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The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state
Materials Chemistry and Physics 114 (2009) 134–138
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state Stefan Lis ∗ , Zbigniew Piskuła, Maciej Kubicki Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Pozna´ n, Poland
a r t i c l e
i n f o
Article history: Received 17 May 2008 Accepted 26 August 2008 Keywords: Europium(III) Complexes Picolinic acid N-oxide Luminescence Crystal structure
a b s t r a c t The spectroscopic characteristics and the crystal structure of Eu(III) complex with picolinic acid N-oxide ligand, picNO, at room and liquid-nitrogen temperatures are discussed. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the 5 D0 → 7 F0 transition) are presented. The selective excitation luminescence spectroscopy of Eu(III) in the range of the 5 D0 → 7 F0 transition is used for the study of Eu/picNO complexes in solution equilibria. In the crystal the complex molecules build the two-dimensional structures with additional Na+ cations and water molecules. This structure consists of edge-sharing chains of Na distorted octahedral, interconnected by Eu polyhedra (distorted square antiprisms). The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the Eu(III) ion as an ionic bidentate chelate, forming the Na[Eu(picNO)4 ] complex of six-membered chelate rings with the bite angles of ca. 70.5◦ . The complex is symmetrical; the Eu(III) ion is eight-coordinated. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Lanthanide complexes of pyridine carboxylic acid N-oxides and their substituted derivatives have been subjects of several publications [1–7] due to their interesting photophysical properties. Complexes of Ln(III) ions with isomers of pyridine carboxylic acid, namely picolinic acid N-oxide, nicotinic acid N-oxide, and isonicotinic acid N-oxide, have been investigated because of their possible applications [4,7]. The pyridine N-oxide group often acts as O donor coordination mode [5]. So it is self-evident that systems bearing N-oxide groups form more stable complexes with lanthanides than the parent ligands [5,6]. Pyridine carboxylic acid N-oxides and their substituted derivatives, having oxygen donor atoms, form thermodynamically stable six-membered ring complexes. Only Ln(III) complexes with nicotinic acid N-oxide, isonicotinic acid N-oxide, and 6-methyl-picolinic acid N-oxide have been structurally determined [7,8]. In this paper, we describe the crystal structure and the spectroscopic characteristics of Eu(III) complexes with picNO ligand at room and liquid-nitrogen temperatures. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the 5 D0 → 7 F0 transition) are presented. We used luminescence spectroscopy of the 5 D0 → 7 F0 transition of Eu(III) for the study of its complexes that are in equilibrium in solution [9,10].
Aqueous solutions of systems studied containing the Eu(III) ion were prepared using Eu(ClO4 )3 and the appropriate amount of picolinic acid N-oxide (picNO) ligand. The required pH values of the aqueous solutions were adjusted by additions of NaOH or HClO4 . The concentration of Eu(III) ions was 0.02 M in all experiments. The luminescence lifetime of the Eu(III) excited state and the excitation spectra of the Eu(III) 5 D0 → 7 F0 transition, in the 578–581 nm region, were registered using an experimental laser system [11], consisting of a nitrogen laser and a tunable dye laser working on the P3CDOMAT dye in toluene. The Eu(III) 5 D0 → 7 F0 excitation spectra were measured at room temperature and liquid-nitrogen temperature. The emission spectra of the solid state were recorded using a PerkinElmer spectrofluorometer MPF3.
∗ Corresponding author. Tel.: +48 61 829 1345. E-mail address: [email protected] (S. Lis). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.08.089
2.1. Synthesis of Na[Eu(picNO)4 ] complex Picolinic acid N-oxide (0.5 mmol) was completely dissolved in 5 cm3 of distilled water by addition of NaOH to form a clear solution, to which 5 cm3 of Eu(ClO4 )3 (0.1 mmol) solution was added with stirring. The resultant solution was filtered off. Storage of the solution in a desiccator charged with drierite for several days’ yielded crystals of the complex. 2.2. X-ray crystallographic study Data collections were performed by ω-scan technique in the range 2–25◦ on a KUMA KM4CCD [12] four-circle diffractometer with CCD detector, using graphite-monochromated Mo K␣ radiation ( = 0.71073 Å). Data were corrected for Lorentz-polarization effects and for absorption [13]. The structures were solved by direct methods with SIR-92 [14] and refined with SHELXL-97 [15]. Non-hydrogen atoms were refined anisotropically, hydrogen atoms were found in the difference Fourier maps and freely refined in 3 and 5, in all other structures they were placed geometrically and refined as ‘riding model’, with Uis o’s set at 1.2 times Ueq of appropriate carrier atoms. The hydrogen atoms from water molecules were found in F maps and refined with constrainted O–H distances. Relevant crystallographic data are listed in Table 1.
