Journal of Inorganic and General Chemistry ARTICLE www.zaac.wiley-vch.de Zeitschrift für anorganische und allgemeine Chemie DOI: 10.1002/zaac.201500158 Novel Lanthanide(III) Ternary Complexes with Naphthoyltrifluoroacetone: A Synthetic and Spectroscopic Study Thi-Nguyet Trieu,*[a] Thi-Hien Dinh,[a,b] Hung-Huy Nguyen,[a] Ulrich Abram,[c] and Minh-Hai Nguyen*[a] Keywords: Lanthanide complexes; Bipyridine N-oxide; β-Diketonate; X-ray structure Abstract A series of lanthanide complexes with general formula [Ln(NTA)3X] were prapared [Ln = Y (a), Er (b), Eu (c), NTA = naphthoyltrifluoroacetone, X = H2O (1), phen = phenanthroline (2), bpyO1 = 2,2Ј-bipyridine N-oxide (3), and bpyO2 = 2,2Ј-bipyridineN,NЈ-dioxide (4)] The crystal structures of [Eu(NTA)3bpyO2] (4b), [Er(NTA)3bpyO1] (3c), and [Er(NTA)3phen] (2c) were determined X- ray crystallographic analysis reveals that the complexes are of mononuclear structure with three NTA and one ancillary ligand The photoluminescence spectra of 3c and 4b exhibit strong characteristic emissions arising from Eu3+ central ion due to the efficient sensitization of bpyO1 and bpyO2, respectively Introduction gands may enhance luminescence intensities.[5] Therefore, ancillary ligands of 2,2Ј-bipyridine and o-phenanthroline type have been extensively used.[4,6–9] Nonetheless, much attention has not been paid to their N-oxide derivatives such as bpyO1 and bpyO2.[10–12] The compounds may serve as excellent ligands towards Ln3+ due to the presence of hard O donor atom as well as efficient sensitizers for the lanthanide emission.[1,13,14] In the presented work, we describe the syntheses, crystal structures and emission properties of a series of lanthanide (Y3+, Er3+, Eu3+) ternary complexes containing naphthoyltrifluoroacetone (NTA) (Scheme 1) and various ancillary ligands (Scheme 2) Our results showed that bpyO1 and bpyO2 can The lanthanide β-diketonates have attracted much attention, due partially to their facile syntheses, but mainly to their intriguing properties spanning from magnetism to photoluminescence.[1] In recent years, the design of lanthanide β-diketonates has been directed towards applications in optical devices, luminescence sensors for chemical species, fluorescent lighting and electroluminescent devices.[2–4] The luminescence is lanthanide-centered but not able to be obtained in good yield by direct excitation as 4f–4f transition is Laporte-forbidden The strategy to achieve lanthanide emission includes the use of βdiketone ligands, which exert stable chelation with Ln3+ ions and strong π–π* absorption The ligand in its excited state, as an antenna, may undergo effective energy transfer to Ln3+ ion, thus switching on the Ln3+ emission The syntheses of lanthanide β-diketonates typically in the first step involve formation of the complexes with two crystalwater molecules coordinating to the central metal atom Unfortunately, the quenching of lanthanide emission by O–H sketches in water is rather effective It is well-known that replacement of the coordinated water by ancillary chelating li* Dr T.-N Trieu Fax: +84-4382-41140 E-Mail: nguyetdhkhtn@gmail.com * Dr M.