong, Y. Cui, Angew. Chem., Int. Ed. 50 (2011) 1154; (c) X. Liu, J.A. McAllister, M.P. de Miranda, E.J.L. McInnes, C.A. Kilner, M.A. Halcrow, Chem. Eur. J. 10 (2004) 1827. (a) A. Charette, A. Beauchemin, S. Francoeur, F. Belanger-Gariepy, G.D. Enright, Chem. Commun. (2002) 466; (b) M.L. Ziegler, J. Weiss, Angew. Chem. 82 (1970) 931; (c) J. Lewin´ski, K. Suwała, M. Kubisiak, Z. Ochal, I. Justyniak, J. Lipkowski, Angew. Chem. Int. Ed. 47 (2008) 7888; (d) J. Lewin´ski, W. Marciniak, J. Lipkowski, I. Justyniak, J. Am. Chem. Soc. 125 (2003) 12698; (e) T.J. Boyle, S.D. Bunge, N.L. Andrews, L.E. Matzen, K. Sieg, M.A. Rodriguez, T.J. Headley, Chem. Mater. 16 (2004) 3279; (f) S. Jana, R.J.F. Berger, R. Fröhlich, T. Pape, N.W. Mitzel, Inorg. Chem. 46 (2007) 4293. I. Busching, H. Strasdeit, J. Chem. Soc., Chem. Commun. (1994) 2789. K.M. Fromm, Chem. Commun. (1999) 1659. A. Das, F.J. Klinke, S. Demeshko, S. Meyer, S. Dechert, F. Meyer, Inorg. Chem. 51 (2012) 8141.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Research paper
Template effect using aroylhydrazone ligand: Synthesis, crystal structure and magnetic properties of a novel ferromagnetically coupled heptanuclear nickel(II) cluster with a vertex-shared dicubane structure Samir Mameri Laboratoire de Chimie Moléculaire, UMR CNRS 7509, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
a r t i c l e
i n f o
Article history: Received 31 August 2016 Received in revised form 24 October 2016 Accepted 11 November 2016 Available online 12 November 2016 Keywords: Template effect Crystal structure Magnetic properties Coordination cluster Aroylhydrazone Nickel(II) Cubanes
a b s t r a c t The reaction of aroylhydrazone ligand H2L with Ni(II) metal ions afforded, upon crystallization under aerobic conditions, a novel heptanuclear Ni(II) cluster without this ligand (template effect of aroylhydrazone ligand). The heptanuclear [NiII7] compound 1 displays a metallic core which can be presented as a vertexshared dicubane structure. Noteworthy, (i) this ligand is used for the first time in coordination chemistry, and (ii) this cluster does represent the first example in Nickel chemistry that possesses this topology with a structure not supported by any organic bridging ligand. Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of magnetic bistability in dodecamanganese acetate [1,2], scientific interest in molecular clusters containing magnetic transition-metal ions has soared. Among the diverse reasons for this are the search for models of metal-containing biological sites [3], and new high-spin clusters and single-molecule magnets [4,5]. There continues to be a need for new synthetic methods to such molecules. One fertile approach is to use chelates containing good bridging groups that can foster formation of polynuclear products. However, the design and synthesis of molecular materials with predictable magnetic properties continues to remain a challenging task, because the structural factors that govern exchange coupling between paramagnetic centres are complex and elusive. Thus, new ligands are needed to provide us with the opportunity to attain new structural types and spin topologies. Conventional stepwise covalent construction face limitations. Indeed, coordinative processes that take place in solution always accompany with great complication, which hampers the designable synthesis of such compounds. However, the utilization
E-mail address: [email protected] http://dx.doi.org/10.1016/j.ica.2016.11.011 0020-1693/Ó 2016 Elsevier B.V. All rights reserved.
of supramolecular methods, e.g. hydrogen-bonding, metalmediated aggregation via reversible metal-ligand interactions, and template effects, can result in spectacular supramolecular structures. As part of our investigations on polynuclear systems exhibiting SMM properties, one approach is to prepare new open-chain compartmentalized ligands with the aim of capturing different types of paramagnetic centres to produce magnetically interesting systems in which their interconnection would be potentially left to the appreciation of the bridging ligands [6,7]. In particular, metal complexes of aroylhydrazone ligands have remained an attractive area of research for coordination chemists and structural chemists because of their versatile coordination chemistry and capability to generate varied molecular architecture and coordination geometry [8]. In this paper we wish to report the synthesis, crystal structure, and magnetic properties of an unexpected heptanuclear [NiII7(l3-OH)8(DMF)20(ClO4)6] coordination compound based on aroylhydrazone ligand H2L (Scheme 1). It is worth noting that (i) this ligand (although herein acting as template agent) is used for the first time in coordination chemistry, and (ii) this coordination compound represents the first example in Nickel chemistry that possesses this topology with a structure not supported by any organic ligand.
232
S. Mameri / Inorganica Chimica Acta 455 (2017) 231–234 Table 1 Crystal data and structure refinement summary for compounds 1.
