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Synthesis and structures of dioxouranium complexes with 2-pyridineformamide thiosemicarbazones
Inorganic Chemistry Communications 7 (2004) 440–442 www.elsevier.com/locate/inoche
Synthesis and structures of dioxouranium complexes with 2-pyridineformamide thiosemicarbazones Isabel Garcia Santos, Ulrich Abram
*
Institut fur € Chemie, Freie Universit€at Berlin, Fabeckstr. 34-36, D-14195 Berlin, Germany Received 1 December 2003; accepted 11 January 2004 Published online: 4 February 2004
Abstract 2-Pyridineformamide thiosemicarbazone (HL1 ) reacts with UO2 (NO3 )2 6H2 O or [NBu4 ]2 [UO2 Cl4 ] under deprotonation and formation of neutral uranyl complexes. The composition of the products is dependent on the solvents used: [UO2 (L1 )(OH)]2 is formed when acetonitrile is used, whereas the hydrogen-bonded dimer [UO2 (L1 )(MeO)(MeOH)]2 is the product in methanol. Both products have been studied by X-ray crystallography showing uranium–uranium distances of 3.750 and 5.385 A. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Uranium; Thiosemicarbazones; Actinides; Crystal structure
Despite thiosemicarbazone complexes of uranium have attracted considerable interest during the recent years [1], there is only one report which contains X-ray structural data of such compounds [2]. This describes the products of reactions of 2-acetylpyridine thiosemicarbazone (HL2 ) with uranyl nitrate or [NBu4 ]2 [UO2 Cl4 ]. Complexes of the compositions [UO2 (L2 )(MeO) (MeOH)]2 and [NBu4 ][UO2 (L2 )Cl2 ] have been isolated, both containing deprotonated, tridentate thiosemicarbazones. The water-solubility of the thiosemicarbazone ligands (and of their metal complexes) can be increased when derivatives of 2-pyridineformamide are used instead of 2-acetylpyridine as has been demonstrated for metal ions such as Hg2þ , Pt2þ , Cd2þ and Ni2þ [3]. Here, we present syntheses and structures of the first dioxouranium complexes with 2-pyridineformamide 3-dimethylthiosemicarbazone (HL1 ).
*
Corresponding author. Tel.: +49-308-385-4002; fax: +49-308-3852676. E-mail address: [email protected] (U. Abram). 1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2004.01.005
NH2
N
N NH S
CH3
N
N NH N
Me
S
H
R
Me HL1
N
HL2
UO2 (NO3 )2 6H2 O or [NBu4 ]2 [UO2 Cl4 ] react with HL1 under formation of orange-brown precipitates. The composition of the products is dependent on the solvents used, but not on the uranium starting material. This is remarkable in the light that [NBu4 ][UO2 (L2 )Cl2 ] is formed by a reaction of [NBu4 ]2 [UO2 Cl4 ] with 2acetylpyridine applying the same reaction conditions [2]. A complex of the composition [UO2 (L1 )(MeOH)(MeO)]2 with a deprotonated thiosemicarbazonato ligand is formed when the reaction is performed in methanol [4], while a dimeric, hydroxo-bridged compound, [UO2 (L1 )(l-OH)]2 , is the product when a nonprotic solvent such as acetonitrile is used [5]. The formation of [UO2 (L1 )(MeO)(MeOH)] corresponds to the reaction pattern which has been observed with HL2 . Each two of the complex molecules are connected by hydrogen bonds which are established
I. Garcia Santos, U. Abram / Inorganic Chemistry Communications 7 (2004) 440–442
