- Email: [email protected]
Cobalt(II) coordination compounds with acetate and 2-aminopyridine ligands: Synthesis, characterization, structures and magnetic properties of two polymorphic forms
Inorganica Chimica Acta 363 (2010) 1343–1347
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Cobalt(II) coordination compounds with acetate and 2-aminopyridine ligands: Synthesis, characterization, structures and magnetic properties of two polymorphic forms Brina Dojer a,*, Andrej Pevec b, Primozˇ Šegedin b, Zvonko Jaglicˇic´ c,d, Cˇrtomir Stropnik a, Matjazˇ Kristl a, Miha Drofenik a,e a
Faculty of Chemistry and Chemical Technology, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškercˇeva 5, 1000 Ljubljana, Slovenia c Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana, Slovenia d Faculty of Civil and Geodetic Engineering, Jamova 2, University of Ljubljana, 1000 Ljubljana, Slovenia e Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b
a r t i c l e
i n f o
Article history: Received 11 November 2009 Received in revised form 24 December 2009 Accepted 29 December 2009 Available online 6 January 2010 Keywords: Cobalt acetate tetrahydrate 2-Aminopyridine X-ray crystal structure Magnetic measurements
a b s t r a c t The synthesis and characterization of two polymorphic modifications of new cobalt coordination compound with 2-aminopyridine are reported. The modifications were prepared by the reaction of a solution of cobalt acetate tetrahydrate and 2-aminopyridine. The crystal structures of both polymorphic modifications have been determined by single-crystal X-ray diffraction analysis. The structures of both modifications are quite similar. In both of them the Co2+ is six coordinated by four O atoms from two bidentate chelate acetate ligands and by two N atoms from two 2-aminopyridine molecules. Acetate and 2-aminopyridine ligands are lying cis about the metal centre. The most important difference is in asymmetry of acetate ligand chelate bonding and in H-bonding network. Compounds exhibit an extensive system of intra and intermolecular hydrogen bonding. Magnetic properties of both modifications were studied between 2 K and 300 K giving the result leff = 4.6 BM for modification I and leff = 4.7 BM for modification II in paramagnetic region. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction The chemistry of copper [1–4], zinc [5,6], cadmium [7], nickel [8,9] and cobalt [10–17] mononuclear carboxylate complexes, especially with N-donor ligands, has been extensively studied over the past decades. That kind of complexes are interesting because of their crystal structures, distorted geometry and some other properties (fungicidal activity, wood preservation, photoluminescent behaviours, catalysis, enzymatic reactions, magnetic interactions [1,7,8,11]). Besides di- and polynuclear complexes of cobalt carboxylates with different pyridine derivatives as ligands, which have received a great deal of attention over the last years due to their interesting coordination chemistry, unusual structures and comprehensive applications as dyes, drugs, extractants and pesticides [18], there have also been some reports of mononuclear cobalt complexes with carboxylates of different chain (butanoate, benzoate) with 2-aminopyridine [13–15]. In continuation of this interest, we report here the synthesis, spectroscopic characterization, magnetic studies of two modifications of bisacetatobis(2-aminopyri* Corresponding author. Tel.: +386 2 229 44 15. E-mail address: [email protected] (B. Dojer). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.12.052
dine)cobalt(II) and their single crystal X-ray structures. Till now there have been no reports in literature about polymorphic modifications of that kind of complexes. 2. Experimental 2.1. General experimental procedures All starting compounds and solvents were used as purchased. Infrared spectra were recorded on a Perkin–Elmer FT-1720X spectrometer. Electronic spectra of 0.01 M methanol solution were measured by a Perkin-Elmer UV/VIS/NIR Spectrophotometer Lambda 19. Elemental analyses were carried out on a Perkin-Elmer 2400 CHN analyzer at the University of Ljubljana. Magnetic properties of both modifications were studied with a Quantum Design MPMS-XL-5 SQUID magnetometer at University of Ljubljana (Institute of Mathematics, Physics and Mechanics). 2.2. Synthesis of modification I A solid 2-aminopyridine (0.07 g; 0.75 mmol) was slowly added to a hot methanol solution (20.0 mL) of cobalt acetate tetrahydrate
1344
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
(0.05 g; 0.2 mmol). A new solution was heated and stirred at about 55 °C for a half an hour. After filtration, the solution was left in air, the solvent was slowly evaporated to yield violet crystalline product in 2 days. The crystals of [Co(O2CCH3)2(C5H6N2)2] were dried in desiccator above KOH. Yield: 0.047 g (64%). UV–Vis electronic absorption spectral data [kmax/nm]: 253, 319, 538; Anal. Calc. for C14H18CoN4O4 (Mr = 365.25): C, 46.04; H, 4.79; N, 15.34. Found: C, 46.27; H, 4.72; N, 15.25%.
was stirred at room temperature for 5 min. After filtration, the solution was left in air, the solvent was slowly evaporated to yield violet crystalline product in two days. The crystals of [Co(O2CCH3)2(C5H6N2)2] were dried in desiccator above KOH. Yield: 0.338 g (62%). UV–Vis electronic absorption spectral data [kmax/nm]: 248, 319, 536; Anal. Calc. for C14H18CoN4O4 (Mr = 365.25): C, 46.04; H, 4.79; N, 15.34. Found: C, 46.19; H, 4.65; N, 15.24%.
