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Synthesis and characterization of Cu(II), Zn(II) and Fe(II) complexes supported by pyridylamide ligands
Inorganica Chimica Acta 421 (2014) 465–472
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Synthesis and characterization of Cu(II), Zn(II) and Fe(II) complexes supported by pyridylamide ligands Ethan P. McMoran a, Joshua A. Goodner a, Douglas R. Powell b, Lei Yang a,⇑ a b
Department of Chemistry, University of Central Arkansas, Conway, AR 72035, USA Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
a r t i c l e
i n f o
Article history: Received 9 May 2014 Received in revised form 29 June 2014 Accepted 2 July 2014 Available online 16 July 2014 Keywords: Pyridylamide ligands Zn(II) complexes Cu(II) complexes Fe(II) complexes Crystal structure DFT calculation
a b s t r a c t Six new coordination complexes of Zn(II), Cu(II) and Fe(II) supported by pyridylamide ligands N-2-acetamidopyridine (Haap), N,N0 -2,6-diacetamidopyridine (H2daap) and N,N0 -2,6-pyridyl-bis[2,2,2-trifluoroacetamide] (H2ptaa) were synthesized. The structures of the six complexes were characterized by X-ray crystallography, showing a N2O4 environment of the metal centers with octahedral geometries. Complexes 1 and 2 are mononuclear Zn(II) complexes supported by two Haap ligands or one H2daap ligand. The Cu(II) centers in complexes 3 and 4 showed a tetragonally elongated structure due to the John–Teller effect of the d9 electronic configuration of Cu(II). The two –CF3 groups on ligand H2ptaa led to the weaker interactions between the ligand and the Cu(II) center, which is supported by the Xray crystal structure analysis and IR studies. For complexes 5 and 6, 1:1 and 2:1 ligand-to-metal ratios were observed in the mononuclear structures respectively. Evans’ method indicated both Fe(II) centers are high spin with four unpaired electrons in solution state. The theoretical studies of the complexes 1–6 included geometry optimization and IR vibrational frequencies calculation, which was compared with experimental spectra to assign the characteristic bands. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The coordination chemistry of pyridylamide ligands with the first-row transition metal ions has received great attention recently due to their versatile coordination behaviors in the construction of metal complexes with varying nuclearities and geometric features [1–11]. Systematic studies on the structures, spectroscopic properties, catalytic activities and host–guest chemistry of these coordination complexes have been informative, in particular for obtaining a better understanding of ligand design, complexes synthesis and potential applications [12–20]. It is known that the neutral and anionic form of an amide group will exhibit different coordination modes towards metal centers. Usually, the neural amide group will have the C@O group bind to metal ion, while the –NH– group stays free as a potential hydrogen bonding site. With the application of base to deprotonate the –NH– group, both oxygen and nitrogen atoms of the amidate group are potential coordination donors, leading to very interesting yet diversified structural features. Pyridylacetamide ligands based on 2-aminopyridine and 2,6-diaminopyridine have been synthesized and studied for decades, but only a few examples of transition ⇑ Corresponding author. Fax: +1 501 4503623. E-mail address: [email protected] (L. Yang). http://dx.doi.org/10.1016/j.ica.2014.07.012 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
metal complexes supported by these ligands were reported [21–26]. As part of our effort to investigate the coordination chemistry of pyridylamide ligand systems, here in we report the synthesis and characterization of Zn(II), Cu(II) and Fe(II) complexes with N-2-acetamidopyridine (Haap), N,N0 -2,6-diacetamidopyridine (H2daap) and N,N0 -2,6-pyridyl-bis[2,2,2-trifluoro-acetamide] (H2ptaa). DFT calculations were performed to optimize the geometries and assign the characteristic vibrational frequencies. 2. Experimental 2.1. Physical measurements Elemental analyses were carried out by Atlantic Microlabs, Norcross, GA. 1H NMR spectra were recorded on Bruker AVANCE 300 MHz spectrometer at room temperature. Chemical shifts (d) were referenced to residual solvent signal. UV–Vis spectra were recorded on a Cary 50 spectrometer. X-band EPR spectra were recorded on Resonance Instrument 8400 EPR spectrometer. The g factors and A coupling constants of EPR spectra were obtained from simulation using Bruker SimFonia software (version 1.25). FT-IR spectra were collected on a Nocolet Magna 560 FTIR spectrometer with an ATR attachment. Solution magnetic susceptibility was measured by using Evans’ method in CD3CN at room temperature.
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2.2. Chemicals All reagents were obtained from commercial sources and used as received unless otherwise noted. Ligands N-2-acetamidopyridine (Haap), N,N0 -2,6-Diacetamidopyridine (H2daap) and N,N0 2,6-pyridyl-bis[2,2,2-trifluoro-acetamide] (H2ptaa) were synthesized according to literatures [22,27]. All solvents were dried over CaH2 and distilled under vacuum. [Fe(NCCH3)2(OTf)2] was prepared based on literature [28,29]. 2.3. Synthesis of the metal complexes 2.3.1. [Zn(Haap)2(OTf)2] (1) A solution of Zn(OTf)2 (0.067 g, 0.18 mmol) in 1 mL CH2Cl2 was added to a stirred solution of Haap (0.050 g, 0.37 mmol) in 2 mL CH2Cl2. The white suspension was stirred for 3 h and the solvent was removed under vacuum. The white powder was collected and washed with Et2O (5 mL 3). Vapor diffusion of Et2O into a methanol solution of the product led to the formation of colorless crystals suitable for X-ray crystallographic characterization (0.093 g, 75% yield). Anal. Calc. for C16H16F6N4O8S2Zn: C, 30.22; H, 2.54; N, 8.81. Found: C, 30.36; H, 2.62; N, 8.65%. FT-IR: 1672 (C@O), 1621, 1538 (C–N), 1480, 1435, 1376, 1343, 1284, 1228 (C–F), 1188, 1160 (S@O), 1069, 1031, 971, 864, 786, 763, 633, 612, 573, 584, 516, 422 cm1. 1H NMR (methanol-d4, 298 K): d = 8.52–7.38 (m, 4 H), 2.39 (s, 3H) ppm. 2.3.2. General procedures of synthesis of [Zn(H2daap)(OTf)2] (2), [Cu(H2daap)(OTf)2] (3) and [Cu(H2ptaa)(OTf)2] (4) A solution of M(OTf)2, (0.15 g, 0.41 mmol) (M = Zn2+ for 2; M = Cu2+ for 3 and 4) in 1 mL CH3CN was added to a stirred solution of ligand (0.080 g of H2daap for 2 and 3, 0.10 g H2ptaa for 4), (0.41 mmol) in 2 mL CH3CN. The mixture was stirred for 2–3 h and then filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of crystals suitable for X-ray Crystallographic characterization. [Zn(H2daap)(NCCH3)(OTf)2] (2) (0.204 g, 82.4% yield). Anal. Calc. for C13H14F6N4O8S2Zn: C, 26.12; H, 2.36; N, 9.37. Found: C, 25.80; H, 2.45; N, 8.91. FT-IR: 1682 (C@O), 1633, 1523 (C–N), 1450, 1426, 1219 (C–F), 1170 (S@O), 1025, 812, 631, 604, 573, 514 cm1. 1H NMR (acetonitrile-d3, 298 K): d = 10.20 (s, 2H), 8.03 (m, 1H), 7.02 (m, 2H), 3.38 (s, 3H), 2.29 (s, 6H), ppm. [Cu(H2daap)(NCCH3)(OTf)2] (3) (0.140 g, 56.7% yield). Anal. Calc. for C13H14F6N4O8S2Cu: C, 26.20; H, 2.37; N, 9.40. Found: C, 26.57; H, 2.21; N, 9.29%. FT-IR: 1684 (C@O), 1639, 1617, 1526 (C–N), 1481, 1450, 1350, 1281, 1239 (C–F), 1150 (S@O), 1027, 948, 920, 811, 776, 661, 631, 514 cm1. UV–Vis [CH3CN, kmax, nm (e, M1cm1)]: 317 (2114), 731 (22). EPR (9.434 GHz, 0.02 mM, acetone, 298 K): giso = 1.99, Aiso = 56 104 cm1; EPR (9.434 GHz, solid, 298 K): g|| = 2.36, g\ = 2.11, A|| = 147 104 cm1. [Cu(H2ptaa)(NCCH3)(OTf)2] (4) (0.185 g, 64.1% yield). Anal. Calc. for C13H8F12N4O8S2Cu: C, 22.18; H, 1.15; N, 7.96. Found: C, 21.90; H, 1.58; N, 7.73%. FT-IR: 1716 (C@O), 1677, 1644, 1589 (C-N), 1469, 1245 (C–F of triflate), 1224 (C–F of H2ptaa), 1150 (S@O), 1027, 797, 763, 746, 631, 510 cm1. UV–Vis [CH3CN, kmax, nm (e, M1 cm1)]: 327 (2982), 419 (shoulder, 130), 898 (76). EPR: no hyperfine signals. 2.3.3. [Fe(H2daap)(H2O)(OTf)]OTf (5) A solution of Fe(OTf)2 (0.145 g, 0.410 mmol) in 1 mL CH3CN was added to a stirred solution of ligand H2daap (0.080 g, 0.41 mmol) in 2 mL CH3CN. The mixture was stirred for 3 h and filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of green crystals suitable for X-ray Crystallographic characterization (0.133 g, 53.5% yield). Anal. Calc. for C13H16F6N4O9S2Fe: C, 25.75; H, 2.66; N, 9.24. Found: C, 25.37; H, 2.49; N, 9.42%. FT-IR:
1657 (C@O), 1624, 1514 (C–N), 1448, 1418, 1374, 1315, 1290, 1218 (C–F), 1165 (S@O), 1024, 814, 763, 633, 611, 573, 511 cm1. UV– Vis [CH3CN, kmax, nm (e, M1 cm1)]: 307 (5950). Solution magnetic moment (Evans’ method, 22.0 °C, 5.21 102 M, CD3CN): 5.14 lB/Fe. 2.3.4. [Fe(H2daap)2(OTf)2] (6) A solution of [Fe(NCCH3)2(OTf)2] (0.092 g, 0.21 mmol) in 2 mL CH3CN was added to a stirred solution of ligand (0.080 g, 0.41 mmol) in 1 mL CH3CN. The mixture was stirred for 2 h and then filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of yellow crystals suitable for X-ray Crystallographic characterization (0.065 g, 42% yield). Anal. Calc. for C20H22F6N6O10S2Fe: C, 32.44; H, 3.00; N, 11.35. Found: C, 32.73; H, 3.28; N, 11.19%. FT-IR: 1634 (C@O), 1633 (C@O), 1562, 1510, 1449, 1415, 1383, 1326, 1269 (S@O), 1247, 1220 (C–F), 1176, 1159, 1026, 806, 760, 627, 609, 573, 518 cm1. UV–Vis [CH3CN, kmax, nm (e, M1 cm1)]: 354 (5572). Solution magnetic moment (Evans’ method, 22.0 °C, 1.98 102 M, CD3CN): 5.21 lB/Fe. 2.4. X-ray crystallography X-ray crystallographic data were collected on crystals with dimensions of 0.46 0.38 0.24 mm for 1, 0.38 0.19 0.18 mm for 2, 0.46 0.43 0.20 mm for 3, 0.38 0.27 0.26 mm for 4, 0.52 0.24 0.12 mm for 5 and 0.50 0.08 0.05 mm for 6. Data were collected at 100 K using a diffractometer with a Bruker APEX CCD area detector [30] and graphite-monochromated Mo Ka radiation (k = 0.71073 Å). All six structures were solved by direct methods and refined by full-matrix least-square methods on F2 [31]. The crystal parameters, data collection and refinement are summarized in Table 1. Non-hydrogen atoms were refined with anisotropic displacement parameters. The positions of hydrogen bonded to carbons and nitrogens were initially determined by geometry and were refined using a riding model. For complex 3, the data are separated into the twin components by the integration and absorption correction programs. For complex 4, one triflate group bond to the metal was probably dynamically disordered. The occupancies for this triflate are refined to 0.711(3), 0.167(3), and 0.121(2) for the unprimed, primed, and double-primed atoms. One of the two diethyl ether molecules is disordered. The occupancies of the solvent molecule are refined to 0.585(6) and 0.415(6) separately. For complex 6, the sample exhibited twinning which was removed by the data reduction and scaling programs. 2.5. Computational details Density Functional Theory (DFT) calculations were preformed with the Gaussian09 software package [32] under the Windows operating system. All input files were prepared using Gaussview 5.0 [33]. Input files were prepared from the crystal structure of each compound determined by X-ray Crystallographic characterization. All calculations were ran using the B3LYP [34–36] function with a 6-31G(d,p) basis set for all atoms. Optimized geometries were calculated under standard conditions with symmetry. Vibrational frequency analysis was preformed using the freq keyword for comparison with experimental data. 3. Results and discussion 3.1. Syntheses and characterization The ligand Haap, H2daap and H2ptaa were synthesized based on the reported procedures [22,27]. In this work, the three ligands were applied as a neutral form in the reactions with metal salts.
