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Synthesis, crystal structure and magnetic properties of nickel(II) and cobalt(III) complexes of a pentadentate Schiff base
Journal of Molecular Structure 1036 (2013) 422–426
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Synthesis, crystal structure and magnetic properties of nickel(II) and cobalt(III) complexes of a pentadentate Schiff base Manas Layek a, Mahendra Ghosh a, Saugata Sain a, Michel Fleck b, Packianathan Thomas Muthiah c, Samson Jegan Jenniefer c, Joan Ribas d, Debasis Bandyopadhyay a,⇑ a
Department of Chemistry, Bankura Christian College, Bankura, West Bengal, India Institute of Mineralogy and Crystallography Geozentrum, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria School of Chemistry, Bharathidasan University, Tiruchirappalli, Tamilnadu, India d Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain b c
h i g h l i g h t s " A less-studied pentadentate Schiff base was used to synthesize Ni(II) and Co(III) complexes. " Syntheses were achieved by the reaction of the respective metal perchlorate with ligand plus azide. " The same synthetic system yielded an azido-bridged Ni(II) and a mononuclear Co(III) complex. " Low temperature magnetic studies establish the ferromagnetic nature of the Ni(II) complex.
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Article history: Received 24 September 2012 Received in revised form 6 November 2012 Accepted 27 November 2012 Available online 7 December 2012 Keywords: Nickel(II) Cobalt(III) Pentadentate Schiff base Crystal structure Azido bridge Magnetic properties
a b s t r a c t Two new Schiff base complexes, [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) where L = 2,20 {(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenolate ion, have been synthesized by the reaction of equimolar amounts of nickel(II) or cobalt(II) perchlorate with the pentadentate Schiff base ligand (H2L) in presence of azide ion. The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1 is an end-to-end azido-bridged binuclear complex in which each nickel(II) adopts irregular octahedral geometry. In contrast, 2 is a mononuclear octahedral cobalt(III) complex containing the azide ion in one of its apical positions. Low temperature magnetic measurements on 1 indicate noticeable intradimer ferromagnetic interactions. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Transition metal complexes containing Schiff base ligands have been of specific interest for many years. Studies on such complexes of the first series transition metals including nickel and cobalt have received overwhelming attention in recent times due to their important catalytic, magnetic and biological properties [1–14]. Although metal complexes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine have been thoroughly investigated [15–18], report on synthesis of nickel(II) or cobalt(III) complexes containing Schiff base derived from the triamine and salicylaldehyde is scanty [19]. In addition, some complexes of this type are known to exhibit
⇑ Corresponding author. Tel./fax: +91 3242 250924. E-mail address: [email protected] (D. Bandyopadhyay). 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.11.068
magnetic exchange interactions in presence of bridging pseudohalides like azide [5–12]. In a recent communication [20], we have described the synthesis and characterization of few copper(II) complexes containing the above mentioned triamine and its Schiff bases. With the aim of extending the work, we attempted the synthesis of nickel(II) and cobalt(III) complexes using analogous ligand system in presence of azide ion. In the present work, we describe the result of the study, which includes synthesis and characterization of two new complexes, viz. [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) where L = 2,20 -{(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenolate ion. Structure of the pentadentate NNNOO-donor Schiff base ligand (H2L) and relevant equations for the formation of the complexes are presented in Scheme 1. Both 1 and 2 have been characterized by microanalytical, spectroscopic and other physicochemical studies, including single crystal X-ray
M. Layek et al. / Journal of Molecular Structure 1036 (2013) 422–426
N H3C
423
HO
N
HO
N
H2L M = Ni
M(ClO 4)2.6H2O
H 2 L + NaN3 MeCN
M = Co
[Ni 2(HL)2(N3)]ClO 4.H2O (1) [Co(L)(N3)] (2)
Scheme 1. Structure of the Schiff base (H2L) and formation of the complexes.
structural analysis. Besides, variable temperature magnetic susceptibility measurements have been carried out to study the magnetic behavior of the azido-bridged complex 1. 2. Experimental 2.1. Physical measurements Elemental analyses for carbon, hydrogen and nitrogen were carried out using a Perkin–Elmer 2400-II elemental analyzer. The infrared spectra were recorded on a Perkin–Elmer Spectrum 65 FT-IR spectrophotometer with KBr disks (4000–400 cm1). Molar conductances of the complexes in dry methanol were measured using a digital conductivity meter of Systronics (Type 304). Variable-temperature magnetic susceptibility measurements on polycrystalline samples (30 mg) of 1 were carried out with a Quantum Design SQUID MPMS-XL magnetometer (at Servei de Magnetoquímica, Universitat de Barcelona) in 2–300 K range under an applied field of 0.1 T. The diamagnetic corrections were evaluated from Pascal’s constants. Room temperature solid phase magnetic susceptibility of 2 was measured by Gouy’s method using Hg[Co(NCS)4] as calibrant. 2.2. Materials Reagent grade nickel(II) perchlorate hexahydrate, cobalt(II) perchlorate hexahydrate, N-(3-aminopropyl)-N-methylpropane-1,3diamine [CH3N(CH2CH2CH2NH2)2], salicylaldehyde and sodium azide were purchased from reputed manufacturers and used as received. All other chemicals and solvents were of analytical grade. The pentadentate Schiff base ligand, 2,20 -{(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenol (H2L) was obtained by the usual method of condensation of salicylaldehyde with N(3-aminopropyl)-N-methylpropane-1,3-diamine in 2:1 M ratio. Caution! Compounds containing perchlorate and azide are potentially explosive. Therefore, only a small amount of the materials should be used at a time and handled with proper care.