2.3. Synthesis of modification II
2.4. X-ray crystallography
A methanol solution (2.5 mL) of cobalt acetate tetrahydrate (0.373 g; 1.5 mmol) was slowly added to acetonitrile solution (2.5 mL) of 2-aminopyridine (0.565 g; 6.0 mmol). A new solution
Crystal data and refinement parameters for both modifications are listed in Table 1. The carefully selected crystals were glued on glass thread. Diffraction data were collected at room temperature on a Nonius Kappa CCD diffractometer. A graphite monochromated Mo Ka radiation (k = 0.71073 Å) was employed. The structures were solved by direct methods using SIR-92 [19] and refined against F2 on all data by a full-matrix least squares with SHELXL-97 [20]. All non-hydrogen atoms were refined anisotropically while the hydrogen atoms bonded to carbon were included in the model at geometrically calculated positions and refined using a riding model. The hydrogen atoms attached to nitrogen atoms were localized in the difference Fourier synthesis and refined freely (modification I) or with the help of distance restraints (modification II). All the calculations were performed using the WINGX System, Version 1.80.01 [21].
Table 1 Experimental data for the X-ray diffraction studies on modification I and II.
Formula Fw (g mol1) Crystal size (mm) Crystal color Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) F(0 0 0) h range (°) Number of collected reflections Number of independent reflections Rint Number of reflections used Number of parameters R[I > 2r(I)]a wR2 (all data)b Goodness-of-fit, Sc Maximum/minimum residual electron density (e Å3)
I
II
C14H18CoN4O4 365.25 0.20 0.10 0.05 violet triclinic P1
C14H18CoN4O4 365.25 0.25 0.05 0.03 violet orthorhombic Pbca 14.3835(4) 14.9969(3) 15.2216(4) 90 90 90 3283.42(14) 8 1.478 1512 3.32–27.47 6995 3727 0.0381 2310 222 0.0573 0.1324 1.087 +0.52/0.34
8.4449(3) 9.8790(3) 11.7172(3) 65.188(2) 78.770(2 71.684(2) 840.10(4) 2 1.444 378 3.57–27.44 6352 3750 0.0193 3163 232 0.0317 0.0845 1.046 +0.26/0.32
P P R = ||Fo||Fc||/ Fo|. P P wR2 ¼ f ½wðF 2o F 2c Þ2 = ½wðF 2o Þ2 g1=2 . P c S ¼ f ½wðF 2o F 2c Þ2 =ðn=pg1=2 where n is the number of reflections and p is the total number of parameters refined. a
b
2.5. Magnetic measurements Magnetic properties of both modifications were studied between 2 K and 300 K in magnetic field H = 1000 Oe and at a constant temperature of 5 K between H = ±5 T with a Quantum Design MPMS-XL-5 SQUID magnetometer. The measured data on Figs. 4 and 5 are already corrected for a sample holder contribution and for a temperature independent Larmor diamagnetism of core electrons vdia = 1.8 104 emu/mol obtained from Pascal’s tables. [22]
3. Results and discussion By changing the conditions (temperature, solvent, amounts of the reagents) we synthesized and characterized two polymorphic forms of [Co(O2CCH3)2(C5H6N2)2] by the reaction of 2-aminopyridine and methanolic solution of cobalt acetate tetrahydrate.
Fig. 1. An ORTEP view (30% probability) of the molecular structure of modification I (left) and modification II (right).
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
3.1. Structures of both modifications Both modifications crystallize as violet crystals, modification I and modification II in orthorhombic in triclinic (space group P 1) (space group Pbca) crystal system. As can be seen from Fig. 1, the Co ion in both structures is coordinated by two bidentate chelate acetate ligands and by two 2-aminopyridine molecules. The geometry around the metal centre is distorted cis octahedral. The distances from Co ion to the acetate oxygen atoms range from 2.0257(15) to 2.2779(14) Å, except one of them in modification I which is beyond other bonding distances (Co1–O4: 2.4751(18) Å). In accordance with the latter case, the distances
Table 2 Selected bond lengths (Å) and angles (°) for modification I and II. I
II
Co1–O1 Co1–O2 Co1–O3 Co1–O4 Co1–N1 Co1–N3 C1–O1 C1–O2 C3–O3 C3–O4
2.0593(14) 2.2779(14) 2.0257(15) 2.4751(18) 2.0833(15) 2.0875(15) 1.273(2) 1.242(2) 1.266(2) 1.242(2)
2.091(3) 2.222(3) 2.095(3) 2.263(3) 2.096(3) 2.109(4) 1.272(5) 1.247(6) 1.277(5) 1.244(5)
N1–Co1–N3 N1–Co1–O1 N1–Co1–O2 N1–Co1–O3 N1–Co1–O4 O1–C1–O2 O3–C3–O4
94.67(6) 105.74(6) 88.12(6) 103.18(6) 160.04(6) 118.74(18) 120.61(19)
92.73(14) 99.41(14) 93.41(13) 102.73(12) 162.46(12) 118.4(4) 119.9(4)
1345
from the acetate carbons to the oxygen atoms which are nearer the Co ion, are shorter then the oxygen atoms farther from the Co. Greatest asymmetry of chelate acetate bonding is also connected with larger deviation from ideal octahedral angles in modification I. The most distorted bond angles are O3Co1N3 (105.94(6)°) and O3Co1O4 (56.86(6)°) in modification I and O3Co1N1 (102.73(12)°) and O3Co1O4 (59.96(11)°) in modification II. Selected angles are given in Table 2 and as can be seen, just a few of them are close to 90°. The reason, why two of the CoO bonds (Co1O2 and Co1O4 in both modifications) are longer then the other two (Co1O1 and Co1O3 again in both modifications) are intramolecular hydrogen bonds NHO. There are two of them in modification I (N2H2O3 and N4H3O1) and two in modification II (N2H2O3 and N4H4O1) (Figs. 2 and 3). Selected hydrogen bond lengths and angles are given in Table 3. Furthermore, there are also two intermolecular hydrogen bonds NHO in both modifications. Only one of the oxygen atoms is not involved in hydrogen bond formation (O2 in modification II). On the other hand one of the oxygen atoms in modification II is a bifurcated acceptor.