-H Nguyen E-Mail: nmhai@vnu.edu.vn [a] Department of Chemistry Hanoi University of Science 19 Le Thanh Tong Hanoi, Vietnam [b] Department of Chemistry Hanoi National University of Education 136 Xuan Thuy Hanoi, Vietnam [c] Institute of Chemistry and Biochemistry Freie Universität Berlin Fabeckstr 34/36 14195 Berlin, Germany Z Anorg Allg Chem 2015, 641, (11), 1934–1940 Scheme General formula of lanthanide complexes discussed in this work Scheme The ancillary ligands used in this work 1934 © 2015 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Journal of Inorganic and General Chemistry ARTICLE www.zaac.wiley-vch.de Zeitschrift für anorganische und allgemeine Chemie bind strongly to the Ln3+ and sensitize efficiently the characteristic red emission of Eu3+ Results and Discussion Synthesis and Characterization The ternary complexes 2–4 [Ln(NTA)3X] were synthesized by reacting [Ln(NTA)3(H2O)2] (Ln = Y, Er, Eu) with relevant ancillary ligands (X) (Scheme 3) in a 1:1 ratio The displacement of H2O by the ligands occurs readily as H2O is a weak coordinating solvent and chelating effect also favors the substitution There were dramatic changes in solubility of the complexes upon the substitution of polar fragment H2O by relatively non-polar moieties such as phen, bpyO1, and bpyO2 Consequently, [Ln(NTA)3(H2O)2] are highly soluble in methanol, whereas 2–4 can be well dissolved in chloroform This may serve as a good indication that the reaction in chloroform is complete when [Ln(NTA)3(H2O)2] solids disappear ing the complexation of Ln3+ ion with bpyO1 and bpyO2 ligands through oxygen atoms The study of rare earth complexes by NMR spectroscopy is often limited due to the paramagnetism of the metal ions except for YIII Hence, it is reasonable to investigate the NMR spectroscopy of YIII complexes as representatives for the congeners of other metal ions The 1H NMR spectra of the complexes display singlet signals at 6.4–6.6 ppm, which are responsible for the methine proton of diketonate moiety of NTA ligand (Ha) The overlapping signals in the region 7.3–8.4 ppm are common for aromatic protons of naphthalene rings Notably, the H1 resonances were found in lower field regions (8.3–8.4 ppm) This fact is reasonable given the steric repulsion (peri effect) between H1 and H8 In the 1H-NMR spectrum of 1a, the proton signal of water was not observed due to its rapid exchange with MeOD For 2–4a, the presence of phen, bpyO1, and bpyO2 is evidenced by an extra set of signals in the aromatic region in addition to those of the napthalene rings The integral ratios suggest the complex composition is of three NTA and one ancillary ligand The 13C NMR spectrum of exhibits the two most downfield signals at 188–189 ppm and 171–172 ppm, which are ascribable to two C=O groups While the former is a singlet, the latter is a quartet arising from spin coupling between 13C and 19F nuclei (3JC,F = 127 Hz) Another resonance, which is common to –CF3 appears as quartet at 119–120 ppm (2JC,F = 1135 Hz) The CH group of diketonate fragment gives a singlet at 92–93 ppm, confirming the formation of chelate ring with metal ion The signals in the region 120–153 ppm are typical for aromatic carbons of naphthalene rings and ancillary ligands X-ray Structural Characterization Scheme Syntheses of the complexes 2, 3, and The complexes were characterized by infra-red spectroscopy, 1H and 13C NMR spectroscopy, mass spectrometry (MALDI-TOF), and elemental analysis The elemental analysis results reveal the correct formulation of the complexes, implying the presence of three NTA ligands, one ancillary ligands and one central metal ion The IR spectra of all shows characteristic broad bands in the 3000–3500 cm–1 region, which are in line with the presence of the water coordinated to the metal ion The disappearance of the bands in the IR spectra of 2–4 confirms that the water molecules were displaced by bidentate ligands The absorption at 1601 cm–1, which is typical for C=O sketch in the ligand is hypsochromically shifted to 1608–1615 cm–1 in the complexes It might be due to the delocalization of π electrons among the diketonate moiety and naphthalene ring upon complexation The sketching frequency of N–O bonds in free bpyO1 and bpyO2 are 1252 and 1255 cm–1, respectively.