Synthesis, structural characterization, and magnetism of a butterfly-shaped hexanuclear Ni(II) complex

Inorganic Chemistry Communications 11 (2008) 769–771

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Synthesis, structural characterization, and magnetism of a butterfly-shaped hexanuclear Ni(II) complex Wei Luo a, Xiu-Teng Wang b, Gong-Zhen Cheng a, Song Gao b, Zhen-Ping Ji a,* a

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, PR China Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China

b

a r t i c l e

i n f o

Article history: Received 28 February 2008 Accepted 26 March 2008 Available online 1 April 2008 Keywords: Hexanuclear Butterfly-shaped Nickel Magnetism

a b s t r a c t A new butterfly-shaped hexanuclear complex [Ni6L4H2O(C5H5N)4]  2DMF (L = anion of N-(3-t-butylbenzoyl)-5-bromosalicylhydrazide) has been synthesized and characterized structurally and magnetically, which contains two trinuclear [Ni3L2(py)2] subunits bridged by two l2-O(carbonyl) and one l2-O(H2O) groups. It exhibits obvious ferromagnetic interaction owe to the central Ni(II) dimer with octahedral geometries. Ó 2008 Elsevier B.V. All rights reserved.

The development of routes and strategies for the design and preparation of polynuclear complexes of 3d metals in moderate oxidation states is of great importance in bioinorganic chemistry, magnetochemistry, materials chemistry and solid-state chemistry [1–4]. Multidentate ligands containing N, O donors, especially phenolic O donor, have been widely used to form polynuclear complexes with interesting structural motif [5]. The trianionic pentadentate N-acyl-salicylhydrazide ligands, have been utilized to construct many interesting polynuclear complexes. Trivalent metal ions such as Co, Fe and Mn that can easily form stable octahedral coordination are found to yield hexanuclear, octanuclear, decanuclear and dodecanuclear metallamacrocycles with these kinds of ligands, known as metallacrowns [6,7]. Concerning bivalent metal complexes of N-acyl-salicylhydrazide ligands, only a few trinuclear nickel(II)/copper(II) compounds have been obtained up to date [8]. In this study, we report the synthesis of a new pentadentate ligand, N-(3-t-butylbenzoyl)-5-bromosalicylhydrazide (H3L,C18H19N2O3Br) [9] and the first hexanuclear nickel complex [Ni6L4H2O(C5H5N)4]  2DMF 1 [10] of these kinds of pentadentate ligands. The molecular structure [11] of the title hexanuclear nickel complex is shown in Fig. 1. It exhibits a discrete butterfly-shaped hexanuclear Ni(II) complex. There are three crystallographically independent Ni(II) centers in the asymmetric unit. The terminal nickel ions, Ni(1) and Ni(3), adopt square-planar NiN2O2 geome* Corresponding author. Tel.: +86 2787218274. E-mail address: [email protected] (Z.-P. Ji). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.028

tries coordinated by carbonyl oxygen, hydrazine nitrogen, and phenolic oxygen of one ligand and the pyridine nitrogen atom; while the central Ni(2), is six-coordinated by the configuration of three carbonyl oxygen atoms, l2-O(2), l2-O(2a), O(5), two hydrazine nitrogen atoms, N(2), N(5), and one l2-O(H2O) group. Around Ni(2), the N2O4 donor set forms a distorted octahedral coordination geometry. The average bond lengths of Ni–O, Ni–N in Ni(1) and Ni(3) are 1.820 and 1.812 Å, respectively, which are shorter than the corresponding bond lengths of the Ni(2) ion (2.079 and 2.041 Å, respectively). This difference may be attributed to the difference in stereochemistry between the central and terminal Ni atoms. (octahedral versus square-planar) and the polymerization in Ni(2) ion. The most striking feature of 1 is the connection of two [Ni3L2(py)2] subunits through two l2-O(carbonyl) and one l2-O(H2O) groups to form a hexanuclear Ni(II) complex. The three nickel ions in the two [Ni3L2(py)2] subunits are bent with an angle Ni(1)  Ni(2)  Ni(3) of 132.45°, and the closest Ni  Ni distance between the two [Ni3L2(py)2] subunits is 2.969 Å. The magnetic measurements of 1 have been carried out with a Quantum Design (SQUID) magnetometer MPMS-XL-5 in a field of 1 kOe with the temperature ranging from 2 to 300 K (Fig. 2). As mentioned above, within this cluster Ni(1) and Ni(3) adopt square-planar geometries and are diamagnetic carriers and thus, from the magnetic point of view, the cluster can be viewed as a dimer of S = 1 Ni(II) ions. Indeed, at room temperature, the vMT value of 2.27 cm3 mol1 K is almost equal to the expected value calculated for two isolated Ni(II) ions (ca. 2.0 cm3 mol1 K, assuming g = 2.0). Upon lowering the temperature, the vMT values increase