between the methanol and methanolato ligands. [UO2 (HL1 )(MeO)2 ] can be isolated as a orange-red solid. The infrared spectrum gives evidence for the dioxo 1 unit of UOþ and the 2 by a strong band at 912 cm typical pattern for 2-pyridineformamide thiosemicarbazone with C@N and C@C vibrations between 1487 and 1611 cm1 . An X-ray crystal structure determination [5] confirms the composition and the dimeric structure of [UO2 (L1 )(MeO)(MeOH)]2 . An ellipsoid representation of the molecular structure is given in Fig. 1. The two [UO2 (L1 )(MeO)(MeOH)] units are symmetry-related via a centre of inversion forming dimers with a long U1–U2 The bridging hydrogen atom has distance of 5.385 A. been located in the final Fourier map of the structure calculation and refined. It can be assigned to O30 and establishes an unexceptional, asymmetric hydrogen bond to O20 with an O30–H30 bond length of 0.88(7) A 0 and an H30. . .O20 distance (symmetry operation (O30. . .O20 ¼ 2.481(4) A, angle x; y; z) of 1.60(7) A O30–H30–O20 ¼ 174(6)°). This contrasts the situation in [UO2 (L2 )(MeO)(MeOH)], where the bridging hydrogen atom has been localised almost in between the methanol oxygen atom and could not be assigned to a distinct molecule [2]. The co-ordination sphere of uranium can be described as a distorted pentagonal bipyramide with the oxo ligands in the apical positions. Main distortions are due to the restricting bite angles of the thiosemicarbazone ligand which results in bond angles between neighbouring donor atoms inside the pentagonal plane between 63.9(1)° and 80.5(1)°. The thiosemicarbazone is coplanar with a maximum deviation from a mean (r.m.s. 0.043). The U– least-square plane of 0.093(3) A is in the same range as has been S1 bond of 2.825(2) A observed for the 2-acetylpyridine thiosemicarbazonato complex and suggests a weak bonding to the sulphur
site of the thiosemicarbazone moiety. The U–N1 and howU–N2 bond lengths of 2.575(3) and 2.551(3) A, ever, indicate a stronger bond between uranium and the thiosemicarbazone nitrogen than with the pyridine one. The opposite has been observed for the 2-acetylpyridine thiosemicarbazone complex [2] and suggests an increase of the basicity of the thiosemicarbazone ligand system by the use of a formamide instead of an acetyl function. When the reactions of uranyl nitrate or [NBu4 ]2 [UO2 Cl4 ] with HL1 are performed in acetonitrile, the thiosemicarbazone deprotonates and a dimeric complex of the composition [UO2 (L1 )(l-OH)]2 is formed which can be isolated as a red-brown microcrystalline solid [5]. Recrystallisation from pyridine results in single crystals of a pyridine solvate which were suitable for X-ray crystallography [6]. Fig. 2 shows the molecular structure of the neutral complex. The bonding situation inside the chelate rings of the thiosemicarbazone is similar to that in [UO2 (L1 )(MeO)(MeOH)]2 . The co-ordination environments of the uranium atoms are pentagonal pyramidal with the dioxo oxygen atoms in apical positions. The U–S bonds are somewhat shorter than that in the monomeric complex and the U–N bonds are almost equal with values between 2.549(11) and 2.565(10) A. The U1–U2 distance is 3.750(1) A and the bridging hydroxo ligands are constituents of an extended network of hydrogen bonds which also includes the formamide hydrogen atoms and pyridine solvent molecules. The results of the present study underline the versatility of thiosemicarbazone ligands and show that minor substitutions in their backbone can significantly influence their complex formation behaviour. Further studies, which also include the capabilities of various thiosemicarbazones in actinide extraction, are planed for the near future.
N4
O2
C6
O20
C7
O2
O20
O4
N3
N5
N2
U
N2
S1
C20
N1
441
U1
N11
C15 C16 N15 N12
U2
N13
C6
N3
N5
O1 O30 C7
C5
N1 O1
O10
O3 C17
N14
S2 S1
Fig. 1. Ellipsoid representation [8] of the molecular structure of the [UO2 (L1 )(MeO)(MeOH)]2 dimer. Selected bond lengths: U–O1, 1.784(3); U–O2, 1.780(3); U–S1, 2.825(2); U–N1, 2.575(3); U–N2, 2.551(3); U–O20, 2.258(3); U–O30, 2.368(3) A.
