Tris(6-carb­oxy­pyridine-2-carboxyl­ato)terbium(III) 2.75-hydrate

Soumaila Zebret; Céline Besnard; Josef Hamacek

doi:10.1107/S1600536811024135

. 2011 Jun 25;67(Pt 7):m968–m969. doi: 10.1107/S1600536811024135

Tris(6-carboxypyridine-2-carboxylato)terbium(III) 2.75-hydrate

Soumaila Zebret ^a, Céline Besnard ^b, Josef Hamacek ^a,^*

PMCID: PMC3151876 PMID: 21836945

Abstract

In the title compound, [Tb(C₇H₄NO₄)₃]·2.75H₂O, the Tb³⁺ atom is coordinated by three tridentate 6-carboxypyridine-2-carboxylate ligands and lies on a crystallographic threefold rotation axis. The coordination polyhedron around Tb^III adopts a distorted tricapped trigonal–prismatic geometry. Disordered water molecules with partial occupancy are also present in the crystal, one of which is associated with each of the carboxylate O atoms of the complex unit.

Related literature

For details of the synthesis, see: Zebret et al. (2009 ▶). For related structures, see: D’Aléo, et al. (2007 ▶, 2008 ▶); Borthwick (1980 ▶); Albertsson (1970 ▶); Hamacek et al. (2009 ▶). For isotypic structures, see: Brayshaw et al. (2005 ▶); Chen et al. (2002 ▶); Iwamura et al. (2007 ▶); Lunstroot et al. (2009 ▶); Pompidor et al. (2008 ▶); Shengzhi et al. (1989 ▶); Van Meervelt et al. (1997 ▶). For the Squeeze/bypass procedure, see: van der Sluis & Spek (1990 ▶). For a description of the Cambridge Structural Database, see: Allen (2002) ▶.

Experimental

Crystal data

[Tb(C₇H₄NO₄)₃]·2.75H₂O
M _r = 706.79
Trigonal,
a = 13.0115 (15) Å
c = 9.4142 (13) Å
V = 1380.3 (5) Å³
Z = 2
Mo Kα radiation
μ = 2.63 mm⁻¹
T = 200 K
0.15 × 0.10 × 0.05 mm

Data collection

Stoe IPDS diffractometer
Absorption correction: Gaussian (Busing & Levy, 1957 ▶) T _min = 0.72, T _max = 0.88
3830 measured reflections
1569 independent reflections
1464 reflections with I > 2.0σ(I)
R _int = 0.035

Refinement

R[F ² > 2σ(F ²)] = 0.037
wR(F ²) = 0.082
S = 1.00
1566 reflections
122 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.57 e Å⁻³
Δρ_min = −1.01 e Å⁻³
Absolute structure: Flack (1983 ▶), 679 Friedel pairs
Flack parameter: −0.05 (2)

Data collection: IPDS (Stoe & Cie, 1996 ▶); cell refinement: IPDS; data reduction: X-RED (Stoe & Cie 1996 ▶); program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 ▶); molecular graphics: CAMERON (Watkin et al., 1996) ▶; software used to prepare material for publication: CRYSTALS.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811024135/zs2104sup1.cif

e-67-0m968-sup1.cif^{(15.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811024135/zs2104Isup2.hkl

e-67-0m968-Isup2.hkl^{(78.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Tb1—O2	2.435 (6)
Tb1—N6	2.545 (6)
Tb1—O9	2.436 (6)

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

Financial support from the University of Geneva and the SNF is gratefully acknowledged.