S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138
135
Table 1 Crystal data, data collection and structure refinement Compounds 1
2
3
4
5
6
7
(C6 H4 NO3 )4 Sm Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Eu Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Gd Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Y Na3 (H2 O)4 ·(ClO4 )2
1042.69 Orthorhombic
1044.30 Orthorhombic
1049.59 Orthorhombic
(C6 H4 NO3 )4 Ho Na3 (H2 O)4 ·(ClO4 )2 1057.27 Orthorhombic
(C6 H4 NO3 )4 Er Na3 (H2 O)4 ·(ClO4 )2
Formula weight Crystal system
(C6 H4 NO3 )4 Pr Na3 (H2 O)4 ·(ClO4 )2 1033.25 Orthorhombic
1059.60 Orthorhombic
981.25 Orthorhombic
Space group a Å) b (Å) c (Å) V (Å3 ) Z
Pbcn 27.028(2) 9.2534(8) 14.0866(12) 3523.1(5) 4
Pbcn 27.185(4) 9.3440(10) 14.076(2) 3575.5(8) 4
Pbcn 27.0136(8) 9.2699(3) 13.9487(4) 3492.9(2) 4
Pbcn 27.0365(8) 9.2733(3) 13.9279(4) 3492.0(2) 4
Pbcn 27.1909(9) 9.3214(4) 13.8498(5) 3510.3(2) 4
Pbcn 27.0180(12) 9.2841(4) 13.7540(6) 3450.0(3) 4
Pbcn 27.268(2) 9.3408(8) 13.9740(15) 3559.2(6) 4
Dx (g cm−3 ) F (0 0 0) (mm−1 ) T (K) range (◦ )
1.95 2056 1.68 100(1) 2.7–29.3
1.94 2068 1.93 295(2) 1.5–26.0
1.99 2072 2.09 100(1) 2.7–29.8
2.00 2076 2.19 100(1) 2.7–29.7
2.00 2088 2.55 100(1) 2.9–29.0
2.04 2092 2.73 100(1) 3.0–29.0
1.83 1976 1.93 293(2) 2.7–26.0
Reflections: Collected Unique (Rint ) Final R(F) [I > 2(I)] Final wR(F2 ) [I > 2(I)] Goodness of fit max/min (e Å−3 )
22,309 4,563 (0.075) 0.067 0.147 1.18 1.96/−2.02
6875 3478 (0.107) 0.081 0.230 1.24 2.61/−3.16
30594 4632 (0.016) 0.021 0.045 1.14 0.45/−0.56
31521 4665 (0.029) 0.049 0.093 1.47 0.96/−1.66
19621 4430 (0.017) 0.019 0.040 1.06 0.42/−0.52
15504 4282 (0.018) 0.040 0.079 1.37 0.88/−1/04
18073 3496 (0.033) 0.038 0.092 1.09 0.64/−0.54
Formula
CCDC, 675652 (1) and 675402–675407 (2–7) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.) +44-1223/336-033; E-mail: [email protected]].
3. Results and discussion Excitation and emission spectra of the Na[Eu(picNO)4 ] complex are presented in Fig. 1. The 4f electronic configuration of the Eu(III) ion has a nondegenerate ground state (7 F0 ) and a non-degenerate long-lived emitting state (5 D0 ). The 5 D0 → 7 F0 band cannot be further split by the ligand field, and the absorption band corresponding to the transition between these levels must consist of a single peak for a given Eu(III) ion environment. Thus, the number of peaks observed in the spectra directly corresponds to the number of Eu(III) sites present
Fig. 1. Eu(III) excitation and emission spectra of Na[Eu(picNO)4 ]: em = 618 nm, (A) exc = 300 nm and (B) exc = 394 nm.
in the system under study. The Eu(III) ion may be selectively excited by tuning a dye laser to the wavelength of the 5 D0 → 7 F0 transition in the 578–581 nm region, and the emission can be monitored at 615 nm (5 D0 → 7 F2 ) [16]. In the Eu(III)/picNO system, we observed four bands (Fig. 2) of different frequencies at room temperature and five bands (Fig. 3) of different frequencies at liquid-nitrogen temperature. Eq. (1) was used for calculation of the total ligand coordination number, CNL (where = 17276 − at 298 K [9,16] and = 17268 − for 77 K) and Eq. (2) at 298 K and (3) at 77 K for calculation of the total formal negative charge of the ligand, p [17]: CNL = 0.237 · + 0.628
(1)
Fig. 2. Eu(III) selective excitation spectra of 5 D0 → 7 F0 band of Eu(III)/picNO system, at 298 K, in water solution: M:L (A) 1:1, (B) 1:3 and (C) 1:5 (pH 5.0, CEu(III) = 0.02 M).
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S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138 Table 2 Frequency of the 5 D0 → 7 F0 band of the Eu(III) excitation spectra at 298 K and 77 K Peak
(cm−1 )
(s)
CNL
CNH2 O
1 2 3 4
17274.25 17268.19 17260.30 17252.41
0.21 2.48 4.35 6.22
112.3 145.6 191.3 317.2
298 K 8.65 6.51 4.79 2.61
1 2 3 4 5
17267.58 17258.64 17250.00 17242.57 17226.53
0.73 2.85 4.89 6.65 10.46
116.3 148.6 206.4 326.8 792.9
77 K 8.77 7.03 4.94 3.12 1.29
CNT
p Actual
Calculated
8.86 8.99 9.14 8.83
– −1 −2 −3
– −0.46 −1.03 −1.50
9.50 9.71 9.83 9.77 11.75
– −1 −2 −3 −4
– −1.76 −3.18 −4.13 −5.77
Total ligand coordination numbers, CNL , luminescence lifetime of excited states of Eu(III) ion, , number of water molecules, CNH2 O , total coordination numbers, CNT , (CNT = CNL + CNH2 O ) and total formal negative charge of the ligand, p.
Fig. 3. Eu(III) selective excitation spectra of 5 D0 → 7 F0 band of Eu(III)/picNO system, at 77 K, in water solution: M:L (A) 1:1, (B) 1:3 and (C) 1:5 (pH 5.0, CEu(III) = 0.02 M).
