A. A. Tripolskaya, E. A. Mainicheva, T. V. Mit'kina, O. A. Geras'ko,. D. Yu. Naumov, and V. P. Fedin. Institute of Inorganic Chemistry, Siberian Division, Russian ...
Russian Journal of Coordination Chemistry, Vol. 31, No. 11, 2005, pp. 768–774. Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 11, 2005, pp. 810–817. Original Russian Text Copyright © 2005 by Tripolskaya, Mainicheva, Mit’kina, Geras’ko, Naumov, Fedin.
Sc(III), Eu(III), and Gd(III) Complexes with Macrocyclic Cavitand Cucurbit[6]uril: Synthesis and Crystal Structures A. A. Tripolskaya, E. A. Mainicheva, T. V. Mit’kina, O. A. Geras’ko, D. Yu. Naumov, and V. P. Fedin Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences, pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia Received February 16, 2005
Abstract—Slow evaporation of solutions of Sc and Eu nitrates with macrocyclic cavitand cucurbit[6]uril gives crystals of isostructural complexes [Sc(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 8.5H2O (space group Pna21, a = 32.0065(18) Å, b = 14.7904(8) Å, c = 11.5774(6) Å, V = 5480.6(5) Å3, Z = 4) and [Eu(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 6.75H2O (space group Pna21, a = 31.9525(17) Å, b = 14.7203(8) Å, c = 11.8592(6) Å, V = 5578.0(5) Å3, Z = 4). The metal to ligand ratio in these complexes is 1 : 1; the complexes are obtained at 0.025–0.1 mol/l concentrations of the metals in solutions. With higher lanthanide concentrations (0.7–1 mol/l), the 2 : 1 complex with cucurbit[6]uril is formed of the composition [{Gd(NO3)(H2O)5}2(C36H36N24O12)](NO3)4 · 6.5H2O (space group P 1 , a = 13.3972(6) Å, b = 14.4994(5) Å, c = 18.3290(8) Å, α = 73.5610(10)°, β = 87.2590(10)°, γ = 87.5540(10)°, V = 3409.4(2) Å3, Z = 2) and isotypical complex [{Gd(NO3)(H2O)5}2{(ë5H5N) ⊂ (C36H36N24O12)}](NO3)4 · 8H2O with a pyridine molecule inside the cucurbit[6]uril cavity (space group P21/n, a = 14.8263(6) Å, b = 13.3688(7) Å, c = 18.5970(9) Å, β = 107.5860(10)°, V = 3513.8(3) Å3, Z = 2). According to X-ray diffraction data, the metal atoms of the title complexes coordinate the O atoms in portals of cucurbit[6]uril molecules.
The studies performed in recent years showed that organic macrocyclic cavitand cucurbit[6]uril (C36H36N24O12), which consists of six glycoluryl fragments bonded by methylene bridges, can form complexes with some oxophillic metals due to its 12 polarized carbonyl groups and act as polydentate ligand [1– 7]. cucurbit[6]uril was found to be efficient as a polydentate ligand used in isolation of the kinetically labile lanthanide(III) complexes from aqueous solutions [8– 10]. The lanthanide complexes are known to show interesting spectral and magnetic properties. Different compounds of rare-earth metals are widely used as luminescence marks in biology or medicine [11]. In aqueous solutions, cations of f elements form aqua complexes with different coordination numbers and coordination surrounding of a metal. Such complexes are kinetically labile, and therefore, their separation from aqueous solutions into a solid phase is difficult. This difficulty can be successfully overcome by making use of the chelate and macrocyclic effects. It is not infrequent that complexation with polydentate N- and O-donor ligands, such as crown ethers or calixarenes, is used in order to separate lanthanide aqua complexes [12, 13]. Data are also available on the separation of aqua complexes of metals, such as yttrium and scandium, in a solid phase using macrocyclic ligands. The following aqua complexes of these metals with crown ethers were synthesized and structurally
[14], characterized: [Y(H2O)8]Cl3(15-crown-5) [Y(NO3)3(H2O)3](15-crown-5) [15], [Sc(NO3)3(H2O)3](18-crown-8) [16], [Sc(NO3)3(H2O)3](benzo-15-crown-5) [17]. In these compounds, aqua complex is united with microcycle by hydrogen bonds between the water molecules and the O atoms of crown ether. The use of cucurbit[6]uril as a polydentate ligand turned efficient. Cucurbit[6]uril is similar to 18-crown-6 in size, but has a higher negative charge on the donor O atoms of portals, which makes its compounds with the metal cations more stable. Previously, we synthesized and studied the structures of its complexes with L‡3+, Ce3+, Sm3+, Gd3+, Ho3+, Yb3+ with the metal : cucurbit[6]uril ratios 1 : 1, 2 : 2, and 2 : 3 [8], where the cucurbit[6]uril molecule is coordinated by the lanthanide cations through the O atoms of portals in bi- or tetradentate mode. The yttrium complex with cucurbit[6]uril (H)2[Y(H2O)8]2(NO3)8(C36H36N24O12) · 13H2O, where aqua complex of yttrium is not bonded with the microcyclic ligand, was synthesized and structurally characterized [18]. The aim of this work was to synthesize and study the crystal structure of new Cs(III), Eu(III), and Gd(III) complexes with cucurbit[6]uril: [Sc(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 8.5H2O (I), [Eu(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 6.75H2O (II),
1070-3284/05/3111-0768 © 2005 Pleiades Publishing, Inc.
