Sheets of Tetranuclear Ni(II) [2 Ã 2] Square Grids Structure with Infinite

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Sheets of Tetranuclear Ni(II) [2 × 2] Square Grids Structure with Infinite Orthogonal Two-Dimensional Water−Chlorine Chains Mouhamadou Moustapha-Sow,† Ousmane Diouf,*,† Mohamed Gaye,† Abdou Salam-Sall,† Goretti Castro,‡ Paulo Pérez-Lourido,*,‡ Laura Valencia,‡ Andrea Caneschi,§ and Lorenzo Sorace§ †

Department of Chemistry, University Cheikh Anta Diop, Bp 5005 Dakar, Sénégal Departamento de Química Inorgánica, Facultad de Química, Universidad de Vigo, 36310 Vigo, Pontevedra, Spain § Dipartimento di Chimica “U. Schiff” and INSTM Research Unit, Università di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy ‡

S Supporting Information *

ABSTRACT: The tetranuclear nickel(II) complex [Ni4(HL)4]Cl4·4H2O {H2L = 1,5bis[1-(pyridin-2-yl)ethylidene]carbono hydrazone} has been prepared by reaction in methanol of nickel(II) chloride and H2L in 2:1, M:L molar ratio. The single crystal Xray diffraction analysis revealed a 2 × 2 square grid of tetramer units with the metal ions joined in pairs by the alkoxide oxygen atom in the μ2 mode with octahedral geometry around each nickel ion. The supramolecular structure shows that the tetramer units are linked through edge-to-face (T shape) C−H···π interactions, forming sheets with hydrophobic- (occupied by infinite 2D water−chlorine chains) and hydrophilic(occupied by chlorine anions) channels. Variable temperature magnetic studies suggest an antiferromagnetic coupling between the adjacent Ni(II) centers with a coupling constant of J = −6.6 cm−1.

T

involve oxygen donor atoms.10 In this way, self-assembly of transition metal ions with designed Schiff bases allow for the synthesis of stable metal complexes with interest and potential applications in many fields.11 On the other hand, owing to its ability to adopt various geometries, the coordination chemistry of nickel(II) ions was widely explored in this past decade12 and complexes with esthetical architectures were synthesized.13 The use of the nickel compounds in development of new magnetic materials or in biochemistry led to increased interest in the synthesis of complexes with original architectures from ligands with mixed donating sites.14 In this work, as a result of our ongoing study of the coordination properties of N-heterocyclic-based polytopic Schiff-base ligands,15 we report the structure of a tetranuclear Ni(II) complex with the Schiff base derived from the acetyl pyridine and carbonohydrazide precursors, H2L (Scheme 1). To the best of our knowledge, few tetranuclear Ni(II) complexes structurally characterized with the N4O2 core are described in the literature.16 The tetranuclear Ni(II) complex with formula [Ni4(HL)4]Cl4·4H2O was obtained by reaction of nickel dichloride hexahydrate with the Schiff-base ligand, H2L,17 in 2:1 M:L molar ratio, under reflux in methanol.18 The complex

he binding of transition metal ions to properly designed multifunctional organic ligands for the construction of original metallosupramolecular architectures1 continue to attract scientific attention for several reasons, such as magnetic, electronic, catalytic, or biological properties.2 For example, the packing of some compounds can give rise to diverse nature channels, similar to those present in natural proteins as aquaporins involved in water transport.3 It might seem that hydrophobic channels should repel water; however, they can be hydrated and their nature promoted rapid water flow.4 It is well-known that if discrete metallo-supramolecular species contain additional peripheral binding sites, they can assemble to give polymeric structures.5 Similarly, aggregation to give polymers can be supported by additional bridging ligands6 or counterions.7 A knowledge of the principles of structure formation through polymerization is important not only from the viewpoint of coordination chemistry but also for the future development of increasingly intricate and functional coordination networks. In this sense, noncovalent interactions such as hydrogen bonds and π,π-stacking are the main driving forces behind this self-assembly process.8 One of the main targets in this field is the design and synthesis of new polytopic ligands that can be used for synthesis of molecular metal grids. Thompson and cowokers have successfully produced many tetranuclear [n × n] grids using directed self-assembly polydentate ligands with transition metal ions.9 They have synthesized tetranuclear complexes using templated cyclization methods, where the bridging arrays among the metal ions © 2013 American Chemical Society