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E.P. McMoran et al. / Inorganica Chimica Acta 421 (2014) 465–472 Table 1 Summary of crystal data and refinement parameters for complexes 1–6.
Formula Formula weight T (K) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Z V (Å3) qcalcd (g/cm3) l (mm1) R1 [I > 2r(I)] wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2
1
2
3
4
5
6
C16H16F6N4O8S2Zn 635.82 100(2) Pbca 14.2244(5) 8.9350(3) 18.8069(6) 90 90 90 4 2390.26(14) 1.767 1.300 0.0285 0.0884 1.010
C13H14F6N4O8S2Zn 597.77 100(2) P21/n 22.041(3) 9.2035(14) 22.084(3) 90 98.579(3) 90 8 4429.7(11) 1.793 1.396 0.0510 0.1486 1.005
C13H14CuF6N4O8S2 595.94 100(2) P21/n 11.2630(5) 14.4384(7) 13.3025(6) 90 95.631(2) 90 4 2152.81(17) 1.839 1.310 0.0318 0.1002 1.001
C17H18CuF12N4O9S2 778.01 100(2) P1
C13H16F6FeN4O9S2 606.27 100(2) P1
C24H28F6FeN8O10S2 822.51 100(2) P1
8.6473(3) 12.7566(5) 13.2641(5) 84.809(2) 73.830(2) 82.865(2) 2 1392.00(9) 1.856 1.069 0.0822 0.2403 1.099
8.3019(9) 10.8131(11) 13.4664(14) 72.796(2) 79.956(2) 81.192(2) 2 1130.4(2) 1.781 0.954 0.0302 0.0843 1.000
10.925(2) 12.439(3) 13.574(3) 110.808(5) 97.972(5) 96.312(5) 2 1682.1(6) 1.624 0.670 0.0781 0.2161 1.056
Reactions with the anionic form of the ligands obtained by adding bases, such as triethyl amine and NaH, only led the formation of uncharacterizable products. The idea of replacing the two methyl groups in H2daap with two –CF3 groups in H2ptaa is to increase the solubility of the product and obtain a better understanding of the impact of different ligand manifolds on the electronic properties of the metal complexes. Complex 1 was synthesized by mixing two equiv. of Haap ligand with one equiv. of Zn(OTf)2 in CH2Cl2 (Scheme 1). The white powder yielded was recrystallized by vapor diffusion of Et2O into a CH3OH solution of the product at room temperature. The 1:1 reaction led to the same product, indicating the high stability of complex 1. No changes were observed after the storage of complex 1 in air for months. Complexes 2–6 were synthesized by mixing the neutral ligand H2daap or H2ptaa with the corresponding metal salts in CH3CN in either 1:1 or 2:1 ligand-to-metal ratio (Scheme 2). The vapor diffusion of Et2O into the acetonitrile solution at room temperature afforded the formation of colorless (complex 2), green (complexes 3–5) and yellow (complex 6) crystals. Compound 2–3 and 5–6 were stable in solid and solution when exposed to air and no apparent changes were observed in weeks. Complex 4 is stable towards dry oxygen, but is sensitive towards moisture. When exposed to air, the green solid turned to deep brown oil in about 10 min. 1H NMR of complexes 1 and 2 showed similar signals of the free ligands. Scheme 2. Syntheses of complexes 2–6.
3.2. Complexes [Zn(Haap)2(OTf)2] (1) and [Zn(H2daap)(NCCH3)(OTf)2] (2) X-ray crystal structure analysis showed that complexes 1 and 2 are mononuclear Zn(II) complexes (Fig. 1). Selected bond lengths and angles for the two complexes are listed in Table 2. A 2:1 ligand-to-metal ratio was observed in the crystal structure of complex 1. The zinc center with an octahedral geometry is chelated by two Haap ligands in a trans fashion through the pyridyl nitrogens and amide oxygens, with Zn–Npy and Zn–OC@O distances of 2.085
Scheme 1. Synthesis of complex [Zn(Haap)2(OTf)2] (1).
and 2.047 Å respectively. Since the molecule sits on a crystallographic center of symmetry, Npy–Zn–Npy, OC@O–Zn–OC@O and Otriflate–Zn–Otriflate have a bond angle of 180°. The axial positions of the octahedral are occupied by the two oxygen atoms from the two triflate anions, with a Zn–Otriflate distance of 2.199 Å, which is longer than the Zn–OC@O distance (2.047 Å). On the equatorial plane, the Npy–Zn–OC@O bite angle of the six-member ring is 86.53°, indicating the slight distortion of the equatorial plane to a rectangle shape. A Zn(II) complex of the ligand Haap, [Zn(Haap)2(H2O)2](NO3)2, with a different coordination sphere was reported by Martin et al. [23]. Unlike the participation of OTf anions in the coordination of the Zn(II) center in complex 1, the two axial positions of the octahedral geometry in [Zn(Haap)2 (H2O)2](NO3)2 are occupied by two water molecules with an Ow– Zn–Ow bond angle of 180°, and the two NO 3 anions stay free in the outer-sphere. Due to the weaker steric hindrance of the axial water molecules, the Zn–Ow bond (2.159 Å) in [Zn(Haap)2(H2O)2](NO3)2 is shorter than the Zn–Otriflate bond in complex 1 (2.199 Å).
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Fig. 1. X-ray structures of complex 1 (left) and 2 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms are omitted for clarity.