atmosphere. After 5–6 days, green crystals of 1 appeared. The crystals were collected by filtration, washed with little acetonitrile and finally dried. Yield: 0.15 g (62%). Anal. Calc. for C42H52ClN9Ni2O9 (1): C, 51.49; H, 5.35; N, 12.87. Found: C, 51.43; H, 5.32; N, 12.82%. FTIR (KBr, cm1): 3460(s), 2923(m), 2858(m), 2072(s), 1632(s), 1599(s), 1448(m), 1107(s), 864(m), 757(m). KM (MeOH, X1cm2 mol1): 120. Complex 2 was prepared by the same synthetic procedure as described above for 1. In this case, 0.18 g (0.5 mmol) of Co(ClO4)26H2O was used instead of the nickel salt. Deep brown crystals of 2 were grown and collected after a week. Yield: 0.15 g (67%). Anal. Calc. for C21H25CoN6O2 (2): C, 55.75; H, 5.57; N, 18.58. Found: C, 55.73; H, 5.52; N, 18.52%. FTIR (KBr, cm1): 2042(s), 1630(s), 1600(s), 1452(m), 1307(w), 752(m). KM (MeOH, X1 cm2 mol1): 7. Diamagnetic. 2.4. Crystal structure determination and refinement Suitable single crystals of 1 and 2 with approximate dimensions of 0.06 0.05 0.05 and 0.60 0.40 0.30 mm3, respectively, were manually selected. The crystals were mounted on a BrukerNonius APEX II diffractometer, equipped with CCD area detector and graphite-monochromated Mo Ka radiation (k = 0.71073 Å). The reflection data were collected and processed using the Bruker-Nonius program suites COLLECT, DENZO-SMN and related analysis software [21,22]. The structures were solved by direct methods and subsequent Fourier and difference Fourier syntheses, followed by full-matrix least-square refinements on F2, using the program SHELX [23]. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were partially located from difference Fourier maps, partially placed geometrically, and refined keeping restrains (riding mode) in 1. In compound 2, however, all hydrogen atoms were refined in riding mode. A summary of the crystallographic data, structural parameters and refinement details for the compounds is presented in Table 1. 3. Results and discussion
2.3. Synthesis of [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) 3.1. Synthesis A solution of nickel(II) perchlorate hexahydrate (0.18 g, 0.5 mmol) in acetonitrile (10 mL) was added dropwise to a mixture of H2L (0.18 g, 0.5 mmol) and sodium azide (0.03 g, 0.5 mmol) in acetonitrile (20 mL) with constant stirring. Sodium azide was dissolved in 3–4 drops of water followed by 5 ml of acetonitrile prior to mixing with H2L. Stirring of the whole mixture was then continued for half an hour and the resulting green solution was left for slow evaporation at room temperature in a beaker open to the
The reaction of nickel(II) perchlorate with the pentadentate Schiff base (H2L) in presence of azide ions in acetonitrile medium yielded 1, a binuclear complex containing l1,3-N3 bridge. However, attempts to prepare analogous cobalt complex gave rise to the mononuclear octahedral complex 2 with a terminal azide. Both complexes have been characterized by elemental analysis, IR spectroscopy, electrical conductivity and magnetic susceptibility
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Table 1 Crystallographic data and refinement parameters for 1 and 2. Parameters
1
2
Formula Formula weight (g mol1) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (g cm3) l (mm1) F(000) hkl range T (K) k (Mo Ka) (Å) Reflections measured Reflections unique Data with Fo > 4r(Fo) Rint Parameters refined R wR2 S Dqmax/Dqmin (e Å–3)
C42H52ClN9Ni2O9 979.76 Orthorhombic P212121 11.1063(7) 16.9545(1) 24.4064(1) 90 90 90 4595.8(5) 4 1.416 0.94 2048 ±12, ±19, ±28 296(2) 0.71073 68044 7352 6459 0.056 588 0.034 0.086 1.042 0.41/0.26
C21H25CoN6O2 452.40 Monoclinic P21/c 8.3875(1) 14.881(2) 17.487(3) 90 112.060(1) 90 2022.8(5) 4 1.485 0.88 944 11/12, 20/21, ±25 293(2) 0.71073 27283 6224 4498 0.028 272 0.058 0.158 1.061 1.58/0.62
measurements as well as by single crystal X- ray structural analysis. In methanol solvent, 1 and 2 behave as a 1:1 electrolyte and a non-electrolyte, respectively, as evident from the KM values. Room temperature magnetic susceptibility measurement indicates that 2 is diamagnetic. This conforms to the presence of a singlet ground state with t62g e0g configuration, as expected for low-spin octahedral Co(III) complexes. As usual, CoII underwent aerial oxidation to CoIII during the formation of 2 to accommodate ligands with harder donor atoms and to gain higher CFSE. All the results along with the Xray structural analysis are consistent with the proposed formulae of 1 and 2.
