КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 3, с. 143-148
УДК 541.49
SYNTHESIS, CRYSTAL STRUCTURES, AND MAGNETIC PROPERTIES OF COBALT(II)-HEXAFLUORO-ACETYLACETONATE COMPLEXES WITH TWO NEW TRIAZOLE-SUBSTITUTED NITRONYL AND IMINO NITROXIDE
© 2014 J. Chen1, 2, *, Y. J. Zhang1, J. J. Wang1, and Q. Huang2
1College of Chemistry and Chemical Engineering, Anyang Normal University, Anyang, 455002 P.R. China 2School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou, 450052 P.R. China
*E-mail: chenjinghao2008@163.com Received October 18, 2012
Two new chelating radical ligands, NITphtrz (4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazo-line-1-oxyl-3-oxide) and IMphtrz (4,4,5,5-tetramethyl-2-(2-phenyl-1,2,3-triazole-4-yl)imidazoline-1-oxyl), and their cobalt(II) complexes [Co(Hfac)2(NITphtrz)] (I) and [Co(Hfac)2(IMphtrz)] (II) (Hfac = hexafluo-roacetylacetonate) have been prepared and characterized by IR, magnetic, and single-crystal X-ray analysis. The magnetic behaviors of the lignad NITphtrz and complex I have been discussed.
DOI: 10.7868/S0132344X14030037
INTRODUCTION
Metal-radical hybrid solids have been well investigated toward molecule-based magnets, where a radical center is directly bonded to the metal ion, affording appreciable magnetic exchange coupling [1]. In the past decades, there has been a number of investigations concerning paramagnetic metal complexes with nitronyl nitroxide (NITR: 4,4,5,5-tetramethyl-2-R-imidazolin-1-oxyl-3-oxide) and imino nitroxide (IMR: 4,4,5,5-tetramethyl-2-R-imidazolin-1-oxyl) radicals in order to reveal the magnetic interactions between paramagnetic centres for the design of molecular-based ferromagnets [2—5]. As anticipated the feature of R-group linked to the nitronyl nitroxide not only influences the intermolecular spin-spin interactions, but also affects the coordination mode of the nitronyl nitroxides with metal ions. This is particularly true if there are potential coordination sites available in the R-group [6, 7]. Therefore, modification of the R-group would tune the coordination mode between the nitroxides and metal ions and thus alter the magnetic interaction between the nitroxides and metal ions.
In order to extend our knowledge of the extremely rich chemistry of such systems, we are devoted to the exploration of new building blocks for molecule-based magnetic materials. In this paper, we will report two new nitroxide ligands NITphtrz (L1) and IMphtrz (L2):
O*
(L1) (L2)
Due to the presence of the N-triazole moieties, L1 and L2 can coordinate to metal ions as chelate ligands. Reactions of L1 and L2 with Co(Hfac)2 (Hfac = = hexafluoroacetylacetonate) afforded two heterospin complexes. The crystal structures and magnetic characterizations of the related compounds will be described and discussed.
EXPERIMENTAL
Materials and equipment. 2-Phenyl-1,2,3-triazole-4-carboxaldehyde is prepared according to literature method [8]. Co(Hfac)2 • 2H2O (Hfac = hexafluoro-acetylacetone) as prepared as the previous reported [9]. All the other chemicals purchased were of reagent grade and used without purification. Elemental analyses (C, H, and N) were carried out with a PerkinElmer 240C elemental analyzer. IR spectra were recorded in the region of 4000—400 cm-1 on an Avatar-360 spectrophotometer using KBr pellets. Variable-temperature magnetic susceptibilities were measured with a MPMS-7 SQUID magnetometer. Diamagnetic cor-
rections were made with Pascal's constants for all constituent atoms.
Ligands L1 and L2 were prepared as previously described in [10] and [11], respectively. The yields were 76 (L1), 52% (L2).
For C15H18N5O2 (L1)
anal. calcd., %: C, 60.00; H, 6.00; N, 23.33. Found, %: C, 60.31; H, 6.12; N, 23.18.