Accordingly, the bonds on the equatorial plane of [Zn(Haap)2 (H2O)2](NO3)2 (Zn–OC@O = 2.058 Å, Zn–Npy = 2.111 Å) are slightly longer than those bonds in complex 1 (Zn–OC@O = 2.047 Å, Zn– Npy = 2.085 Å). The structure of complex 1 is stabilized by a hydrogen bond network formed between the free –NH– groups on the amide side arm of the Haap ligands and the neighboring OTf anions. For each mononuclear unit [Zn(Haap)2(OTf)2], the two triflate anions are hydrogen bonded to two –NH– groups from two neighboring mononuclear units with a H O distance of 2.06 Å. Meanwhile, the two –NH– groups from the same mononuclear unit connect with two neighboring triflate anions in the opposite direction of the equatorial plane. These hydrogen bonding interactions extend to form a two dimensional supramolecular grid in the yz plane of the crystal lattice (Fig. S1 in Supporting information). The Zn(II) center of complex 2 also has an octahedral geometry with a 1:1 ligand-to-metal ratio. The neutral H2daap ligand acts as a tridentate ligand, bracing the Zn(II) center through one pyridyl N and two amide side arms and forming two six-member rings (Zn–O–C–N–C–N) with an average chelated angle of 90.06°. Due to the restrain effect of the two six-member rings, the pyridyl ring is slightly tilted with respect to the equatorial plan of the octahedral geometry with an angle of 12.12°. The equatorial plan is fulfilled by an acetonitrile molecule sitting on the trans position of the pyridyl nitrogen and the Npy–Zn–NCH3CN bond angle is 176.48°. The two oxygen donors at axial positions are from by two trans triflate anions with a Otriflate–Zn–Otriflate bond angle of 172.36°. The average bond lengths of the two Zn–N bonds is 2.148 Å, and the average Zn–Otriflate bond length is 2.162 Å, which is slightly longer than the average Zn–OC@O bond (1.989 Å). This elongation along the Otriflate–Zn–Otriflate axis may be attributed to the steric effect of CF3 groups of the triflate anions. A complicated hydrogen bond network connects the neighboring mononuclear units and triflate anions, and extends along the z axis to form a one dimensional ladder-like supramolecular structure (Fig. S2 in Supporting information). The optimized geometries of both complexes 1 and 2 matched well with the crystal structure data. The IR spectra of complexes 1 and 2 were collected and compared with the calculated vibrational frequencies. The calculated C@O stretching frequencies at 1731 (complex 1) and 1744 cm1
(complex 2) are in reasonable correlation with the experimental values observed at 1672 (complex 1) and 1682 cm1 (complex 2). The two experimental IR peaks at 1538 (complex 1) and 1523 cm1 (complex 2) can be assigned to the C–N stretching frequency of the amide group coupled with C–C stretching of the pyridine ring, giving calculated values of 1528 (complex 1) and 1572 cm1 (complex 2). The medium peaks of S@O stretching of the triflate anions at 1160 (complex 1) and 1170 cm1 (complex 2) in experimental spectra were also confirmed by the calculated values at 1161 (complex 1) and 1165 cm1 (complex 2). 3.3. Complexes [Cu(H2daap)(NCCH3)(OTf)2] (3) and [Cu(H2ptaa)(NCCH3)(OTf)2] (4) The mononuclear Cu(II) complexes 3 and 4 are structural analogues of the complex 2 (Fig. 2). Selected bond lengths and angles for the two complexes are listed in Table 2. Both ligands H2daap and H2ptaa have a tridentate coordination mode towards the Cu(II) center. The N2O4 coordination environment of the Cu(II) center with an octahedral geometry is fulfilled by one tridentate ligand, one acetonitrile molecule (equatorial plan) and two triflate anions (axial positions). The same tridentate coordination mode of H2daap ligand has been reported in a mononuclear Cu(II) complex with one H2daap and two chlorides, in which a square pyramidal geometry of the metal center was proposed based on the spectroscopic characterization only [22]. For complex 3, the average Cu–Otriflate bond length (2.403 Å) is significantly longer than the average Cu–OC@O bond length (1.910 Å) and Cu–N bond length (2.009 Å). This axial elongation of the octahedral geometry is attributed to the Jahn–Teller effect of the d9 configuration of the Cu(II) center. Interestingly, a less tetragonal distortion is observed in the Cu(II) center of complex 4. The average Cu–Otriflate bond length (2.333 Å) on the axial positions in complex 4 is shorter than that of complex 3 (2.403 Å). A similar structural difference was also observed in optimized geometries of complexes 3 and 4. The major factor for this difference between the two complexes is the –CF3 groups in ligand H2ptaa. The strong electron withdrawing effect from the –CF3 groups significantly strengthen the C@O bond in ligand H2ptaa, causing the shorter C@O bond in complex 4 (1.225 Å) than the C@O bond in complex 3 (1.242 Å) observed
E.P. McMoran et al. / Inorganica Chimica Acta 421 (2014) 465–472 Table 2 Selected bond lengths (Å) and angles (°) for complexes 1–6. Complex 1 Zn1–O1 Zn1–N1 O1–Zn1–O1A O1–Zn1–N1A O1–Zn1–N1 N1A–Zn1–N1 O2A–Zn1–O2 Complex 2 Zn1–O1 Zn1–N4 Zn1–O3 O1–Zn1–O2 O2–Zn1–N4 O2–Zn1–N1 O1–Zn1–O3 N4–Zn1–O3 O1–Zn1–O6 N4–Zn1–O6 Complex 3 Cu1–O1 Cu1–N1 Cu1–O3 O1–Cu1–O2 O2–Cu1–N1 O2–Cu1–N4 O1–Cu1–O3 N1–Cu1–O3 O1–Cu1–O6 N1–Cu1–O6 O3–Cu1–O6 Complex 4 Cu1–O1 Cu1–N4 Cu1–O6 O1–Cu1–O2 O2–Cu1–N4 O2–Cu1–N1 O1–Cu1–O6 N4–Cu1–O6 O1–Cu1–O3 N4–Cu1–O3 O6–Cu1–O3 Complex 5 Fe1–O1 Fe1–O3 Fe1–O4 O1–Fe1–O2 O2–Fe1–O3 O2–Fe1–N4 O1–Fe1–O4 O3–Fe1–O4 O1–Fe1–N1 O3–Fe1–N1 O4–Fe1–N1 Complex 6 Fe1–O1B Fe1–O2B Fe1–N1B O1B–Fe1–O2A O2A–Fe1–O2B O2A–Fe1–O1A O1B–Fe1–N1B O2B–Fe1–N1B O1B–Fe1–N1A O2B–Fe1–N1A N1B–Fe1–N1A
2.0467(9) 2.0851(11) 180.0 93.47(4) 86.53(4) 180.0 180.0
Zn1–O2
2.1988(10)
O1–Zn1–O2A N1–Zn1–O2A O1–Zn1–O2 N1–Zn1–O2
92.67(4) 88.64(4) 87.33(4) 91.36(4)
1.982(3) 2.144(4) 2.160(3) 177.13(13) 90.29(14) 90.83(13) 91.84(12) 86.23(14) 95.08(13) 88.78(14)
Zn1–O2 Zn1–N1 Zn1–O6 O1–Zn1–N4 O1–Zn1–N1 N4–Zn1–N1 O2–Zn1–O3 N1–Zn1–O3 O2–Zn1–O6 N1–Zn1–O6
1.995(3) 2.152(3) 2.164(3) 88.74(14) 90.11(13) 178.75(14) 85.40(13) 93.31(13) 87.60(13) 91.82(13)
1.9041(15) 2.0027(17) 2.3416(16) 172.54(7) 94.21(7) 86.08(7) 93.09(6) 95.52(6) 94.64(6) 81.66(6) 171.91(6)
Cu1–O2 Cu1–N4 Cu1–O6 O1–Cu1–N1 O1–Cu1–N4 N1–Cu1–N4 O2–Cu1–O3 N4–Cu1–O3 O2–Cu1–O6 N4–Cu1–O6
1.9154(15) 2.0154(18) 2.4645(16) 93.18(7) 86.63(7) 175.70(7) 85.20(6) 88.78(7) 87.43(6) 94.07(6)
1.929(4) 1.987(4) 2.303(3) 173.32(14) 85.22(17) 92.49(15) 88.67(15) 89.22(15) 90.17(12) 93.49(15) 177.03(13)
Cu1–O2 Cu1–N1 Cu1–O3 O1–Cu1–N4 O1–Cu1–N1 N4–Cu1–N1 O2–Cu1–O6 N1–Cu1–O6 O2–Cu1–O3 N1–Cu1–O3
1.936(4) 2.012(4) 2.363(3) 89.42(18) 92.93(16) 177.48(17) 95.24(15) 89.93(13) 86.19(13) 87.40(13)
2.0255(12) 2.1145(12) 2.1598(11) 171.01(4) 92.11(5) 92.15(5) 91.35(5) 175.27(5) 85.23(5) 88.08(5) 96.54(5)
Fe1–O2 Fe1–N4 Fe1–N1 O1–Fe1–O3 O1–Fe1–N4 O3–Fe1–N4 O2–Fe1–O4 N4–Fe1–O4 O2–Fe1–N1 N4–Fe1–N1
2.0534(11) 2.1269(14) 2.1856(12) 90.03(5) 96.72(5) 85.36(5) 87.22(5) 89.99(5) 86.12(4) 173.15(5)
2.060(3) 2.078(3) 2.144(4) 90.02(15) 92.04(14) 170.68(14) 87.47(14) 87.35(14) 96.21(15) 88.96(14) 176.27(15)
Fe1–O2A Fe1–O1A Fe1–N1A O1B–Fe1–O2B O1B–Fe1–O1A O2B–Fe1–O1A O2A–Fe1–N1B O1A–Fe1–N1B O2A–Fe1–N1A O1A–Fe1–N1A
2.060(4) 2.080(4) 2.146(4) 174.59(14) 89.24(14) 89.54(14) 95.67(15) 93.58(14) 84.98(15) 85.86(15)
in X-ray crystal structures. Accordingly, the interaction between the Cu(II) center and C@O group becomes weaker in complex 4 (Cu–OC@O = 1.933 Å) than that in complex 3 (Cu–OC@O = 1.910 Å). Therefore, the complex 3 exhibits larger tetragonal distortion along the Otriflate–Cu–Otriflate axis. The C@O stretching frequency change observed in the IR spectra of complexes 3 and 4 (see the following
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discussion) also support this conclusion. Hydrogen bonding interactions between amide N–H group and triflate anion connect mononuclear units to form either two-dimensional (complex 3) or one-dimensional (complex 4) supramolecular network (Fig. S3 and S4 in Supporting information). The IR spectrum of complex 3 shows a C@O stretching at 1684 cm1, which is close to the C@O frequency in complex 2 (1682 cm1). While in complex 4, the C@O frequency shifts to 1716 cm1 due to the electron withdrawing (EWR) effect of the – CF3 groups of the ligand H2ptaa, indicating the stronger C@O bond in ligand H2ptaa. The calculated C@O stretching frequencies in complexes 3 and 4 are 1727 and 1748 cm1, which confirm the peak assignment for the complexes and EWR effect of the ligand H2ptaa. Complex 3 showed one strong transition at 317 nm with an absorption coefficient of 2114 M1 cm1 corresponding to the ligand to metal charge transfer (LMCT). A weak broad band observed at 731 nm was assigned as the d–d transition of the Cu(II) center. Both LMCT and d–d transition bands of complex 4 red shift to the 327 and 898 nm, indicating the weaker interaction between the ligand H2ptaa and copper site. This matches with the structural differences of the two complexes caused by the strong electron withdrawing –CF3 group in ligand H2ptaa. The X-band EPR spectrum of complex 3 in both solid and solution states showed the typical hyperfine signal of a mononuclear d9 Cu(II) complexes (Fig. 3). In acetone solution at room temperature, an isotropic signal was observed. The simulated spectrum showed a g value giso = 1.99 and a coupling constant Aiso = 56 104 cm1. In solid state, the signal is axial with g|| = 2.36, g\ = 2.11 and A|| = 147 104 cm1 obtained from simulation, indicating the dx22 y ground state and tetragonally distorted octahedral geometry of the copper center [37]. Although extensive effort were devoted to measure the EPR spectra of complex 4 in different solvents such as CH3CN, CH3OH, acetone and CH2Cl2, only isotropic signals without any hyperfine structures were observed. 3.4. Complexes [Fe(H2daap)(H2O)(OTf)]OTf (5) and [Fe(H2daap)2(OTf)2] (6) Complex 5 is a product of the reaction between one equiv. of ligand H2daap and one equiv. of Fe(OTf)2. The X-ray crystal structure of complex 5 reveals a six-coordinate Fe(II) center with one H2daap ligand chelating to the metal ion in a tridentate fashion (Fig. 4, left). The octahedral geometry is completed by the coordination of one water molecule, one acetonitrile molecule and one triflate anion. The possible source of the water molecule is the trace amount of moisture in the CH3CN solvent. The equatorial plane formed by N, O donors from the ligand and acetonitrile nitrogen is twisted with respect to the pyridyl plane with an angle of 17.239°, which is higher than those angles found in complexes 2–4 (9.796°–12.115°). The two six-member rings formed by amide side arms with the Fe(II) center have OC@O–Fe–Npy bite angles of 85.23(5)° and 86.12(4)°. This observation, plus the OC@O–Fe–CC@O angle of 171.014°, indicates the structural distortion of the Fe center away from the pyridine ring with a Fe–Npy bond of 2.1856(12) Å and a Fe–Nacetonitrile bond of 2.1269(14) Å. No appreciable elongation of the Fe–O and Fe–N bonds is observed. Interesting hydrogen bonding interactions are observed among ligand, water molecule and triflate anions. One of the two hydrogens from the water molecule interacts with one triflate ion with a H O distance of 1.979 Å, which coordinates to another mononuclear Fe(II) unit. The other hydrogen from the water molecule forms a hydrogen bond interaction with a free triflate ion (H O distance = 2.083 Å) that interacts with two different mononuclear units through N–H O interactions (2.09 and 2.02 Å, Fig. S5 in Supporting information).
