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Near-infrared luminescence of Yb3+, Nd3+ and Er3+ in complexes with organic dyes
Journal of Alloys and Compounds 374 (2004) 311–314
Near-infrared luminescence of Yb3+, Nd3+ and Er3+ in complexes with organic dyes Yu. Korovin∗ , N. Rusakova A.V. Bogatsky Physico-Chemical Institute, Odessa 65080, Ukraine
Abstract Spectral-luminescence characteristics of Ln3+ ions, emitting in the near-infrared (IR) spectral region, in solutions of their complexes with some organic ligands (dyes) have been considered. Complexes can be excited with visible light (λexc = 532 nm). 4f-Luminescence as a result of energy transfer from the dye moiety to the lanthanide ion has been shown. The luminescence is higher with complexes of macrocyclic polydentate ligands as compared with their acyclic analogues due to less content of water molecules in the coordination center. © 2003 Elsevier B.V. All rights reserved. Keywords: Lanthanides; Luminescence; Organic ligands
1. Introduction It is known that there are a large number of organic ligands in complexes with which the luminescence of Ln3+ ions in the near-infrared (IR) spectral region is observed. For example, there are fluorinated -diketones [1,2], 1,4,7,10-tetraazacyclododecane and m-terphenyl derivatives [3,4], calix [4] arenes [5,6], and porphyrins [7,8]. However to obtain a high 4f-luminescence characteristics it is necessary to eliminate the nonradiative losses through the creation of proper composition of coordination center of complexes. The main requirements to ligand complexes featured by high IR-luminescence of Ln3+ (first of all, Yb3+ , Nd3+ , and Er3+ ) are the following: high denticity, triplet (T) levels position is no less than 12 500–13 500 cm−1 , high light absorption at the wavelength of excitation, possibility of ligands functionalization by chromophoric aromatic groups as well as by additional coordination-active ones. But these requirements are not sufficient. A high luminescence can be obtained when certain organic ligand meets all above mentioned requirements. Undoubtedly, polydentate macrocyclic ligands are promising components of corresponding complexes. In this work the comparative study of the luminescence properties of complexes with some of organic ∗ Corresponding author. Tel.: +38-482-652-038; fax: +38-482-652-012. E-mail address: [email protected] (Yu. Korovin).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.11.097
dyes-1-phenylazo-2-naphtol (PAN), xylenol blue (XB), phthalexone S (PS) and their macrocyclic derivatives L1 –L3 (Fig. 1) are given.
2. Experimental Solutions of Ln3+ nitrates were obtained by dissolving appropriate amounts of lanthanide oxides of spectral purity (99.98%). All chemicals and solvents were purchased from Aldrich and used as received. The details about preparation of ligands L1 –L3 are known [9,10]. The lanthanide complexes were prepared by the interaction of their hydrated nitrates and aqueous solutions of ligands as described previously [10,11]. All complexes were isolated in the solid state and characterized by elemental analysis, IR-, UV- and luminescence-spectroscopy. All luminescence measurements were made with a SDL-1 spectrofluorimeter (LOMO Association, St. Petersburg, Russia) with a Nd:YAG laser (λexc = 532 nm) as the excitation source. The position of ligand triplet levels was obtained from phosphorescence spectra of ligands in complexes with gadolinium at 77 K. The relative quantum yields of 4f-luminescence (ϕ) of the Yb3+ and Nd3+ ions in the complexes (a methanolic solution of Zn-tetraphenylporphyrin as a standard, ϕ = 0.0315) and the luminescence lifetime (τ) (a LGI-21 nitrogen laser was the excitation source, λmax = 337 nm, pulse duration 10 ns) were determined using a published procedure [10].
312
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314 O H3C
CH3
O
OH
O O N O
N
O
O
H3C
O
HO
O
O O
CH3
L2
L1
O
OH
OH
O
HO
O
N
N N
N O
N
N
O
N
N
HO
SO3H
OH O
O OH
HO
L3 Fig. 1. Structures of the macrocyclic ligands L1 –L3 .