= −0.76p2 + 2.29p + 17273
(2)
2
= −0.76p + 2.29p + 17265
(3)
Calculated results are presented in Table 2. In this system four Eu(III) species, such as the forms of M, ML, ML2 , and ML3 at 298 K and M, ML, ML2 , ML3 , and ML4 at 77 K have been found. Maxima of particular peaks in the 5 D0 → 7 F0 spectra and calculated values of ligand coordination numbers, CNL , are shown in Table 2. Studies of Ln(III) hydration in concentrated aqueous salt solutions in the fluid and the frozen state [18,19] have shown the correlation between luminescence decay constants, kobs , and the number of water molecules in the inner-sphere of the Eu(III) ion as presented in Eq. (4) at 298 K and (5) at 77 K. CNH2 O = 1.05 × 10−3 · kobs − 0.70 −3
CNH2 O = 1.02 × 10
(4)
· kobs − 0.17
(5)
where kobs = 1/ , = luminescence lifetime of the Eu(III) ion.
Results of the Eu(III) luminescence lifetime, , measured for the Eu(III)/picNO system and the number of water molecules, CNH2 O , are presented in Table 2. The measured Eu(III) luminescence lifetimes and, corresponding to them, the hydration numbers: 110.3 s (9 H2 O), 145.6 s (7 H2 O), 191.3 s (5 H2 O), and 317.2 s (3 H2 O), indicated that the following complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , and [EuL3 (H2 O)3 ] at room temperature. The luminescence lifetimes and hydration numbers measured in a frozen state were: 116.3 s (9 H2 O), 148.6 s (7 H2 O), 206.4 s (5 H2 O), 326.8 s (3 H2 O), and 792.9 s (1 H2 O), and indicating the complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , [EuL3 (H2 O)3 ], and [EuL4 (H2 O)]− . The Eu(III) ion in the system under study has the coordination number (CNT ) 9. All complexes are highly isomorphous; they crystallize in the same orthorhombic space group Pbcn, and the unit-cell dimensions are similar for 1–7. Moreover, the positions of the atoms in the unit cells are almost identical in all the complexes, so also the geometry of the complexes and their crystal packing is virtually identical. Therefore, we will discuss in detail the crystal structure of one complex (Eu(III), 3. All the observations and structure details can be directly transformed to all other complexes. The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the europium(III) ion as an ionic bidentate chelate. Six-membered chelate rings are formed with the bite angles of ca. 70.5◦ . The rele-
Table 3 Selected geometrical parameters (Å, ◦ ) 1(Pr) M-O22A M-O22B M-O1A M-O1B N1A-O1A N1B-O1B Na1-O1W Na1-O2W Na1-O1Aa Na1-O21Ab Na1-O21B Na1-O21Ba Na2-O1W Na2-O2W Na2-O22Ab A/COO B/COO A/B a b
2.419(4) 2.372(5) 2.476(4) 2.440(5) 1.348(7) 1.329(7) 2.373(6) 2.332(6) 2.332(5) 2.390(5) 2.410(5) 2.829(5) 2.481(5) 2.281(5) 2.335(5) 50.2(3) 29.2(4) 38.2(2)
Symmetry codes: 1 − x, 1 − y, −z. Symmetry codes: x, −1 + y, z.
2(Sm) 2.308(7) 2.362(6) 2.384(8) 2.399(7) 1.315(12) 1.360(13) 2.384(10) 2.354(10) 2.424(9) 2.415(10) 2 2.527(10) 2.285(8) 2.362(8)
3(Eu) 2.3612(1) 2.3236(1) 2.4170(1) 2.3907(1) 1.343(2) 1.327(2) 2.369(2) 2.331(2) 2.342(2) 2.389(2) 2.389(2) 2.803(2) 2.477(2) 2.279(2) 2.341(1) 46.80(8) 29.31(12) 37.85(4)
4(Gd) 2.353(3) 2.314(3) 2.407(3) 2.381(3) 1.346(4) 1.330(4) 2.365(4) 2.332(4) 2.344(3) 2.391(3) 2.410(3) 2.805(4) 2.477(3) 2.281(3) 2.343(3) 46.3(2) 29.2(3) 37.56(9)
5(Ho) 2.3221(12) 2.2882(13) 2.3818(13) 2.3607(13) 1.351(2) 1.337(2) 2.373(2) 2.343(2) 2.355(2) 2.399(2) 2.420(2) 2.814(2) 2.480(1) 2.292(2) 2.358(2) 43.75(8) 28.64(12) 37.06(4)
6(Er) 2.301(3) 2.265(3) 2.358(3) 2.333(3) 1.342(4) 1.332(4) 2.360(3) 2.331(3) 2.344(3) 2.389(3) 2.405(3) 2.795(3) 2.464(3) 2.281(3) 2.350(3) 42.8(2) 28.5(3) 37.07(9)
7(Y) 2.311(3) 2.284(3) 2.376(3) 2.346(3) 1.376(4) 2.329(3) 2.375(4) 2.359(4) 2.376(3) 2.424(3) 2.398(3) 2.783(4) 2.514(4) 2.359(4) 2.367(3) 43.6(2) 29.5(3) 37.12(10)
S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138
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Fig. 4. The coordination of Eu(III) cation; thermal ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres of arbitrary radii. The atoms without labels are symmetry related with the labeled ones (symmetry code: −x + 1, y, −z + 1/2).
Fig. 5. A fragment of a chain built by sodium cations; the ellipsoids are drawn at 50% probability level.
vant geometrical parameters (for all complexes) are listed in Table 3. The bond lengths and angles are generally typical, with characteristic elongation of the N O bond as a result of the coordination, and – caused by the same reason – the different values of C O bonds within the carboxylate group. The complex is symmetrical;
Fig. 6. Coordination polyhedra representation of a network made by metal cations.
the Eu(III) ion and one of the Na(I) ions lie on the two-fold axis along y. The Eu(III) ion is eight-coordinated (cf. Fig. 4), while both Na(I) ions are six-coordinated. Probably in order to accommodate such a symmetrical arrangement of ligands, the coordination of the
Fig. 7. Crystal packing as seen approximately along [0 0 1] direction. Hydrogen bonds are depicted as dashed lines.