3.2. FTIR spectra Infrared spectra of 1 and 2 are similar with distinct absorption bands at around 1600 and 1630 cm1, assignable to the stretching
1
vibrations of the C@N bond [mCN] of the Schiff base ligand. The strong and sharp absorptions at 2072 and 2042 cm1 for 1 and 2, respectively, are attributed to the asymmetric stretch of the azide groups. The asymmetric single and sharp band expected for the ClO4 anion is observed at 1107 cm1 in 1. The broad and strong bands at around 3460 cm1 indicate the presence of H2O molecules in this compound. Few other characteristic vibrations of the metalbound Schiff bases are located in the range 600–1600 cm1. Thus, the infrared spectra of the compounds are found to be in good agreement [24] with their respective structural features. 3.3. Crystal structures of 1 and 2 The molecular structures and coordination polyhedra of the complexes 1 and 2 are displayed in Figs. 1 and 2, respectively. A few selected bond distances and angles are summarized in Table 2. X-ray structural studies reveal that these complexes comprise a common pentadentate Schiff base ligand and azide ion but adopt different geometries in presence of two different metal ions. In 1, the main structural unit can be described as a binuclear species comprising of two asymmetric [Ni(LH)]+ units, connected through a l1,3-N3 bridge. The electroneutrality of 1 is maintained by the presence of the perchlorate anions in the lattice. The two [Ni(LH)]+ units are nearly equivalent as evident from the minor variations in their bond lengths and angles. In both the units, each Ni(II) ion adopts a distorted octahedral geometry with NiN4O2 chromophore. The hexacoordination environment is maintained by two imino nitrogen (N4, N6 for Ni1; N1, N3 for Ni2), a protonated oxygen (O3 for Ni1; O1 for Ni2), a phenolate oxygen atom (O4 for Ni1; O2 for Ni2), the tertiary amine nitrogen (N5 for Ni1; N2 for Ni2) of the pentadentate Schiff base anion (HL) and the bridging azide anion (N7 for Ni1; N9 for Ni2). All the NiAN and NiAO bond lengths of 1 fall in the range 2.029–2.170 Å and are comparable with the corresponding bonds in similar other dimeric Ni(II) complexes [8–12]. The two Ni(II) centers within one dimer of 1 are separated by a distance of 5.087 Å and bridged by the azide ion in an end-to-end fashion. The nickel(II)–azide distances vary to some extent e.g. Ni1AN7 and Ni2AN9 are 2.148 and 2.104 Å, respectively. Each complex part has undergone some distortions from ideal geometry which is evident from the cisoid and transoid angles around the Ni(II) ions in 1, being in the range 82.8–99.6° and 169.5–178.5°, respectively. X-ray structural studies show that complex 2 is a mononuclear non-electrolyte, [Co(L)(N3] in which the central Co(III) ion is a
2
Fig. 1. Molecular structures of 1 and 2 with atom labeling.
M. Layek et al. / Journal of Molecular Structure 1036 (2013) 422–426
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The crystal packing diagrams of the compounds 1 and 2 are presented in Fig. S1 (see Supplementary data). In the solid state of 1, the two Schiff base molecules of the same binuclear unit are connected to each other via hydrogen bonds. Each O2 atom of phenolate group of the Schiff base in one [Ni(LH)]+ unit interacts with the hydrogen atom (H30) linked to the protonated phenolic oxygen atom (O3) of another unit. In addition, the second protonated oxygen atom extends a bond towards a water molecule (O1AH31 O1w), which itself is involved in O1wAH2w O4 hydrogen bonding to the next binuclear unit. Thus, an infinite chain comprising binuclear units with alternating water molecules is formed along the crystallographic bc plane. Another hydrogen bond extending from the water molecule connects the perchlorate anion (O1wAH1w O7), which is located in the interstices between the chains of the lattice of 1. In 2, the building units are packed rather loosely and isolated from each other. Weak intermolecular van der Waals and p p interactions are only operative in 2 to hold the molecules together. 3.4. Magnetic properties of 1 Fig. 2. Coordination polyhedra of Ni2+ in 1 and Co3+ in 2.
Table 2 Selected bond lengths [Å] and bond angles [°] for 1 and 2. 1 Ni1AO3 Ni1AO4 Ni1AN4 Ni1AN5 Ni1AN6 Ni1AN7 Ni2AO1 Ni2AO2 Ni2AN1 Ni2AN2 Ni2AN3 Ni2AN9 O3AH30 O2. . .H30 Ni1. . .Ni2
2.118(2) 2.029(2) 2.050(3) 2.165(3) 2.039(3) 2.148(3) 2.145(2) 2.058(2) 2.052(3) 2.170(3) 2.054(3) 2.104(3) 1.060(4) 1.413 5.087
O3ANi1AO4 O3ANi1AN4 O3ANi1AN5 O3ANi1AN6 O3ANi1AN7 O4ANi1AN4 O4ANi1AN5 O4ANi1AN6 O4ANi1AN7 N4ANi1AN5 N4ANi1AN6 N4ANi1AN7 N5ANi1AN6 N5ANi1AN7 N6ANi1AN7 Ni1AN7AN8
87.72(9) 84.8(1) 172.5(1) 90.6(1) 85.3(1) 85.1(1) 99.6(1) 88.3(1) 172.3(1) 97.3(1) 172.0(1) 91.0(1) 88.2(1) 87.4(1) 95.1(1) 120.4(3)
O1ANi2AO2 O1ANi2AN1 O1ANi2AN2 O1ANi2AN3 O1ANi2AN9 O2ANi2AN1 O2ANi2AN2 O2ANi2AN3 O2ANi2AN9 N1ANi2AN2 N1ANi2AN3 N1ANi2AN9 N2ANi2AN3 N2ANi2AN9 N3ANi2AN9 Ni2ANi9AN8
88.15(9) 82.8(1) 93.6(1) 88.2(1) 178.5(1) 89.0(1) 175.8(1) 85.4(1) 90.6(1) 87.5(1) 169.5(1) 96.5(1) 98.4(1) 87.6(1) 92.5(1) 122.0(3)
2 Co1AN1A Co1AO1 Co1AN1 Co1AN3 Co1AO2 Co1AN2
1.962(3) 1.882(2) 1.930(2) 1.927(2) 1.909(2) 2.054(3)