Fig. 2. Ellipsoid representation [8] of the molecular structure of [UO2 (L1 )(OH)]2 . Selected bond lengths: U1–O1, 1.790(8); U1–O2, 1.779(8); U2–O3, 1.784(8); U2–O4, 1.775(8); U1–S1, 2.782(4); U2–S2, 2.793(4); U1–N1, 2.55(1); U2–N11, 2.44(1); U1–N2, 2.57(1), U2–N12, 2.55(1); U1–O10, 2.35(2); U1–O20, 2.31(1); U2–O10, 2.32(2); U2–O20, 2.31(1) A.
442
I. Garcia Santos, U. Abram / Inorganic Chemistry Communications 7 (2004) 440–442
Acknowledgements We gratefully acknowledge financial support from the DAAD and CAPES (U.A.) and a postdoctoral grant from the Xunta de Galicia (I.G.). References [1] (a) U. El-Ayaan, G.A. El-Reash, P. Weinberger, W. Linert, Synth. React. Inorg. Met.-Org. Chem. 30 (2000) 1759; (b) R.K. Agarwal, D.X. West, J.A. Ives, NUCAR 95: Proceedings of the Nuclear Radiochemistry Symposium, 1995, p. 206; (c) R.K. Agarwal, H. Agarwal, I. Chakraborti, React. Inorg. Met.Org. Chem. 25 (1995) 679; (d) Guosheng, Huang, YongMin Liang, Yongxian Ma, J. Coord. Chem. 26 (1992) 237; (e) A.A. El-Asmy, Y.M. Shaibi, S. Abdallah, M. Mounir, S.A. Ashour, Transition Met. Chem. 13 (1988) 332; (f) D.G. Chuguryan, V.I. Dzyubenko, Radiokhimiya 29 (1987) 280. [2] U. Abram, E. Schulz Lang, E. Bonfada, Z. Anorg. Allg. Chem. 628 (2002) 1873. [3] I. Garcia Santos, PhD thesis, University of Santiago de Compostela, Spain, 2001. [4] Synthesis of [UO2 (L1 )(OMe)(MeOH)]2 : HL1 (44 mg, 0.2 mmol) was dissolved in 15 ml of methanol and added to a solution of UO2 (NO3 )2 6H2 O (100 mg, 0.2 mmol) in 5 ml methanol. The mixture was heated under reflux for 1 h after adding a few drops of triethylamine. Orange-red crystals precipitated upon cooling which were filtered off and dried in vacuum. Yield: 73 mg, 66%. U2 C18 H26 N10 O6 S; C 21.2 (calc. 23.8); H 2.7 (3.5); N 13.1 (12.6); S 7.0 (5.8)%. IR (mmax /cm1 ): 3470, 3346 (NH); 1611–1487 (C@N, C@C), 912 (U@O). The same product was obtained in similar yields when the reaction started from [NBu4 ]2 [UO2 Cl4 ]. [5] Synthesis of [UO2 (l-OH)(L1 )]2 : The complex was prepared following the same protocol given above for the synthesis of
[UO2 (L1 )(MeO)(MeOH)]2 with the exception that methanol was used as solvent. Recrystallization from hot methanol gave red crystals which were suitable for X-ray crystallography. Yield: 65 mg, 65%. U2 C18 H26 N10 O6 S; C 21.2 (calc. 21.7); H 2.6 (2.7); N 13.8 (13.1); S 6.3 (6.9)%. IR (mmax /cm1 ): 3418, 3333 (NH, OH); 1601– 1462 (C@N, C@C), 914 (U@O). 1 H NMR (dmso-d6 , ppm): 11.30 (1H, s, OH), 8.41 (1H, d, H1), 8.19 (1H, t, H4), 7.33 (1H, m, H2), 7.18 (3H, s,a, H3 + NH2 ), 3.33 (6H, s, CH3 ). The same product was obtained in similar yields when the reaction started from [NBu4 ]2 [UO2 Cl4 ]. The microcrystalline solid was recrystallized from pyridine giving orange-brown needles of [UO2 (l-OH)(L1 )]2 6 pyridine which were suitable for X-ray crystallography. [6] Crystal data for [UO2 (L1 )(MeO)(MeOH)]2 MeOH: Monoclinic, space group C2/c, a ¼ 21:238ð6Þ, b ¼ 12:116ð4Þ, c ¼ 14:454ð4Þ A, 3 , Z ¼ 4. BRUKER Smart, Mo Ka b ¼ 