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S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138
chelate rings is different: the molecule B is much more planar than in A (maximum deviation from the least-squares plane is 0.14 Å in the ligand B, but almost 0.5 Å in the ligand A). This stress is also transferred into the rings: maximum deviation from the pyridine ring plane in A is 0.017(1) Å while in B is 0.009(1) Å; the carboxylate groups are twisted with respect to the ring planes by 46.80(8)◦ in A and by 29.31(13)◦ in B (cf. Table 3). Additionally, the stability of the complex might be enhanced by weak – interactions between ligands A and B; the distance between the rings is ca. 3.4 Å while the inclination angle is 17.8◦ . There are some examples of lanthanide–sodium polynuclear complexes, but usually there are one-dimensional chains of alternating Ln and Na complexes (e.g. [20–22]). The present structure is actually polymeric, it is an example of a two-dimensional structure (Fig. 6). For one of the sodium ions, Na1, one of the Na–O distances is longer than the remaining one; however it seems to be six-coordinated anyway. The coordination polyhedra of Na ions are close to edge-sharing octahedrons (Fig. 5), while those of the Eu(III) ions (c.n. 8) are close to square-antiprisms. In the crystal structure, the Na polyhedra are arranged into the infinite edge-sharing chains, and the Eu polyhedra are between these chains, sharing one edge with one chain and two corners with another one (Fig. 6). This structure is filled by the perchlorate counterions that are connected by hydrogen bonds with water molecules additional hydrogen bonds are strengthening the structure (Table 3, Fig. 7). 4. Conclusions Luminescence studies of Eu(III) (lifetime measurements and analysis of excitation spectra of the 5 D0 → 7 F0 transition at room and liquid-nitrogen temperatures), indicated in the Eu(III)/picNO system an existence of various nine-coordinated europium species. At room temperature the following species: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , and [EuL3 (H2 O)3 ] were found, while in a frozen state the complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ ,
[EuL2 (H2 O)5 ]+ , [EuL3 (H2 O)3 ], and [EuL4 (H2 O)]− were identified. Synthesized complex characterized by X-ray crystallography showed that [Eu(C6 H4 NO3 )4 Na3 (H2 O)4 ]2+ · 2ClO4 − is symmetrical with eight-coordinated Eu(III) ions. In the crystal the complex molecules build the two-dimensional structures with additional Na+ cations and water molecules. This structure consists of edgesharing chains of Na distorted octahedral, interconnected by Eu polyhedra. References [1] G.F. de Sa, O.L. Malta, C. de Mello Donega, A.M. Simas, R.L. Longo, P.A. SantaCruz, E.F. da Silva Jr., Coord. Chem. Rev. 196 (2000) 165. [2] C.C.F. Nunez, K. Zinner, L.B. Zinner, C.C. Calvarho, J. Zukerman-Schpector, G. Vicentini, Inorg. Chim. Acta 293 (1999) 249. [3] H. Yoneda, G.R. Choppin, J.L. Bear, A.J. Graffeo, Inorg. Chem. 4 (1965) 244. [4] S. Lis, Z. Hnatejko, P. Barczynski, M. Elbanowski, J. Alloys Compd. 341 (2002) 45. [5] H.-J. Zhang, G. Li, L. Yan, R.-D. Yang, J. Luminescence 127 (2007) 316. [6] G. Meinrath, S. Lis, U. Böhme, J. Alloys Compd. 408–412 (2006) 962. [7] J.-G. Mao, H.-J. Zhang, J.-Z. Ni, S.-B. Wang, T.C.W. Mak, Polyhedron 17 (1998) 3999. [8] L. Yan, J. Liu, X. Wang, R. Yang, F. Song, Polyhedron 14 (1995) 3545. [9] S. Lis, Z. Wang, G.R. Choppin, Inorg. Chim. Acta 239 (1995) 139. [10] S. Lis, J. Alloys Compd. 341 (2002) 45. [11] S. Lis, Z. Hnatejko, Z. Stryla, Opt. Appl. 31 (2001) 643. [12] CrysAlis CCD, Oxford Diffraction Ltd., Version 1.171.31.5 (release August 28, 2006 CrysAlis171.NET). [13] CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.31.5 (release August 28, 2006 CrysAlis171.NET), 1990. [14] G.M. Sheldrick, Acta Cryst. A46 (199) 467. [15] G.M. Sheldrick, SHELXL97. Program For the Refinement of Crystal Structures, University of Göttingen, Germany, 1997. [16] G.R. Choppin, Z.M. Wang, Inorg. Chem. 36 (1997) 249. [17] M. Albin, W.D. Horrocks Jr., Inorg. Chem. 24 (1985) 895. [18] P.P. Barthelemey, G.R. Choppin, Inorg. Chem. 23 (1989) 2044. [19] T. Kimura, Y. Kato, J. Alloys Compd. 278 (1998) 92. [20] C. Tedeschi, J. Azema, H. Gornitzka, P. Tisnes, C. Picard, Dalton Trans. (2003) 1738. [21] J.-P. Costes, F. Dahan, F. Nicodeme, Inorg. Chem. 42 (2003) 6556. [22] A.S. Gajadhar-Plummer, I.A. Kahwa, A.J.P. White, D.J. Williams, Inorg. Chem. 38 (1999) 1745.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state Stefan Lis ∗ , Zbigniew Piskuła, Maciej Kubicki Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Pozna´ n, Poland
a r t i c l e
i n f o