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Fig. 2. X-ray structures of complex 3 (left) and 4 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms are omitted for clarity.
Fig. 3. X-band EPR spectra of complex 3 in acetone solution (a) and solid state (b) at room temperature. Black is experimental data and red is simulation. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The structure of complex 6 consists of a [FeII(H2daap)2]2+ cation (Fig. 4, right) and two triflate anions. The coordination geometry of the Fe(II) center is a slightly distorted octahedron, including two pyridyl nitrogen atoms and four C@O groups from two H2daap ligands, which chelate the Fe(II) center in a trans fashion with a dihedral angle of 40.191° between the two pyridyl planes. The average Fe–Npy and Fe–OC@O bond lengths are 2.145 and 2.070 Å. The distortion of the FeN2O4 octahedral geometry is a result from the small bite angles (average 86.413°) of the OC@O–Fe–Npy imposed by the six-member chelate rings formed by H2daap ligand and the Fe(II) center. Each [FeII(H2daap)2]2+ cation is connected to the neighboring triflate anions through N–H Otriflate hydrogen bonds with distances ranging from 2.821(5) to 3.184(6) Å (Fig. S6
in Supporting information). Selected bond lengths and angles for the complexes 5 and 6 are listed in Table 2. The IR spectrum of complex 5 shows a C@O stretching frequency of the amide side arm at 1657 cm1, which is confirmed by the calculated frequency at 1708 cm1 from DFT calculation. An interesting feature observed in the IR spectrum of the complex 6 is the two peaks with medium intensity at 1634 and 1633 cm1. DFT calculation indicates that the two peaks come from the antisymmetrically coupled stretching from two pairs of C@O group on the trans positions of the octahedral geometry (C@O1A/C@O2A and C@O1B/C@O2B in crystal structure, Fig. 4). The calculated frequencies are 1714 and 1713 cm1 respectively. The UV–Vis spectra of complexes 5 and 6 were recorded in acetonitrile and presented
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Fig. 4. X-ray structures of [Fe(H2daap)(H2O)(OTf)]+ cation in complex 5 (left) and [Fe(H2daap)2]2+ cation in complex 6 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms except those on the water molecule are omitted for clarity.
in Figs. S11 and S12. The spectra are dominated by strong absorptions at 307 nm (e = 5950 M1 cm1, complex 5) and 354 nm (e = 5572 M1 cm1, complex 6), respectively. Both bands are attributed to metal-to-ligand charge transfer (MLCT) for Fe(II)-topyridine (t2g-p⁄py) transition [38]. 1H NMR of both complexes showed broad paramagnetic signals, suggesting a high-spin d6 configuration. In an effort to confirm the spin state of Fe(II) centers in the complex 5 and 6, Evans’ method was performed to obtain the magnetic susceptibilities in solution state at room temperature. The 5.14 lB (complex 5) and 5.21 lB (complex 6) based on Evans method indicated that both complexes possess a Fe(II) center with four unpaired electrons. 4. Conclusions In summery, six Zn(II), Cu(II) and Fe(II) complexes supported by pyridylamide ligands with one or two amide side arms were synthesized and characterized. X-ray crystallography characterization showed that all six complexes have a mononuclear structure with an octahedral geometry at the metal center. Complexes 1 and 2 are diamagnetic species with a Zn(II) center. For complexes 3 and 4, the geometry distortion caused by Jahn–Teller effect from the d9 configuration of the Cu(II) center was observed in the X-ray crystal structures of both complexes. Analysis of geometric and spectroscopic data revealed a weaker Cu(II)–OC@O interaction in complex 4, which is attributed to the strong electron withdrawing effect from the two –CF3 groups attached on the ligand H2ptaa. DFT calculation of vibrational frequencies also supports this conclusion. Complexes 5 and 6 have a Fe(II) center with the same N2O4 coordination environment. 1H NMR and magnetic studies indicted that both complexes are paramagnetic species with effective magnetic moments of 5.14 lB and 5.21 lB, indicating four unpaired electrons (high spin) on the Fe(II) center. The optimized geometric data through DFT calculation matched with X-ray crystallography data well. In addition, the IR frequency calculation was performed to assign some characteristic peaks in the IR spectra of the six complexes. Acknowledgments We thank Dr. Donald A. Perry (University of Central Arkansas) for helpful discussions on DFT calculations. This work was supported by the start-up fund provided by the College of Natural
Sciences and Mathematics (CNSM) and University Research Council Fund (URCF) from University of Central Arkansas. Appendix A. Supplementary material CCDC 973652–973657 contains the supplementary crystallographic data for 1–6. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http:// dx.doi.org/10.1016/j.ica.2014.07.012. References [1] Z.N. Zheng, S.W. Lee, Polyhedron 69 (2014) 197. [2] W. Xu, W.J. Pan, Y.Q. Zheng, J. Coord. Chem. 66 (2013) 4415. [3] H. Lin, C. Xu, X. Wang, Z. Chang, A. Tian, G. Liu, J. Zhang, Inorg. Chem. Commun. 36 (2013) 81. [4] F.A. Saad, J.C. Knight, B.M. Kariuki, A.J. Amoroso, Dalton Trans 42 (2013) 14826. [5] E.S. Elton, T. Zhang, R. Prabhakar, A.M. Arif, L.M. Berreau, Inorg. Chem. 52 (2013) 11480. [6] X. Wang, J. Huang, L. Liu, G. Liu, H. Lin, J. Zhang, N. Chen, Y. Qu, RSC Adv. 3 (2013) 13944. [7] H.H. Lee, S.H. Jung, S. Park, K.M. Park, J.H. Jung, New J. Chem. 37 (2013) 2330. [8] M. Abdul-Kadir, L.R. Hanton, C.J. Sumby, Dalton Trans. 41 (2012) 4497. [9] S. Banerjee, P. Dastidar, Cryst. Growth Des. 11 (2011) 5592. [10] Z. Wang, D.R. Powell, R.P. Houser, Inorg. Chem. Commun. 12 (2009) 511. [11] R. Shakya, A. Jozwiuk, D.R. Powell, R.P. Houser, Inorg. Chem. 48 (2009) 4083. [12] X. Wang, J. Lian, H. Lin, C. Liu, G. Zhang, A. Tian, CrystEngComm 15 (2013) 9995. [13] S. Banerjee, P. Dastidar, CrystEngComm 15 (2013) 9415. [14] X.L. Wang, B. Wu, H.Y. Lin, S. Yang, G.C. Liu, J. Mol. Struct. 1036 (2013) 380. [15] X. Wang, J. Huang, L. Liu, G. Liu, H. Lin, J. Zhang, N. Chen, Y. Qu, CrystEngComm 15 (2013) 1960. [16] S.K. Chatterjee, R. Suprakash, S.K. Barman, R.C. Maji, M.M. Olmstead, A.K. Patra, Inorg. Chem. 51 (2012) 7625. [17] A. Mohamdou, J. Moreau, L. Dupont, E. Wenger, Inorg. Chim. Acta 383 (2012) 267. [18] Y. Yano, T. Kojima, S. Fukuzumi, Inorg. Chim. Acta 374 (2011) 104. [19] V.A. Corden, A.K. Duhme-Klair, S. Hostachy, R.N. Perutz, N. Reddig, Inorg. Chem. 50 (2011) 1105. [20] N.N. Adarsh, D.K. Kumar, E. Suresh, P. Dastidar, Inorg. Chim. Acta 363 (2010) 1448. [21] M. Monoyama, S. Tomita, K. Yamasaki, Inorg. Chim. Acta 12 (1975) 33. [22] M.F. El-Shazly, Inorg. Chim. Acta 40 (1980) 1. [23] V. Scheller-Krattiger, K.H. Scheller, E. Sinn, R.B. Martin, Inorg. Chim. Acta 60 (1982) 45. [24] G.A.V. Albada, I. Dominicus, I. Mutikainen, U. Turpeinen, J. Reedijk, Polyhedron 26 (2007) 3713. [25] M.Y. Huang, C.Y. Yeh, G.H. Lee, S.M. Peng, Dalton Trans. (2006) 5683. [26] W.B. Blanton, S.W. Gordon-Wylie, G.R. Clark, K.D. Jordan, J.T. Wood, U. Geiser, T.J. Collins, J. Am. Chem. Soc. 121 (1999) 3551. [27] E.R. Bissell, R.W. Swansiger, J. Chem. Eng. Data 26 (1981) 234.