N1AACo1AO1 N1AACo1AN1 N1AACo1AN3 N1AACo1AO2 N1AACo1AN2 O1ACo1AN1 O1ACo1AN3 O1ACo1AO2
89.2(1) 87.4(1) 92.4(1) 88.7(1) 177.0(1) 91.3(1) 88.3(1) 177.0(1)
O1ACo1AN2 N1ACo1AN3 N1ACo1AO2 N1ACo1AN2 N3ACo1AO2 N3ACo1AN2 O2ACo1AN2
91.3(1) 179.6(1) 90.8(1) 89.6(1) 89.6(1) 90.6(1) 90.9(1)
member of four six-membered rings. In this complex, the central Co(III) ion adopts a slightly distorted octahedral geometry. The equatorial plane of the polyhedron is formed by the coordination of two nitrogen (N1, N3) and two phenolate oxygen atoms (O1, O2) contributed by the Schiff base. One of the apical positions is occupied by the tertiary amine nitrogen atom (N2) and another by the terminal azide ion (N1A). The CoAN and CoAO bond distances ranging from 1.882 to 2.054 Å agree well with similar other Schiff base complexes of cobalt(III) [13,14]. The cisoid and transoid angles around the Co(III) ion in 2 are in the range of 87.4–92.4° and 177.0–179.6°, respectively. However, the equatorial plane containing the Co(III) ion achieves almost perfect planarity as evidenced from the very low torsion angle (O1AN1AO2AN3 = 1.4°) and the complex unit of 2 is rather less distorted.
The result of variable-temperature magnetic studies on complex 1 is displayed as the vMT vs. T plot (Fig. 3). The vMT value of 2.6 cm3 mol1 K at 300 K is in good agreement with the expected contribution of two magnetically non-interacting or weakly interacting spin triplets (g > 2.00). It increases gradually upon lowering of temperature to reach a maximum (3.2 cm3 mol1 K) at around 25 K. With further lowering of temperature, a sharp decrease of vMT is observed to finally attain a value of 2.3 cm3 mol1 K at 2 K. These features are characteristic of significant intramolecular ferromagnetic interactions in 1, indicating the presence of both D (zero-field-splitting parameter) and z0 J0 (intermolecular antiferromagnetic interactions). ˆ = JS1S2, the fit of the susceptibility From the Hamiltonian H data was carried out applying two different approaches, viz. by considering the z0 J0 parameter (by means of molecular-field approximation) [1] or the D parameter by a full-diagonalization program [25]. The best-fit parameters obtained with the first approach are J = 7.0 ± 0.5 cm1, J0 = 0.49 cm1, g = 2.26 ± 0.01 and R = 2.7 104. Slightly different J value was obtained by the full-diagonalization method, when the D parameter was introduced. In this case, the best-fit parameters obtained are J = 6.5 ± 0.5 cm1, D = 4.9 ± 0.5 cm1, g = 2.26 ± 0.01 and R = 3.2 104. These calculations give D parameter which is likely to be overestimated since the logical J0 parameter has not been considered. As a consequence, we can postulate that J is closer to 6.5 cm1 and J0 could be of the order of 0.4 cm1. Thus, D will most likely be less than 4.9 cm1 (the standard value for isolated nickel(II) complexes is close to 6 cm1) [6]. Complexes containing analogous [Ni2(l1,3-N3)]3+ can either be discrete or one-dimensional. According to the available literature and theoretical calculations [5,12], this kind of bridging azido ligand usually generates antiferromagnetic coupling. In some cases, however, depending on the NiANAN(azido) bond angles and the NiANANANANi torsion angles, the coupling could be ferromagnetic also [12]. Mainly, great torsion angles are known to cause ferromagnetic coupling. Therefore, it is most likely that the ferromagnetic character is dominant in 1 due to its large torsion angle [12], being close to 90°. 4. Conclusion Synthesis and characterization of two new complexes of nickel(II) and cobalt(III) containing a common pentadentate Schiff base ligand have been described in this paper. The reaction of the Schiff base with nickel(II) perchlorate in presence of azide yielded a
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Appendix A. Supplementary material 3.2
CCDC 856954 and 856953 contain the supplementary crystallographic data of 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2012.11.068.
2.8
3
-1
χmT / cm mol K
3.0
2.6
References [1] [2] [3] [4]
2.4
2.2
[5]
0
50
100
150
200
250
300
T/K Fig. 3. Plot of vMT vs. T for 1. Solid lines represent the best fit using the J0 or the D approach (the fit curve is practically identical in both cases).
[6] [7] [8] [9] [10]
binuclear nickel(II) complex containing l1,3-N3-bridge. In contrast, the same synthetic system in presence of cobalt(II) perchlorate resulted in a mononuclear Co(III) species with terminal azide ion. In addition to the synthetic and structural investigations on the complexes, low temperature magnetic measurements were performed to establish the ferromagnetic character of the binuclear Ni(II) complex.
Acknowledgements
[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
One of the authors (S.S.) gratefully acknowledges the financial support under MRP (No. F. PSW-001/10-11) from UGC, Eastern region, Kolkata, India. PTM and SJJ thank the D.S.T-India (F.I.S.T programme) for the use of Bruker Smart APEX II diffractometer at the School of Chemistry, Bharathidasan University. J.R. acknowledges the financial support from Spanish Government (Grant CTQ2009/ 07264).