Article history: Received 17 May 2008 Accepted 26 August 2008 Keywords: Europium(III) Complexes Picolinic acid N-oxide Luminescence Crystal structure
a b s t r a c t The spectroscopic characteristics and the crystal structure of Eu(III) complex with picolinic acid N-oxide ligand, picNO, at room and liquid-nitrogen temperatures are discussed. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the 5 D0 → 7 F0 transition) are presented. The selective excitation luminescence spectroscopy of Eu(III) in the range of the 5 D0 → 7 F0 transition is used for the study of Eu/picNO complexes in solution equilibria. In the crystal the complex molecules build the two-dimensional structures with additional Na+ cations and water molecules. This structure consists of edge-sharing chains of Na distorted octahedral, interconnected by Eu polyhedra (distorted square antiprisms). The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the Eu(III) ion as an ionic bidentate chelate, forming the Na[Eu(picNO)4 ] complex of six-membered chelate rings with the bite angles of ca. 70.5◦ . The complex is symmetrical; the Eu(III) ion is eight-coordinated. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Lanthanide complexes of pyridine carboxylic acid N-oxides and their substituted derivatives have been subjects of several publications [1–7] due to their interesting photophysical properties. Complexes of Ln(III) ions with isomers of pyridine carboxylic acid, namely picolinic acid N-oxide, nicotinic acid N-oxide, and isonicotinic acid N-oxide, have been investigated because of their possible applications [4,7]. The pyridine N-oxide group often acts as O donor coordination mode [5]. So it is self-evident that systems bearing N-oxide groups form more stable complexes with lanthanides than the parent ligands [5,6]. Pyridine carboxylic acid N-oxides and their substituted derivatives, having oxygen donor atoms, form thermodynamically stable six-membered ring complexes. Only Ln(III) complexes with nicotinic acid N-oxide, isonicotinic acid N-oxide, and 6-methyl-picolinic acid N-oxide have been structurally determined [7,8]. In this paper, we describe the crystal structure and the spectroscopic characteristics of Eu(III) complexes with picNO ligand at room and liquid-nitrogen temperatures. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the 5 D0 → 7 F0 transition) are presented. We used luminescence spectroscopy of the 5 D0 → 7 F0 transition of Eu(III) for the study of its complexes that are in equilibrium in solution [9,10].
Aqueous solutions of systems studied containing the Eu(III) ion were prepared using Eu(ClO4 )3 and the appropriate amount of picolinic acid N-oxide (picNO) ligand. The required pH values of the aqueous solutions were adjusted by additions of NaOH or HClO4 . The concentration of Eu(III) ions was 0.02 M in all experiments. The luminescence lifetime of the Eu(III) excited state and the excitation spectra of the Eu(III) 5 D0 → 7 F0 transition, in the 578–581 nm region, were registered using an experimental laser system [11], consisting of a nitrogen laser and a tunable dye laser working on the P3CDOMAT dye in toluene. The Eu(III) 5 D0 → 7 F0 excitation spectra were measured at room temperature and liquid-nitrogen temperature. The emission spectra of the solid state were recorded using a PerkinElmer spectrofluorometer MPF3.
∗ Corresponding author. Tel.: +48 61 829 1345. E-mail address: [email protected] (S. Lis). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.08.089
2.1. Synthesis of Na[Eu(picNO)4 ] complex Picolinic acid N-oxide (0.5 mmol) was completely dissolved in 5 cm3 of distilled water by addition of NaOH to form a clear solution, to which 5 cm3 of Eu(ClO4 )3 (0.1 mmol) solution was added with stirring. The resultant solution was filtered off. Storage of the solution in a desiccator charged with drierite for several days’ yielded crystals of the complex. 2.2. X-ray crystallographic study Data collections were performed by ω-scan technique in the range 2–25◦ on a KUMA KM4CCD [12] four-circle diffractometer with CCD detector, using graphite-monochromated Mo K␣ radiation ( = 0.71073 Å). Data were corrected for Lorentz-polarization effects and for absorption [13]. The structures were solved by direct methods with SIR-92 [14] and refined with SHELXL-97 [15]. Non-hydrogen atoms were refined anisotropically, hydrogen atoms were found in the difference Fourier maps and freely refined in 3 and 5, in all other structures they were placed geometrically and refined as ‘riding model’, with Uis o’s set at 1.2 times Ueq of appropriate carrier atoms. The hydrogen atoms from water molecules were found in F maps and refined with constrainted O–H distances. Relevant crystallographic data are listed in Table 1.