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Synthesis and characterization of Cu(II), Zn(II) and Fe(II) complexes supported by pyridylamide ligands Ethan P. McMoran a, Joshua A. Goodner a, Douglas R. Powell b, Lei Yang a,⇑ a b
Department of Chemistry, University of Central Arkansas, Conway, AR 72035, USA Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
a r t i c l e
i n f o
Article history: Received 9 May 2014 Received in revised form 29 June 2014 Accepted 2 July 2014 Available online 16 July 2014 Keywords: Pyridylamide ligands Zn(II) complexes Cu(II) complexes Fe(II) complexes Crystal structure DFT calculation
a b s t r a c t Six new coordination complexes of Zn(II), Cu(II) and Fe(II) supported by pyridylamide ligands N-2-acetamidopyridine (Haap), N,N0 -2,6-diacetamidopyridine (H2daap) and N,N0 -2,6-pyridyl-bis[2,2,2-trifluoroacetamide] (H2ptaa) were synthesized. The structures of the six complexes were characterized by X-ray crystallography, showing a N2O4 environment of the metal centers with octahedral geometries. Complexes 1 and 2 are mononuclear Zn(II) complexes supported by two Haap ligands or one H2daap ligand. The Cu(II) centers in complexes 3 and 4 showed a tetragonally elongated structure due to the John–Teller effect of the d9 electronic configuration of Cu(II). The two –CF3 groups on ligand H2ptaa led to the weaker interactions between the ligand and the Cu(II) center, which is supported by the Xray crystal structure analysis and IR studies. For complexes 5 and 6, 1:1 and 2:1 ligand-to-metal ratios were observed in the mononuclear structures respectively. Evans’ method indicated both Fe(II) centers are high spin with four unpaired electrons in solution state. The theoretical studies of the complexes 1–6 included geometry optimization and IR vibrational frequencies calculation, which was compared with experimental spectra to assign the characteristic bands. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The coordination chemistry of pyridylamide ligands with the first-row transition metal ions has received great attention recently due to their versatile coordination behaviors in the construction of metal complexes with varying nuclearities and geometric features [1–11]. Systematic studies on the structures, spectroscopic properties, catalytic activities and host–guest chemistry of these coordination complexes have been informative, in particular for obtaining a better understanding of ligand design, complexes synthesis and potential applications [12–20]. It is known that the neutral and anionic form of an amide group will exhibit different coordination modes towards metal centers. Usually, the neural amide group will have the C@O group bind to metal ion, while the –NH– group stays free as a potential hydrogen bonding site. With the application of base to deprotonate the –NH– group, both oxygen and nitrogen atoms of the amidate group are potential coordination donors, leading to very interesting yet diversified structural features. Pyridylacetamide ligands based on 2-aminopyridine and 2,6-diaminopyridine have been synthesized and studied for decades, but only a few examples of transition ⇑ Corresponding author. Fax: +1 501 4503623. E-mail address: [email protected] (L. Yang). http://dx.doi.org/10.1016/j.ica.2014.07.012 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
metal complexes supported by these ligands were reported [21–26]. As part of our effort to investigate the coordination chemistry of pyridylamide ligand systems, here in we report the synthesis and characterization of Zn(II), Cu(II) and Fe(II) complexes with N-2-acetamidopyridine (Haap), N,N0 -2,6-diacetamidopyridine (H2daap) and N,N0 -2,6-pyridyl-bis[2,2,2-trifluoro-acetamide] (H2ptaa). DFT calculations were performed to optimize the geometries and assign the characteristic vibrational frequencies. 2. Experimental 2.1. Physical measurements Elemental analyses were carried out by Atlantic Microlabs, Norcross, GA. 1H NMR spectra were recorded on Bruker AVANCE 300 MHz spectrometer at room temperature. Chemical shifts (d) were referenced to residual solvent signal. UV–Vis spectra were recorded on a Cary 50 spectrometer. X-band EPR spectra were recorded on Resonance Instrument 8400 EPR spectrometer. The g factors and A coupling constants of EPR spectra were obtained from simulation using Bruker SimFonia software (version 1.25). FT-IR spectra were collected on a Nocolet Magna 560 FTIR spectrometer with an ATR attachment. Solution magnetic susceptibility was measured by using Evans’ method in CD3CN at room temperature.
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2.2. Chemicals All reagents were obtained from commercial sources and used as received unless otherwise noted. Ligands N-2-acetamidopyridine (Haap), N,N0 -2,6-Diacetamidopyridine (H2daap) and N,N0 2,6-pyridyl-bis[2,2,2-trifluoro-acetamide] (H2ptaa) were synthesized according to literatures [22,27]. All solvents were dried over CaH2 and distilled under vacuum. [Fe(NCCH3)2(OTf)2] was prepared based on literature [28,29]. 2.3. Synthesis of the metal complexes 2.3.1. [Zn(Haap)2(OTf)2] (1) A solution of Zn(OTf)2 (0.067 g, 0.18 mmol) in 1 mL CH2Cl2 was added to a stirred solution of Haap (0.050 g, 0.37 mmol) in 2 mL CH2Cl2. The white suspension was stirred for 3 h and the solvent was removed under vacuum. The white powder was collected and washed with Et2O (5 mL 3). Vapor diffusion of Et2O into a methanol solution of the product led to the formation of colorless crystals suitable for X-ray crystallographic characterization (0.093 g, 75% yield). Anal. Calc. for C16H16F6N4O8S2Zn: C, 30.22; H, 2.54; N, 8.81. Found: C, 30.36; H, 2.62; N, 8.65%. FT-IR: 1672 (C@O), 1621, 1538 (C–N), 1480, 1435, 1376, 1343, 1284, 1228 (C–F), 1188, 1160 (S@O), 1069, 1031, 971, 864, 786, 763, 633, 612, 573, 584, 516, 422 cm1. 1H NMR (methanol-d4, 298 K): d = 8.52–7.38 (m, 4 H), 2.39 (s, 3H) ppm. 2.3.2. General procedures of synthesis of [Zn(H2daap)(OTf)2] (2), [Cu(H2daap)(OTf)2] (3) and [Cu(H2ptaa)(OTf)2] (4) A solution of M(OTf)2, (0.15 g, 0.41 mmol) (M = Zn2+ for 2; M = Cu2+ for 3 and 4) in 1 mL CH3CN was added to a stirred solution of ligand (0.080 g of H2daap for 2 and 3, 0.10 g H2ptaa for 4), (0.41 mmol) in 2 mL CH3CN. The mixture was stirred for 2–3 h and then filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of crystals suitable for X-ray Crystallographic characterization. [Zn(H2daap)(NCCH3)(OTf)2] (2) (0.204 g, 82.4% yield). Anal. Calc. for C13H14F6N4O8S2Zn: C, 26.12; H, 2.36; N, 9.37. Found: C, 25.80; H, 2.45; N, 8.91. FT-IR: 1682 (C@O), 1633, 1523 (C–N), 1450, 1426, 1219 (C–F), 1170 (S@O), 1025, 812, 631, 604, 573, 514 cm1. 1H NMR (acetonitrile-d3, 298 K): d = 10.20 (s, 2H), 8.03 (m, 1H), 7.02 (m, 2H), 3.38 (s, 3H), 2.29 (s, 6H), ppm. [Cu(H2daap)(NCCH3)(OTf)2] (3) (0.140 g, 56.7% yield). Anal. Calc. for C13H14F6N4O8S2Cu: C, 26.20; H, 2.37; N, 9.40. Found: C, 26.57; H, 2.21; N, 9.29%. FT-IR: 1684 (C@O), 1639, 1617, 1526 (C–N), 1481, 1450, 1350, 1281, 1239 (C–F), 1150 (S@O), 1027, 948, 920, 811, 776, 661, 631, 514 cm1. UV–Vis [CH3CN, kmax, nm (e, M1cm1)]: 317 (2114), 731 (22). EPR (9.434 GHz, 0.02 mM, acetone, 298 K): giso = 1.99, Aiso = 56 104 cm1; EPR (9.434 GHz, solid, 298 K): g|| = 2.36, g\ = 2.11, A|| = 147 104 cm1. [Cu(H2ptaa)(NCCH3)(OTf)2] (4) (0.185 g, 64.1% yield). Anal. Calc. for C13H8F12N4O8S2Cu: C, 22.18; H, 1.15; N, 7.96. Found: C, 21.90; H, 1.58; N, 7.73%. FT-IR: 1716 (C@O), 1677, 1644, 1589 (C-N), 1469, 1245 (C–F of triflate), 1224 (C–F of H2ptaa), 1150 (S@O), 1027, 797, 763, 746, 631, 510 cm1. UV–Vis [CH3CN, kmax, nm (e, M1 cm1)]: 327 (2982), 419 (shoulder, 130), 898 (76). EPR: no hyperfine signals. 2.3.3. [Fe(H2daap)(H2O)(OTf)]OTf (5) A solution of Fe(OTf)2 (0.145 g, 0.410 mmol) in 1 mL CH3CN was added to a stirred solution of ligand H2daap (0.080 g, 0.41 mmol) in 2 mL CH3CN. The mixture was stirred for 3 h and filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of green crystals suitable for X-ray Crystallographic characterization (0.133 g, 53.5% yield). Anal. Calc. for C13H16F6N4O9S2Fe: C, 25.75; H, 2.66; N, 9.24. Found: C, 25.37; H, 2.49; N, 9.42%. FT-IR:
1657 (C@O), 1624, 1514 (C–N), 1448, 1418, 1374, 1315, 1290, 1218 (C–F), 1165 (S@O), 1024, 814, 763, 633, 611, 573, 511 cm1. UV– Vis [CH3CN, kmax, nm (e, M1 cm1)]: 307 (5950). Solution magnetic moment (Evans’ method, 22.0 °C, 5.21 102 M, CD3CN): 5.14 lB/Fe. 2.3.4. [Fe(H2daap)2(OTf)2] (6) A solution of [Fe(NCCH3)2(OTf)2] (0.092 g, 0.21 mmol) in 2 mL CH3CN was added to a stirred solution of ligand (0.080 g, 0.41 mmol) in 1 mL CH3CN. The mixture was stirred for 2 h and then filtered with a Celite plug. Vapor diffusion of Et2O into the filtrate led to the formation of yellow crystals suitable for X-ray Crystallographic characterization (0.065 g, 42% yield). Anal. Calc. for C20H22F6N6O10S2Fe: C, 32.44; H, 3.00; N, 11.35. Found: C, 32.73; H, 3.28; N, 11.19%. FT-IR: 1634 (C@O), 1633 (C@O), 1562, 1510, 1449, 1415, 1383, 1326, 1269 (S@O), 1247, 1220 (C–F), 1176, 1159, 1026, 806, 760, 627, 609, 573, 518 cm1. UV–Vis [CH3CN, kmax, nm (e, M1 cm1)]: 354 (5572). Solution magnetic moment (Evans’ method, 22.0 °C, 1.98 102 M, CD3CN): 5.21 lB/Fe. 2.4. X-ray crystallography X-ray crystallographic data were collected on crystals with dimensions of 0.46 0.38 0.24 mm for 1, 0.38 0.19 0.18 mm for 2, 0.46 0.43 0.20 mm for 3, 0.38 0.27 0.26 mm for 4, 0.52 0.24 0.12 mm for 5 and 0.50 0.08 0.05 mm for 6. Data were collected at 100 K using a diffractometer with a Bruker APEX CCD area detector [30] and graphite-monochromated Mo Ka radiation (k = 0.71073 Å). All six structures were solved by direct methods and refined by full-matrix least-square methods on F2 [31]. The crystal parameters, data collection and refinement are summarized in Table 1. Non-hydrogen atoms were refined with anisotropic displacement parameters. The positions of hydrogen bonded to carbons and nitrogens were initially determined by geometry and were refined using a riding model. For complex 3, the data are separated into the twin components by the integration and absorption correction programs. For complex 4, one triflate group bond to the metal was probably dynamically disordered. The occupancies for this triflate are refined to 0.711(3), 0.167(3), and 0.121(2) for the unprimed, primed, and double-primed atoms. One of the two diethyl ether molecules is disordered. The occupancies of the solvent molecule are refined to 0.585(6) and 0.415(6) separately. For complex 6, the sample exhibited twinning which was removed by the data reduction and scaling programs. 2.5. Computational details Density Functional Theory (DFT) calculations were preformed with the Gaussian09 software package [32] under the Windows operating system. All input files were prepared using Gaussview 5.0 [33]. Input files were prepared from the crystal structure of each compound determined by X-ray Crystallographic characterization. All calculations were ran using the B3LYP [34–36] function with a 6-31G(d,p) basis set for all atoms. Optimized geometries were calculated under standard conditions with symmetry. Vibrational frequency analysis was preformed using the freq keyword for comparison with experimental data. 3. Results and discussion 3.1. Syntheses and characterization The ligand Haap, H2daap and H2ptaa were synthesized based on the reported procedures [22,27]. In this work, the three ligands were applied as a neutral form in the reactions with metal salts.