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Synthesis, crystal structure and magnetic properties of nickel(II) and cobalt(III) complexes of a pentadentate Schiff base Manas Layek a, Mahendra Ghosh a, Saugata Sain a, Michel Fleck b, Packianathan Thomas Muthiah c, Samson Jegan Jenniefer c, Joan Ribas d, Debasis Bandyopadhyay a,⇑ a
Department of Chemistry, Bankura Christian College, Bankura, West Bengal, India Institute of Mineralogy and Crystallography Geozentrum, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria School of Chemistry, Bharathidasan University, Tiruchirappalli, Tamilnadu, India d Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain b c
h i g h l i g h t s " A less-studied pentadentate Schiff base was used to synthesize Ni(II) and Co(III) complexes. " Syntheses were achieved by the reaction of the respective metal perchlorate with ligand plus azide. " The same synthetic system yielded an azido-bridged Ni(II) and a mononuclear Co(III) complex. " Low temperature magnetic studies establish the ferromagnetic nature of the Ni(II) complex.
a r t i c l e
i n f o
Article history: Received 24 September 2012 Received in revised form 6 November 2012 Accepted 27 November 2012 Available online 7 December 2012 Keywords: Nickel(II) Cobalt(III) Pentadentate Schiff base Crystal structure Azido bridge Magnetic properties
a b s t r a c t Two new Schiff base complexes, [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) where L = 2,20 {(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenolate ion, have been synthesized by the reaction of equimolar amounts of nickel(II) or cobalt(II) perchlorate with the pentadentate Schiff base ligand (H2L) in presence of azide ion. The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1 is an end-to-end azido-bridged binuclear complex in which each nickel(II) adopts irregular octahedral geometry. In contrast, 2 is a mononuclear octahedral cobalt(III) complex containing the azide ion in one of its apical positions. Low temperature magnetic measurements on 1 indicate noticeable intradimer ferromagnetic interactions. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Transition metal complexes containing Schiff base ligands have been of specific interest for many years. Studies on such complexes of the first series transition metals including nickel and cobalt have received overwhelming attention in recent times due to their important catalytic, magnetic and biological properties [1–14]. Although metal complexes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine have been thoroughly investigated [15–18], report on synthesis of nickel(II) or cobalt(III) complexes containing Schiff base derived from the triamine and salicylaldehyde is scanty [19]. In addition, some complexes of this type are known to exhibit
⇑ Corresponding author. Tel./fax: +91 3242 250924. E-mail address: [email protected] (D. Bandyopadhyay). 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.11.068
magnetic exchange interactions in presence of bridging pseudohalides like azide [5–12]. In a recent communication [20], we have described the synthesis and characterization of few copper(II) complexes containing the above mentioned triamine and its Schiff bases. With the aim of extending the work, we attempted the synthesis of nickel(II) and cobalt(III) complexes using analogous ligand system in presence of azide ion. In the present work, we describe the result of the study, which includes synthesis and characterization of two new complexes, viz. [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) where L = 2,20 -{(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenolate ion. Structure of the pentadentate NNNOO-donor Schiff base ligand (H2L) and relevant equations for the formation of the complexes are presented in Scheme 1. Both 1 and 2 have been characterized by microanalytical, spectroscopic and other physicochemical studies, including single crystal X-ray
M. Layek et al. / Journal of Molecular Structure 1036 (2013) 422–426
N H3C
423
HO
N
HO
N
H2L M = Ni
M(ClO 4)2.6H2O
H 2 L + NaN3 MeCN
M = Co
[Ni 2(HL)2(N3)]ClO 4.H2O (1) [Co(L)(N3)] (2)
Scheme 1. Structure of the Schiff base (H2L) and formation of the complexes.
structural analysis. Besides, variable temperature magnetic susceptibility measurements have been carried out to study the magnetic behavior of the azido-bridged complex 1. 2. Experimental 2.1. Physical measurements Elemental analyses for carbon, hydrogen and nitrogen were carried out using a Perkin–Elmer 2400-II elemental analyzer. The infrared spectra were recorded on a Perkin–Elmer Spectrum 65 FT-IR spectrophotometer with KBr disks (4000–400 cm1). Molar conductances of the complexes in dry methanol were measured using a digital conductivity meter of Systronics (Type 304). Variable-temperature magnetic susceptibility measurements on polycrystalline samples (30 mg) of 1 were carried out with a Quantum Design SQUID MPMS-XL magnetometer (at Servei de Magnetoquímica, Universitat de Barcelona) in 2–300 K range under an applied field of 0.1 T. The diamagnetic corrections were evaluated from Pascal’s constants. Room temperature solid phase magnetic susceptibility of 2 was measured by Gouy’s method using Hg[Co(NCS)4] as calibrant. 2.2. Materials Reagent grade nickel(II) perchlorate hexahydrate, cobalt(II) perchlorate hexahydrate, N-(3-aminopropyl)-N-methylpropane-1,3diamine [CH3N(CH2CH2CH2NH2)2], salicylaldehyde and sodium azide were purchased from reputed manufacturers and used as received. All other chemicals and solvents were of analytical grade. The pentadentate Schiff base ligand, 2,20 -{(methylimino)bis[propane-3,1-diylnitrilomethylylidene]}diphenol (H2L) was obtained by the usual method of condensation of salicylaldehyde with N(3-aminopropyl)-N-methylpropane-1,3-diamine in 2:1 M ratio. Caution! Compounds containing perchlorate and azide are potentially explosive. Therefore, only a small amount of the materials should be used at a time and handled with proper care.