3.2. Magnetic measurements In order to check ionization state of cobalt ions and investigate possible magnetic interactions in the two compounds we have measured temperature dependent susceptibility and isothermal magnetization. The susceptibility (Fig. 4) of both samples monotonically increases with decreasing temperature. In inset in Fig. 4 the product vT as a function of temperature is shown. In high temperature region the product vT for both samples remains constant. As the temperature independent product vT reflects a
Fig. 2. Part of the crystal structure of modification I, showing N–HO hydrogen bonds. [Symmetry codes: (i) –x + 2, y, z + 1; (ii) x + 1, y + 1, z.]
Fig. 3. Part of the crystal structure of modification II, showing N–HO hydrogen bonds. [Symmetry code: (i) x + 1/2, y, z + 3/2.]
1346
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
Table 3 Hydrogen bonding geometry for modification I and II. D–H A
d(D–H) (Å)
d(H A) (Å)
d(D A) (Å)
\(DHA) (°)
Symmetry transformation for acceptors
Complex I N2–H1 O2 N2–H2 O3 N4–H3 O1 N4–H4 O4
0.91(3) 0.88(3) 0.86(3) 0.87(3)
2.03(3) 2.10(3) 2.11(3) 2.13(3)
2.905(2) 2.924(2) 2.924(2) 3.000(2)
159(2) 156(2) 157(2) 176(3)
x + 2, y, z + 1
Complex II N2–H1 4 N2–H2 O3 N4–H3 O3 N4–H4 O1
0.87(2) 0.874(19) 0.89(2) 0.90(2)
2.11(2) 2.24(4) 2.56(4) 2.02(3)
2.974(5) 3.000(5) 3.251(6) 2.852(6)
180(6) 146(5) 136(5) 153(5)
x + 1/2, y, z + 3/2
paramagnetic behaviour we fitted the susceptibility for T > 150 K with the Curie–Weiss law:
v ¼ C=ðT hÞ
ð1Þ
The fitting results, namely Curie constant C and Curie–Weiss parameter h, are collected in Table 4. From the Curie constants we have calculated the effective Bohr magneton numbers: peff = 4.6 for modification I and peff = 4.7 for modification II, respectively. These values are close to other experimentally obtained values for Co2+ ions with basic electron configuration 3d7 (e.g. in [23] an average value of peff = 4.9 is quoted) and larger than the spin S = 3/2 only value pspin-only = 3.9. A small but significant difference between two samples is not surprising. Cobalt(II) is a member of iron group ions where 3d electrons responsible for magnetism are very sensitive to the inhomogeneous electric field produced by neighbouring ions. Small differences in the structure of two polymorph samples causes different coupling of orbital and spin angular momenta that results in slightly different effective Bohr magneton numbers. Below 100 K the product vT slowly decreases with decreasing temperature. This is in agreement with obtained negative Curie– Weiss parameters h in Table 4 for both samples and indicates only a weak antiferromagnetic coupling between magnetic moments of cobalt ions. However, no long range magnetic order is established down to the lowest measured temperature of 2 K. An isothermal magnetization of both samples measured at 5 K is shown on Fig. 5. The measured data can be reproduced with a function:
M ¼ M0 BJ ðg lB J H=kB TÞ
ð2Þ
Fig. 4. Susceptibility and product v(T) (inset) as a function of temperature for modification I and II.
x + 1, y + 1, z
x 1/2, y, z + 3/2
where BJ(x) is the Brilloiun function and M0 is the saturation magnetization.During the fitting procedure the Landé g-factor was set to 2.1 and only M0 and J were used as fitting parameters. As the Brillouin function describes non-interacting spins only, and very well fits to the measured data we can again conclude that no considerable magnetic order has been established between Co ions down to 5 K. The obtained parameters from the fit are collected in Table 4. The total spin quantum number J = 1.8 for modification I and J = 1.7 for modification II, respectively, are slightly larger then the spin only value J = S = 3/2. This is in agreement with the measured effective Bohr magneton numbers from v(T) curves, where we have also obtained effective Bohr magneton numbers (peff) larger then the spin only value. 3.3. IR spectra In the case of that kind of compounds, the values of the asymmetric and symmetric vibrations of NH2 and COO are important. The IR spectra of both modifications have been compared to each other and to information found in the literature [24]. In the IR spectrum of modification I the vibration observed at 1563 cm1 was assigned as mas(COO) and that at 1336 cm1 as ms(COO) compared to modification II, where the vibration observed at 1568 cm1 was assigned as mas(COO) and that at 1329 cm1 as ms(COO). There are significant differences in COO stretching region due to the differences in asymmetry of acetate chelate bonding and also differences between modifications in NH2 stretching region because of the differences in hydrogen bonding scheme. In the IR spectrum of modification I the streching vibration at 3413 cm1 was assigned as mas(NH2) and that at 3339 cm1 as ms(NH2), and also in the
Fig. 5. Magnetization at constant temperature of 5 K. Full lines are function (2) with parameters M0 and J from Table 4.