[17,18] The bands are shifted to lower wave numbers in and (1193 and 1196 cm–1), thus confirm- Z Anorg Allg Chem 2015, 1934–1940 The structures of 2c, 3c, and 4b were determined by singlecrystal X-ray diffraction (Figure 1, Figure 2, and Figure 3) Selected bond lengths and angles are provided in Table Crystal data and data collection parameters for the complexes are given in Table Table Selected bond lengths /Å and angles /° for complexes 2c, 3c, and 4b Ln–O1 Ln–O2 Ln–O3 Ln–O4 Ln–O5 Ln–O6 Ln–X1a) Ln–X2a) O1–Ln–O2 O3–Ln–O4 O5–Ln–O6 X1–Ln–X2a) 2c 3c 4b 2.313(4) 2.296(4) 2.310(5) 2.314(4) 2.323(4) 2.274(4) 2.519(5) 2.555(5) 72.5(2) 72.4(2) 72.4(2) 64.9(2) 2.299(5) 2.305(5) 2.295(5) 2.325(5) 2.311(5) 2.293(5) 2.594(6) 2.313(5) 72.1(2) 72.9(2) 72.1(2) 67.5(2) 2.379(7) 2.335(7) 2.378(8) 2.407(8) 2.368(7) 2.374(7) 2.467(6) 2.343(7) 70.6(3) 71.3(2) 72.8(2) 69.4(3) a) X1, X2 = donor atom of the ancillary ligands 1935 © 2015 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Journal of Inorganic and General Chemistry www.zaac.wiley-vch.de ARTICLE Zeitschrift für anorganische und allgemeine Chemie Figure (a) ORTEP plot of 2c (thermal ellipsoids drawn at the 50 % probability level) Hydrogen atoms are omitted for clarity Color scheme: Er, green; F, yellow; C, gray; N, pale blue (b) π–π interactions in 2c Figure ORTEP plot of 3c (thermal ellipsoids drawn at the 50 % probability level) Hydrogen atoms are omitted for clarity Color scheme: Er, green; F, yellow; C, gray; N, pale blue The structures of the complexes reveal a coordination number of each central metal ion, in which Ln3+ are bonded to six oxygen atoms from three NTA and two donor atoms (X1, X2) from the ancillary ligands, namely, N, N for phen, N, O for bpyO1, O, O for bpyO2 The coordinating atoms form a distorted square antiprism, which consists of two square facets In each facet four donor atoms are (X1, X2, O5, O6) and (O1, Z Anorg Allg Chem 2015, 1934–1940 Figure (a) ORTEP plot of 4b (thermal ellipsoids drawn at the 50 % probability level) Hydrogen atoms are omitted for clarity Color scheme: Eu, green; F, yellow; C, gray; N, pale blue (b), (c) π–π interactions in 4b O2, O3, O4), respectively The Ln–O bond lengths (2.274– 2.467 Å) and O–Ln–O angles (70.6–72.8°) are similar to reported values in literature.[9,19] Notably, the C–C and C–O bonds in the diketonate moiety are in the ranges between car- 1936 © 2015 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Journal of Inorganic and General Chemistry ARTICLE www.zaac.wiley-vch.de Zeitschrift für anorganische und allgemeine Chemie Table Crystal data and structure refinement for complexes 2c, 3c, and 4b Formula Mw /g·mol–1 Crystal system a /Å b /Å c /Å α /° β /° γ /° V /Å3 Space group Z Dcalcd /g·cm–3 μ /mm–1 Reflections collected Independent reflections Data/restraints/parameters R1/wR2 [I Ͼ 2σ (I)] GOF 2c 3c 4b C57H35Cl9ErF9N2O6 1501.18 monoclinic 12.4905(7) 41.885(2) 11.4630(6) 90 107.238(2) 