atmosphere. After 5–6 days, green crystals of 1 appeared. The crystals were collected by filtration, washed with little acetonitrile and finally dried. Yield: 0.15 g (62%). Anal. Calc. for C42H52ClN9Ni2O9 (1): C, 51.49; H, 5.35; N, 12.87. Found: C, 51.43; H, 5.32; N, 12.82%. FTIR (KBr, cm1): 3460(s), 2923(m), 2858(m), 2072(s), 1632(s), 1599(s), 1448(m), 1107(s), 864(m), 757(m). KM (MeOH, X1cm2 mol1): 120. Complex 2 was prepared by the same synthetic procedure as described above for 1. In this case, 0.18 g (0.5 mmol) of Co(ClO4)26H2O was used instead of the nickel salt. Deep brown crystals of 2 were grown and collected after a week. Yield: 0.15 g (67%). Anal. Calc. for C21H25CoN6O2 (2): C, 55.75; H, 5.57; N, 18.58. Found: C, 55.73; H, 5.52; N, 18.52%. FTIR (KBr, cm1): 2042(s), 1630(s), 1600(s), 1452(m), 1307(w), 752(m). KM (MeOH, X1 cm2 mol1): 7. Diamagnetic. 2.4. Crystal structure determination and refinement Suitable single crystals of 1 and 2 with approximate dimensions of 0.06 0.05 0.05 and 0.60 0.40 0.30 mm3, respectively, were manually selected. The crystals were mounted on a BrukerNonius APEX II diffractometer, equipped with CCD area detector and graphite-monochromated Mo Ka radiation (k = 0.71073 Å). The reflection data were collected and processed using the Bruker-Nonius program suites COLLECT, DENZO-SMN and related analysis software [21,22]. The structures were solved by direct methods and subsequent Fourier and difference Fourier syntheses, followed by full-matrix least-square refinements on F2, using the program SHELX [23]. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were partially located from difference Fourier maps, partially placed geometrically, and refined keeping restrains (riding mode) in 1. In compound 2, however, all hydrogen atoms were refined in riding mode. A summary of the crystallographic data, structural parameters and refinement details for the compounds is presented in Table 1. 3. Results and discussion
2.3. Synthesis of [Ni2(HL)2(l1,3-N3)]ClO4H2O (1) and [Co(L)(N3)] (2) 3.1. Synthesis A solution of nickel(II) perchlorate hexahydrate (0.18 g, 0.5 mmol) in acetonitrile (10 mL) was added dropwise to a mixture of H2L (0.18 g, 0.5 mmol) and sodium azide (0.03 g, 0.5 mmol) in acetonitrile (20 mL) with constant stirring. Sodium azide was dissolved in 3–4 drops of water followed by 5 ml of acetonitrile prior to mixing with H2L. Stirring of the whole mixture was then continued for half an hour and the resulting green solution was left for slow evaporation at room temperature in a beaker open to the
The reaction of nickel(II) perchlorate with the pentadentate Schiff base (H2L) in presence of azide ions in acetonitrile medium yielded 1, a binuclear complex containing l1,3-N3 bridge. However, attempts to prepare analogous cobalt complex gave rise to the mononuclear octahedral complex 2 with a terminal azide. Both complexes have been characterized by elemental analysis, IR spectroscopy, electrical conductivity and magnetic susceptibility
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Table 1 Crystallographic data and refinement parameters for 1 and 2. Parameters
1
2
Formula Formula weight (g mol1) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalcd (g cm3) l (mm1) F(000) hkl range T (K) k (Mo Ka) (Å) Reflections measured Reflections unique Data with Fo > 4r(Fo) Rint Parameters refined R wR2 S Dqmax/Dqmin (e Å–3)
C42H52ClN9Ni2O9 979.76 Orthorhombic P212121 11.1063(7) 16.9545(1) 24.4064(1) 90 90 90 4595.8(5) 4 1.416 0.94 2048 ±12, ±19, ±28 296(2) 0.71073 68044 7352 6459 0.056 588 0.034 0.086 1.042 0.41/0.26
C21H25CoN6O2 452.40 Monoclinic P21/c 8.3875(1) 14.881(2) 17.487(3) 90 112.060(1) 90 2022.8(5) 4 1.485 0.88 944 11/12, 20/21, ±25 293(2) 0.71073 27283 6224 4498 0.028 272 0.058 0.158 1.061 1.58/0.62
measurements as well as by single crystal X- ray structural analysis. In methanol solvent, 1 and 2 behave as a 1:1 electrolyte and a non-electrolyte, respectively, as evident from the KM values. Room temperature magnetic susceptibility measurement indicates that 2 is diamagnetic. This conforms to the presence of a singlet ground state with t62g e0g configuration, as expected for low-spin octahedral Co(III) complexes. As usual, CoII underwent aerial oxidation to CoIII during the formation of 2 to accommodate ligands with harder donor atoms and to gain higher CFSE. All the results along with the Xray structural analysis are consistent with the proposed formulae of 1 and 2.