Received: June 11, 2013 Revised: July 22, 2013 Published: July 26, 2013 4172

dx.doi.org/10.1021/cg400885f | Cryst. Growth Des. 2013, 13, 4172−4176

Crystal Growth & Design

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Analysis of intramolecular interactions in the 2 × 2 square grids reveals the presence of four face-to-face π−π stacking between pyridinic rings of adjacent ligands (Figure 1). A near face-to-face alignment of the rings in π−π interactions are extremely rare, and usual π interactions are an offset or slipped stacking (i.e., the rings are parallel displaced). The centroid-tocentroid distance (dCg−Cg) is 3.929 Å with a dihedral angle between planes containing the rings of 6.67°. The average distance between planes of the stacked rings is 3.69 Å, shorter than the normal packing distance between aromatic rings in organic aromatic molecules (4.0 Å), evidence of a typical π−π interaction between the pyridine rings.23Therefore, the ring normal and the vector between the ring centroids form an angle of 20.09°, as is usual for these kind of interactions.24 The study of the supramolecular structure reveals that the 2 × 2 square grid tetramer unities of the complex are arranged in a two-dimensional (2D) network through edge-to-face (T shape) C−H···π interactions,25 involving the pyridine rings [N(4), C(9)−C(13)] as acceptors and the C(3)−H(3) groups from the pyridine rings [N(1), C(1)−C(5)] as donors (Figure 2).

Scheme 1. Tautomeric Forms of H2L Ligand

crystallizes in the tetragonal space group I4(1)/a.19 The molecular structure of the [Ni4(HL)4]4+ cation complex together with the atomic numbering scheme adopted is illustrated in Figure 1. The complex consists of a 2 × 2 square

Figure 1. Crystal structure of the cation [Ni4(HL)4]4+ showing the intramolecular face-to-face π−π interactions present in the 2 × 2 square grid.

grid involving four nickel(II) centers bridged by four ligand molecules through the alkoxide oxygen atom. One chloride anion and one lattice water molecule are present in the asymmetric unit. Each ligand molecule behaves as a monoanionic (HL−) pentadentate N4O donor, where the alkoxide group acts as a bridging atom between two adjacent Ni(II) centers. Each individual nickel ion is coordinated by one pyridyl, one imine, and one μ-alkoxide group from two orthogonal ligand molecules, resulting in the metal ions in a hexacoordinated N4O2 core. All bond distances and angles around the nickel ions are the expected ones20 and comparable to those found in similar hexacoordinated Ni(II) complexes.21 The Ni−O bonds show the asymmetric bridge behavior of the alkoxide groups and are in good agreement with the average of Ni−O bond lengths when the oxygen atom acts as bridge between two Ni(II) centers.22 The environment geometry around each Ni(II) center can be regarded as distorted octahedral. The pyridyl nitrogen atoms, N1 and N4, and the two oxygen atoms, O1 and O1#1, from two different orthogonal ligand molecules form the equatorial plane (rms 0.4516) with the Ni ion 0.008(3) Å out of it. The axial positions are occupied by the imine nitrogen of two orthogonal ligands [N2−Ni1−N5, 177.0(3)°]. The adjacent Ni···Ni distance is of 3.992 Å, forming a perfect Ni4 [2 × 2] square grid. The oxygen atoms are situated alternatively up and down [0.747(8) Å] the mean plane (rms 0.2508) formed by the four Ni(II) atoms, resulting in a boatlike arrangement.

Figure 2. Edge-to-face (T shape) C−H···π interactions between the pyridine rings of adjacent ligands giving rise to a 2D supramolecular structure.