90 5727.7(6) P21/c 1.741 1.968 75885 14114 [R(int) = 0.0485] 14114/0/775 R1 = 0.0701, wR2 = 0.1774 1.033 C52H32ErF9N2O7 1135.05 monoclinic 25.4201(17) 19.2938(15) 9.5627(6) 90 91.319(5) 90 4688.8(6) P21/c 1.608 1.881 27233 9047 [R(int) = 0.1484] 9047/282/731 R1 = 0.0476, wR2 = 0.1502 0.678 C52H32EuF9N2O8 1135.75 orthorhombic 17.0488(13) 17.1993(13) 17.8632(15) 90 90 90 5238.0(7) P212121 1.440 1.281 84277 9568 [R(int) = 0.0875] 9568/66/649 R11 = 0510, wR2 = 0683 1.062 bon–carbon and carbon–oxygen single and double bonds, respectively This again confirms the delocalization of π electrons in diketonate moiety upon complexation, which is consistent with IR results For 3c and 4b, the formation of six- and seven-membered chelate rings leads to the staggered conformations of aromatic rings in bpyO1 and bpyO2 moieties The dihedral angles of the rings are 42.9° and 56.0°, respectively In addition, the X1–Ln–X2 bite angle in 4b (69.4°) was found larger than that in 3c (67.5°) The N–O bond lengths (1.303–1.349 Å) lie in the normal range of N-oxide metal complexes.[11,17,18] Interestingly, compounds 2c and 4b exhibit large π–π stacking in solid state (Figure 1b and Figure 3c) 2c shows the overlap mainly between naphthalene ring and diketonate moiety of adjacent molecules The two head-to-tail overlapped naphthalene rings in 4b are offset along long axes of the rings The overlap area is up to 60 % Also, π–π interactions are detected between naphthalene and pyridine N-oxide fragments The separations of the rings in the stacking are 3.299 Å (2c), 3.435 and 3.330 Å (4b), falling in the range of π–π interactions.[20–22] NTA,[3] suggesting the perturbation of the Eu3+ upon complexation The bands at lower wavelength around 260 nm are naphthalene-centered π–π* transition The absorption of N-oxide ligands coincides with the naphthalene feature The extinction coefficient values of the complexes are much larger than that of the free NTA (about three times), indicating, therefore, the presence of three NTA in the complexes Absorption and Emission Spectra Figure Absorption spectra of 3b and 4b in CHCl3 at room temperature The absorption spectra of 3b and 4b in CHCl3 solution are displayed in Figure The spectroscopic data are summarized in Table The broad bands observed at 336 and 337 nm are ascribable to singlet-singlet π–π* enolic transition arising from β-diketonate fragment.[23] The absorption maxima are slightly red-shifted 540 cm–1 in comparison with that of the free Figure shows the emission spectra of 3b and 4b in CHCl3 The excitation spectra of the complexes are similar to relevant absorptions in the 250–400 nm region (Figure 6) The result is reasonable in light of the energy transfer from the ligands to Eu3+ ion, to which the bands around 270 nm indicate the con- Table Absorption and emission spectroscopic data of the compounds [6] 2b 3b 4b Band /nm (ε /10–4 M–1·cm–1) Emission max /nm Emission quantum yield Φfl 268 (7.93), 290 (5.65), 337 (7.60) 266 (8.31), 290 (5.55), 337 (7.85) 264 (7.75), 293 (5.72), 336 (7.59) 580, 592, 612, 650, 703 538, 595, 614, 655, 704 539, 592, 614, 651, 703 0.40 0.12 0.17 Z Anorg Allg Chem 2015, 1934–1940 1937 © 2015 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Journal of Inorganic and General Chemistry ARTICLE www.zaac.wiley-vch.de Zeitschrift für anorganische und allgemeine Chemie tribution of bipyridine oxides (Figure 7) The absence of absorption band arising from 4f-4f transition of the Eu3+ ion further confirms the efficient sensitization Upon excitation at 324 nm, the complexes give the typical Eu3+ emission lines assigned to 5D0 Ǟ 7F0–4 transitions, of which 5D0 Ǟ 7F2 transition at 614 nm is the strongest emission.