3.2. FTIR spectra Infrared spectra of 1 and 2 are similar with distinct absorption bands at around 1600 and 1630 cm1, assignable to the stretching
1
vibrations of the C@N bond [mCN] of the Schiff base ligand. The strong and sharp absorptions at 2072 and 2042 cm1 for 1 and 2, respectively, are attributed to the asymmetric stretch of the azide groups. The asymmetric single and sharp band expected for the ClO4 anion is observed at 1107 cm1 in 1. The broad and strong bands at around 3460 cm1 indicate the presence of H2O molecules in this compound. Few other characteristic vibrations of the metalbound Schiff bases are located in the range 600–1600 cm1. Thus, the infrared spectra of the compounds are found to be in good agreement [24] with their respective structural features. 3.3. Crystal structures of 1 and 2 The molecular structures and coordination polyhedra of the complexes 1 and 2 are displayed in Figs. 1 and 2, respectively. A few selected bond distances and angles are summarized in Table 2. X-ray structural studies reveal that these complexes comprise a common pentadentate Schiff base ligand and azide ion but adopt different geometries in presence of two different metal ions. In 1, the main structural unit can be described as a binuclear species comprising of two asymmetric [Ni(LH)]+ units, connected through a l1,3-N3 bridge. The electroneutrality of 1 is maintained by the presence of the perchlorate anions in the lattice. The two [Ni(LH)]+ units are nearly equivalent as evident from the minor variations in their bond lengths and angles. In both the units, each Ni(II) ion adopts a distorted octahedral geometry with NiN4O2 chromophore. The hexacoordination environment is maintained by two imino nitrogen (N4, N6 for Ni1; N1, N3 for Ni2), a protonated oxygen (O3 for Ni1; O1 for Ni2), a phenolate oxygen atom (O4 for Ni1; O2 for Ni2), the tertiary amine nitrogen (N5 for Ni1; N2 for Ni2) of the pentadentate Schiff base anion (HL) and the bridging azide anion (N7 for Ni1; N9 for Ni2). All the NiAN and NiAO bond lengths of 1 fall in the range 2.029–2.170 Å and are comparable with the corresponding bonds in similar other dimeric Ni(II) complexes [8–12]. The two Ni(II) centers within one dimer of 1 are separated by a distance of 5.087 Å and bridged by the azide ion in an end-to-end fashion. The nickel(II)–azide distances vary to some extent e.g. Ni1AN7 and Ni2AN9 are 2.148 and 2.104 Å, respectively. Each complex part has undergone some distortions from ideal geometry which is evident from the cisoid and transoid angles around the Ni(II) ions in 1, being in the range 82.8–99.6° and 169.5–178.5°, respectively. X-ray structural studies show that complex 2 is a mononuclear non-electrolyte, [Co(L)(N3] in which the central Co(III) ion is a
2
Fig. 1. Molecular structures of 1 and 2 with atom labeling.
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The crystal packing diagrams of the compounds 1 and 2 are presented in Fig. S1 (see Supplementary data). In the solid state of 1, the two Schiff base molecules of the same binuclear unit are connected to each other via hydrogen bonds. Each O2 atom of phenolate group of the Schiff base in one [Ni(LH)]+ unit interacts with the hydrogen atom (H30) linked to the protonated phenolic oxygen atom (O3) of another unit. In addition, the second protonated oxygen atom extends a bond towards a water molecule (O1AH31 O1w), which itself is involved in O1wAH2w O4 hydrogen bonding to the next binuclear unit. Thus, an infinite chain comprising binuclear units with alternating water molecules is formed along the crystallographic bc plane. Another hydrogen bond extending from the water molecule connects the perchlorate anion (O1wAH1w O7), which is located in the interstices between the chains of the lattice of 1. In 2, the building units are packed rather loosely and isolated from each other. Weak intermolecular van der Waals and p p interactions are only operative in 2 to hold the molecules together. 3.4. Magnetic properties of 1 Fig. 2. Coordination polyhedra of Ni2+ in 1 and Co3+ in 2.
Table 2 Selected bond lengths [Å] and bond angles [°] for 1 and 2. 1 Ni1AO3 Ni1AO4 Ni1AN4 Ni1AN5 Ni1AN6 Ni1AN7 Ni2AO1 Ni2AO2 Ni2AN1 Ni2AN2 Ni2AN3 Ni2AN9 O3AH30 O2. . .H30 Ni1. . .Ni2
2.118(2) 2.029(2) 2.050(3) 2.165(3) 2.039(3) 2.148(3) 2.145(2) 2.058(2) 2.052(3) 2.170(3) 2.054(3) 2.104(3) 1.060(4) 1.413 5.087
O3ANi1AO4 O3ANi1AN4 O3ANi1AN5 O3ANi1AN6 O3ANi1AN7 O4ANi1AN4 O4ANi1AN5 O4ANi1AN6 O4ANi1AN7 N4ANi1AN5 N4ANi1AN6 N4ANi1AN7 N5ANi1AN6 N5ANi1AN7 N6ANi1AN7 Ni1AN7AN8
87.72(9) 84.8(1) 172.5(1) 90.6(1) 85.3(1) 85.1(1) 99.6(1) 88.3(1) 172.3(1) 97.3(1) 172.0(1) 91.0(1) 88.2(1) 87.4(1) 95.1(1) 120.4(3)
O1ANi2AO2 O1ANi2AN1 O1ANi2AN2 O1ANi2AN3 O1ANi2AN9 O2ANi2AN1 O2ANi2AN2 O2ANi2AN3 O2ANi2AN9 N1ANi2AN2 N1ANi2AN3 N1ANi2AN9 N2ANi2AN3 N2ANi2AN9 N3ANi2AN9 Ni2ANi9AN8
88.15(9) 82.8(1) 93.6(1) 88.2(1) 178.5(1) 89.0(1) 175.8(1) 85.4(1) 90.6(1) 87.5(1) 169.5(1) 96.5(1) 98.4(1) 87.6(1) 92.5(1) 122.0(3)
2 Co1AN1A Co1AO1 Co1AN1 Co1AN3 Co1AO2 Co1AN2
1.962(3) 1.882(2) 1.930(2) 1.927(2) 1.909(2) 2.054(3)
N1AACo1AO1 N1AACo1AN1 N1AACo1AN3 N1AACo1AO2 N1AACo1AN2 O1ACo1AN1 O1ACo1AN3 O1ACo1AO2