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E.P. McMoran et al. / Inorganica Chimica Acta 421 (2014) 465–472 Table 1 Summary of crystal data and refinement parameters for complexes 1–6.
Formula Formula weight T (K) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Z V (Å3) qcalcd (g/cm3) l (mm1) R1 [I > 2r(I)] wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2
1
2
3
4
5
6
C16H16F6N4O8S2Zn 635.82 100(2) Pbca 14.2244(5) 8.9350(3) 18.8069(6) 90 90 90 4 2390.26(14) 1.767 1.300 0.0285 0.0884 1.010
C13H14F6N4O8S2Zn 597.77 100(2) P21/n 22.041(3) 9.2035(14) 22.084(3) 90 98.579(3) 90 8 4429.7(11) 1.793 1.396 0.0510 0.1486 1.005
C13H14CuF6N4O8S2 595.94 100(2) P21/n 11.2630(5) 14.4384(7) 13.3025(6) 90 95.631(2) 90 4 2152.81(17) 1.839 1.310 0.0318 0.1002 1.001
C17H18CuF12N4O9S2 778.01 100(2) P1
C13H16F6FeN4O9S2 606.27 100(2) P1
C24H28F6FeN8O10S2 822.51 100(2) P1
8.6473(3) 12.7566(5) 13.2641(5) 84.809(2) 73.830(2) 82.865(2) 2 1392.00(9) 1.856 1.069 0.0822 0.2403 1.099
8.3019(9) 10.8131(11) 13.4664(14) 72.796(2) 79.956(2) 81.192(2) 2 1130.4(2) 1.781 0.954 0.0302 0.0843 1.000
10.925(2) 12.439(3) 13.574(3) 110.808(5) 97.972(5) 96.312(5) 2 1682.1(6) 1.624 0.670 0.0781 0.2161 1.056
Reactions with the anionic form of the ligands obtained by adding bases, such as triethyl amine and NaH, only led the formation of uncharacterizable products. The idea of replacing the two methyl groups in H2daap with two –CF3 groups in H2ptaa is to increase the solubility of the product and obtain a better understanding of the impact of different ligand manifolds on the electronic properties of the metal complexes. Complex 1 was synthesized by mixing two equiv. of Haap ligand with one equiv. of Zn(OTf)2 in CH2Cl2 (Scheme 1). The white powder yielded was recrystallized by vapor diffusion of Et2O into a CH3OH solution of the product at room temperature. The 1:1 reaction led to the same product, indicating the high stability of complex 1. No changes were observed after the storage of complex 1 in air for months. Complexes 2–6 were synthesized by mixing the neutral ligand H2daap or H2ptaa with the corresponding metal salts in CH3CN in either 1:1 or 2:1 ligand-to-metal ratio (Scheme 2). The vapor diffusion of Et2O into the acetonitrile solution at room temperature afforded the formation of colorless (complex 2), green (complexes 3–5) and yellow (complex 6) crystals. Compound 2–3 and 5–6 were stable in solid and solution when exposed to air and no apparent changes were observed in weeks. Complex 4 is stable towards dry oxygen, but is sensitive towards moisture. When exposed to air, the green solid turned to deep brown oil in about 10 min. 1H NMR of complexes 1 and 2 showed similar signals of the free ligands. Scheme 2. Syntheses of complexes 2–6.
3.2. Complexes [Zn(Haap)2(OTf)2] (1) and [Zn(H2daap)(NCCH3)(OTf)2] (2) X-ray crystal structure analysis showed that complexes 1 and 2 are mononuclear Zn(II) complexes (Fig. 1). Selected bond lengths and angles for the two complexes are listed in Table 2. A 2:1 ligand-to-metal ratio was observed in the crystal structure of complex 1. The zinc center with an octahedral geometry is chelated by two Haap ligands in a trans fashion through the pyridyl nitrogens and amide oxygens, with Zn–Npy and Zn–OC@O distances of 2.085
Scheme 1. Synthesis of complex [Zn(Haap)2(OTf)2] (1).
and 2.047 Å respectively. Since the molecule sits on a crystallographic center of symmetry, Npy–Zn–Npy, OC@O–Zn–OC@O and Otriflate–Zn–Otriflate have a bond angle of 180°. The axial positions of the octahedral are occupied by the two oxygen atoms from the two triflate anions, with a Zn–Otriflate distance of 2.199 Å, which is longer than the Zn–OC@O distance (2.047 Å). On the equatorial plane, the Npy–Zn–OC@O bite angle of the six-member ring is 86.53°, indicating the slight distortion of the equatorial plane to a rectangle shape. A Zn(II) complex of the ligand Haap, [Zn(Haap)2(H2O)2](NO3)2, with a different coordination sphere was reported by Martin et al. [23]. Unlike the participation of OTf anions in the coordination of the Zn(II) center in complex 1, the two axial positions of the octahedral geometry in [Zn(Haap)2 (H2O)2](NO3)2 are occupied by two water molecules with an Ow– Zn–Ow bond angle of 180°, and the two NO 3 anions stay free in the outer-sphere. Due to the weaker steric hindrance of the axial water molecules, the Zn–Ow bond (2.159 Å) in [Zn(Haap)2(H2O)2](NO3)2 is shorter than the Zn–Otriflate bond in complex 1 (2.199 Å).
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Fig. 1. X-ray structures of complex 1 (left) and 2 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms are omitted for clarity.