S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138
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Table 1 Crystal data, data collection and structure refinement Compounds 1
2
3
4
5
6
7
(C6 H4 NO3 )4 Sm Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Eu Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Gd Na3 (H2 O)4 ·(ClO4 )2
(C6 H4 NO3 )4 Y Na3 (H2 O)4 ·(ClO4 )2
1042.69 Orthorhombic
1044.30 Orthorhombic
1049.59 Orthorhombic
(C6 H4 NO3 )4 Ho Na3 (H2 O)4 ·(ClO4 )2 1057.27 Orthorhombic
(C6 H4 NO3 )4 Er Na3 (H2 O)4 ·(ClO4 )2
Formula weight Crystal system
(C6 H4 NO3 )4 Pr Na3 (H2 O)4 ·(ClO4 )2 1033.25 Orthorhombic
1059.60 Orthorhombic
981.25 Orthorhombic
Space group a Å) b (Å) c (Å) V (Å3 ) Z
Pbcn 27.028(2) 9.2534(8) 14.0866(12) 3523.1(5) 4
Pbcn 27.185(4) 9.3440(10) 14.076(2) 3575.5(8) 4
Pbcn 27.0136(8) 9.2699(3) 13.9487(4) 3492.9(2) 4
Pbcn 27.0365(8) 9.2733(3) 13.9279(4) 3492.0(2) 4
Pbcn 27.1909(9) 9.3214(4) 13.8498(5) 3510.3(2) 4
Pbcn 27.0180(12) 9.2841(4) 13.7540(6) 3450.0(3) 4
Pbcn 27.268(2) 9.3408(8) 13.9740(15) 3559.2(6) 4
Dx (g cm−3 ) F (0 0 0) (mm−1 ) T (K) range (◦ )
1.95 2056 1.68 100(1) 2.7–29.3
1.94 2068 1.93 295(2) 1.5–26.0
1.99 2072 2.09 100(1) 2.7–29.8
2.00 2076 2.19 100(1) 2.7–29.7
2.00 2088 2.55 100(1) 2.9–29.0
2.04 2092 2.73 100(1) 3.0–29.0
1.83 1976 1.93 293(2) 2.7–26.0
Reflections: Collected Unique (Rint ) Final R(F) [I > 2(I)] Final wR(F2 ) [I > 2(I)] Goodness of fit max/min (e Å−3 )
22,309 4,563 (0.075) 0.067 0.147 1.18 1.96/−2.02
6875 3478 (0.107) 0.081 0.230 1.24 2.61/−3.16
30594 4632 (0.016) 0.021 0.045 1.14 0.45/−0.56
31521 4665 (0.029) 0.049 0.093 1.47 0.96/−1.66
19621 4430 (0.017) 0.019 0.040 1.06 0.42/−0.52
15504 4282 (0.018) 0.040 0.079 1.37 0.88/−1/04
18073 3496 (0.033) 0.038 0.092 1.09 0.64/−0.54
Formula
CCDC, 675652 (1) and 675402–675407 (2–7) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.) +44-1223/336-033; E-mail: [email protected]].
3. Results and discussion Excitation and emission spectra of the Na[Eu(picNO)4 ] complex are presented in Fig. 1. The 4f electronic configuration of the Eu(III) ion has a nondegenerate ground state (7 F0 ) and a non-degenerate long-lived emitting state (5 D0 ). The 5 D0 → 7 F0 band cannot be further split by the ligand field, and the absorption band corresponding to the transition between these levels must consist of a single peak for a given Eu(III) ion environment. Thus, the number of peaks observed in the spectra directly corresponds to the number of Eu(III) sites present
Fig. 1. Eu(III) excitation and emission spectra of Na[Eu(picNO)4 ]: em = 618 nm, (A) exc = 300 nm and (B) exc = 394 nm.
in the system under study. The Eu(III) ion may be selectively excited by tuning a dye laser to the wavelength of the 5 D0 → 7 F0 transition in the 578–581 nm region, and the emission can be monitored at 615 nm (5 D0 → 7 F2 ) [16]. In the Eu(III)/picNO system, we observed four bands (Fig. 2) of different frequencies at room temperature and five bands (Fig. 3) of different frequencies at liquid-nitrogen temperature. Eq. (1) was used for calculation of the total ligand coordination number, CNL (where = 17276 − at 298 K [9,16] and = 17268 − for 77 K) and Eq. (2) at 298 K and (3) at 77 K for calculation of the total formal negative charge of the ligand, p [17]: CNL = 0.237 · + 0.628
(1)
Fig. 2. Eu(III) selective excitation spectra of 5 D0 → 7 F0 band of Eu(III)/picNO system, at 298 K, in water solution: M:L (A) 1:1, (B) 1:3 and (C) 1:5 (pH 5.0, CEu(III) = 0.02 M).
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S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138 Table 2 Frequency of the 5 D0 → 7 F0 band of the Eu(III) excitation spectra at 298 K and 77 K Peak
(cm−1 )
(s)
CNL
CNH2 O
1 2 3 4
17274.25 17268.19 17260.30 17252.41
0.21 2.48 4.35 6.22
112.3 145.6 191.3 317.2
298 K 8.65 6.51 4.79 2.61
1 2 3 4 5
17267.58 17258.64 17250.00 17242.57 17226.53
0.73 2.85 4.89 6.65 10.46
116.3 148.6 206.4 326.8 792.9
77 K 8.77 7.03 4.94 3.12 1.29
CNT
p Actual
Calculated
8.86 8.99 9.14 8.83
– −1 −2 −3
– −0.46 −1.03 −1.50
9.50 9.71 9.83 9.77 11.75
– −1 −2 −3 −4
– −1.76 −3.18 −4.13 −5.77
Total ligand coordination numbers, CNL , luminescence lifetime of excited states of Eu(III) ion, , number of water molecules, CNH2 O , total coordination numbers, CNT , (CNT = CNL + CNH2 O ) and total formal negative charge of the ligand, p.
Fig. 3. Eu(III) selective excitation spectra of 5 D0 → 7 F0 band of Eu(III)/picNO system, at 77 K, in water solution: M:L (A) 1:1, (B) 1:3 and (C) 1:5 (pH 5.0, CEu(III) = 0.02 M).