89.2(1) 87.4(1) 92.4(1) 88.7(1) 177.0(1) 91.3(1) 88.3(1) 177.0(1)
O1ACo1AN2 N1ACo1AN3 N1ACo1AO2 N1ACo1AN2 N3ACo1AO2 N3ACo1AN2 O2ACo1AN2
91.3(1) 179.6(1) 90.8(1) 89.6(1) 89.6(1) 90.6(1) 90.9(1)
member of four six-membered rings. In this complex, the central Co(III) ion adopts a slightly distorted octahedral geometry. The equatorial plane of the polyhedron is formed by the coordination of two nitrogen (N1, N3) and two phenolate oxygen atoms (O1, O2) contributed by the Schiff base. One of the apical positions is occupied by the tertiary amine nitrogen atom (N2) and another by the terminal azide ion (N1A). The CoAN and CoAO bond distances ranging from 1.882 to 2.054 Å agree well with similar other Schiff base complexes of cobalt(III) [13,14]. The cisoid and transoid angles around the Co(III) ion in 2 are in the range of 87.4–92.4° and 177.0–179.6°, respectively. However, the equatorial plane containing the Co(III) ion achieves almost perfect planarity as evidenced from the very low torsion angle (O1AN1AO2AN3 = 1.4°) and the complex unit of 2 is rather less distorted.
The result of variable-temperature magnetic studies on complex 1 is displayed as the vMT vs. T plot (Fig. 3). The vMT value of 2.6 cm3 mol1 K at 300 K is in good agreement with the expected contribution of two magnetically non-interacting or weakly interacting spin triplets (g > 2.00). It increases gradually upon lowering of temperature to reach a maximum (3.2 cm3 mol1 K) at around 25 K. With further lowering of temperature, a sharp decrease of vMT is observed to finally attain a value of 2.3 cm3 mol1 K at 2 K. These features are characteristic of significant intramolecular ferromagnetic interactions in 1, indicating the presence of both D (zero-field-splitting parameter) and z0 J0 (intermolecular antiferromagnetic interactions). ˆ = JS1S2, the fit of the susceptibility From the Hamiltonian H data was carried out applying two different approaches, viz. by considering the z0 J0 parameter (by means of molecular-field approximation) [1] or the D parameter by a full-diagonalization program [25]. The best-fit parameters obtained with the first approach are J = 7.0 ± 0.5 cm1, J0 = 0.49 cm1, g = 2.26 ± 0.01 and R = 2.7 104. Slightly different J value was obtained by the full-diagonalization method, when the D parameter was introduced. In this case, the best-fit parameters obtained are J = 6.5 ± 0.5 cm1, D = 4.9 ± 0.5 cm1, g = 2.26 ± 0.01 and R = 3.2 104. These calculations give D parameter which is likely to be overestimated since the logical J0 parameter has not been considered. As a consequence, we can postulate that J is closer to 6.5 cm1 and J0 could be of the order of 0.4 cm1. Thus, D will most likely be less than 4.9 cm1 (the standard value for isolated nickel(II) complexes is close to 6 cm1) [6]. Complexes containing analogous [Ni2(l1,3-N3)]3+ can either be discrete or one-dimensional. According to the available literature and theoretical calculations [5,12], this kind of bridging azido ligand usually generates antiferromagnetic coupling. In some cases, however, depending on the NiANAN(azido) bond angles and the NiANANANANi torsion angles, the coupling could be ferromagnetic also [12]. Mainly, great torsion angles are known to cause ferromagnetic coupling. Therefore, it is most likely that the ferromagnetic character is dominant in 1 due to its large torsion angle [12], being close to 90°. 4. Conclusion Synthesis and characterization of two new complexes of nickel(II) and cobalt(III) containing a common pentadentate Schiff base ligand have been described in this paper. The reaction of the Schiff base with nickel(II) perchlorate in presence of azide yielded a
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Appendix A. Supplementary material 3.2
CCDC 856954 and 856953 contain the supplementary crystallographic data of 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2012.11.068.
2.8
3
-1
χmT / cm mol K
3.0
2.6
References [1] [2] [3] [4]
2.4
2.2
[5]
0
50
100
150
200
250
300
T/K Fig. 3. Plot of vMT vs. T for 1. Solid lines represent the best fit using the J0 or the D approach (the fit curve is practically identical in both cases).
[6] [7] [8] [9] [10]
binuclear nickel(II) complex containing l1,3-N3-bridge. In contrast, the same synthetic system in presence of cobalt(II) perchlorate resulted in a mononuclear Co(III) species with terminal azide ion. In addition to the synthetic and structural investigations on the complexes, low temperature magnetic measurements were performed to establish the ferromagnetic character of the binuclear Ni(II) complex.
Acknowledgements
[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
One of the authors (S.S.) gratefully acknowledges the financial support under MRP (No. F. PSW-001/10-11) from UGC, Eastern region, Kolkata, India. PTM and SJJ thank the D.S.T-India (F.I.S.T programme) for the use of Bruker Smart APEX II diffractometer at the School of Chemistry, Bharathidasan University. J.R. acknowledges the financial support from Spanish Government (Grant CTQ2009/ 07264).
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