3. Results and discussion Data of elemental analysis and FAB+ mass spectra (m-nitrobenzyl alcohol matrix) prove that complexes with the ratio Ln:ligand = 1:1 are formed. But the ratio 2:1 was obtained only for the complexes with ligands PS and L3 . There are two macrocyclic fragments 1,4,7,10-tetraaza-cyclododecane-1,4,7-triacetic acid (DO3A) in ligand L3 to the contrast of two iminodiacetate groups in ligand PS. The typical changes in the IR spectra of Ln–L1 and Ln–L2 complexes are rather similar to those ones for the complexes with benzo-15-crown-5 [12,13]. This fact suggests the coordination of the Ln3+ ions to five oxygen atoms of the macrocycle and O-atoms of bidentate NO3 - groups. It is noteworthy that the IR spectra of the complexes with ligands L1 and L2 have no absorption in the region from 3350 to 3300 cm−1 (typical for water molecules in the inner coordination sphere). Data on the luminescence measurements prove this conclusion. It is supposed that in the case of ligand L1 lanthanide ion can coordinate with the oxygen atom of the inaphthol group and with the nitrogen atom of the diazo group. However, by analogy to the lanthanide-PAN complex such the coordination can occur only at pH > 6. We have established that each of two lanthanide ions is coordinated by four nitrogen atoms of azacycle and three oxygen atoms of carboxylic groups in complexes with ligand L3 . These complexes contain two innersphere waters (total four molecules in the complex). All complexes are stable for several days in solutions at room temperature. It is proved by the absence of changes in the absorption spectra with broad maxima (Fig. 2). The almost complete coincidence of the excitation and absorption spectra of the Ln-complexes indicates that the excitation en-
ergy is transferred from the organic moiety of the complex molecule to the radiative levels of the lanthanides due to the intramolecular mechanism of transfer. The positions of the T-levels are equal to 16 270, 15 850, and 14 205 cm−1 for ligands L1 , L2 , and L3 , respectively. The molecular luminescence of the ligands (λexc = 365 nm) characterized by the broad diffuse bands in the regions of 490–555 nm (L1 ), 475–560 nm (L2 ), and 480–550 nm (L3 ) is completely quenched in the complexes, i.e. the efficiency of the intramolecular transfer of the excitation energy is high. All complexes exhibit the 4f-luminescence of the Yb3+ (λmax = 980 nm, 2 F5/2 → 2 F7/2 transition) and Nd3+ ions (λmax = 880, 1060, and 1340 nm, 4 F3/2 → 4 I9/2 , 4 F3/2 → 4I 4 4 11/2 , and F3/2 → I13/2 transitions, respectively) (Fig. 3). Some data on the 4f-luminescence are given in the Table 1. As it is seen from the Table the quantum yield and lifetime of luminescence are higher for the Yb-complexes as compared
Fig. 2. Absorption spectra of an aqueous solution (2.5 × 10−4 M, pH 6) of (1) Yb–L1 ; (2) Yb–L2 ; (3) Nd–L1 ; and (4) Nd–L2 .
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314
313
Fig. 4. Emission spectrum of DMSO-d6 solution (5.0 × 10−4 M) of Er–L3 at 295 K, λexc = 532 nm. Fig. 3. Emission spectra of an aqueous solutions (2.5 × 10−4 M, pH 6) of (1) Yb–L1 ; (2) Yb–L2 ; (3) Nd–L1 ; and (4) Nd–L2 at 295 K, λexc = 532 nm.