The H(3)−Cg distance is 3.16 Å, and the perpendicular distance from H(3) to the pyridine plane is 2.74(1) Å. This arrangement results in sheets that are arranged parallel to each other along the c axis (Figure 3). Packing scheme of these 2 × 2 square grids give rise to both hydrophobic (comprised by the aromatic rings) and hydrophilic channels (where they go the N−H atoms from the hydrazone groups), separated by the methyl groups. Both the hydrophobic and hydrophilic channels are arranged parallel to the sheets formed by the tetramer units. The symmetry properties of the tetragonal I4(1)/a spatial group leading to both kinds of channels are alternately placed along the orthogonal a and b axis (Figure 3). The crystallization water molecules together with half chloride ions are situated into the hydrophobic channels, giving rise to 2D zigzag fashion infinite water-chloride chains along the orthogonal a and b axes through hydrogen bonds 4173



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Figure 3. View of the 3D supramolecular structure, showing the hydrophobic (with the zigzag fashion water chains represented in the space-filling mode along the a and b axes) and hydrophilic channels (with the chloride ions).

Figure 5. Experimental (symbols) and best fit (continuous line) χT vs T data for the [Ni4(HL)4]Cl4·4H2O complex. The inset graphic shows the isothermal magnetization curve, measured at 2 K (○) and at 4.5 K (■).

between them (Figure 3). [O1W···Cl2 (1) 3.129(8); O1W···Cl2 (2) 3.129(8); O1W···O1W (3) 3.053(9). (1) −x + 1, −y + 1, −z + 1; (2) x, +y − 1/2, −z + 1; (3) −x + 1, −y, −z + 2]. The hydrophilic channels are occupied by the remaining chloride ions, which are strongly held in the lattice through N− H···Cl hydrogen bonds with two dangling −NH groups from parallel ligand molecules (Figure 4). [N3−H3A···Cl1 (1) 2.414(4), 144(1)°; N3−H3A···Cl1 and (2) 2.414(4), 144(1)°. (1) x, +y, +z + 1; (2) −x, −y + 1/2, +z + 1].

parameter in the magneto-structural correlations for Ni4O4 cores is the average value of the Ni−O−Ni angles.27 When the value of the angle Ni−O−Ni is lower than 99°, the ferromagnetic exchange interaction must be expected between the two Ni(II) ions, whereas the antiferromagnetic interaction must be observed when the Ni−O−Ni angle is greater than 99°.28 In our case, the observed antiferromagnetic interaction is clearly in agreement with these correlations, since the Ni−O− Ni is as large as 138.7°. The large Ni···Ni separations of 5.601 Å and the absence of efficient exchange coupling paths allowed us to safely consider the coupling interaction between the nonadjacent Ni(II) ions to be negligible. Further, due to the tetragonal symmetry of the cluster, we considered a single constant J to describe the coupling (Scheme 2). Scheme 2. Exchange Coupling Pattern in [Ni4(HL)4]Cl4·4H2O Complex

Figure 4. Hydrogen bond interactions between chlorine ions located in hydrophilic channels and the hydrazone (−NH) groups.

The temperature-dependent magnetic susceptibilities for the tetranuclear nickel(II) complex at a magnetic field of 1000 Oe was measured over the range of 2−300 K. The results of the plots of χMT versus T are depicted in Figure 5. At room temperature, the χMT value of the complex is evaluated at 5.01 emu K mol−1. This experimental value is in agreement with the expected for four noninteracting Ni(II) ions (5.06 emu K mol−1, g = 2.25).26 Upon cooling from 300 to 80 K, the χMT values decrease gradually. Below 80 K, the χMT values decrease more rapidly, reaching a value of 0.50 emu K mol−1 at 2 K, indicating the presence of antiferromagnetic interactions between the adjacent nickel ions. It is firmly established by previous studies from the literature that the most important

The best fit curve (solid line, Figure 5) provided the following parameters: gav = 2.248 ± 0.006, J = −6.6 ± 0.2 cm−1, ρ = 0.05 ± 0.01, which provide a singlet ground state with a first excited state triplet ca. 6.6 cm−1 above it in energy. The antiferromagnetic coupling obtained for the J value is consistent with the large Ni−O−Ni angles but is somewhat smaller than most of those reported for similar μ−O bridged square complexes with comparable bridge angles (J = −13 to −14 cm−1).29 On the other hand, it is in line with a couple of reports 4174