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347 Table 4 Fit parameters of the v(T) (Eq. (1)) and M(H) (Eq. (2)) curves.
Modification I Modification II
Curie–Weiss fit of v(T)
Brillouin fit of M(H) at 5 K
C
h
J
M0
2.6 emu K/mol 2.8 emu K/mol
8.7 K 6.2 K
1.7 1.8
12.1 103 emu/mol 13.2 103 emu/mol
IR spectrum of modification II the vibrations observed at 3447 and 3342 cm1 can be assigned as mas(NH2) and ms(NH2) [25]. 4. Conclusions The present work describes the synthesis and characterization of two new polymorphic forms of coordination compound with a formula [Co(O2CCH3)2(C5H6N2)2]. It was found out that in both modifications the Co ion is six coordinated by four oxygen atoms from two bidentate chelate acetate ligands an by two nitrogen atoms from two 2-aminopyridine molecules. Acetate and 2-aminopyridine ligands are lying cis about the metal centre. We can summarize that the main reason for asymmetry of acetate chelate bonding in both modification are intra- and intermolecular hydrogen bonds. Magnetic measurements reveals the 2+ ionic state of cobalt, paramagnetic behaviour and no long range magnetic order down to the lowest investigated temperature of 2 K. Acknowledgements This work was supported by the Grant P1-0175-103 from the Ministry of Higher Education, Science and Technology, Republic of Slovenia. Appendix A. Supplementary material CCDC 746963 and 746964 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
1347
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2009.12.052. References [1] B. Kozlevcˇar, N. Lah, D. Zˇlindra, I. Leban, P. Šegedin, Acta Chim. Slov. 48 (2001) 363. [2] B. Kozlevcˇar, A. Murn, K. Podlipnik, N. Lah, I. Leban, P. Šegedin, Croat. Chem. Acta 77 (2004) 613. [3] N. Lah, P. Šegedin, I. Leban, Struct. Chem. 13 (2002) 357. [4] N. Lah, G. Giester, J. Lah, P. Šegedin, I. Leban, New J. Chem. (1987)25 (2001) 753. [5] L. Mei, T.H. Ming, Asian J. Chem. 20 (2008) 6589. [6] Y.N. Zou, Y.H. Fan, C.F. Bi, D.M. Zhang, Y.Y. Li, Chin. J. Struct. Chem. 25 (2006) 261. [7] D.C. Zhong, G.Q. Guo, J.H. Deng, Acta Crystallogr., Sect. E 63 (2007) m3091. [8] Q. Wang, D.Q. Wang, Acta Crystallogr., Sect. E 64 (2008) m194. [9] H.L. Zhu, S.C. Shao, J.L. Ma, Acta Crystallogr., Sect. E 59 (2003) m843. [10] A. Bailey, W.P. Griffith, D.W.C. Leung, A.J.P. White, D.J. Williams, Polyhedron 23 (2004) 2631. [11] A. Majumder, V. Gramlich, G.M. Rosair, S.R. Batten, J.D. Masuda, M.S. El Fallah, J. Ribas, J.-P. Sutter, C. Desplanches, S. Mitra, Cryst. Growth Des. 6 (2006) 2355. [12] L.L. Kong, S. Gao, L.H. Huo, Acta Crystallogr., Sect. E 63 (2007) m2554. [13] D.-C. Zhong, G.-Q. Guo, X.-H. Zuo, J.-H. Deng, L. Yuan, R.-H. Zhu, Acta Crystallogr., Sect. E 64 (2008) m88. [14] W.-Z. Ju, R.-H. Jiao, P. Cao, R.-Q. Fang, Acta Crystallogr., Sect. E 62 (2006) m1012. [15] N.A. Bokach, V.Y. Kukushkin, M. Haukka, T.B. Mikhailova, A.A. Sidrov, I.L. Eremenko, Russ. Chem. Bull. 55 (2006) 36. [16] Z.B. Zhu, S. Gao, J.W. Liu, L.-H. Huo, H. Zhao, Acta Crystallogr., Sect. E 60 (2004) m808. [17] H.Y. He, L.G. Zhu, Acta Crystallogr., Sect. E 59 (2003) m1192. [18] S.G. Baca, I.G. Filippova, C. Ambrus, M. Gdaniec, Y.A. Simonov, N. Gerbeleu, O.A. Gherco, S. Decurtins, Eur. J. Inorg. Chem. 15 (2005) 3118. [19] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26 (1993) 343. [20] G.M. Sheldrick, SHELXL97, Program for Crystal Structure Analysis, Institüt für Anorganische Chemie der Universität, Göttingen, Germany, 1998. [21] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837. [22] O. Kahn, Molecular Magnetism, VCH Publishing, 1993. [23] N.W. Ashcroft, N.D. Mermin, Solid State Phys., Saunders College Publishing, USA, 1976. p. 657. [24] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 184, Chapman and Hall, London, 1975. [25] S. Akyuz, T. Akyuz, J.E.D. Davies, J. Struct. Chem. 40 (1999) 796.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Cobalt(II) coordination compounds with acetate and 2-aminopyridine ligands: Synthesis, characterization, structures and magnetic properties of two polymorphic forms Brina Dojer a,*, Andrej Pevec b, Primozˇ Šegedin b, Zvonko Jaglicˇic´ c,d, Cˇrtomir Stropnik a, Matjazˇ Kristl a, Miha Drofenik a,e a
Faculty of Chemistry and Chemical Technology, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškercˇeva 5, 1000 Ljubljana, Slovenia c Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana, Slovenia d Faculty of Civil and Geodetic Engineering, Jamova 2, University of Ljubljana, 1000 Ljubljana, Slovenia e Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b
a r t i c l e