105:193ð6Þ, V ¼ 3589ð2Þ A T ¼ 193 K, 21,719 reflections measured, radiation (k ¼ 0:71073 A), 5471 independent, 223 parameters, l ¼ 9:187 mm1 , absorption correction: SADABS: Tmin ¼ 0:490, Tmax ¼ 1:000. Structure solution and refinement: SHELXS 97, SHELXL 97 [7], R1 ¼ 0:0285, wR2 ¼ 0:0711, GooF ¼ 1:048. Further details have been deposited with the Cambridge Crystallographic Data Centre under the deposition number CCDC-225498. Crystal data for [UO2 (L2 )(OH)]2 6 pyridine: Monoclinic, space group P21 /c, a ¼ 10:224ð1Þ, b ¼ 17:746ð2Þ, c ¼ 30:508ð5Þ A, 3 , Z ¼ 4. BRUKER Smart, Mo Ka b ¼ 94:88ð2Þ, V ¼ 5515ð1Þ A T ¼ 193 K, 11334 reflections measured, radiation (k ¼ 0:71073 A), 9583 independent, 675 parameters, l ¼ 1:798 mm1 , absorption correction: SADABS: Tmin ¼ 0:894, Tmax ¼ 1:000. Structure solution and refinement: SHELXS 97, SHELXL 97 [7], R1 ¼ 0:0554, wR2 ¼ 0:0889, GooF ¼ 0:967. Further details have been deposited with the Cambridge Crystallographic Data Centre under the deposition number CCDC-225499. [7] G.M. Sheldrick, SHELXS 97 and SHELXL 97 – programs for the solution and refinement of crystal structures, University of G€ ottingen, Germany, 1997. [8] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
Synthesis and structures of dioxouranium complexes with 2-pyridineformamide thiosemicarbazones Isabel Garcia Santos, Ulrich Abram
*
Institut fur € Chemie, Freie Universit€at Berlin, Fabeckstr. 34-36, D-14195 Berlin, Germany Received 1 December 2003; accepted 11 January 2004 Published online: 4 February 2004
Abstract 2-Pyridineformamide thiosemicarbazone (HL1 ) reacts with UO2 (NO3 )2 6H2 O or [NBu4 ]2 [UO2 Cl4 ] under deprotonation and formation of neutral uranyl complexes. The composition of the products is dependent on the solvents used: [UO2 (L1 )(OH)]2 is formed when acetonitrile is used, whereas the hydrogen-bonded dimer [UO2 (L1 )(MeO)(MeOH)]2 is the product in methanol. Both products have been studied by X-ray crystallography showing uranium–uranium distances of 3.750 and 5.385 A. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Uranium; Thiosemicarbazones; Actinides; Crystal structure
Despite thiosemicarbazone complexes of uranium have attracted considerable interest during the recent years [1], there is only one report which contains X-ray structural data of such compounds [2]. This describes the products of reactions of 2-acetylpyridine thiosemicarbazone (HL2 ) with uranyl nitrate or [NBu4 ]2 [UO2 Cl4 ]. Complexes of the compositions [UO2 (L2 )(MeO) (MeOH)]2 and [NBu4 ][UO2 (L2 )Cl2 ] have been isolated, both containing deprotonated, tridentate thiosemicarbazones. The water-solubility of the thiosemicarbazone ligands (and of their metal complexes) can be increased when derivatives of 2-pyridineformamide are used instead of 2-acetylpyridine as has been demonstrated for metal ions such as Hg2þ , Pt2þ , Cd2þ and Ni2þ [3]. Here, we present syntheses and structures of the first dioxouranium complexes with 2-pyridineformamide 3-dimethylthiosemicarbazone (HL1 ).