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on tetranuclear nickel clusters30 for which effects of the ligand charge have been postulated in the reduction of the coupling. In summary, we have synthesized and structurally characterized a tetranuclear nickel(II) compound from a carbonohydrazide-derivated Schiff base ligand (H2L). The ligands adopt a monoanionic and pentadentated coordination nature, acting as an asymmetric bridge between two metal centers giving rise to a tetranuclear complex with Ni4 [2 × 2]. The supramolecular structure shows that those square grids are connected through edge-to-face (T shape) C−H···π interactions giving rise to 2D sheets that are arranged parallel to each other along the c axis forming hydrophobic and hydrophilic channels, which are alternately placed along the orthogonal a and b axis. Two-dimensional zigzag fashion infinite water−chlorine chains are situated into the hydrophobic channels, while the hydrophilic ones are occupied by the chloride anions interacting with the hydrazone groups through the hydrogen bond. The compound exhibits an intramolecular antiferromagnetic exchange with a coupling constant of J = −6.6 cm−1 between the adjacent Ni(II) centers.

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(8) (a) Custelcean, R.; Afloroaei, C.; Vlassa, M.; Polverejan, M. Angew. Chem. 2000, 112, 3224. (b) Moorthy, J. N.; Natarajan, R.; Venugopalan, P. Angew. Chem. 2002, 41, 3417. (9) (a) Thompson, L .K.; Matthews, C. J.; Zhao, L.; Xu, Z.; Miller, D. O.; Wilson, C.; Leech, M. A.; Howard, J. A. K.; Heath, S. L.; Whittaker, A. G.; Winpenny, R. E. P. J. Solid State Chem. 2001, 159, 308. (b) Milway, V. A.; Abedin, S. M. T.; Niel, V.; Kelly, T. L.; Dawe, L. N.; Dey, S. K.; Thompson, D. W.; Miller, D. O.; Alam, M. S.; Müller, P.; Thompson, L. K. Dalton Trans. 2006, 2835. (c) Dey, S. K.; Thompson, L. K.; Dawe, L. N. Chem. Commun. (Cambridge, U.K.) 2006, 4947. (d) Dawe, L. N.; Thompson, L. K. Angew. Chem., Int. Ed. 2007, 46, 7440. (e) Dey, S. K.; Abedin, T. S. M.; Dawe, L. N.; Tandon, S. S.; Collins, J. L.; Thompson, L. K.; Postnikov, A. V.; Alam, M. S.; Müller, P. Inorg. Chem. 2007, 46, 7767. (f) Dawe, L. N.; Abedin, T. S. M.; Thompson, L. K. Dalton Trans. 2008, 1661. (10) (a) Matthews, C. J.; Avery, K.; Xu, Z.; Thompson, L. K.; Zhao, L.; Miller, D. O.; Biradha, K.; Poirier, K.; Zaworotko, M. J.; Wilson, C.; Goeta, A. E.; Howard, J. A. K. Inorg. Chem. 1999, 38, 5266. (b) Zhao, L.; Matthews, C. J.; Thompson, L. K.; Heath, S. L. Chem. Commun. (Cambridge, U.K.) 2000, 265. (11) (a) Resanović, S.; Wylie, R. S.; Quail, J. W.; Foucher, D. A.; Gossage, R. A. Inorg. Chem. 2011, 50, 9930. (b) Leilei-Chen, Q. S.; Liu, D.; Wu, J.; Wu, L.; Zhu, L.; Cheng, Q.; Lu, R.; Fan, D.; Lü, X. Inorg. Chem. Commun. 2013, 29, 22. (12) (a) Wikstrom, J. P.; Nazarenko, A. Y.; Reiff, W. M.; RybakAkimova, E. V. Inorg. Chim. Acta 2007, 360, 3733. (b) Ainooson, M. K.; Guzei, I. A.; Spencer, L. C.; Darkwa, J. Polyhedron 2013, 53, 295. (c) Feng, X.; Ma, L.-F.; Wang, L.-Y.; Zhao, J.-S. Inorg. Chem. Commun. 2011, 14, 584. (d) Mochizuki, K.; Kumagai, K.; Takishima, M.; Hayano, K. Inorg. Chem. Commun. 