with Nd-complexes as well as for the ytterbium complexes with other macrocyclic ligands [14]. At the comparison of luminescence characteristics in complexes matches (Ln-PAN and Ln–L1 ), (Ln-XB and Ln–L2 ), (Ln-PS and Ln–L3 ) was founded that these characteristics are higher in 3–8 times in complexes with macrocyclic ligands due to coordination centers of complexes with macrocyclic ligands L1 –L3 contain less amount of water molecules (q), namely: q = 2 (Ln-PAN), q = 3 (Ln-XB, Ln-PS), and q = 0 (Ln–L1 , Ln–L2 ), q = 2 (Ln–L3 ). Taking into account that the luminescence of Yb3+ and Nd3+ ions in the complexes with PAN, XB, PS (benzo-15-crown-5 and DO3A were reported as well [15,16]) is relatively low, one can suggest that the molecules of polydentate macrocyclic ligands L1 –L3 have the dual function: (1) the macrocyclic moiety shields the complex-forming ion from O–H- and C–H-oscillators of the solvent molecules; (2) these ligands behave as absorbing groups suitable for an efficient antenna effect. It should be noted that 4f-luminescence of Er3+ which a wide band (maximum at 1535 nm, 4 I13/2 → 4 I15/2 transition) (Fig. 4) was registered only in case of DMSO-d6 solution of complexes with L3 (absorption maximum at 550 nm)
from all complexes investigated by us. The obtained value τ (1.8 s) is in the series of the higher ones for Er3+ [17,18].
4. Conclusion These obtained results demonstrated clearly that, firstly, high characteristics of luminescence of ions emitting in the near IR spectral region can be obtained in complexes with the macrocyclic ligands; secondly, these characteristics are higher than in complexes with their acyclic analogs. On the other hand, it is rather complicated to predict obtaining of new complexes (with acyclic and macrocyclic ligands as well), where luminescence of Yb3+ and Nd3+ will be substantially higher as compared to the known for now. Thus, above data give new opportunity to study the spectral-luminescence properties of Yb3+ , Nd3+ , and Er3+ in solutions. It could be useful for practical application as well.
Acknowledgements This work was partly supported by the National Academy of Sciences of Ukraine, project No. 261/2002.
References Table 1 Some luminescent characteristicsa of the ytterbium and neodymium complexes with acyclic and macrocyclic dyes at 295 K (λexc = 532 nm) Ligand
PAN XB PS L1 L2 L3
Yb-complexb
Nd-complexb
ϕ × 103
τ (s)
ϕ × 103
τ ()
1.2 1.1 4.1 6.6 8.8 14.5
0.7 0.6 3.2 3.8 4.2 12.6
– – 0.7 0.9 1.2 2.3
– – 0.4 0.8 0.9 1.5
a Errors in measurement of luminescence lifetime are ±15%, while for the luminescence quantum yield, errors are ±20%. b Solutions in D O. 2
[1] Y. Hasegawa, K. Murakoshi, Y. Wada, S. Yanagida, J.-H. Kim, N. Nakashima, T. Yamanaka, Chem. Phys. Lett. 248 (1996) 8. [2] S. Meshkova, J. Fluoresc. 10 (2000) 333. [3] D. Parker, Coord. Chem. Rev. 205 (2000) 109. [4] M.P. Oude Wolbers, F.C.J.M. van Veggel, B.H.M. Snellink-Ruël, J.W. Hofstraat, F.A.J. Geurts, D.N. Reinhoudt, J. Chem. Soc., Perkin Trans. 2 (1998) 2141. [5] J.W. Hofstraat, M.P. Oude Wolbers, F.C.J.M. van Veggel, D.N. Reinhoudt, M.H.V. Werts, J.W. Verhoeven, J. Fluores. 8 (1998) 301. [6] S. Shevchuk, N. Rusakova, A. Turianskaya, Yu. Korovin, N. Nazarenko, A. Gren, As. J. Spectrosc. 3 (1999) 155. [7] M. Tsvirko, G. Stelmakh, V. Pyatosin, K. Solovyov, T. Kachura, A. Piskarskas, R. Gadonas, Chem. Phys. 106 (1986) 467. [8] Yu. Korovin, Z. Zhilina, N. Rusakova, V. Kuz’min, S. Vodzinsky, Yu. Ishkov, J. Porphyrins Phthalocyanines 5 (2001) 217.