i n f o
Article history: Received 11 November 2009 Received in revised form 24 December 2009 Accepted 29 December 2009 Available online 6 January 2010 Keywords: Cobalt acetate tetrahydrate 2-Aminopyridine X-ray crystal structure Magnetic measurements
a b s t r a c t The synthesis and characterization of two polymorphic modifications of new cobalt coordination compound with 2-aminopyridine are reported. The modifications were prepared by the reaction of a solution of cobalt acetate tetrahydrate and 2-aminopyridine. The crystal structures of both polymorphic modifications have been determined by single-crystal X-ray diffraction analysis. The structures of both modifications are quite similar. In both of them the Co2+ is six coordinated by four O atoms from two bidentate chelate acetate ligands and by two N atoms from two 2-aminopyridine molecules. Acetate and 2-aminopyridine ligands are lying cis about the metal centre. The most important difference is in asymmetry of acetate ligand chelate bonding and in H-bonding network. Compounds exhibit an extensive system of intra and intermolecular hydrogen bonding. Magnetic properties of both modifications were studied between 2 K and 300 K giving the result leff = 4.6 BM for modification I and leff = 4.7 BM for modification II in paramagnetic region. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction The chemistry of copper [1–4], zinc [5,6], cadmium [7], nickel [8,9] and cobalt [10–17] mononuclear carboxylate complexes, especially with N-donor ligands, has been extensively studied over the past decades. That kind of complexes are interesting because of their crystal structures, distorted geometry and some other properties (fungicidal activity, wood preservation, photoluminescent behaviours, catalysis, enzymatic reactions, magnetic interactions [1,7,8,11]). Besides di- and polynuclear complexes of cobalt carboxylates with different pyridine derivatives as ligands, which have received a great deal of attention over the last years due to their interesting coordination chemistry, unusual structures and comprehensive applications as dyes, drugs, extractants and pesticides [18], there have also been some reports of mononuclear cobalt complexes with carboxylates of different chain (butanoate, benzoate) with 2-aminopyridine [13–15]. In continuation of this interest, we report here the synthesis, spectroscopic characterization, magnetic studies of two modifications of bisacetatobis(2-aminopyri* Corresponding author. Tel.: +386 2 229 44 15. E-mail address: [email protected] (B. Dojer). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.12.052
dine)cobalt(II) and their single crystal X-ray structures. Till now there have been no reports in literature about polymorphic modifications of that kind of complexes. 2. Experimental 2.1. General experimental procedures All starting compounds and solvents were used as purchased. Infrared spectra were recorded on a Perkin–Elmer FT-1720X spectrometer. Electronic spectra of 0.01 M methanol solution were measured by a Perkin-Elmer UV/VIS/NIR Spectrophotometer Lambda 19. Elemental analyses were carried out on a Perkin-Elmer 2400 CHN analyzer at the University of Ljubljana. Magnetic properties of both modifications were studied with a Quantum Design MPMS-XL-5 SQUID magnetometer at University of Ljubljana (Institute of Mathematics, Physics and Mechanics). 2.2. Synthesis of modification I A solid 2-aminopyridine (0.07 g; 0.75 mmol) was slowly added to a hot methanol solution (20.0 mL) of cobalt acetate tetrahydrate
1344
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
(0.05 g; 0.2 mmol). A new solution was heated and stirred at about 55 °C for a half an hour. After filtration, the solution was left in air, the solvent was slowly evaporated to yield violet crystalline product in 2 days. The crystals of [Co(O2CCH3)2(C5H6N2)2] were dried in desiccator above KOH. Yield: 0.047 g (64%). UV–Vis electronic absorption spectral data [kmax/nm]: 253, 319, 538; Anal. Calc. for C14H18CoN4O4 (Mr = 365.25): C, 46.04; H, 4.79; N, 15.34. Found: C, 46.27; H, 4.72; N, 15.25%.
was stirred at room temperature for 5 min. After filtration, the solution was left in air, the solvent was slowly evaporated to yield violet crystalline product in two days. The crystals of [Co(O2CCH3)2(C5H6N2)2] were dried in desiccator above KOH. Yield: 0.338 g (62%). UV–Vis electronic absorption spectral data [kmax/nm]: 248, 319, 536; Anal. Calc. for C14H18CoN4O4 (Mr = 365.25): C, 46.04; H, 4.79; N, 15.34. Found: C, 46.19; H, 4.65; N, 15.24%.