*
Corresponding author. Tel.: +49-308-385-4002; fax: +49-308-3852676. E-mail address: [email protected] (U. Abram). 1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2004.01.005
NH2
N
N NH S
CH3
N
N NH N
Me
S
H
R
Me HL1
N
HL2
UO2 (NO3 )2 6H2 O or [NBu4 ]2 [UO2 Cl4 ] react with HL1 under formation of orange-brown precipitates. The composition of the products is dependent on the solvents used, but not on the uranium starting material. This is remarkable in the light that [NBu4 ][UO2 (L2 )Cl2 ] is formed by a reaction of [NBu4 ]2 [UO2 Cl4 ] with 2acetylpyridine applying the same reaction conditions [2]. A complex of the composition [UO2 (L1 )(MeOH)(MeO)]2 with a deprotonated thiosemicarbazonato ligand is formed when the reaction is performed in methanol [4], while a dimeric, hydroxo-bridged compound, [UO2 (L1 )(l-OH)]2 , is the product when a nonprotic solvent such as acetonitrile is used [5]. The formation of [UO2 (L1 )(MeO)(MeOH)] corresponds to the reaction pattern which has been observed with HL2 . Each two of the complex molecules are connected by hydrogen bonds which are established
I. Garcia Santos, U. Abram / Inorganic Chemistry Communications 7 (2004) 440–442
between the methanol and methanolato ligands. [UO2 (HL1 )(MeO)2 ] can be isolated as a orange-red solid. The infrared spectrum gives evidence for the dioxo 1 unit of UOþ and the 2 by a strong band at 912 cm typical pattern for 2-pyridineformamide thiosemicarbazone with C@N and C@C vibrations between 1487 and 1611 cm1 . An X-ray crystal structure determination [5] confirms the composition and the dimeric structure of [UO2 (L1 )(MeO)(MeOH)]2 . An ellipsoid representation of the molecular structure is given in Fig. 1. The two [UO2 (L1 )(MeO)(MeOH)] units are symmetry-related via a centre of inversion forming dimers with a long U1–U2 The bridging hydrogen atom has distance of 5.385 A. been located in the final Fourier map of the structure calculation and refined. It can be assigned to O30 and establishes an unexceptional, asymmetric hydrogen bond to O20 with an O30–H30 bond length of 0.88(7) A 0 and an H30. . .O20 distance (symmetry operation (O30. . .O20 ¼ 2.481(4) A, angle x; y; z) of 1.60(7) A O30–H30–O20 ¼ 174(6)°). This contrasts the situation in [UO2 (L2 )(MeO)(MeOH)], where the bridging hydrogen atom has been localised almost in between the methanol oxygen atom and could not be assigned to a distinct molecule [2]. The co-ordination sphere of uranium can be described as a distorted pentagonal bipyramide with the oxo ligands in the apical positions. Main distortions are due to the restricting bite angles of the thiosemicarbazone ligand which results in bond angles between neighbouring donor atoms inside the pentagonal plane between 63.9(1)° and 80.5(1)°. The thiosemicarbazone is coplanar with a maximum deviation from a mean (r.m.s. 0.043). The U– least-square plane of 0.093(3) A is in the same range as has been S1 bond of 2.825(2) A observed for the 2-acetylpyridine thiosemicarbazonato complex and suggests a weak bonding to the sulphur
site of the thiosemicarbazone moiety. The U–N1 and howU–N2 bond lengths of 2.575(3) and 2.551(3) A, ever, indicate a stronger bond between uranium and the thiosemicarbazone nitrogen than with the pyridine one. The opposite has been observed for the 2-acetylpyridine thiosemicarbazone complex [2] and suggests an increase of the basicity of the thiosemicarbazone ligand system by the use of a formamide instead of an acetyl function. When the reactions of uranyl nitrate or [NBu4 ]2 [UO2 Cl4 ] with HL1 are performed in acetonitrile, the thiosemicarbazone deprotonates and a dimeric complex of the composition [UO2 (L1 )(l-OH)]2 is formed which can be isolated as a red-brown microcrystalline solid [5]. Recrystallisation from pyridine results in single crystals of a pyridine solvate which were suitable for X-ray crystallography [6]. Fig. 2 shows the molecular structure of the neutral complex. The bonding situation inside the chelate rings of the thiosemicarbazone is similar to that in [UO2 (L1 )(MeO)(MeOH)]2 . The co-ordination environments of the uranium atoms are pentagonal pyramidal with the dioxo oxygen atoms in apical positions. The U–S bonds are somewhat shorter than that in the monomeric complex and the U–N bonds are almost equal with values between 2.549(11) and 2.565(10) A. The U1–U2 distance is 3.750(1) A and the bridging hydroxo ligands are constituents of an extended network of hydrogen bonds which also includes the formamide hydrogen atoms and pyridine solvent molecules. The results of the present study underline the versatility of thiosemicarbazone ligands and show that minor substitutions in their backbone can significantly influence their complex formation behaviour. Further studies, which also include the capabilities of various thiosemicarbazones in actinide extraction, are planed for the near future.