supplementary crystallographic information

Comment

Since the first structural investigation of tris(dipicolinato)ytterbium complex (Albertsson, 1970), a number of different lanthanide complexes with dipic (= hydrogen 2,6-pyridinedicarboxylate) have been reported. Their brief overview can be found, e.g. in the report of the Hamacek group (Hamacek et al., 2009). Recently, we have reported on the self-assembly of a trinuclear luminescent europium complex with bis(6-methoxycarbonyl-2-carbonylpyridine)amine (L) (Zebret et al., 2009). In an attempt to synthesize the analogous terbium(III) compound with L using the same procedure, small transparent crystals were isolated from the resulting DMSO solution. However, these X-ray quality crystals had a different shape than expected (cubic crystals for Eu₃L₃). Structural studies reveal the formation of a partially hydrated tris(dipicolinato^-1)terbium complex, the title compound [Tb(dipic)₃] . 2.75H₂O (I) (Fig. 1). Accordingly, the presence of dipicolinate anions is explained by the complete hydrolysis of both ester and amide functions of the ligand L. In addition to crystallography, the obtained crystalline material was analysed using spectroscopic methods. Fig. 2 shows the typical emission spectrum of [Tb(dipic)₃]^3- with characteristic ⁵D₄ -> ⁷F_j transitions (D'Aléo et al., 2007, 2008). The luminescent lifetime at room temperature was found to be 1.45 ms, which is a somewhat lower value compared to the D'Aleo's value (2.02 ms) probably due to additional quenching of surrounding water molecules. The IR spectrum on Fig. 3 shows stretching O—H vibrations at about 3400 cm^-1 and water bending vibrations at 1637 cm^-1.

From the bond lengths, the valence of the Tb atom was calculated to be 3.15. Taking into account the oxidation state of the Tb atom and in the absence of any other charged species in the crystals, the ligand has to be partially protonated. However, the quality of the data does not allow the localion of the position of this extra hydrogen on each of the ligands. Apart from the complex, additional partial water molecules are present in the crystal, one of which (O17) is associated with the carboxyl oxygens of the ligand (details of the refinement are given elsewhere).

In the complex, the Tb^III cation is nine-coordinated by three monoanionic dipic^1- ligands and lies on the threefold rotation axis. The Tb atom lies 0.081 Å from the plane defined by the three nitrogen donors, so that these four atoms are nearly coplanar (Fig. 4). The two planes defined by the three O2 and three O9 donors, respectively, form a discrete tricapped trigonal prism with the distance to the central terbium atom equal to 1.581 Å and 1.635 Å, respectively. The asymmetric unit comprises one dipicolinate ligand and 1/3 of a Tb atom and the partial water O17 (S.O.F = 0.50). The unit cell consists of two molecules of [Tb(dipic)₃] . 2.75H₂O with two different configurations (Δ and Λ) for the complex unit; the crystal is thus a racemate. The overall structure of the Tb^III complex does not significantly differ from those previously reported for other lanthanides. A search of the Cambridge Structural Database [CSD, Version 5.30 of September 2009 (Allen, 2002)] restricted only to tris(dipicolinato)terbium complexes gives eight crystal structures already reported in the literature, details of which are summarized in Table 2. As it can be seen, the Tb—O distances are not completely symmetrical within the complex ranging from 2.38 to 2.45 Å. Similar results are found for complex (I) (Table 1) with the Tb—O2 and Tb—O9 distances equal to 2.434 (6) Å and 2.437 (6) Å, respectively. The Tb—N6 distance is equal to 2.544 (6) Å, apparently the longest distance for all reported structures.

Concerning the crystal packing, the [Tb(dipic)₃] units are arranged in the plane around disordered partial water molecules, occupying the available spaces, which resemble channels (Fig. 5a). The underlayer is shifted along the b axis in order to optimize hydrogen bonding interactions (Fig. 5b). A comparison of structural data in Table 2 shows that the choice of the counter-ion [absent in the case of (I)] has a significant influence on the final crystal packing (seven space groups for nine tris(dipicolinato)terbium complexes), and also on the coordinate bonds within the complex (various Tb—N and Tb—O distances).

Experimental

To a solution of 60.8 mg (0.18 mmol) of the pyridine-containing ligand L and 152.5 mg (0.18 mmol) of Tb(Otf)₃ . 13.7H₂O in 5 ml DMF was added NaH (26 mg 3.5 eq). The mixture was stirred for three hours under a nitrogen atmosphere, filtered and then evaporated to dryness. The residue was dissolved in DMSO, filtered and water was allowed to diffuse into this solution. The IR spectrum of the isolated solid was measured at room tempeature with a Perkin-Elmer Spectrum 1 (equipped with a Specac Golden Gate ATR accessory). The phosphorescence spectrum was obtained under the same conditions with a Perkin-Elmer Lambda 900 (λ_exc = 273 nm).