Accordingly, the bonds on the equatorial plane of [Zn(Haap)2 (H2O)2](NO3)2 (Zn–OC@O = 2.058 Å, Zn–Npy = 2.111 Å) are slightly longer than those bonds in complex 1 (Zn–OC@O = 2.047 Å, Zn– Npy = 2.085 Å). The structure of complex 1 is stabilized by a hydrogen bond network formed between the free –NH– groups on the amide side arm of the Haap ligands and the neighboring OTf anions. For each mononuclear unit [Zn(Haap)2(OTf)2], the two triflate anions are hydrogen bonded to two –NH– groups from two neighboring mononuclear units with a H O distance of 2.06 Å. Meanwhile, the two –NH– groups from the same mononuclear unit connect with two neighboring triflate anions in the opposite direction of the equatorial plane. These hydrogen bonding interactions extend to form a two dimensional supramolecular grid in the yz plane of the crystal lattice (Fig. S1 in Supporting information). The Zn(II) center of complex 2 also has an octahedral geometry with a 1:1 ligand-to-metal ratio. The neutral H2daap ligand acts as a tridentate ligand, bracing the Zn(II) center through one pyridyl N and two amide side arms and forming two six-member rings (Zn–O–C–N–C–N) with an average chelated angle of 90.06°. Due to the restrain effect of the two six-member rings, the pyridyl ring is slightly tilted with respect to the equatorial plan of the octahedral geometry with an angle of 12.12°. The equatorial plan is fulfilled by an acetonitrile molecule sitting on the trans position of the pyridyl nitrogen and the Npy–Zn–NCH3CN bond angle is 176.48°. The two oxygen donors at axial positions are from by two trans triflate anions with a Otriflate–Zn–Otriflate bond angle of 172.36°. The average bond lengths of the two Zn–N bonds is 2.148 Å, and the average Zn–Otriflate bond length is 2.162 Å, which is slightly longer than the average Zn–OC@O bond (1.989 Å). This elongation along the Otriflate–Zn–Otriflate axis may be attributed to the steric effect of CF3 groups of the triflate anions. A complicated hydrogen bond network connects the neighboring mononuclear units and triflate anions, and extends along the z axis to form a one dimensional ladder-like supramolecular structure (Fig. S2 in Supporting information). The optimized geometries of both complexes 1 and 2 matched well with the crystal structure data. The IR spectra of complexes 1 and 2 were collected and compared with the calculated vibrational frequencies. The calculated C@O stretching frequencies at 1731 (complex 1) and 1744 cm1
(complex 2) are in reasonable correlation with the experimental values observed at 1672 (complex 1) and 1682 cm1 (complex 2). The two experimental IR peaks at 1538 (complex 1) and 1523 cm1 (complex 2) can be assigned to the C–N stretching frequency of the amide group coupled with C–C stretching of the pyridine ring, giving calculated values of 1528 (complex 1) and 1572 cm1 (complex 2). The medium peaks of S@O stretching of the triflate anions at 1160 (complex 1) and 1170 cm1 (complex 2) in experimental spectra were also confirmed by the calculated values at 1161 (complex 1) and 1165 cm1 (complex 2). 3.3. Complexes [Cu(H2daap)(NCCH3)(OTf)2] (3) and [Cu(H2ptaa)(NCCH3)(OTf)2] (4) The mononuclear Cu(II) complexes 3 and 4 are structural analogues of the complex 2 (Fig. 2). Selected bond lengths and angles for the two complexes are listed in Table 2. Both ligands H2daap and H2ptaa have a tridentate coordination mode towards the Cu(II) center. The N2O4 coordination environment of the Cu(II) center with an octahedral geometry is fulfilled by one tridentate ligand, one acetonitrile molecule (equatorial plan) and two triflate anions (axial positions). The same tridentate coordination mode of H2daap ligand has been reported in a mononuclear Cu(II) complex with one H2daap and two chlorides, in which a square pyramidal geometry of the metal center was proposed based on the spectroscopic characterization only [22]. For complex 3, the average Cu–Otriflate bond length (2.403 Å) is significantly longer than the average Cu–OC@O bond length (1.910 Å) and Cu–N bond length (2.009 Å). This axial elongation of the octahedral geometry is attributed to the Jahn–Teller effect of the d9 configuration of the Cu(II) center. Interestingly, a less tetragonal distortion is observed in the Cu(II) center of complex 4. The average Cu–Otriflate bond length (2.333 Å) on the axial positions in complex 4 is shorter than that of complex 3 (2.403 Å). A similar structural difference was also observed in optimized geometries of complexes 3 and 4. The major factor for this difference between the two complexes is the –CF3 groups in ligand H2ptaa. The strong electron withdrawing effect from the –CF3 groups significantly strengthen the C@O bond in ligand H2ptaa, causing the shorter C@O bond in complex 4 (1.225 Å) than the C@O bond in complex 3 (1.242 Å) observed
E.P. McMoran et al. / Inorganica Chimica Acta 421 (2014) 465–472 Table 2 Selected bond lengths (Å) and angles (°) for complexes 1–6. Complex 1 Zn1–O1 Zn1–N1 O1–Zn1–O1A O1–Zn1–N1A O1–Zn1–N1 N1A–Zn1–N1 O2A–Zn1–O2 Complex 2 Zn1–O1 Zn1–N4 Zn1–O3 O1–Zn1–O2 O2–Zn1–N4 O2–Zn1–N1 O1–Zn1–O3 N4–Zn1–O3 O1–Zn1–O6 N4–Zn1–O6 Complex 3 Cu1–O1 Cu1–N1 Cu1–O3 O1–Cu1–O2 O2–Cu1–N1 O2–Cu1–N4 O1–Cu1–O3 N1–Cu1–O3 O1–Cu1–O6 N1–Cu1–O6 O3–Cu1–O6 Complex 4 Cu1–O1 Cu1–N4 Cu1–O6 O1–Cu1–O2 O2–Cu1–N4 O2–Cu1–N1 O1–Cu1–O6 N4–Cu1–O6 O1–Cu1–O3 N4–Cu1–O3 O6–Cu1–O3 Complex 5 Fe1–O1 Fe1–O3 Fe1–O4 O1–Fe1–O2 O2–Fe1–O3 O2–Fe1–N4 O1–Fe1–O4 O3–Fe1–O4 O1–Fe1–N1 O3–Fe1–N1 O4–Fe1–N1 Complex 6 Fe1–O1B Fe1–O2B Fe1–N1B O1B–Fe1–O2A O2A–Fe1–O2B O2A–Fe1–O1A O1B–Fe1–N1B O2B–Fe1–N1B O1B–Fe1–N1A O2B–Fe1–N1A N1B–Fe1–N1A
2.0467(9) 2.0851(11) 180.0 93.47(4) 86.53(4) 180.0 180.0
Zn1–O2
2.1988(10)
O1–Zn1–O2A N1–Zn1–O2A O1–Zn1–O2 N1–Zn1–O2
92.67(4) 88.64(4) 87.33(4) 91.36(4)
1.982(3) 2.144(4) 2.160(3) 177.13(13) 90.29(14) 90.83(13) 91.84(12) 86.23(14) 95.08(13) 88.78(14)
Zn1–O2 Zn1–N1 Zn1–O6 O1–Zn1–N4 O1–Zn1–N1 N4–Zn1–N1 O2–Zn1–O3 N1–Zn1–O3 O2–Zn1–O6 N1–Zn1–O6
1.995(3) 2.152(3) 2.164(3) 88.74(14) 90.11(13) 178.75(14) 85.40(13) 93.31(13) 87.60(13) 91.82(13)
1.9041(15) 2.0027(17) 2.3416(16) 172.54(7) 94.21(7) 86.08(7) 93.09(6) 95.52(6) 94.64(6) 81.66(6) 171.91(6)
Cu1–O2 Cu1–N4 Cu1–O6 O1–Cu1–N1 O1–Cu1–N4 N1–Cu1–N4 O2–Cu1–O3 N4–Cu1–O3 O2–Cu1–O6 N4–Cu1–O6
1.9154(15) 2.0154(18) 2.4645(16) 93.18(7) 86.63(7) 175.70(7) 85.20(6) 88.78(7) 87.43(6) 94.07(6)
1.929(4) 1.987(4) 2.303(3) 173.32(14) 85.22(17) 92.49(15) 88.67(15) 89.22(15) 90.17(12) 93.49(15) 177.03(13)
Cu1–O2 Cu1–N1 Cu1–O3 O1–Cu1–N4 O1–Cu1–N1 N4–Cu1–N1 O2–Cu1–O6 N1–Cu1–O6 O2–Cu1–O3 N1–Cu1–O3
1.936(4) 2.012(4) 2.363(3) 89.42(18) 92.93(16) 177.48(17) 95.24(15) 89.93(13) 86.19(13) 87.40(13)
2.0255(12) 2.1145(12) 2.1598(11) 171.01(4) 92.11(5) 92.15(5) 91.35(5) 175.27(5) 85.23(5) 88.08(5) 96.54(5)
Fe1–O2 Fe1–N4 Fe1–N1 O1–Fe1–O3 O1–Fe1–N4 O3–Fe1–N4 O2–Fe1–O4 N4–Fe1–O4 O2–Fe1–N1 N4–Fe1–N1
2.0534(11) 2.1269(14) 2.1856(12) 90.03(5) 96.72(5) 85.36(5) 87.22(5) 89.99(5) 86.12(4) 173.15(5)
2.060(3) 2.078(3) 2.144(4) 90.02(15) 92.04(14) 170.68(14) 87.47(14) 87.35(14) 96.21(15) 88.96(14) 176.27(15)
Fe1–O2A Fe1–O1A Fe1–N1A O1B–Fe1–O2B O1B–Fe1–O1A O2B–Fe1–O1A O2A–Fe1–N1B O1A–Fe1–N1B O2A–Fe1–N1A O1A–Fe1–N1A
2.060(4) 2.080(4) 2.146(4) 174.59(14) 89.24(14) 89.54(14) 95.67(15) 93.58(14) 84.98(15) 85.86(15)
in X-ray crystal structures. Accordingly, the interaction between the Cu(II) center and C@O group becomes weaker in complex 4 (Cu–OC@O = 1.933 Å) than that in complex 3 (Cu–OC@O = 1.910 Å). Therefore, the complex 3 exhibits larger tetragonal distortion along the Otriflate–Cu–Otriflate axis. The C@O stretching frequency change observed in the IR spectra of complexes 3 and 4 (see the following
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discussion) also support this conclusion. Hydrogen bonding interactions between amide N–H group and triflate anion connect mononuclear units to form either two-dimensional (complex 3) or one-dimensional (complex 4) supramolecular network (Fig. S3 and S4 in Supporting information). The IR spectrum of complex 3 shows a C@O stretching at 1684 cm1, which is close to the C@O frequency in complex 2 (1682 cm1). While in complex 4, the C@O frequency shifts to 1716 cm1 due to the electron withdrawing (EWR) effect of the – CF3 groups of the ligand H2ptaa, indicating the stronger C@O bond in ligand H2ptaa. The calculated C@O stretching frequencies in complexes 3 and 4 are 1727 and 1748 cm1, which confirm the peak assignment for the complexes and EWR effect of the ligand H2ptaa. Complex 3 showed one strong transition at 317 nm with an absorption coefficient of 2114 M1 cm1 corresponding to the ligand to metal charge transfer (LMCT). A weak broad band observed at 731 nm was assigned as the d–d transition of the Cu(II) center. Both LMCT and d–d transition bands of complex 4 red shift to the 327 and 898 nm, indicating the weaker interaction between the ligand H2ptaa and copper site. This matches with the structural differences of the two complexes caused by the strong electron withdrawing –CF3 group in ligand H2ptaa. The X-band EPR spectrum of complex 3 in both solid and solution states showed the typical hyperfine signal of a mononuclear d9 Cu(II) complexes (Fig. 3). In acetone solution at room temperature, an isotropic signal was observed. The simulated spectrum showed a g value giso = 1.99 and a coupling constant Aiso = 56 104 cm1. In solid state, the signal is axial with g|| = 2.36, g\ = 2.11 and A|| = 147 104 cm1 obtained from simulation, indicating the dx22 y ground state and tetragonally distorted octahedral geometry of the copper center [37]. Although extensive effort were devoted to measure the EPR spectra of complex 4 in different solvents such as CH3CN, CH3OH, acetone and CH2Cl2, only isotropic signals without any hyperfine structures were observed. 3.4. Complexes [Fe(H2daap)(H2O)(OTf)]OTf (5) and [Fe(H2daap)2(OTf)2] (6) Complex 5 is a product of the reaction between one equiv. of ligand H2daap and one equiv. of Fe(OTf)2. The X-ray crystal structure of complex 5 reveals a six-coordinate Fe(II) center with one H2daap ligand chelating to the metal ion in a tridentate fashion (Fig. 4, left). The octahedral geometry is completed by the coordination of one water molecule, one acetonitrile molecule and one triflate anion. The possible source of the water molecule is the trace amount of moisture in the CH3CN solvent. The equatorial plane formed by N, O donors from the ligand and acetonitrile nitrogen is twisted with respect to the pyridyl plane with an angle of 17.239°, which is higher than those angles found in complexes 2–4 (9.796°–12.115°). The two six-member rings formed by amide side arms with the Fe(II) center have OC@O–Fe–Npy bite angles of 85.23(5)° and 86.12(4)°. This observation, plus the OC@O–Fe–CC@O angle of 171.014°, indicates the structural distortion of the Fe center away from the pyridine ring with a Fe–Npy bond of 2.1856(12) Å and a Fe–Nacetonitrile bond of 2.1269(14) Å. No appreciable elongation of the Fe–O and Fe–N bonds is observed. Interesting hydrogen bonding interactions are observed among ligand, water molecule and triflate anions. One of the two hydrogens from the water molecule interacts with one triflate ion with a H O distance of 1.979 Å, which coordinates to another mononuclear Fe(II) unit. The other hydrogen from the water molecule forms a hydrogen bond interaction with a free triflate ion (H O distance = 2.083 Å) that interacts with two different mononuclear units through N–H O interactions (2.09 and 2.02 Å, Fig. S5 in Supporting information).