[24] This hypersensitive transition which is of electric dipole in nature is much more intense than the magnetic 5D0 Ǟ 7F1 transition at 592 and 595 nm The large intensity ratios IED/IMD of the two transitions which are 8.86 for 3b and 10.98 for 4b clearly validate the low Eu3+ local symmetry, namely, the absence of inversion center in the complexes Figure Absorption spectra of bpyO1 and bpyO2 in ethanol at room temperature Conclusions Figure Emission spectra of 3b and 4b in CHCl3 at room temperature Excitation wavelength = 324 nm The 5D0 Ǟ 7D0–4 transitions are indicated A series of lanthanide complexes with NTA ligands were synthesized with the ancillary ligands being varied The Xray structures reveal six- and seven-membered chelate rings of bpyO1 and bpyO2 with lanthanide ions The Eu3+ complexes of the ligands are strongly emissive in red region The good emission quantum yields implied comparable antenna effects of bpyO1 and bpyO2 to that of phen Ongoing studies about coordination chemistry of such N-oxide ligands with lanthanide ions are presently underway in our laboratories Experimental Section General Methods: All the solvents used for synthesis and spectroscopic measurements were purified according to literature procedures 1,10-Phenanthroline monohydrate (phen) (99 %, ACROS Organics), 2,2’-bipyridine N-oxide (bpyO1) (98 %, Sigma-Aldrich) and 2,2Ј-bipyridine N,NЈ-dioxide (bpyO2) (98 %, Sigma-Aldrich) were used as received without further purification Figure Excitation spectra of 3b and 4b in CHCl3 at room temperature Emission wavelength = 614 nm Displacement of the coordinated water in 1b by strong chelating bpyO1 and bpyO2 in 3b and 4b significantly enhance the luminescent intensities It is well-documented that phen is able to efficiently sensitize Eu3+ ion.[25,26] Indeed, the emission quantum yields of 3b (0.12) and 4b (0.17) are comparable to that of 2b (0.40) Hence, this fact affirms significant antenna effect of bpyO1 and bpyO2 Also, stronger emission of 4b might serve as a good indication that seven-membered chelate ring by bpyO2 is more rigid than six-membered chelate ring by bpyO1 Z Anorg Allg Chem 2015, 1934–1940 Physical Methods: The FT-IR spectra of the complexes were measured with a FT-IR 8700 infrared spectrophotometer (4000–400 cm–1) in KBr pellets The 1H NMR spectra were recorded with a Bruker500MHz spectrometer in CDCl3 solution at 300 K Elemental analysis of carbon, hydrogen, and nitrogen was determined with a Heraeus vario EL elemental analyzer MALDI-TOF-MS spectra were recorded with a Bruker Daltonics UltrafleXtreme spectrometer using α-Cyano4-hydroxycinnamic acid as matrix Spectroscopic Measurements: Absorption and emission spectra of the complexes were measured in chloroform at room temperature on Cary 5000 UV/Vis spectrometer and fluorescence spectrophotometer Rhodamine 640 was used as emission quantum yield standard The syntheses of 1b, 1c, and 2b have been reported elsewhere.