314
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314
[9] T. Yamashita, H. Nakamura, M. Takagi, K. Ueno, Bull. Chem. Soc. Jpn. 53 (1980) 1550. [10] Yu. Korovin, N. Rusakova, J. Fluores. 12 (2002) 159. [11] Yu. Korovin, N. Rusakova, Yu. Popkov, Russ. Chem. Bull. Int. Ed. 51 (2002) 2303. [12] J.-C.G. Bunzli, B. Klein, G. Chapuis, K.J. Schenk, Inorg. Chem. 21 (1982) 808. [13] C.-M. Yin, Y.-H. Kong, Z.-R. Liu, C.-Y. Wu, D.-H. Ren, M.-A. He, H.-F. Xue, J. Therm. Anal. 35 (1989) 2471. [14] Yu. Korovin, N. Rusakova, Rev. Inorg. Chem. 21 (2001) 299.
[15] T. Yamamura, W. Sugiyama, H. Hotokezaka, M. Harada, H. Tomiyasu, Y. Nakamura, Inorg. Chim. Acta 320 (2001) 75. [16] A. Beeby, I.A. Clarkson, R.S. Dickins, S. Faulkner, D. Parker, L. Royle, A.S. de Sousa, J.A. Gareth Williams, M. Woods, J. Chem. Soc., Perkin Trans. 2 (1999) 493. [17] M.P. Oude Wolbers, F.C.J.M. van Veggel, F.G.A. Peters, E.S.E. van Beelen, J.W. Hofstraat, F.A.J. Geurts, D.N. Reinhoudt, Chem. Eur. J. 4 (1998) 772. [18] M.H.V. Werts, J.W. Hofstraat, F.A.J. Geurts, J.W. Verhoeven, Chem. Phys. Lett. 276 (1997) 196.
Near-infrared luminescence of Yb3+, Nd3+ and Er3+ in complexes with organic dyes Yu. Korovin∗ , N. Rusakova A.V. Bogatsky Physico-Chemical Institute, Odessa 65080, Ukraine
Abstract Spectral-luminescence characteristics of Ln3+ ions, emitting in the near-infrared (IR) spectral region, in solutions of their complexes with some organic ligands (dyes) have been considered. Complexes can be excited with visible light (λexc = 532 nm). 4f-Luminescence as a result of energy transfer from the dye moiety to the lanthanide ion has been shown. The luminescence is higher with complexes of macrocyclic polydentate ligands as compared with their acyclic analogues due to less content of water molecules in the coordination center. © 2003 Elsevier B.V. All rights reserved. Keywords: Lanthanides; Luminescence; Organic ligands
1. Introduction It is known that there are a large number of organic ligands in complexes with which the luminescence of Ln3+ ions in the near-infrared (IR) spectral region is observed. For example, there are fluorinated -diketones [1,2], 1,4,7,10-tetraazacyclododecane and m-terphenyl derivatives [3,4], calix [4] arenes [5,6], and porphyrins [7,8]. However to obtain a high 4f-luminescence characteristics it is necessary to eliminate the nonradiative losses through the creation of proper composition of coordination center of complexes. The main requirements to ligand complexes featured by high IR-luminescence of Ln3+ (first of all, Yb3+ , Nd3+ , and Er3+ ) are the following: high denticity, triplet (T) levels position is no less than 12 500–13 500 cm−1 , high light absorption at the wavelength of excitation, possibility of ligands functionalization by chromophoric aromatic groups as well as by additional coordination-active ones. But these requirements are not sufficient. A high luminescence can be obtained when certain organic ligand meets all above mentioned requirements. Undoubtedly, polydentate macrocyclic ligands are promising components of corresponding complexes. In this work the comparative study of the luminescence properties of complexes with some of organic ∗ Corresponding author. Tel.: +38-482-652-038; fax: +38-482-652-012. E-mail address: [email protected] (Yu. Korovin).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.11.097
dyes-1-phenylazo-2-naphtol (PAN), xylenol blue (XB), phthalexone S (PS) and their macrocyclic derivatives L1 –L3 (Fig. 1) are given.