2.3. Synthesis of modification II
2.4. X-ray crystallography
A methanol solution (2.5 mL) of cobalt acetate tetrahydrate (0.373 g; 1.5 mmol) was slowly added to acetonitrile solution (2.5 mL) of 2-aminopyridine (0.565 g; 6.0 mmol). A new solution
Crystal data and refinement parameters for both modifications are listed in Table 1. The carefully selected crystals were glued on glass thread. Diffraction data were collected at room temperature on a Nonius Kappa CCD diffractometer. A graphite monochromated Mo Ka radiation (k = 0.71073 Å) was employed. The structures were solved by direct methods using SIR-92 [19] and refined against F2 on all data by a full-matrix least squares with SHELXL-97 [20]. All non-hydrogen atoms were refined anisotropically while the hydrogen atoms bonded to carbon were included in the model at geometrically calculated positions and refined using a riding model. The hydrogen atoms attached to nitrogen atoms were localized in the difference Fourier synthesis and refined freely (modification I) or with the help of distance restraints (modification II). All the calculations were performed using the WINGX System, Version 1.80.01 [21].
Table 1 Experimental data for the X-ray diffraction studies on modification I and II.
Formula Fw (g mol1) Crystal size (mm) Crystal color Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) F(0 0 0) h range (°) Number of collected reflections Number of independent reflections Rint Number of reflections used Number of parameters R[I > 2r(I)]a wR2 (all data)b Goodness-of-fit, Sc Maximum/minimum residual electron density (e Å3)
I
II
C14H18CoN4O4 365.25 0.20 0.10 0.05 violet triclinic P1
C14H18CoN4O4 365.25 0.25 0.05 0.03 violet orthorhombic Pbca 14.3835(4) 14.9969(3) 15.2216(4) 90 90 90 3283.42(14) 8 1.478 1512 3.32–27.47 6995 3727 0.0381 2310 222 0.0573 0.1324 1.087 +0.52/0.34
8.4449(3) 9.8790(3) 11.7172(3) 65.188(2) 78.770(2 71.684(2) 840.10(4) 2 1.444 378 3.57–27.44 6352 3750 0.0193 3163 232 0.0317 0.0845 1.046 +0.26/0.32
P P R = ||Fo||Fc||/ Fo|. P P wR2 ¼ f ½wðF 2o F 2c Þ2 = ½wðF 2o Þ2 g1=2 . P c S ¼ f ½wðF 2o F 2c Þ2 =ðn=pg1=2 where n is the number of reflections and p is the total number of parameters refined. a
b
2.5. Magnetic measurements Magnetic properties of both modifications were studied between 2 K and 300 K in magnetic field H = 1000 Oe and at a constant temperature of 5 K between H = ±5 T with a Quantum Design MPMS-XL-5 SQUID magnetometer. The measured data on Figs. 4 and 5 are already corrected for a sample holder contribution and for a temperature independent Larmor diamagnetism of core electrons vdia = 1.8 104 emu/mol obtained from Pascal’s tables. [22]
3. Results and discussion By changing the conditions (temperature, solvent, amounts of the reagents) we synthesized and characterized two polymorphic forms of [Co(O2CCH3)2(C5H6N2)2] by the reaction of 2-aminopyridine and methanolic solution of cobalt acetate tetrahydrate.
Fig. 1. An ORTEP view (30% probability) of the molecular structure of modification I (left) and modification II (right).
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
3.1. Structures of both modifications Both modifications crystallize as violet crystals, modification I and modification II in orthorhombic in triclinic (space group P 1) (space group Pbca) crystal system. As can be seen from Fig. 1, the Co ion in both structures is coordinated by two bidentate chelate acetate ligands and by two 2-aminopyridine molecules. The geometry around the metal centre is distorted cis octahedral. The distances from Co ion to the acetate oxygen atoms range from 2.0257(15) to 2.2779(14) Å, except one of them in modification I which is beyond other bonding distances (Co1–O4: 2.4751(18) Å). In accordance with the latter case, the distances
Table 2 Selected bond lengths (Å) and angles (°) for modification I and II. I
II
Co1–O1 Co1–O2 Co1–O3 Co1–O4 Co1–N1 Co1–N3 C1–O1 C1–O2 C3–O3 C3–O4
2.0593(14) 2.2779(14) 2.0257(15) 2.4751(18) 2.0833(15) 2.0875(15) 1.273(2) 1.242(2) 1.266(2) 1.242(2)
2.091(3) 2.222(3) 2.095(3) 2.263(3) 2.096(3) 2.109(4) 1.272(5) 1.247(6) 1.277(5) 1.244(5)
N1–Co1–N3 N1–Co1–O1 N1–Co1–O2 N1–Co1–O3 N1–Co1–O4 O1–C1–O2 O3–C3–O4
94.67(6) 105.74(6) 88.12(6) 103.18(6) 160.04(6) 118.74(18) 120.61(19)
92.73(14) 99.41(14) 93.41(13) 102.73(12) 162.46(12) 118.4(4) 119.9(4)
1345
from the acetate carbons to the oxygen atoms which are nearer the Co ion, are shorter then the oxygen atoms farther from the Co. Greatest asymmetry of chelate acetate bonding is also connected with larger deviation from ideal octahedral angles in modification I. The most distorted bond angles are O3Co1N3 (105.94(6)°) and O3Co1O4 (56.86(6)°) in modification I and O3Co1N1 (102.73(12)°) and O3Co1O4 (59.96(11)°) in modification II. Selected angles are given in Table 2 and as can be seen, just a few of them are close to 90°. The reason, why two of the CoO bonds (Co1O2 and Co1O4 in both modifications) are longer then the other two (Co1O1 and Co1O3 again in both modifications) are intramolecular hydrogen bonds NHO. There are two of them in modification I (N2H2O3 and N4H3O1) and two in modification II (N2H2O3 and N4H4O1) (Figs. 2 and 3). Selected hydrogen bond lengths and angles are given in Table 3. Furthermore, there are also two intermolecular hydrogen bonds NHO in both modifications. Only one of the oxygen atoms is not involved in hydrogen bond formation (O2 in modification II). On the other hand one of the oxygen atoms in modification II is a bifurcated acceptor.