Sc(III), Eu(III), AND Gd(III) COMPLEXES
[{Gd(NO3)(H2O)5}2(C36H36N24O12)](NO3)4 · 6.5H2O (III), [{Gd(NO3)(H2O)5}2{(ë5H5N) ⊂ (C36H36N24O12)}](NO3)4 · 8H2O (IV). EXPERIMENTAL Scandium nitrate was prepared by dissolving scandium oxide in concentrated nitric acid with further dilution and crystallization as tetrahydrate [19]. The analytical grade europium oxide and gadolinium nitrate were used as received. Cucurbit[6]uril was synthesized
769
according to an improved procedure [20, 21] from glyoxal, carbamide, and paraform in an acid medium with further recrystallization from hydrochloric acid. Synthesis of I. Cucurbit[6]uril hexahydrate (ë36H36N24O12 · 6H2O) (0.010 g) was added to a solution of Sc(NO3)3 · 4H2O (0.106 g) in 6 ml of water and the mixture was heated to 50°C with vigorous stirring until cucurbit[6]uril dissolved completely. The solution obtained was cooled, filtered, and allowed to stand for slow evaporation in air at room temperature. Colorless
Table 1. Crystallographic parameters and details of data collection and refinement of structures for I and II Value
Parameter Empirical formula Molecular weight Crystal system Space group Unit cell parameters: a, Å b, Å c, Å V, Å3 Z ρ(calcd.), g cm–3 T, K Diffractometer λ, Å 2θmax, deg Crystal size, mm µ, mm–1 Tmin/Tmax Measured reflections Independent reflections Rint Reflections with I > 2σ(I) Refined parameters Restrictions R-factors on I > 2σ(I) R1 wR2 R-factors on all reflections R1 wR2 GOOF on F2 Residual electron density (min/max, e Å–3) RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
I
II
C36H61N27O33.50Sc 1453.08 Orthorhombic Pna21
C36H57.50N27O31.75Eu 1528.55 Orthorhombic Pna21
32.0065(18) 14.7904(8) 11.5774(6) 5480.6(5) 4 1.761 173(2) Bruker Nonius X8Apex CCD area-detector 0.71073 (MoKα) 46.6 0.37 × 0.30 × 0.25 0.265 0.9083/0.9367 23078 7729 0.0473 6669 972 151
31.9525(17) 14.7203(8) 11.8592(6) 5578.0(5) 4 1.820 173(2) Nonius Kappa CCD 0.71073 (MoKα) 46.6 0.36 × 0.33 × 0.20 1.249 0.1300/0.2504 23521 7971 0.0552 6798 908 81
0.0749 0.1882
0.0533 0.1347
0.0814 0.1951 1.047 0.768/–0.675
0.0610 0.1387 1.039 4.935/–0.737
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O
Sc
C
Fig. 1. The cationic complex {[å(NO3)(H2O)4](C36H36N24O12)}2+ (M = Eu, Sc) in structures I and II. Hydrogen bonds are shown in dashed lines. Hydrogen atoms are omitted.