2. Experimental Solutions of Ln3+ nitrates were obtained by dissolving appropriate amounts of lanthanide oxides of spectral purity (99.98%). All chemicals and solvents were purchased from Aldrich and used as received. The details about preparation of ligands L1 –L3 are known [9,10]. The lanthanide complexes were prepared by the interaction of their hydrated nitrates and aqueous solutions of ligands as described previously [10,11]. All complexes were isolated in the solid state and characterized by elemental analysis, IR-, UV- and luminescence-spectroscopy. All luminescence measurements were made with a SDL-1 spectrofluorimeter (LOMO Association, St. Petersburg, Russia) with a Nd:YAG laser (λexc = 532 nm) as the excitation source. The position of ligand triplet levels was obtained from phosphorescence spectra of ligands in complexes with gadolinium at 77 K. The relative quantum yields of 4f-luminescence (ϕ) of the Yb3+ and Nd3+ ions in the complexes (a methanolic solution of Zn-tetraphenylporphyrin as a standard, ϕ = 0.0315) and the luminescence lifetime (τ) (a LGI-21 nitrogen laser was the excitation source, λmax = 337 nm, pulse duration 10 ns) were determined using a published procedure [10].
312
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314 O H3C
CH3
O
OH
O O N O
N
O
O
H3C
O
HO
O
O O
CH3
L2
L1
O
OH
OH
O
HO
O
N
N N
N O
N
N
O
N
N
HO
SO3H
OH O
O OH
HO
L3 Fig. 1. Structures of the macrocyclic ligands L1 –L3 .
3. Results and discussion Data of elemental analysis and FAB+ mass spectra (m-nitrobenzyl alcohol matrix) prove that complexes with the ratio Ln:ligand = 1:1 are formed. But the ratio 2:1 was obtained only for the complexes with ligands PS and L3 . There are two macrocyclic fragments 1,4,7,10-tetraaza-cyclododecane-1,4,7-triacetic acid (DO3A) in ligand L3 to the contrast of two iminodiacetate groups in ligand PS. The typical changes in the IR spectra of Ln–L1 and Ln–L2 complexes are rather similar to those ones for the complexes with benzo-15-crown-5 [12,13]. This fact suggests the coordination of the Ln3+ ions to five oxygen atoms of the macrocycle and O-atoms of bidentate NO3 - groups. It is noteworthy that the IR spectra of the complexes with ligands L1 and L2 have no absorption in the region from 3350 to 3300 cm−1 (typical for water molecules in the inner coordination sphere). Data on the luminescence measurements prove this conclusion. It is supposed that in the case of ligand L1 lanthanide ion can coordinate with the oxygen atom of the inaphthol group and with the nitrogen atom of the diazo group. However, by analogy to the lanthanide-PAN complex such the coordination can occur only at pH > 6. We have established that each of two lanthanide ions is coordinated by four nitrogen atoms of azacycle and three oxygen atoms of carboxylic groups in complexes with ligand L3 . These complexes contain two innersphere waters (total four molecules in the complex). All complexes are stable for several days in solutions at room temperature. It is proved by the absence of changes in the absorption spectra with broad maxima (Fig. 2). The almost complete coincidence of the excitation and absorption spectra of the Ln-complexes indicates that the excitation en-
ergy is transferred from the organic moiety of the complex molecule to the radiative levels of the lanthanides due to the intramolecular mechanism of transfer. The positions of the T-levels are equal to 16 270, 15 850, and 14 205 cm−1 for ligands L1 , L2 , and L3 , respectively. The molecular luminescence of the ligands (λexc = 365 nm) characterized by the broad diffuse bands in the regions of 490–555 nm (L1 ), 475–560 nm (L2 ), and 480–550 nm (L3 ) is completely quenched in the complexes, i.e. the efficiency of the intramolecular transfer of the excitation energy is high. All complexes exhibit the 4f-luminescence of the Yb3+ (λmax = 980 nm, 2 F5/2 → 2 F7/2 transition) and Nd3+ ions (λmax = 880, 1060, and 1340 nm, 4 F3/2 → 4 I9/2 , 4 F3/2 → 4I 4 4 11/2 , and F3/2 → I13/2 transitions, respectively) (Fig. 3). Some data on the 4f-luminescence are given in the Table 1. As it is seen from the Table the quantum yield and lifetime of luminescence are higher for the Yb-complexes as compared
Fig. 2. Absorption spectra of an aqueous solution (2.5 × 10−4 M, pH 6) of (1) Yb–L1 ; (2) Yb–L2 ; (3) Nd–L1 ; and (4) Nd–L2 .