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Fig. 2. X-ray structures of complex 3 (left) and 4 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms are omitted for clarity.
Fig. 3. X-band EPR spectra of complex 3 in acetone solution (a) and solid state (b) at room temperature. Black is experimental data and red is simulation. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The structure of complex 6 consists of a [FeII(H2daap)2]2+ cation (Fig. 4, right) and two triflate anions. The coordination geometry of the Fe(II) center is a slightly distorted octahedron, including two pyridyl nitrogen atoms and four C@O groups from two H2daap ligands, which chelate the Fe(II) center in a trans fashion with a dihedral angle of 40.191° between the two pyridyl planes. The average Fe–Npy and Fe–OC@O bond lengths are 2.145 and 2.070 Å. The distortion of the FeN2O4 octahedral geometry is a result from the small bite angles (average 86.413°) of the OC@O–Fe–Npy imposed by the six-member chelate rings formed by H2daap ligand and the Fe(II) center. Each [FeII(H2daap)2]2+ cation is connected to the neighboring triflate anions through N–H Otriflate hydrogen bonds with distances ranging from 2.821(5) to 3.184(6) Å (Fig. S6
in Supporting information). Selected bond lengths and angles for the complexes 5 and 6 are listed in Table 2. The IR spectrum of complex 5 shows a C@O stretching frequency of the amide side arm at 1657 cm1, which is confirmed by the calculated frequency at 1708 cm1 from DFT calculation. An interesting feature observed in the IR spectrum of the complex 6 is the two peaks with medium intensity at 1634 and 1633 cm1. DFT calculation indicates that the two peaks come from the antisymmetrically coupled stretching from two pairs of C@O group on the trans positions of the octahedral geometry (C@O1A/C@O2A and C@O1B/C@O2B in crystal structure, Fig. 4). The calculated frequencies are 1714 and 1713 cm1 respectively. The UV–Vis spectra of complexes 5 and 6 were recorded in acetonitrile and presented
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Fig. 4. X-ray structures of [Fe(H2daap)(H2O)(OTf)]+ cation in complex 5 (left) and [Fe(H2daap)2]2+ cation in complex 6 (right). Thermal ellipsoids are shown at the 30% level. Hydrogen atoms except those on the water molecule are omitted for clarity.
in Figs. S11 and S12. The spectra are dominated by strong absorptions at 307 nm (e = 5950 M1 cm1, complex 5) and 354 nm (e = 5572 M1 cm1, complex 6), respectively. Both bands are attributed to metal-to-ligand charge transfer (MLCT) for Fe(II)-topyridine (t2g-p⁄py) transition [38]. 1H NMR of both complexes showed broad paramagnetic signals, suggesting a high-spin d6 configuration. In an effort to confirm the spin state of Fe(II) centers in the complex 5 and 6, Evans’ method was performed to obtain the magnetic susceptibilities in solution state at room temperature. The 5.14 lB (complex 5) and 5.21 lB (complex 6) based on Evans method indicated that both complexes possess a Fe(II) center with four unpaired electrons. 4. Conclusions In summery, six Zn(II), Cu(II) and Fe(II) complexes supported by pyridylamide ligands with one or two amide side arms were synthesized and characterized. X-ray crystallography characterization showed that all six complexes have a mononuclear structure with an octahedral geometry at the metal center. Complexes 1 and 2 are diamagnetic species with a Zn(II) center. For complexes 3 and 4, the geometry distortion caused by Jahn–Teller effect from the d9 configuration of the Cu(II) center was observed in the X-ray crystal structures of both complexes. Analysis of geometric and spectroscopic data revealed a weaker Cu(II)–OC@O interaction in complex 4, which is attributed to the strong electron withdrawing effect from the two –CF3 groups attached on the ligand H2ptaa. DFT calculation of vibrational frequencies also supports this conclusion. Complexes 5 and 6 have a Fe(II) center with the same N2O4 coordination environment. 1H NMR and magnetic studies indicted that both complexes are paramagnetic species with effective magnetic moments of 5.14 lB and 5.21 lB, indicating four unpaired electrons (high spin) on the Fe(II) center. The optimized geometric data through DFT calculation matched with X-ray crystallography data well. In addition, the IR frequency calculation was performed to assign some characteristic peaks in the IR spectra of the six complexes. Acknowledgments We thank Dr. Donald A. Perry (University of Central Arkansas) for helpful discussions on DFT calculations. This work was supported by the start-up fund provided by the College of Natural
Sciences and Mathematics (CNSM) and University Research Council Fund (URCF) from University of Central Arkansas. Appendix A. Supplementary material CCDC 973652–973657 contains the supplementary crystallographic data for 1–6. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http:// dx.doi.org/10.1016/j.ica.2014.07.012. References [1] Z.N. Zheng, S.W. Lee, Polyhedron 69 (2014) 197. [2] W. Xu, W.J. Pan, Y.Q. Zheng, J. Coord. Chem. 66 (2013) 4415. [3] H. Lin, C. Xu, X. Wang, Z. Chang, A. Tian, G. Liu, J. Zhang, Inorg. Chem. Commun. 36 (2013) 81. [4] F.A. Saad, J.C. Knight, B.M. Kariuki, A.J. Amoroso, Dalton Trans 42 (2013) 14826. [5] E.S. Elton, T. Zhang, R. Prabhakar, A.M. Arif, L.M. Berreau, Inorg. Chem. 52 (2013) 11480. [6] X. Wang, J. Huang, L. Liu, G. Liu, H. Lin, J. Zhang, N. Chen, Y. Qu, RSC Adv. 3 (2013) 13944. [7] H.H. Lee, S.H. Jung, S. Park, K.M. Park, J.H. Jung, New J. Chem. 37 (2013) 2330. [8] M. Abdul-Kadir, L.R. Hanton, C.J. Sumby, Dalton Trans. 41 (2012) 4497. [9] S. Banerjee, P. Dastidar, Cryst. Growth Des. 11 (2011) 5592. [10] Z. Wang, D.R. Powell, R.P. Houser, Inorg. Chem. Commun. 12 (2009) 511. [11] R. Shakya, A. Jozwiuk, D.R. Powell, R.P. Houser, Inorg. Chem. 48 (2009) 4083. [12] X. Wang, J. Lian, H. Lin, C. Liu, G. Zhang, A. Tian, CrystEngComm 15 (2013) 9995. [13] S. Banerjee, P. Dastidar, CrystEngComm 15 (2013) 9415. [14] X.L. Wang, B. Wu, H.Y. Lin, S. Yang, G.C. Liu, J. Mol. Struct. 1036 (2013) 380. [15] X. Wang, J. Huang, L. Liu, G. Liu, H. Lin, J. Zhang, N. Chen, Y. Qu, CrystEngComm 15 (2013) 1960. [16] S.K. Chatterjee, R. Suprakash, S.K. Barman, R.C. Maji, M.M. Olmstead, A.K. Patra, Inorg. Chem. 51 (2012) 7625. [17] A. Mohamdou, J. Moreau, L. Dupont, E. Wenger, Inorg. Chim. Acta 383 (2012) 267. [18] Y. Yano, T. Kojima, S. Fukuzumi, Inorg. Chim. Acta 374 (2011) 104. [19] V.A. Corden, A.K. Duhme-Klair, S. Hostachy, R.N. Perutz, N. Reddig, Inorg. Chem. 50 (2011) 1105. [20] N.N. Adarsh, D.K. Kumar, E. Suresh, P. Dastidar, Inorg. Chim. Acta 363 (2010) 1448. [21] M. Monoyama, S. Tomita, K. Yamasaki, Inorg. Chim. Acta 12 (1975) 33. [22] M.F. El-Shazly, Inorg. Chim. Acta 40 (1980) 1. [23] V. Scheller-Krattiger, K.H. Scheller, E. Sinn, R.B. Martin, Inorg. Chim. Acta 60 (1982) 45. [24] G.A.V. Albada, I. Dominicus, I. Mutikainen, U. Turpeinen, J. Reedijk, Polyhedron 26 (2007) 3713. [25] M.Y. Huang, C.Y. Yeh, G.H. Lee, S.M. Peng, Dalton Trans. (2006) 5683. [26] W.B. Blanton, S.W. Gordon-Wylie, G.R. Clark, K.D. Jordan, J.T. Wood, U. Geiser, T.J. Collins, J. Am. Chem. Soc. 121 (1999) 3551. [27] E.R. Bissell, R.W. Swansiger, J. Chem. Eng. Data 26 (1981) 234.
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