= −0.76p2 + 2.29p + 17273
(2)
2
= −0.76p + 2.29p + 17265
(3)
Calculated results are presented in Table 2. In this system four Eu(III) species, such as the forms of M, ML, ML2 , and ML3 at 298 K and M, ML, ML2 , ML3 , and ML4 at 77 K have been found. Maxima of particular peaks in the 5 D0 → 7 F0 spectra and calculated values of ligand coordination numbers, CNL , are shown in Table 2. Studies of Ln(III) hydration in concentrated aqueous salt solutions in the fluid and the frozen state [18,19] have shown the correlation between luminescence decay constants, kobs , and the number of water molecules in the inner-sphere of the Eu(III) ion as presented in Eq. (4) at 298 K and (5) at 77 K. CNH2 O = 1.05 × 10−3 · kobs − 0.70 −3
CNH2 O = 1.02 × 10
(4)
· kobs − 0.17
(5)
where kobs = 1/ , = luminescence lifetime of the Eu(III) ion.
Results of the Eu(III) luminescence lifetime, , measured for the Eu(III)/picNO system and the number of water molecules, CNH2 O , are presented in Table 2. The measured Eu(III) luminescence lifetimes and, corresponding to them, the hydration numbers: 110.3 s (9 H2 O), 145.6 s (7 H2 O), 191.3 s (5 H2 O), and 317.2 s (3 H2 O), indicated that the following complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , and [EuL3 (H2 O)3 ] at room temperature. The luminescence lifetimes and hydration numbers measured in a frozen state were: 116.3 s (9 H2 O), 148.6 s (7 H2 O), 206.4 s (5 H2 O), 326.8 s (3 H2 O), and 792.9 s (1 H2 O), and indicating the complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , [EuL3 (H2 O)3 ], and [EuL4 (H2 O)]− . The Eu(III) ion in the system under study has the coordination number (CNT ) 9. All complexes are highly isomorphous; they crystallize in the same orthorhombic space group Pbcn, and the unit-cell dimensions are similar for 1–7. Moreover, the positions of the atoms in the unit cells are almost identical in all the complexes, so also the geometry of the complexes and their crystal packing is virtually identical. Therefore, we will discuss in detail the crystal structure of one complex (Eu(III), 3. All the observations and structure details can be directly transformed to all other complexes. The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the europium(III) ion as an ionic bidentate chelate. Six-membered chelate rings are formed with the bite angles of ca. 70.5◦ . The rele-
Table 3 Selected geometrical parameters (Å, ◦ ) 1(Pr) M-O22A M-O22B M-O1A M-O1B N1A-O1A N1B-O1B Na1-O1W Na1-O2W Na1-O1Aa Na1-O21Ab Na1-O21B Na1-O21Ba Na2-O1W Na2-O2W Na2-O22Ab A/COO B/COO A/B a b
2.419(4) 2.372(5) 2.476(4) 2.440(5) 1.348(7) 1.329(7) 2.373(6) 2.332(6) 2.332(5) 2.390(5) 2.410(5) 2.829(5) 2.481(5) 2.281(5) 2.335(5) 50.2(3) 29.2(4) 38.2(2)
Symmetry codes: 1 − x, 1 − y, −z. Symmetry codes: x, −1 + y, z.
2(Sm) 2.308(7) 2.362(6) 2.384(8) 2.399(7) 1.315(12) 1.360(13) 2.384(10) 2.354(10) 2.424(9) 2.415(10) 2 2.527(10) 2.285(8) 2.362(8)
3(Eu) 2.3612(1) 2.3236(1) 2.4170(1) 2.3907(1) 1.343(2) 1.327(2) 2.369(2) 2.331(2) 2.342(2) 2.389(2) 2.389(2) 2.803(2) 2.477(2) 2.279(2) 2.341(1) 46.80(8) 29.31(12) 37.85(4)
4(Gd) 2.353(3) 2.314(3) 2.407(3) 2.381(3) 1.346(4) 1.330(4) 2.365(4) 2.332(4) 2.344(3) 2.391(3) 2.410(3) 2.805(4) 2.477(3) 2.281(3) 2.343(3) 46.3(2) 29.2(3) 37.56(9)
5(Ho) 2.3221(12) 2.2882(13) 2.3818(13) 2.3607(13) 1.351(2) 1.337(2) 2.373(2) 2.343(2) 2.355(2) 2.399(2) 2.420(2) 2.814(2) 2.480(1) 2.292(2) 2.358(2) 43.75(8) 28.64(12) 37.06(4)
6(Er) 2.301(3) 2.265(3) 2.358(3) 2.333(3) 1.342(4) 1.332(4) 2.360(3) 2.331(3) 2.344(3) 2.389(3) 2.405(3) 2.795(3) 2.464(3) 2.281(3) 2.350(3) 42.8(2) 28.5(3) 37.07(9)
7(Y) 2.311(3) 2.284(3) 2.376(3) 2.346(3) 1.376(4) 2.329(3) 2.375(4) 2.359(4) 2.376(3) 2.424(3) 2.398(3) 2.783(4) 2.514(4) 2.359(4) 2.367(3) 43.6(2) 29.5(3) 37.12(10)
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Fig. 4. The coordination of Eu(III) cation; thermal ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres of arbitrary radii. The atoms without labels are symmetry related with the labeled ones (symmetry code: −x + 1, y, −z + 1/2).
Fig. 5. A fragment of a chain built by sodium cations; the ellipsoids are drawn at 50% probability level.
vant geometrical parameters (for all complexes) are listed in Table 3. The bond lengths and angles are generally typical, with characteristic elongation of the N O bond as a result of the coordination, and – caused by the same reason – the different values of C O bonds within the carboxylate group. The complex is symmetrical;
Fig. 6. Coordination polyhedra representation of a network made by metal cations.
the Eu(III) ion and one of the Na(I) ions lie on the two-fold axis along y. The Eu(III) ion is eight-coordinated (cf. Fig. 4), while both Na(I) ions are six-coordinated. Probably in order to accommodate such a symmetrical arrangement of ligands, the coordination of the
Fig. 7. Crystal packing as seen approximately along [0 0 1] direction. Hydrogen bonds are depicted as dashed lines.