crystals I precipitated from the solution as plates in 3 days. The yield in terms of cucurbit[6]uril was 83%. Synthesis of II. A suspension of Eu(III) oxide (Eu2O3) (0.200 g) in 20 ml of water was prepared. Then, a 3M HNO3 solution was added by drops with vigorous stirring and slight heating until the oxide dissolved almost completely (pH ~5, concentration in terms of the metal 0.028 mol/l). The obtained solution was filtered and cooled. Then cucurbit[6]uril hexahydrate (0.053 g) was added to the solution and the mixture was heated to 40°C with vigorous stirring until cucurbit[6]uril dissolved fully. The solution thus formed was cooled, filtered, and allowed to stay for slow evaporation in air at room temperature. Plates of colorless crystals II precipitated from the solution in 4 days. The yield in terms of cucurbit[6]uril was 79%. IR spectrum of II (ν, cm–1): 3369 s, 3001 w, 2930 w, 1735 s, 1488 s, 1418 s, 1383 s, 1325 s, 1293 w, 1263 w, 1235 s, 1189 s, 1147 m, 1046 w, 1023 w, 988 sh, 964 s, 822 m, 803 s, 756 m, 678 m, 632 m, 457 w. For C36H57.5N27O31.5Eu anal. calcd. (%): C, 28.29; H, 3.79; N, 24.74. Found (%): C, 28.62; H, 3.56; N, 24.87. Synthesis of III. Cucurbit[6]uril hexahydrate (0.005 g), Gd(NO3)3 · 5H2O (0.430 g), and 1 ml of water were placed in a glass tube (concentration in terms of a metal 1.000 mol/l). The sealed tube was heated from room temperature to 120°ë for 5 h, then was kept at 120°ë for 30 h, and slowly cooled to room temperature for 50 h. As a result, colorless crystals of
III were obtained in the form of rectangular parallelepipeds. The yield in terms of cucurbit[6]uril was 70%. Synthesis of IV. Cucurbit[6]uril hexahydrate (0.005 g), Gd(NO3)3 · 5H2O (0.430 g), 1 ml of water, and 20 ml of pyridine were placed in a glass tube (concentration in terms of a metal 1.000 mol/l). The solution became turbid. The sealed tube was heated from room temperature to 120°C for 5 h, then was kept at 120°C for 30 h, and slowly cooled to room temperature for 50 h. As a result, amorphous mass and colorless crystals of IV in the form of skewed parallelepipeds were simultaneously obtained. The amorphous mass (probably, amorphous gadolinium hydroxide) was not studied. Crystals IV were mechanically selected for X-ray diffraction analysis. The yield in terms of cucurbit[6]uril was 72%. X-ray diffraction analysis. The main crystallographic parameters and details of data collection for I, II and III, IV are given Tables 1 and 2, respectively. The structures were solved by the direct method and refined by the full-matrix least-squares method in anisotropic approximation (except for the H and O atoms of disordered water molecules) with SHELX97 program package [22]. The hydrogen atoms of cucurbit[6]uril molecules were geometrically localized and refined in a rigid body approximation. The H atoms of water and pyridine molecules were not localized. For compound IV, all the atoms of pyridine molecule inside the cavity were refined as carbon atoms. The crystallographic data and CIF-files for I–IV deposited with the Cambridge Structural Database is available from the authors.
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Table 2. Crystallographic parameters, details of data collection and refinement of structures III and IV Value
Parameter
III
Empirical formula Molecular weight Crystal system
IV
C36H69N30O46.50Gd2 1980.71 Triclinic
Space group
C41H77Gd2N31O48 2086.84 Monoclinic P21/n
P1
Unit cell parameters: a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z ρ(calcd.), g cm–3 T, K Diffractometer λ, Å 2θmax, deg Crystal size, mm µ, mm–1 Tmin/Tmax Measured reflections Independent reflections Rint Reflections with I > 2σ(I) Refined reflections Restrictions R-factors on I > 2σ(I) R1 wR2 R-factors on all reflections R1 wR2 GOOF on F2 Residual electron density (min/max, e Å–3)
13.3972(6) 14.4994(5) 18.3290(8) 73.5610(10) 87.2590(10) 87.5540(10) 3409.4(2) 2 1.929 150(2) Bruker Nonius X8Apex CCD area-detector 0.71073 (MoKα) 50 0.25 × 0.10 × 0.05 2.062 0.6266/0.9039 22440 13614 0.0252 10258 1036 6
14.8263(6) 13.3688(7) 18.5970(9)
3513.8(3) 2 1.972 150(2) Bruker Nonius X8Apex CCD area-detector 0.71073 (MoKα) 50 0.50 × 0.30 × 0.20 2.008 0.4333/0.6895 21554 6656 0.0489 5960 551 0
0.0378 0.0972
0.0459 0.1207
107.5860(10)
0.0527 0.1021 1.007 1.760/–0.663
0.0508 0.1229 1.079 –0.926/2.543
Table 3. The M–O bond lengths in compounds [Gd(NO3)(C2H5OH)(H2O)3(C36H36N24O12)](NO3)2 · 5.5H2O ([GdQ6]), [Ho(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 7H2O ([HoQ6]), [Yb(NO3)(H2O)4(C36H36N24O12)](NO3)2 · 6H2O ([YbQ6]), I and II Bond
[GdQ6]*
[HoQ6]*
[YbQ6]*
I
II
M–O (C36H36N24O12) 2.328(5)–2.430(6) 2.280(5)–2.387(5) 2.343(9)–2.417(10) 2.141(4)–2.277(4) 2.326(6)–2.446(6) M–O (H2O) 2.340(6)–2.394(8) 2.316(5)–2.362(5) 2.325(8)–2.388(11) 2.147(4)–2.244(6) 2.308(6)–2.386(8) M–O (NO3) 2.444(6)–2.507(6) 2.408(5)–2.476(5) 2.431(10)–2.493(9) 2.269(5)–2.356(5) 2.457(7)–2.504(6) M–O (C2H5OH) 2.335(6) * According to the literature data [8]. RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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TRIPOLSKAYA et al. x z
Fig. 2. Chains in crystal structures I and II formed due to hydrogen bonds (projection onto xz plane).