N4
O2
C6
O20
C7
O2
O20
O4
N3
N5
N2
U
N2
S1
C20
N1
441
U1
N11
C15 C16 N15 N12
U2
N13
C6
N3
N5
O1 O30 C7
C5
N1 O1
O10
O3 C17
N14
S2 S1
Fig. 1. Ellipsoid representation [8] of the molecular structure of the [UO2 (L1 )(MeO)(MeOH)]2 dimer. Selected bond lengths: U–O1, 1.784(3); U–O2, 1.780(3); U–S1, 2.825(2); U–N1, 2.575(3); U–N2, 2.551(3); U–O20, 2.258(3); U–O30, 2.368(3) A.
Fig. 2. Ellipsoid representation [8] of the molecular structure of [UO2 (L1 )(OH)]2 . Selected bond lengths: U1–O1, 1.790(8); U1–O2, 1.779(8); U2–O3, 1.784(8); U2–O4, 1.775(8); U1–S1, 2.782(4); U2–S2, 2.793(4); U1–N1, 2.55(1); U2–N11, 2.44(1); U1–N2, 2.57(1), U2–N12, 2.55(1); U1–O10, 2.35(2); U1–O20, 2.31(1); U2–O10, 2.32(2); U2–O20, 2.31(1) A.
442
I. Garcia Santos, U. Abram / Inorganic Chemistry Communications 7 (2004) 440–442
Acknowledgements We gratefully acknowledge financial support from the DAAD and CAPES (U.A.) and a postdoctoral grant from the Xunta de Galicia (I.G.). References [1] (a) U. El-Ayaan, G.A. El-Reash, P. Weinberger, W. Linert, Synth. React. Inorg. Met.-Org. Chem. 30 (2000) 1759; (b) R.K. Agarwal, D.X. West, J.A. Ives, NUCAR 95: Proceedings of the Nuclear Radiochemistry Symposium, 1995, p. 206; (c) R.K. Agarwal, H. Agarwal, I. Chakraborti, React. Inorg. Met.Org. Chem. 25 (1995) 679; (d) Guosheng, Huang, YongMin Liang, Yongxian Ma, J. Coord. Chem. 26 (1992) 237; (e) A.A. El-Asmy, Y.M. Shaibi, S. Abdallah, M. Mounir, S.A. Ashour, Transition Met. Chem. 13 (1988) 332; (f) D.G. Chuguryan, V.I. Dzyubenko, Radiokhimiya 29 (1987) 280. [2] U. Abram, E. Schulz Lang, E. Bonfada, Z. Anorg. Allg. Chem. 628 (2002) 1873. [3] I. Garcia Santos, PhD thesis, University of Santiago de Compostela, Spain, 2001. [4] Synthesis of [UO2 (L1 )(OMe)(MeOH)]2 : HL1 (44 mg, 0.2 mmol) was dissolved in 15 ml of methanol and added to a solution of UO2 (NO3 )2 6H2 O (100 mg, 0.2 mmol) in 5 ml methanol. The mixture was heated under reflux for 1 h after adding a few drops of triethylamine. Orange-red crystals precipitated upon cooling which were filtered off and dried in vacuum. Yield: 73 mg, 66%. U2 C18 H26 N10 O6 S; C 21.2 (calc. 23.8); H 2.7 (3.5); N 13.1 (12.6); S 7.0 (5.8)%. IR (mmax /cm1 ): 3470, 3346 (NH); 1611–1487 (C@N, C@C), 912 (U@O). The same product was obtained in similar yields when the reaction started from [NBu4 ]2 [UO2 Cl4 ]. [5] Synthesis of [UO2 (l-OH)(L1 )]2 : The complex was prepared following the same protocol given above for the synthesis of