3.2. Magnetic measurements In order to check ionization state of cobalt ions and investigate possible magnetic interactions in the two compounds we have measured temperature dependent susceptibility and isothermal magnetization. The susceptibility (Fig. 4) of both samples monotonically increases with decreasing temperature. In inset in Fig. 4 the product vT as a function of temperature is shown. In high temperature region the product vT for both samples remains constant. As the temperature independent product vT reflects a
Fig. 2. Part of the crystal structure of modification I, showing N–HO hydrogen bonds. [Symmetry codes: (i) –x + 2, y, z + 1; (ii) x + 1, y + 1, z.]
Fig. 3. Part of the crystal structure of modification II, showing N–HO hydrogen bonds. [Symmetry code: (i) x + 1/2, y, z + 3/2.]
1346
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347
Table 3 Hydrogen bonding geometry for modification I and II. D–H A
d(D–H) (Å)
d(H A) (Å)
d(D A) (Å)
\(DHA) (°)
Symmetry transformation for acceptors
Complex I N2–H1 O2 N2–H2 O3 N4–H3 O1 N4–H4 O4
0.91(3) 0.88(3) 0.86(3) 0.87(3)
2.03(3) 2.10(3) 2.11(3) 2.13(3)
2.905(2) 2.924(2) 2.924(2) 3.000(2)
159(2) 156(2) 157(2) 176(3)
x + 2, y, z + 1
Complex II N2–H1 4 N2–H2 O3 N4–H3 O3 N4–H4 O1
0.87(2) 0.874(19) 0.89(2) 0.90(2)
2.11(2) 2.24(4) 2.56(4) 2.02(3)
2.974(5) 3.000(5) 3.251(6) 2.852(6)
180(6) 146(5) 136(5) 153(5)
x + 1/2, y, z + 3/2
paramagnetic behaviour we fitted the susceptibility for T > 150 K with the Curie–Weiss law:
v ¼ C=ðT hÞ
ð1Þ
The fitting results, namely Curie constant C and Curie–Weiss parameter h, are collected in Table 4. From the Curie constants we have calculated the effective Bohr magneton numbers: peff = 4.6 for modification I and peff = 4.7 for modification II, respectively. These values are close to other experimentally obtained values for Co2+ ions with basic electron configuration 3d7 (e.g. in [23] an average value of peff = 4.9 is quoted) and larger than the spin S = 3/2 only value pspin-only = 3.9. A small but significant difference between two samples is not surprising. Cobalt(II) is a member of iron group ions where 3d electrons responsible for magnetism are very sensitive to the inhomogeneous electric field produced by neighbouring ions. Small differences in the structure of two polymorph samples causes different coupling of orbital and spin angular momenta that results in slightly different effective Bohr magneton numbers. Below 100 K the product vT slowly decreases with decreasing temperature. This is in agreement with obtained negative Curie– Weiss parameters h in Table 4 for both samples and indicates only a weak antiferromagnetic coupling between magnetic moments of cobalt ions. However, no long range magnetic order is established down to the lowest measured temperature of 2 K. An isothermal magnetization of both samples measured at 5 K is shown on Fig. 5. The measured data can be reproduced with a function:
M ¼ M0 BJ ðg lB J H=kB TÞ
ð2Þ
Fig. 4. Susceptibility and product v(T) (inset) as a function of temperature for modification I and II.
x + 1, y + 1, z
x 1/2, y, z + 3/2
where BJ(x) is the Brilloiun function and M0 is the saturation magnetization.During the fitting procedure the Landé g-factor was set to 2.1 and only M0 and J were used as fitting parameters. As the Brillouin function describes non-interacting spins only, and very well fits to the measured data we can again conclude that no considerable magnetic order has been established between Co ions down to 5 K. The obtained parameters from the fit are collected in Table 4. The total spin quantum number J = 1.8 for modification I and J = 1.7 for modification II, respectively, are slightly larger then the spin only value J = S = 3/2. This is in agreement with the measured effective Bohr magneton numbers from v(T) curves, where we have also obtained effective Bohr magneton numbers (peff) larger then the spin only value. 3.3. IR spectra In the case of that kind of compounds, the values of the asymmetric and symmetric vibrations of NH2 and COO are important. The IR spectra of both modifications have been compared to each other and to information found in the literature [24]. In the IR spectrum of modification I the vibration observed at 1563 cm1 was assigned as mas(COO) and that at 1336 cm1 as ms(COO) compared to modification II, where the vibration observed at 1568 cm1 was assigned as mas(COO) and that at 1329 cm1 as ms(COO). There are significant differences in COO stretching region due to the differences in asymmetry of acetate chelate bonding and also differences between modifications in NH2 stretching region because of the differences in hydrogen bonding scheme. In the IR spectrum of modification I the streching vibration at 3413 cm1 was assigned as mas(NH2) and that at 3339 cm1 as ms(NH2), and also in the
Fig. 5. Magnetization at constant temperature of 5 K. Full lines are function (2) with parameters M0 and J from Table 4.