RESULTS AND DISCUSSION Complexes I and II are isostructural to one another (to an accuracy of the crystallization water molecules) and the previously synthesized gadolinium, holmium, and ytterbium complexes with cucurbit[6]uril [8]. The metal : cucurbit[6]uril ratio in these complexes is 1 : 1. These complexes were obtained by a slow evaporation of solutions of the corresponding metal nitrates with cucurbit[6]uril at the metal cation concentrations from 0.025 to 0.100 mol/l. Crystal structure of compounds I and II represents packing of the metal complexes with cucurbit[6]uril. Macrocyclic cavitand acts as bidentate ligand. Complexes I and II have the structure [å(NO3)(H2O)4(C36H36N24O12)]2+ (M = Sc, Eu), which is shown in Fig. 1. The metal atom coordinates two neighboring carbonyl groups of cavitand, four water molecules and bidentate nitrate anion. The bond lengths of the metal–oxygen bonds in compounds I and II and in the isostructural complexes of Gd, Ho, and Yb [8] are listed in Table 3. The coordination number of a metal atom is equal to 8, the coordination polyhedron is a distorted trigonal dodecahedron. Some of water molecules coordinated by the metal atom form hydrogen bonds with carbonyl O atoms of cucurbit[6]uril and crystallization water molecules (for I, the é···é distance lies within 2.540–2.836 Å, for II it varies within
the limits 2.572–2.901 Å). In addition, the second coordination sphere of a metal includes cucurbit[6]uril molecules of another complex, which can be seen from crystal structures of complexes I and II in Fig. 2. The cationic complexes [å(NO3)(H2O)4(C36H36N24O12)]2+ in I and II are united in chains through hydrogen bonds between the metalcoordinated water molecules of one complex and carbonyl groups of cucurbit[6]uril of another complex. The chains directed along the z axis are shifted by half translation with respect to one another. The space between the chains is filled with crystallization water molecules and nitrate ions. In general the structure of I and II represents a network of hydrogen bonds linking all structural units of a crystal. Complex III is isostructural (to an accuracy of the number of crystallization water molecules) to samarium (III) complex with cucurbit[6]uril {Sm(NO3)(H2O)5}2(C36H36N24O12)](NO3)4 · 6.5H2O we have previously synthesized [9]. Complex IV, which is isotypical to them, contains pyridine molecule in the cavity of cavitand molecule. Compounds III and IV were obtained from a solution on heating in a sealed tube at a higher metal cation concentration (1.000 mol/l) as compared to compounds I and II. The metal : cucurbit[6]uril ratio in complexes III and IV is equal to 2 : 1, and both portals of cucurbit[6]uril
Table 4. The M–O bond lengths (Å) in compounds {Sm(NO3)(H2O)5}2(C36H36N24O12)](NO3)4 · 6.5H2O ([Sm2Q6]), III and IV Bond M–O (C36H36N24O12) M–O (H2O) M–O (NO3)
[Sm2Q6]*
III
IV
2.380(3)–2.490(3) 2.381(3)–2.523(3) 2.499(3)–2.568(3)
2.354(3)–2.468(3) 2.361(3)–2.495(3) 2.478(3)–2.547(3)
2.409(4)–2.459(4) 2.355(4)–2.454(5) 2.480(4)–2.538(4)
* According to the literature data [9]. RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
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x N O
z
Gd
C
Fig. 4. A fragment of crystal structure of IV (projection onto xz plane). Molecules of water of crystallization and nitrate ions are not shown.