Important IR absorptions (KBr; v, cm-1): 1368 s v(NO).
For C15H18N5O (L2)
anal. calcd., %: C, 63.38; H; 6.34; N, 24.65. Found, %: C, 63.51; H, 6.21; N, 24.50.
Important IR absorptions (KBr; v, cm-1): 1360 s v(NO).
Synthesis of [Co(Hfac)2(L1)] (I). Co(Hfac)2 • 2H2O (0.1 mmol) was dissolved in boiling «-heptane (30 mL). The solution was left to boil for 30 min and then cooled down to 60°C, whereupon 0.1 mmol of L1 was added under stirring followed by the addition of 5 mL CH2Cl2. The mixture was stirred for 40 min, then filtered. The dack brown filtrate was set aside at a refrigerator for two weeks. Crystals of complex I suitable for X-ray crystallographic analysis were obtained and filtered. The yield was 58%.
For C25H22N5O6F12Co (I)
anal. calcd., %: C, 38.73; H, 2.86; N, 9.03. Found, %: C, 38.68; H, 2.83; N, 8.95.
Important IR absorptions (KBr; v, cm-1): 1370 v(NO).
Synthesis of complex [Co(Hfac)2(L2)] (II) was carried out using the same procedure as that of complex I, which started from L2 and Co(Hfac)2 • 2H2O. The yield was 36%.
For C25H22N5O5F12Co (II)
anal. calcd., %: C, 39.55; H, 2.92; N, 9.22. Found, %: C, 39.42; H, 2.83; N, 9.13.
Important IR absorptions (KBr; v, cm-1): 1345 v(NO).
X-ray structure determination. Structure measurements of complexes I and II were performed on a Bruker Smart 1000 CCD X-ray single-crystal diffracto-meter with MoZa radiation (A = 0.71073 Â) at 273 K. The intensity data were obtained in a range of 2.10° < < 0 < 25.10° (for complex I) and 1.90° < 0 < 28.37° (for complex II) by using a scan technique. The corrections for the Lp factor and an empirical absorption
correction were applied. The structure was resolved by a direct method using SHELXS-97 [12, 13]. All the non-hydrogen atoms were determined with successive difference Fourier syntheses and refined by full-matrix least squares on F (SHELXL-97). All hydrogen atoms were located at the calculated positions. Crystal data and structure refinement details are summarized in Table 1. Selected bond lengths and bond angles are listed in Table 2.
Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 895285 (I), 895284 (II); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
ORTEP drawings of complex I and complex II are depicted in Fig. 1. In complex I, the Co atom is six-coordinated in a distorted octahedron NO5 environment. The equatorial plane is formed by N(3) from L1, O(3), O(5), and O(6) from two Hfac ligands. The Co-O bond lengths in the basal plane are 2.031(2), 2.057(2), 2.054(2) A, respectively. The Co-N(3) distance is 2.251(2) A. The axial positions are occupied by two oxygen atoms from Hfac and L1, respectively. The Co-O bond lengths are 2.025(3) and 2.030(3) A for Co O(NITphtrz) and Co-O(Hfac), respectively. The O(4)CoO(1) angle is 177.82° and the N(3)CoO(1) angle is 91.03°. The dihedral angle between the triazole rings for L1 and the O-N-C-N moieties (O(1), N(1), C(9), and N(2)) is 11.9°. The fragment O(1)-N(1)-C(9)-N(2)-O(2) forms a dihedral angle of 54.5° with the equatorial plane.