[6–8] Synthesis of [Y(NTA)3(H2O)2] (1a): To an ethanol solution (60 mL) of NTA (0.6 mmol) and NaOH (0.6 mmol) was added YCl3·6H2O (0.2 mmol) The resulting mixture was stirred for 24 h at room temperature and CCl4 (10 mL) was added to afford a white solid The product was washed by a large amount of CCl4 and air-dried Yield: 1938 © 2015 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Journal of Inorganic and General Chemistry ARTICLE www.zaac.wiley-vch.de Zeitschrift für anorganische und allgemeine Chemie 136 mg, 74 % IR (KBr): ν˜ = 3404 (m), 3064 (w), 1613 (s), 1566 (s), 1530 (m), 1460 (m), 1293 (s), 1197 (s), 1143 (s), 962 (m), 801 (s), 692 (m), 571 (m), 457 (s) cm–1 1H NMR (MeOD): δ = 8.54 (s, H, H1, naphthyl), 8.06 (d, J = 8.5 Hz, H, H4, naphthyl), 7.86 (d, J = 8.0 Hz, H, H8, naphthyl), 7.81 (d, J = 8.5 Hz, H, H3, naphthyl), 7.65 (d, J = 7.0 Hz, H, H5, naphthyl), 7.54 (t, J = 7.5 Hz, H, H7, naphthyl), 7.40 (t, J = 7.5 Hz, H, H6, naphthyl), 6.67 (s, H, CH) 13 C NMR (MeOD): δ = 189.6 (s, C=O), 172.5 (q, 3JC,F = 127 Hz, C=O), 137.0–125.2 (naphthyl), 120.7 (q, 2JC,F = 1135 Hz, CF3), 93.3 (s, CH) C42H28F9O8Y: calcd C 54.80; H, 3.07 %; found: C 54.32; H 3.21 % Syntheses of [Y(NTA)3phen] (2a) and [Er(NTA)3phen] (2c): A solution of phen (0.1 mmol) in methanol (5 mL) was added dropwise to a solution of (0.1 mmol) in methanol (15 mL) The mixture was heated to 60 °C and stirred for h, then filtered, washed with methanol, and last dried in vacuo to give product in good yields Single crystals of complexes were harvested in about two weeks by recrystallization from chloroform/hexane 2a and 2c were also prepared using another method: Phen (0.1 mmol) and (mmol) were suspended in chloroform (10 mL) The mixture was stirred for h and the suspension completely disappeared The solvent was reduced to mL and excess hexane was added to afford the title products 2a: Yield: 84 % IR (KBr): ν˜ = 3067 (w), 1611 (s), 1529 (s), 1478 (m), 1301 (s), 1191 (s), 1137 (s), 796 (s), 582 (m), 477 (m) cm–1 1H NMR (CDCl3): δ = 9.78 (d, J = 3.5 Hz, H, Hd, phen), 8.40 (s, H, H1, naphthyl), 8.30 (d, J = 8.0 Hz, H, Hb, phen), 7.92 (d, J = 8.0 Hz, H, H5, naphthyl), 7.80–7.71 (m, 13 H, H3,4,8, naphthyl, Ha,c, phen), 7.50 (t, J = 7.5 Hz, H, H7, naphthyl), 7.44 (t, J = 7.0 Hz, H, H6, naphthyl), 6.47 (s, H, CH) 13C NMR (CDCl3): δ = 188.1 (s, C=O), 171.6 (q, C=O), 151.4–120.3 (m, naphthyl, phen), 119.2 (q, CF3), 92.5 (s, CH) C54H32F9N2O6Y: calcd C 60.91; H 3.03; N 2.63 %; found: C 60.42; H 2.82; N 2.74 % MALDI-TOF-MS: m/z 1165.1, [M + H]+ 2c: Yield : 78 % IR (KBr): ν˜ = 3065 (w), 1608 (s), 1531 (s), 1301 (m), 1190 (s), 1135 (s), 960 (m), 797 (s), 576 (m), 474 (m) cm–1 C54H32F9N2O6Er: calcd C 56.74; H 2.82, N 2.45 %; found: C 56.32; H 3.01; N 2.65 % MALDI-TOF-MS: m/z 1144.1, [M + H]+ Syntheses of [Y(NTA)3bpyO1] (3a), [Eu(NTA)3bpyO1] (3b), and [Er(NTA)3bpyO1] (3c): The compounds were prepared following the procedures for 2, except that 2,2Ј-bipyridine N-oxide was used instead of phen X-ray-quality crystals of 3c were obtained by slow evaporation of chloroform solution at room temperature 3a: Yield: 64 % IR (KBr): ν˜ = 3060 (w), 1613 (s), 1529(m), 1474 (m), 1303 (s), 1190 (s), 1127 (s), 956 (m), 791 (s), 688 (m), 575 (m), 468 (m) cm–1 1H NMR (CDCl3): δ = 9.58 (s, H, Ha, bpyO1), 8.90 (s, H, Ha’, bpyO1), 8.32 (s, H, H1, naphthyl), 7.85 (d, J = 8.5 Hz, H, H5, naphthyl), 7.76–7.46 (m, 18 H, H3,4,7,8 naphthyl, Hb,c,d,b’,c’,d’, bpyO1), 7.39 (t, J = 7.0 Hz, H, H6, naphthyl), 6.42 (s, H, CH) 13 C NMR (CDCl3) δ = 188.0 (s, C=O), 171.0 (q, C=O), 151.0–124.3 (m, naphthyl, bpyO1), 121.0 (q, CF3), 92.6 (s, CH) C52H32YF9N2O7: calcd C 59.10; H, 3.05; N, 2.65 %; found: C 59.20; H 3.15; N 2.95 % MALDI-TOF-MS: m/z 1057.1, [M + H]+ 3b: Yield: 76 % IR (KBr): ν˜ = 3055 (w), 1613 (s), 1526 (m), 1463 (m), 1297 (s), 1193 (s), 1136 (s), 958 (m), 791 (s), 685 (m), 573 (m), 477 (m) cm–1 C52H32EuF9N2O7: calcd C 55.78; H, 2.88; N, 2.50 %; found: C 56.00; H, 2.62; N, 2.92 % MALDI-TOF-MS: m/z 1121.1, [M + H]+ 3c: Yield: 70 % IR (KBr): ν˜ = 3058 (w), 1614 (s), 1534 (m), 1470 (m), 1300 (s), 1190 (s), 1132 (s), 960 (m), 797 (s), 684 (m), 574 (m), Z Anorg Allg Chem 2015, 1934–1940 475 (m) cm–1 C52H32ErF9N2O7: calcd C 55.02; H, 2.84; N, 2.47 %; found: C 55.54; H 2.72; N 2.74 % MALDI-TOF-MS: m/z 1136.1, [M + H]+ Syntheses of [Y(NTA)3bpyO2] (4a), [Eu(NTA)3bpyO2] (4b), and [Er(NTA)3bpyO2] (4c): The compounds were prepared following the procedures for 2, except that 2,2Ј-bipyridine N,NЈ-dioxide was used instead of phen X-ray-quality crystals of 4b were obtained by slow diffusion of ethanol/hexane solution at room temperature 4a: Yield: 74 % IR (KBr): ν˜ = 3058 (w), 1621 (s), 1530 (m), 1429 (m), 1300 (s), 1127 (s), 795 (s), 685 (m), 572 (m), 434 (m) cm–1 1H NMR (CDCl3): 8.56 (d, H, Ha, bpyO2), 8.40 (s, H, H1, naphthyl), 7.94 (d, J = 7.5 Hz, H, H5, naphthyl), 7.80–7.59 (m, 16 H, H3,4,8 naphthyl, Hb,c, bpyO2), 7.50 (t, J = 7.0 Hz, H, H7, naphthyl), 7.39 (t, J = 7.5 Hz, H, H6, naphthyl), 6.48 (s, H, CH) 13C NMR (CDCl3):187.4 (s, C=O), 171.0 (q, C=O), 142.6–126.9 (m, naphthyl, bpyO2), 125.0 (q, CF3), 91.9 (s, CH) C52H32YF9N2O8: calcd C 59.10; H 3.05; N 2.65 %; found: C 59.33; H 3.16; N 2.73 % MALDI-TOFMS: m/z 1073.1, [M + H]+ 4b: Yield: 76 % IR (KBr): ν˜ = 3062 (w), 1610 (s), 1527 (m), 1472 (m), 1298 (s), 1196 (s), 1131 (s), 794 (s), 682 (m), 575 (m), 476 (m) cm–1 C52H32EuF9N2O8: calcd C 55.49; H 2.84; N 2.47 %; found: C 55.19; H 2.68; N 2.57 % MALDI-TOF-MS: m/z 1137.1, [M + H]+ 4c: Yield: 68 % IR (KBr): ν˜ = 3060 (w), 1617 (s), 1303 (s), 959 (m), 574 (m) cm–1 C52H32ErF9N2O8: calcd C 54.26; H 2.80; N 2.43 %; found: C 54.45; H 2.81; N 2.55 % MALDI-TOF-MS: m/z 1152.1, [M + H]+ X-ray Crystallography: The intensities for the X-ray determinations were collected with a Bruker D8 Quest instrument with Mo-Kα radiation (λ = 0.71073 Å) Standard procedures were applied for data reduction and absorption correction Structure solution and refinement were performed with SHELXS97 and SHELXL97 programs.[15] Hydrogen atom positions were calculated for idealized positions and treated with the “riding model” option of SHELXL Two chlorine atoms of disordered chloroform in 2c were refined isotropically The naphthalene ring in 3c occupies two positions with occupancy ratios of 64:36 A highly disordered solvent in 4b was treated by the SQUEEZE option in PLATON.[16] Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK Copies of the data can be obtained free of charge on quoting the depository numbers CCDC-1051791 (2c), CCDC-1051790 (3c), and CCDC-1051789 (4b) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk) Acknowledgements Vietnam’s National Foundation for Science and Technology Development is thanked for financial support (Grant No 104.02–2011.31) 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absorption spectra of 3b and 4b in CHCl3 solution are displayed in Figure The spectroscopic data are summarized in Table The broad bands observed... spectra of 3b and 4b in CHCl3 at room temperature Excitation wavelength = 324 nm The 5D0 Ǟ 7D0–4 transitions are indicated A series of lanthanide complexes with NTA ligands were synthesized with