Fig. 3. The cationic complex [{Gd(NO3)(H2O)5}2{(ë5H5N) ⊂ (C36H36N24O12)}]4+ in structure IV. Hydrogen bonds are shown in dashed lines. Hydrogen atoms are omitted. Pyridine molecule inside cucurbit[6]uril cavity is depicted by balls with van der Waals radii of atoms.
molecules are coordinated by the metal cation through the O atoms of carbonyl groups (two from each portal). The structure of the cationic complex [{Gd(NO3)(H2O)5}2{(ë5H5N) ⊂ (C36H36N24O12)}]4+ in compound IV is shown in Fig. 3. As in the case of the analogous Sm complex [9], crystal III (triclinic crystal system) contains these two crystallographically independent cationic complexes; the compound crystallizes in triclinic crystal system. The symmetry of compound IV is higher (it crystallizes in monoclinic crystal system); the structure contains one crystallographically independent cationic complex. Each Gd3+ cation coordinates, in addition to two carbonyl groups of a macrocycle portal, five water molecules and a bidentate nitrate ion. The Gd–O bond lengths are listed in Table 4. The coordination number of Gd3+ is 9; the coordination polyhedron is a distorted one-cap square antiprism with nitrate ion in the shortest edge. Two aqua ligands are involved in hydrogen bonds with another two noncoordinated CO groups of portal (in III, the O···O distance varies within 2.750–2.840 Å and 2.788–2.862 Å for Gd(1) and Gd(2), respectively; in RUSSIAN JOURNAL OF COORDINATION CHEMISTRY
IV, the distance O···O changes within the limits 2.612– 2.818 Å). The packing of the cationic complexes in IV is shown in Fig. 4. The space between the complexes is occupied by the crystallization water molecules and nitrate ions, which unite all structural units of a crystal by intricate hydrogen bonding system. ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research (project no. 04-03-32304). REFERENCES 1. Freeman, W.A., Acta Crystallogr., Sect. B: Struct. Sci., 1984, vol. 40, no. 4, p. 382. 2. Jeon, Y.M., Kim, J., Whang, D., and Kim, K., J. Am. Chem. Soc., 1999, vol. 118, no. 40, p. 9790. 3. Heo, J., Kim, J., Whang, D., and Kim, K., Inorg. Chim. Acta, 2000, vol. 297, nos. 1–2, p. 307. 4. Heo, J., Kim, S.-Y., Whang, D., and Kim, K., Angew. Chem., Int. Ed. Engl., 1999, vol. 38, no. 5, p. 641. 5. Whang, D., Heo, J., Park, J.H., and Kim, K., Angew. Chem., Int. Ed. Engl., 1998, vol. 37, nos. 1–2, p. 78. 6. Samsonenko, D.G., Sharonova, A.A., Sokolov, M.N., et al., Koord. Khim., 2001, vol. 27, no. 1, p. 12. 7. Geras’ko, O.A., Samsonenko, D.G., and Fedin, V.P., Usp. Khim., 2002, vol. 71, no. 9, p. 840. 8. Samsonenko, D.G., Lipkowski, J., Gerasko, O.A., et al., Eur. J. Inorg. Chem., 2002, no. 9, p. 2380. Vol. 31
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16. Zhong-Sheng, J., Yong-Sheng, L., Shu-Gong, Z., et al., Huaxue Xuebao (Acta Chim. Sinica, Chin.), 1987, vol. 45, no. 11, p. 1048. 17. Minyu, T., Xinmin, G., Ning, T., and Jinpin, Z., Gaodeng Xuexiao Huaxue Xuebao (Chem. J. Chin. Univ.), 1988, vol. 9, no. 12, p. 1217. 18. Tripol’skaya, A.A., Geras’ko, O.A., Naumov, D.Yu., et al., Zh. Strukt. Khim., 2004, vol. 45, no. 2, p. 284. 19. Spravochnik khimika (Chemist’s Handbook), Nikol’skii, B.P., Ed., Leningrad: Khimiya, 1964, vol. 2, p. 210. 20. Freeman, W.A., Mock, W.L., and Shih, N.-Y., J. Am. Chem. Soc., 1981, vol. 103, no. 24, p. 7367. 21. Samsonenko, D.G., Cand. Sci. (Chem.) Dissertation, Novosibirsk: Inst. Inorg. Chem., Siberian Division of the RAS, 2003. 22. Sheldrick, G.M., SHELX97. Release 97-2, Göttingen (Germany): Univ. of Göttingen, 1998.
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