Scheme 1. Chemical structure of 2-hydroxy-N0 -(4-methylpentan-2-ylidene)benzohydrazide (H2L ligand).
2. Results and discussion 2.1. Synthesis of the ligand and complexes Aroylhydrazone ligand H2L can be easily prepared in quantitative yield, using the single MW synthesis developed by Barros’ group [9]. The literature documents no example of this ligand in the construction of coordination compounds. The complexes described in this work were obtained upon reaction of H2L ligand with a base (Et3N) and Ni(ClO4)6H2O in DMF mixture, under aerobic conditions, and crystallized by slow diffusion of Et2O to the mother liquor at room temperature [10]. Various reaction conditions such as reaction components, stoichiometry, concentration, reaction time, pH and temperature were investigated, and we report here the optimum conditions that we have established. It is also worth noting that since the stirring of Ni(ClO4)6H2O salts in DMF solutions have not afforded any structural motif, it can be claimed that H2L notably acts as a template in the construction of this novel heptanuclear Ni(II) cluster. 2.2. Crystal structure of the heptanuclear [Ni7] [11] X-ray structure determination of 1 revealed a heptanuclear Ni (II) coordination cluster (Fig. 1) which crystallizes in the monoclinic C2/c space group. Crystal data and refinement details of the structure determination for 1 are listed in Table 1.
Compound
12DMF
Empirical formula Formula weight Temperature/K Crystal system Space group a/Å b/Å c/Å a/° b/° c/° Volume/Å3 Z qcalcg/cm3 l/mm1 F(0 0 0) Crystal size/mm3 Radiation 2H range for data collection/° Index ranges Reflections collected Independent reflections Data/restraints/parameters Goodness-of-fit on F2 Final R indexes [I P 2r (I)] Final R indexes [all data] Largest diff. peak/hole/e Å3
C60H148Cl6N20Ni7O52 2605.65 173 monoclinic C2/c 21.9453(12) 23.2318(9) 23.5694(13) 90.00 104.245(6) 90.00 11646.9(10) 4 1.486 1.337 5448.0 0.34 0.14 0.1 Mo Ka (k = 0.71073) 5.74–58.42 29 6 h 6 17, 23 6 k 6 29, 30 6 l 6 24 23,173 13,117 [Rint = 0.0308, Rsigma = 0.0584] 13,117/4/692 1.038 R1 = 0.0498, wR2 = 0.1122 R1 = 0.0789, wR2 = 0.1311 0.50/0.52
Notably, no molecules of H2L are present in the complex, as the main core consists entirely of the Ni metal centres, dimethylformamide (DMF) solvent molecules and bridging l3-OH groups. The structure contains a central Ni atom (Ni4) which is located to an inversion centre and linked to the remaining crystallographically independent metal centres (Ni1, Ni2, Ni3) through three O atoms from the l3-OH groups (O2, O3, O4). These bridging groups link two peripheral Ni atoms with the central Ni atom, while a fourth l3-OH group bridges the three peripheral metal centres through the O1 oxygen atom. Additionally, each of these peripheral metal centres also coordinate to three O atoms of DMF solvent molecules. As a result, all Ni atoms do possess a distorted octahedral geometry. Ni1, Ni2 and Ni3 centres have similar coordination, where the basal plane of each octahedron consists of two DMF oxygen atoms and two bridging O atoms from l3-OH groups. The apical positions are occupied by one DMF oxygen atom and one bridging O atom. In the case of Ni4, all positions are occupied by bridging O atoms. Two dimethylformamide solvent molecules are also present in the crystal lattice, as well as six perchlorate anions which complete the charge balance. No hydrogen bonds or other supramolecular interactions are observed within the structure. Selected interatomic bond distances and angles are given in Table 2. From topological point of view, the metallic core of cluster 1 can be presented as a vertex-shared dicubane structure and enumerated as 3,6M7-2 (Fig. 2) [12]. Although fused cubanes are less rare for other transition metals such as iron [13], literature survey indicates that compound 1 represents the fourth example in Nickel chemistry that possess this topology [14–16] and notably the first example whose structure is not supported by any organic ligand. 2.3. Magnetic studies [17]
Fig. 1. Structure of compound 1. For clarity, H atoms, counter-ions and lattice solvent molecules are omitted. Identification of the atoms: Ni green, O red, N blue, C black. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
The actual heptanuclear core of 1 represents corner-shared double cubanes. [Ni7] cluster 1 may be viewed as the condensation of two [Ni4] groups sharing one nickel(II) ion. Despite the tendency of Ni(II) containing clusters to couple ferromagnetically, comparatively few heptanuclear structures are known. Most of the previously reported heptanuclear clusters show low symmetry,