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W. Luo et al. / Inorganic Chemistry Communications 11 (2008) 769–771

susceptibility, and isothermal magnetization at low temperature (Figure S1, S2, S3 of the Supporting Information). Neither bifurcation of the ZFC and FC plots nor in-phase peaks of ac susceptibility were observed, which indicate the absence of the three dimensional long-range magnetic ordering. The magnetic property of 1 is due mainly to intracluster exchange interaction (J) and intercluster exchange interaction (J0 ). A model for Ni(II) dimer [13] is applied to evaluate the magnitude of the exchange coupling, J and J0 , with the isotropic spin Hamiltonian H = 2  J  SA  SB. Considering the effect of the molecular field, the bulk susceptibility vM may be expressed by Eq. (1), vM ¼

vdimer 1  ð2zJ 0 =Ng 2 b2 Þvdimer

ð1Þ

with vdimer ¼

Fig. 1. The molecular structure of complex 1, solvent molecules and all hydrogen atoms have been omitted for clarity.

2Nb2 g 2 expð2J=kTÞ þ 5 expð6J=kTÞ  1 þ 3 expð2J=kTÞ þ 5 expð6J=kTÞ kt

ð2Þ

where z is the number of nearest neighbors of the dimers, and N, b, K, g and T have their usual meanings. The best fitting for the data in the range of 15–300 K gives J = +5.14 cm1, zJ0 = 0.22 cm1 and P P g = 2.10, with R = 1.0  106, ½R ¼ ½ ðvobs  vcalc Þ2 = ðvobs Þ2 . The positive J and the small negative zJ0 values indicate the ferromagnetic coupling between the two paramagnetic Ni(2) ions and slightly antiferromagnetic interaction among the clusters, respectively. These are consistent with the experimental observations. The magnetic behaviour of 1 can be explained in terms of the presence of the monatomic oxygen bridge between the Ni ions with Ni2–O7–Ni2a angle less than 98° (86.66°). This gives rise to moderately obvious ferromagnetic interactions associated with such types of bridges. Early published results on magnetic studies of polynuclear Ni complexes showed that a bridging angle less than 98° in monatomic oxygen bridges in all cases give rise to ferromagnetic coupling, while those that are larger than this threshold value produce antiferromagnetic coupling [14]. Acknowledgement We are grateful to the National Natural Science Foundation of China for the financial support (Grant No. 20171035). Appendix A. Supplementary material

Fig. 2. Temperature dependence of vMT and v1 M of 1 at H = 1 kOe from 2 to 300 K. The line a represents the best fit to Curie–Weiss law, and line b corresponds to the best fit with the dimer model mentioned in the text.

gradually, and reach a maximum of 2.91 cm3 mol1 K at 9.0 K, suggesting intermolecular ferromagnetic coupling between Ni(II) ions. Upon further cooling, vMT drops sharply down to 2.49 cm3 mol1 K at 2 K. This sudden decrease might be mainly attributed to the presence of zero-field splitting (ZFS) and/or the antiferromagnetic interaction between the clusters. Similar behaviour and characteristic shape of the curve was reported for other nickel(II) clusters of different nuclearity with predominant ferromagnetic interactions, in particular, 4-nuclear dicubane-type complexes, hexanuclear 2[Ni3], 4- and 5- nuclear clusters [12]. The temperature dependence of the reciprocal susceptibility is linear above 50 K and obeys the Curie–Weiss law with a Curie constant C = 2.23 cm3 K mol1 and a Weiss constant h = +6.3 K. The positive Weiss constant also indicate an overall ferromagnetic interaction between the Ni(II) ions. The compound 1 was further characterized by zero-field-cooled (ZFC) and field-cooled (FC) measurements, alternating current (ac)

CCDC 665859 contains 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. Supplementary data contain Figure S1, S2, S3 associated with this article can be found in the online version, at doi:10.1016/j.inoche.2008.03.028.