[UO2 (L1 )(MeO)(MeOH)]2 with the exception that methanol was used as solvent. Recrystallization from hot methanol gave red crystals which were suitable for X-ray crystallography. Yield: 65 mg, 65%. U2 C18 H26 N10 O6 S; C 21.2 (calc. 21.7); H 2.6 (2.7); N 13.8 (13.1); S 6.3 (6.9)%. IR (mmax /cm1 ): 3418, 3333 (NH, OH); 1601– 1462 (C@N, C@C), 914 (U@O). 1 H NMR (dmso-d6 , ppm): 11.30 (1H, s, OH), 8.41 (1H, d, H1), 8.19 (1H, t, H4), 7.33 (1H, m, H2), 7.18 (3H, s,a, H3 + NH2 ), 3.33 (6H, s, CH3 ). The same product was obtained in similar yields when the reaction started from [NBu4 ]2 [UO2 Cl4 ]. The microcrystalline solid was recrystallized from pyridine giving orange-brown needles of [UO2 (l-OH)(L1 )]2 6 pyridine which were suitable for X-ray crystallography. [6] Crystal data for [UO2 (L1 )(MeO)(MeOH)]2 MeOH: Monoclinic, space group C2/c, a ¼ 21:238ð6Þ, b ¼ 12:116ð4Þ, c ¼ 14:454ð4Þ A, 3 , Z ¼ 4. BRUKER Smart, Mo Ka b ¼ 105:193ð6Þ, V ¼ 3589ð2Þ A T ¼ 193 K, 21,719 reflections measured, radiation (k ¼ 0:71073 A), 5471 independent, 223 parameters, l ¼ 9:187 mm1 , absorption correction: SADABS: Tmin ¼ 0:490, Tmax ¼ 1:000. Structure solution and refinement: SHELXS 97, SHELXL 97 [7], R1 ¼ 0:0285, wR2 ¼ 0:0711, GooF ¼ 1:048. Further details have been deposited with the Cambridge Crystallographic Data Centre under the deposition number CCDC-225498. Crystal data for [UO2 (L2 )(OH)]2 6 pyridine: Monoclinic, space group P21 /c, a ¼ 10:224ð1Þ, b ¼ 17:746ð2Þ, c ¼ 30:508ð5Þ A, 3 , Z ¼ 4. BRUKER Smart, Mo Ka b ¼ 94:88ð2Þ, V ¼ 5515ð1Þ A T ¼ 193 K, 11334 reflections measured, radiation (k ¼ 0:71073 A), 9583 independent, 675 parameters, l ¼ 1:798 mm1 , absorption correction: SADABS: Tmin ¼ 0:894, Tmax ¼ 1:000. Structure solution and refinement: SHELXS 97, SHELXL 97 [7], R1 ¼ 0:0554, wR2 ¼ 0:0889, GooF ¼ 0:967. Further details have been deposited with the Cambridge Crystallographic Data Centre under the deposition number CCDC-225499. [7] G.M. Sheldrick, SHELXS 97 and SHELXL 97 – programs for the solution and refinement of crystal structures, University of G€ ottingen, Germany, 1997. [8] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.