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S. Mameri / Inorganica Chimica Acta 455 (2017) 231–234 Table 2 Selected bond distances (Å) and angles (°) for 12DMF. Ni1AO1 Ni1AO2 Ni1AO4 Ni1AO5 Ni1AO6 Ni1AO7 Ni2AO1 Ni2AO2 Ni2AO3 Ni2AO8 Ni2AO9 Ni2AO10 Ni3AO1 Ni3AO3 Ni3AO4 Ni3AO11 a
2.063(2) 2.020(2) 2.014(2) 2.075(3) 2.096(2) 2.066(2) 2.084(2) 2.027(2) 2.019(2) 2.049(2) 2.099(2) 2.079(2) 2.066(2) 2.025(2) 2.029(2) 2.043(2)
Ni3AO12 Ni3AO13 Ni4AO2a Ni4AO2 Ni4AO3 Ni4AO3a Ni4AO4 Ni4AO4a Ni1AO1ANi2 Ni1AO1ANi3 Ni1AO2ANi2 Ni1AO2ANi4 Ni1AO4ANi3 Ni1AO4ANi4 Ni2AO1ANi3 Ni2AO2ANi4
2.059(3) 2.086(2) 2.053(2) 2.053(2) 2.047(2) 2.047(2) 2.036(2) 2.036(2) 97.77(10) 96.33(9) 101.08(10) 96.23(9) 99.08(9) 96.93(9) 96.82(9) 94.58(8)
Ni2AO3ANi3 Ni2AO3ANi4 Ni3AO3ANi4 Ni3AO4ANi4 Ni1ANi2 Ni1ANi3 Ni1ANi4 Ni2ANi3 Ni2ANi4 Ni3ANi4
100.26(10) 94.97(8) 96.16(9) 96.37(9) 3.1243(6) 3.0762(6) 3.0319(5) 3.1038(6) 2.9977(4) 3.0299(4)
1/2-X, 3/2-Y, 1-Z.
Fig. 2. Topological representation 3,6M7-2 of heptanuclear [NiII7] cluster 1.
showing a variety of vertex- and edge-sharing of the NiX6 coordination polyhedra [12]. The magnetic studies on 1 show dominant ferromagnetic interactions between the nickel(II) ions, in agreement with the structural feature. Because of unavailability of a simulation program, the theoretical simulation of experimental data was not possible. Such core has been found in hydroxo and alkoxo clusters (Co [18], Ni [12,14], Cu [7], Zn [19], Cd [20], Ca [21]) and in the case of Ni(II) and Co(II) the clusters do exhibit dominant ferromagnetic behavior [22,23]. Direct-current (dc) magnetic susceptibility studies of 1 were performed under an applied magnetic field of 1000 Oe in the 300–4.0 K temperature range (Fig. 3). The value of vT at 300 K of 11.7 cm3 K mol1 is larger than expected for seven isolated NiII ions with g = 2.0 (7.0 cm3 mol1 K) which can be due to the ferromagnetic interactions between nickel ions, together with the contribution of a bigger value of g factor which is usually larger than 2.0 for NiII ion. The compound shows a stable increase of the vT product on decreasing the temperature from 300 to 4 K, reaching a value for vT of 36.7 cm3 K mol1 at 4 K, suggesting that ferromagnetic interactions between paramagnetic centres are present in this molecule. The maximal value of vT 36.7 cm3 mol1 K at low temperature as well the magnetization measurements (Fig. 3, inset) suggest the presence of S = 7 (g 2.3) as the ground state. All the experimental data notably indicate the occurrence of an overall ferromagnetic interaction in complex 1.
Fig. 3. vT and v versus T plots for cluster 1. Inset: Magnetization M vs applied field H at 4.0 K.
Based on X-ray analysis, the coordination heptanuclear core of 1 represents corner-shared double cubanes of Ni4 in which the bridging function between Ni ions are oxygen atoms in which the NiAOANi angles and NiAO distances are similar (Table 2). The average values for the NiAOANi angles in [Ni7] cluster is ca. 97°. According to magneto-structural correlation of cubanes Ni4 alcoxo-bridged clusters [21], this angle matches well with the presence of ferromagnetic interactions between the Ni(II) paramagnetic centres with theoretical value of exchange parameters equal to +8.0 cm1. The experimental values of magnetization at 7.0 T and temperature 4.0 K (Fig. 3, inset) are in agreement with a S = 7 ground state, M = 16.7 Nb against the expected value of 14 Nb for g = 2. Assuming that only the spin ground state S = 7 of the molecule is significantly populated, the magnetization data make us to conclude that the g can have values P 2.3.
3. Conclusions In conclusion, our discovery of coordination compound 1 has revealed the first example of heptanuclear Ni(II) cluster whose
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structure is not supported by any organic ligand. Magnetic measurements on isolated single crystals have interestingly revealed 1 to be in a high symmetry dicubane motif. Magnetically, cluster 1 appears to behave as expected with a ferromagnetic interaction within the Ni(II) ions, yielding a S = 7 ground state.
[11]
Acknowledgments This work was supported by the Centre National de la Recherche Scientifique (CNRS). The author acknowledge the Institute für Anorganische Chemie (KIT, Karlsruhe, GERMANY) for provision of instrumentation on the SQUID. Dr. George E. Kostakis (University of Sussex, UK) is gratefully thanked for the scientific discussions.
[12]
[13]
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