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314
313
Fig. 4. Emission spectrum of DMSO-d6 solution (5.0 × 10−4 M) of Er–L3 at 295 K, λexc = 532 nm. Fig. 3. Emission spectra of an aqueous solutions (2.5 × 10−4 M, pH 6) of (1) Yb–L1 ; (2) Yb–L2 ; (3) Nd–L1 ; and (4) Nd–L2 at 295 K, λexc = 532 nm.
with Nd-complexes as well as for the ytterbium complexes with other macrocyclic ligands [14]. At the comparison of luminescence characteristics in complexes matches (Ln-PAN and Ln–L1 ), (Ln-XB and Ln–L2 ), (Ln-PS and Ln–L3 ) was founded that these characteristics are higher in 3–8 times in complexes with macrocyclic ligands due to coordination centers of complexes with macrocyclic ligands L1 –L3 contain less amount of water molecules (q), namely: q = 2 (Ln-PAN), q = 3 (Ln-XB, Ln-PS), and q = 0 (Ln–L1 , Ln–L2 ), q = 2 (Ln–L3 ). Taking into account that the luminescence of Yb3+ and Nd3+ ions in the complexes with PAN, XB, PS (benzo-15-crown-5 and DO3A were reported as well [15,16]) is relatively low, one can suggest that the molecules of polydentate macrocyclic ligands L1 –L3 have the dual function: (1) the macrocyclic moiety shields the complex-forming ion from O–H- and C–H-oscillators of the solvent molecules; (2) these ligands behave as absorbing groups suitable for an efficient antenna effect. It should be noted that 4f-luminescence of Er3+ which a wide band (maximum at 1535 nm, 4 I13/2 → 4 I15/2 transition) (Fig. 4) was registered only in case of DMSO-d6 solution of complexes with L3 (absorption maximum at 550 nm)
from all complexes investigated by us. The obtained value τ (1.8 s) is in the series of the higher ones for Er3+ [17,18].
4. Conclusion These obtained results demonstrated clearly that, firstly, high characteristics of luminescence of ions emitting in the near IR spectral region can be obtained in complexes with the macrocyclic ligands; secondly, these characteristics are higher than in complexes with their acyclic analogs. On the other hand, it is rather complicated to predict obtaining of new complexes (with acyclic and macrocyclic ligands as well), where luminescence of Yb3+ and Nd3+ will be substantially higher as compared to the known for now. Thus, above data give new opportunity to study the spectral-luminescence properties of Yb3+ , Nd3+ , and Er3+ in solutions. It could be useful for practical application as well.
Acknowledgements This work was partly supported by the National Academy of Sciences of Ukraine, project No. 261/2002.