2003, 6, 935. (e) Lin, S.-Y.; Xu, G.F.; Zhao, L.; Guo, Y.-N.; Tang, J.; Wang, Q.-L.; Liu, G.-X. Inorg. Chim. Acta 2011, 373, 173. (13) (a) Shi, Q.; Chen, L.; Liu, D.; Wu, J.; Wu, L.; Zhu, L.; Cheng, Q.; Lu, R.; Fan, D.; Lü, X. Inorg. Chem. Commun. 2013, 29, 22. (b) Cheng, Q.; Pan, Z.; Zhou, H.; Chen, J. Inorg. Chem. Commun. 2011, 14, 929. (c) Resanović, S.; Wylie, R. S.; Quail, J. W.; Foucher, D. A.; Gossage, R. A. Inorg. Chem. 2011, 50, 9930. (d) Shi, Q.; Chen, l.; Liu, D.; Wu, J.; Wu, L.; Zhu, L.; Cheng, Q.; Lu, R.; Fan, D.; Lü, X. Inorg. Chem. Commun. 2013, 29, 22. (14) Winpenny, R. E. P. J. Chem. Soc., Dalton Trans. 2002, 1 and references therein. (15) (a) Dieng, M.; Diouf, O.; Gaye, M.; Sall, A. S.; Pérez-Lourido, P.; Valencia, L.; Caneschi, A.; Sorace, L. Inorg. Chim. Acta 2013, 394, 741. (b) Diouf, O.; Sall, D. G.; Gaye, M. L.; Sall, A. S. C. R. Chimie 2007, 10, 473. (16) (a) Mandal, T. N.; Roy, S.; Konar, S.; Jana, A.; Ray, S.; Das, K.; Saha, R.; El Fallah, M. S.; Butcher, R. J.; Chatterjee, S.; Kar, S. K. Dalton Trans. 2011, 40, 11866. (b) Sung, N.-D.; Yun, K.-S.; Kim, T.Y.; Choi, K.-Y.; Suh, M.; Kim, J.-G.; Suh, I.-H.; Chin, J. Inorg. Chem. Commun. 2001, 4, 377. (17) Bacchi, A.; Bonini, A.; Carcelli, M.; Ferraro, F.; Leporati, E.; Pelizzi, C.; Pelizzi, G. J. Chem. Soc., Dalton Trans. 1996, 2629. (18) [Ni4(HL)4]Cl4·4H2O: Anal. Calcd (Found) for C60H68N24O8 Cl4Ni4 (FW 1630.02): C, 44.2 (44.4); H, 4.2 (4.1); N, 20.6 (20.3) %. Yield: 75%. FAB-MS (m/z): 1120 [Ni4(HL)3]+, 413[Ni2(HL)]+. IR (KBr, cm−1): 3406, 1614, 1570; 1543; 1466. UV−vis (nm): 250, 309, 880, 1170. (19) Data collection was performed at 293 K on a Bruker SMART CCD Area Detector diffractometer (Mo Kα, λ = 0.71073 Å). Reflections were corrected for Lorentz and polarization effects and for absorption by an empirical method.31 The structure was solved by direct methods and refined with the full-matrix least-squares technique (SHELXL-97)32 to give a final R1 value of 0.0890 for 230 parameters and 4223 unique reflections with I ≥ 2σ(I) and wR2 of 0.2216 for all 4223 reflections. X-ray crystal data for [Ni4(HL)4]Cl4·2H2O: C60H68N24O8Cl4Ni4 (M = 1630.02), tetragonal, I4(1)/a, where a = 14.164(5), b = 14.164(5), c = 34.886(13) Å, V = 6998(5) Å3, Z = 4, T = 293(2) K, ρcalc. = 1.499 g cm−3, and μ = 1.209 mm−1 (CCDC 941871).

ASSOCIATED CONTENT

S Supporting Information *

Sample preparation, characterization and crystallographic data (CIF) for the complex. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

* P . P . - L . : e - m a i l: p a u l o @ u v ig o . e s ; O . D . : e- m a i l : [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Ministerio de Ciencia e Innovación, Plan Nacional de I+D+i (Grant CTQ2011-24487) and Xunta de Galicia (Grant PXIB209028PR) for financial support.

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REFERENCES

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Sheets of Tetranuclear Ni(II) [2 Ã 2] Square Grids Structure with Infinite

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Sheets of Tetranuclear Ni(II) [2 Ã 2] Square Grids Structure with Infinite