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1400 (s). 1H NMR (300 MHz, DMSO-d6), d ppm: 12.09 (s, Ar-OH); 10.72 (s, 1H), 10.66 (s, 1H) (both amide NH’s); 8.04 (m, 1H, Ar); 7.85 (m, 1H, Ar); 7.56(m, 1H, Ar); 7.39 (d, 2H, Bz); 7.04 (d, 2H, Bz); 1.21 (s, 9H, –C(CH3)3. 13C NMR (150.9 MHz, DMSO-d6), d ppm: 169.56; 162.63; 160.28; 153.33; 141.74; 140.13; 136.40; 135.49; 134.86; 132.47; 131.03; 125.17; 50.68; 36.34. Complex [Ni6(C18H16N2O3Br)4(H2O)(C5H5N)4]  2DMF: H3L (39.1 mg, 0.1 mmol) was dissolved in 30 ml of 1:1 methanol/DMF, and then nickel acetate tetrahydrate (24.8 mg, 0.1 mmol) was added followed by four drops of pyridine. The mixture as stirred for 1 h, the resulting solution was filtered. After slow evaporation of the mother liquor for several days, red block crystals suitable for X-ray diffraction were obtained. Yield: 43%. Anal. Calcd for C98H100Br4N14Ni6O15 (%): C, 49.31; H, 4.19; N, 8.22. Found: C, 49.24; H, 4.11; N, 8.24. IR (KBr pellet, cm1): 3440 (m); 1630 (m); 1560 (m); 1500 (m); 1390 (m); 758 (m); 694 (m). Crystal data for the complex 1 of C98H100Br4N14Ni6O15, Mr = 2385.84, monoclinic, space group C2/c with a = 31.696(2) Å, b = 14.214(1) Å, c = 26.724(2) Å, b = 117.987(1)°, V = 10631.7(1) Å3, Z = 4, qcald = 1.492 Mg m3, T = 292(2) K, l = 2.61 mm1. R1 = 0.0818, xR2 = 0.1877. (a) S. Wörl, H. Pritzkow, I.O. Fritsky, R. krämer, Dalton Trans. (2005) 27; (b) Z.E. Serna, L. Lezama, M.K. Urtiaga, M.I. Arriortua, M.G. Barandika, R. Cortes, T. Rojo, Angew. Chem., Int. Ed. 39 (2000) 344; (c) Z.E. Serna, M.K. Urtiaga, M.G. Barandika, R. Cortes, S. Martin, M.I. Arriortua, L. Lezama, T. Rojo, Inorg. Chem. 40 (2001) 4550; (d) P. King, R. Clerac, W. Wernsdorfer, C.E. Anson, A.K. Powell, Dalton Trans. (2004) 2670. P. Román, C. Guzmán-Miralles, A. Luque, J.I. Beitia, J. Cano, F. Lloret, M. Julve, S. Alvarez, Inorg. Chem. 35 (1996) 3741. (a) T.K. Paine, E. Rentschler, T. Weyhermueller, P. Chaudhuri, Eur. J. Inorg. Chem. (2003) 3167; (b) S.T. Ochsenbein, M. Murrie, E. Rusanov, H. Stoeckli-Evans, C. Sekine, H.U. Guedel, Inorg. Chem. 41 (2002) 5133; (c) G. Aromi, A.R. Bell, M. Helliwell, J. Raftery, S.J. Teat, G.A. Timco, O. Roubeau, R.E.P. Winpenny, Chem. Eur. J. 9 (2003) 3024.