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S. Lis et al. / Materials Chemistry and Physics 114 (2009) 134–138
chelate rings is different: the molecule B is much more planar than in A (maximum deviation from the least-squares plane is 0.14 Å in the ligand B, but almost 0.5 Å in the ligand A). This stress is also transferred into the rings: maximum deviation from the pyridine ring plane in A is 0.017(1) Å while in B is 0.009(1) Å; the carboxylate groups are twisted with respect to the ring planes by 46.80(8)◦ in A and by 29.31(13)◦ in B (cf. Table 3). Additionally, the stability of the complex might be enhanced by weak – interactions between ligands A and B; the distance between the rings is ca. 3.4 Å while the inclination angle is 17.8◦ . There are some examples of lanthanide–sodium polynuclear complexes, but usually there are one-dimensional chains of alternating Ln and Na complexes (e.g. [20–22]). The present structure is actually polymeric, it is an example of a two-dimensional structure (Fig. 6). For one of the sodium ions, Na1, one of the Na–O distances is longer than the remaining one; however it seems to be six-coordinated anyway. The coordination polyhedra of Na ions are close to edge-sharing octahedrons (Fig. 5), while those of the Eu(III) ions (c.n. 8) are close to square-antiprisms. In the crystal structure, the Na polyhedra are arranged into the infinite edge-sharing chains, and the Eu polyhedra are between these chains, sharing one edge with one chain and two corners with another one (Fig. 6). This structure is filled by the perchlorate counterions that are connected by hydrogen bonds with water molecules additional hydrogen bonds are strengthening the structure (Table 3, Fig. 7). 4. Conclusions Luminescence studies of Eu(III) (lifetime measurements and analysis of excitation spectra of the 5 D0 → 7 F0 transition at room and liquid-nitrogen temperatures), indicated in the Eu(III)/picNO system an existence of various nine-coordinated europium species. At room temperature the following species: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ , [EuL2 (H2 O)5 ]+ , and [EuL3 (H2 O)3 ] were found, while in a frozen state the complex forms: [Eu(H2 O)9 ]3+ , [EuL(H2 O)7 ]2+ ,
[EuL2 (H2 O)5 ]+ , [EuL3 (H2 O)3 ], and [EuL4 (H2 O)]− were identified. Synthesized complex characterized by X-ray crystallography showed that [Eu(C6 H4 NO3 )4 Na3 (H2 O)4 ]2+ · 2ClO4 − is symmetrical with eight-coordinated Eu(III) ions. In the crystal the complex molecules build the two-dimensional structures with additional Na+ cations and water molecules. This structure consists of edgesharing chains of Na distorted octahedral, interconnected by Eu polyhedra. References [1] G.F. de Sa, O.L. Malta, C. de Mello Donega, A.M. Simas, R.L. Longo, P.A. SantaCruz, E.F. da Silva Jr., Coord. Chem. Rev. 196 (2000) 165. [2] C.C.F. Nunez, K. Zinner, L.B. Zinner, C.C. Calvarho, J. Zukerman-Schpector, G. Vicentini, Inorg. Chim. Acta 293 (1999) 249. [3] H. Yoneda, G.R. Choppin, J.L. Bear, A.J. Graffeo, Inorg. Chem. 4 (1965) 244. [4] S. Lis, Z. Hnatejko, P. Barczynski, M. Elbanowski, J. Alloys Compd. 341 (2002) 45. [5] H.-J. Zhang, G. Li, L. Yan, R.-D. Yang, J. Luminescence 127 (2007) 316. [6] G. Meinrath, S. Lis, U. Böhme, J. Alloys Compd. 408–412 (2006) 962. [7] J.-G. Mao, H.-J. Zhang, J.-Z. Ni, S.-B. Wang, T.C.W. Mak, Polyhedron 17 (1998) 3999. [8] L. Yan, J. Liu, X. Wang, R. Yang, F. Song, Polyhedron 14 (1995) 3545. [9] S. Lis, Z. Wang, G.R. Choppin, Inorg. Chim. Acta 239 (1995) 139. [10] S. Lis, J. Alloys Compd. 341 (2002) 45. [11] S. Lis, Z. Hnatejko, Z. Stryla, Opt. Appl. 31 (2001) 643. [12] CrysAlis CCD, Oxford Diffraction Ltd., Version 1.171.31.5 (release August 28, 2006 CrysAlis171.NET). [13] CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.31.5 (release August 28, 2006 CrysAlis171.NET), 1990. [14] G.M. Sheldrick, Acta Cryst. A46 (199) 467. [15] G.M. Sheldrick, SHELXL97. Program For the Refinement of Crystal Structures, University of Göttingen, Germany, 1997. [16] G.R. Choppin, Z.M. Wang, Inorg. Chem. 36 (1997) 249. [17] M. Albin, W.D. Horrocks Jr., Inorg. Chem. 24 (1985) 895. [18] P.P. Barthelemey, G.R. Choppin, Inorg. Chem. 23 (1989) 2044. [19] T. Kimura, Y. Kato, J. Alloys Compd. 278 (1998) 92. [20] C. Tedeschi, J. Azema, H. Gornitzka, P. Tisnes, C. Picard, Dalton Trans. (2003) 1738. [21] J.-P. Costes, F. Dahan, F. Nicodeme, Inorg. Chem. 42 (2003) 6556. [22] A.S. Gajadhar-Plummer, I.A. Kahwa, A.J.P. White, D.J. Williams, Inorg. Chem. 38 (1999) 1745.