References Table 1 Some luminescent characteristicsa of the ytterbium and neodymium complexes with acyclic and macrocyclic dyes at 295 K (λexc = 532 nm) Ligand
PAN XB PS L1 L2 L3
Yb-complexb
Nd-complexb
ϕ × 103
τ (s)
ϕ × 103
τ ()
1.2 1.1 4.1 6.6 8.8 14.5
0.7 0.6 3.2 3.8 4.2 12.6
– – 0.7 0.9 1.2 2.3
– – 0.4 0.8 0.9 1.5
a Errors in measurement of luminescence lifetime are ±15%, while for the luminescence quantum yield, errors are ±20%. b Solutions in D O. 2
[1] Y. Hasegawa, K. Murakoshi, Y. Wada, S. Yanagida, J.-H. Kim, N. Nakashima, T. Yamanaka, Chem. Phys. Lett. 248 (1996) 8. [2] S. Meshkova, J. Fluoresc. 10 (2000) 333. [3] D. Parker, Coord. Chem. Rev. 205 (2000) 109. [4] M.P. Oude Wolbers, F.C.J.M. van Veggel, B.H.M. Snellink-Ruël, J.W. Hofstraat, F.A.J. Geurts, D.N. Reinhoudt, J. Chem. Soc., Perkin Trans. 2 (1998) 2141. [5] J.W. Hofstraat, M.P. Oude Wolbers, F.C.J.M. van Veggel, D.N. Reinhoudt, M.H.V. Werts, J.W. Verhoeven, J. Fluores. 8 (1998) 301. [6] S. Shevchuk, N. Rusakova, A. Turianskaya, Yu. Korovin, N. Nazarenko, A. Gren, As. J. Spectrosc. 3 (1999) 155. [7] M. Tsvirko, G. Stelmakh, V. Pyatosin, K. Solovyov, T. Kachura, A. Piskarskas, R. Gadonas, Chem. Phys. 106 (1986) 467. [8] Yu. Korovin, Z. Zhilina, N. Rusakova, V. Kuz’min, S. Vodzinsky, Yu. Ishkov, J. Porphyrins Phthalocyanines 5 (2001) 217.
314
Yu. Korovin, N. Rusakova / Journal of Alloys and Compounds 374 (2004) 311–314
[9] T. Yamashita, H. Nakamura, M. Takagi, K. Ueno, Bull. Chem. Soc. Jpn. 53 (1980) 1550. [10] Yu. Korovin, N. Rusakova, J. Fluores. 12 (2002) 159. [11] Yu. Korovin, N. Rusakova, Yu. Popkov, Russ. Chem. Bull. Int. Ed. 51 (2002) 2303. [12] J.-C.G. Bunzli, B. Klein, G. Chapuis, K.J. Schenk, Inorg. Chem. 21 (1982) 808. [13] C.-M. Yin, Y.-H. Kong, Z.-R. Liu, C.-Y. Wu, D.-H. Ren, M.-A. He, H.-F. Xue, J. Therm. Anal. 35 (1989) 2471. [14] Yu. Korovin, N. Rusakova, Rev. Inorg. Chem. 21 (2001) 299.
[15] T. Yamamura, W. Sugiyama, H. Hotokezaka, M. Harada, H. Tomiyasu, Y. Nakamura, Inorg. Chim. Acta 320 (2001) 75. [16] A. Beeby, I.A. Clarkson, R.S. Dickins, S. Faulkner, D. Parker, L. Royle, A.S. de Sousa, J.A. Gareth Williams, M. Woods, J. Chem. Soc., Perkin Trans. 2 (1999) 493. [17] M.P. Oude Wolbers, F.C.J.M. van Veggel, F.G.A. Peters, E.S.E. van Beelen, J.W. Hofstraat, F.A.J. Geurts, D.N. Reinhoudt, Chem. Eur. J. 4 (1998) 772. [18] M.H.V. Werts, J.W. Hofstraat, F.A.J. Geurts, J.W. Verhoeven, Chem. Phys. Lett. 276 (1997) 196.