B. Dojer et al. / Inorganica Chimica Acta 363 (2010) 1343–1347 Table 4 Fit parameters of the v(T) (Eq. (1)) and M(H) (Eq. (2)) curves.
Modification I Modification II
Curie–Weiss fit of v(T)
Brillouin fit of M(H) at 5 K
C
h
J
M0
2.6 emu K/mol 2.8 emu K/mol
8.7 K 6.2 K
1.7 1.8
12.1 103 emu/mol 13.2 103 emu/mol
IR spectrum of modification II the vibrations observed at 3447 and 3342 cm1 can be assigned as mas(NH2) and ms(NH2) [25]. 4. Conclusions The present work describes the synthesis and characterization of two new polymorphic forms of coordination compound with a formula [Co(O2CCH3)2(C5H6N2)2]. It was found out that in both modifications the Co ion is six coordinated by four oxygen atoms from two bidentate chelate acetate ligands an by two nitrogen atoms from two 2-aminopyridine molecules. Acetate and 2-aminopyridine ligands are lying cis about the metal centre. We can summarize that the main reason for asymmetry of acetate chelate bonding in both modification are intra- and intermolecular hydrogen bonds. Magnetic measurements reveals the 2+ ionic state of cobalt, paramagnetic behaviour and no long range magnetic order down to the lowest investigated temperature of 2 K. Acknowledgements This work was supported by the Grant P1-0175-103 from the Ministry of Higher Education, Science and Technology, Republic of Slovenia. Appendix A. Supplementary material CCDC 746963 and 746964 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
1347
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2009.12.052. References [1] B. Kozlevcˇar, N. Lah, D. Zˇlindra, I. Leban, P. Šegedin, Acta Chim. Slov. 48 (2001) 363. [2] B. Kozlevcˇar, A. Murn, K. Podlipnik, N. Lah, I. Leban, P. Šegedin, Croat. Chem. Acta 77 (2004) 613. [3] N. Lah, P. Šegedin, I. Leban, Struct. Chem. 13 (2002) 357. [4] N. Lah, G. Giester, J. Lah, P. Šegedin, I. Leban, New J. Chem. (1987)25 (2001) 753. [5] L. Mei, T.H. Ming, Asian J. Chem. 20 (2008) 6589. [6] Y.N. Zou, Y.H. Fan, C.F. Bi, D.M. Zhang, Y.Y. Li, Chin. J. Struct. Chem. 25 (2006) 261. [7] D.C. Zhong, G.Q. Guo, J.H. Deng, Acta Crystallogr., Sect. E 63 (2007) m3091. [8] Q. Wang, D.Q. Wang, Acta Crystallogr., Sect. E 64 (2008) m194. [9] H.L. Zhu, S.C. Shao, J.L. Ma, Acta Crystallogr., Sect. E 59 (2003) m843. [10] A. Bailey, W.P. Griffith, D.W.C. Leung, A.J.P. White, D.J. Williams, Polyhedron 23 (2004) 2631. [11] A. Majumder, V. Gramlich, G.M. Rosair, S.R. Batten, J.D. Masuda, M.S. El Fallah, J. Ribas, J.-P. Sutter, C. Desplanches, S. Mitra, Cryst. Growth Des. 6 (2006) 2355. [12] L.L. Kong, S. Gao, L.H. Huo, Acta Crystallogr., Sect. E 63 (2007) m2554. [13] D.-C. Zhong, G.-Q. Guo, X.-H. Zuo, J.-H. Deng, L. Yuan, R.-H. Zhu, Acta Crystallogr., Sect. E 64 (2008) m88. [14] W.-Z. Ju, R.-H. Jiao, P. Cao, R.-Q. Fang, Acta Crystallogr., Sect. E 62 (2006) m1012. [15] N.A. Bokach, V.Y. Kukushkin, M. Haukka, T.B. Mikhailova, A.A. Sidrov, I.L. Eremenko, Russ. Chem. Bull. 55 (2006) 36. [16] Z.B. Zhu, S. Gao, J.W. Liu, L.-H. Huo, H. Zhao, Acta Crystallogr., Sect. E 60 (2004) m808. [17] H.Y. He, L.G. Zhu, Acta Crystallogr., Sect. E 59 (2003) m1192. [18] S.G. Baca, I.G. Filippova, C. Ambrus, M. Gdaniec, Y.A. Simonov, N. Gerbeleu, O.A. Gherco, S. Decurtins, Eur. J. Inorg. Chem. 15 (2005) 3118. [19] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26 (1993) 343. [20] G.M. Sheldrick, SHELXL97, Program for Crystal Structure Analysis, Institüt für Anorganische Chemie der Universität, Göttingen, Germany, 1998. [21] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837. [22] O. Kahn, Molecular Magnetism, VCH Publishing, 1993. [23] N.W. Ashcroft, N.D. Mermin, Solid State Phys., Saunders College Publishing, USA, 1976. p. 657. [24] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Vol. 184, Chapman and Hall, London, 1975. [25] S. Akyuz, T. Akyuz, J.E.D. Davies, J. Struct. Chem. 40 (1999) 796.