In complex II, the Co2+ ion is also six-coordinated in a distorted octahedron N2O4 environment. The equatorial plane is formed by N(1) and N(5) from L2, O(3) and O(4) from two Hfac molecules. The Co-O bond lengths in the basal plane are 2.045(2) and 2.069(2) A, respectively. The Co-N distances are 2.287(2) and 2.088(2) A, respectively. The axial positions are occupied by two oxygen atoms from two Hfac ligands. The Co-O bond lengths are 2.044(2) and 2.028(2) A. The O(2)CoO(5) angle is 174.56° and the N(1)CoN(5) angle is 77.07°. The dihedral angle between the triazole rings for L2 and the O-N-C-N moieties (O(1), N(2), C(9), and N(1)) is 1.4°. The fragment O(1)-N(2)-C(9)-N(1) forms a dihedral angle of 7.5° with the equatorial plane.
No short inter-atomic contacts exist in the crystal lattices of complexes I and II.
The temperature dependence of the magnetic susceptibility for radical ligand L1 was investigated in the temperature range 1.8-300 K under a magnetic field of 2000 G. Figure 2 shows the variation of %MT and
Table 1. Crystal data and structure refinement for complexes I and II
Parameter Value
I II
Formula weight 775.11 759.106
Crystal system Triclinic Triclinic
Space group p1 P1
Unit cell dimensions:
a, A 10.208(2) 10.107(2)
b, A 11.67892) 10.983(2)
c, A 14.680(3) 15.168(3)
a, deg 79.02(3) 86.19(3)
P, deg 76.53(3) 76.17(3)
Y, deg 67.98(3) 77.53(3)
Volume, A3; Z 1567.4(5); 2 1596.2(5); 1
F(000) 1160 748
9 Range for data collection, deg 1.89-28.37 1.90-28.37
Limiting indices -13 < h < 13 -13 < h < 12
-15 < k < 15 -14 < k < 14
-19 < l < 19 -20 < l < 17
Reflections collected 37545 28519
Independent reflections 7808 7899 (Rint = 0.0223)
Numder of refinement 442 433
Completeness, % 99.3 98.7
Goodness-of-fit on F 2 1.097 1.515
Final R indices (I> 2ct(I)) R1 = 0.0622, wR2 = 0.1864 R1 = 0.0621, wR2 = 0.1973
R indices (all data) = 0.0782, wR2 = 0.2035 Rx = 0.0781, wR2 = 0.2100
^max^mi^ e A-3 0.907 and -0.524 0.752 and -0.461
1/Xm with temperature for ligand L1, where xM is the molar magnetic susceptibility and T is the absolute temperature. The value of xMT at 300 K is 0.376 emu K mol-1, which is close to that expected for S = 1/2
system (0.375 emu K mol 1). As shown in Fig. 3, %MT kept unchanged from 300 to 50 K. Below 50 K, it decreased sharply, indicating the intermolecular antifer-romagnetic interaction of nitronyl nitroxides. The
Table 2. Selected bond distances (À) and angles (deg) for complexes I and II
Bond d, Â Bond d, Â
Co(1) - O(1) 2.025(3) Co(1)-O(6) 2.031(2)
Co(1)-O(4) 2.030(3) Co(1)-O(5) 2.054(2)
Co(1)-O(3) 2.057(2) Co(1)-N(3) 2.251(2)
N(1)-O(1) 1.289(3) N(2)-O(2) 1.265(4)
N(4)-N(3) 1.332(3) N(3)-C(8) 1.346(4)
N(4)-N(5) 1.324(4) N(4)-C(6) 1.423(4)
N(1)-C(9) 1.338(4) I N(2)-C(9) I 1.349(4)
Co(2)-O(5) j 2.028(2) Co(2)-O(3) 2.045(2)
Co(2)-O(2) 2.044(2) Co(2)-O(4) 2.069(2)
Co(2)-N(1) 2.088(2) Co(2)-N(5) 2.287(2)
N(2)-O(1) 1.275(3) N(3)-N(4) 1.342(3)
N(4)-N(5) 1.327(3) N(5)-C(8) 1.341(4)
N(1)-C(9) 1.295(3) N(2)-C(9) 1.366(4)
Angle ra, deg Angle ra, deg
O(1)Co(1)O(6) 89.30(10) O(1)Co(1)O(4) 177.82(10)
O(6)Co(1)O(4) 91.26(
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