One-dimensional uranium–organic framework in catena-poly[[di-μ₂-hydroxido-bis[dioxouranium(VI)]]-di-μ₂-2-pyridylacetato-κ³O,N:O′;κ³O:O′,N]

In the title compound, {[UO₂(C₇H₆NO₂)(OH)]}_n, the U atom is in a seven-coordinated penta­gonal–bipyramidal environment. Each uranyl ion is bound to the N and one of the O atoms of a 2-pyridylacetate ligand, to one O atom from a second ligand and to two bridging hydroxide groups, all located in the equatorial plane. Hydroxide bridging gives uranyl dimers, which are assembled into planar and rectilinear ribbons by carboxyl­ate bridges. 12-Membered rings are defined by proximal dimers in the ribbons, with two intra-ring hydrogen bonds involving the hydroxide groups and two carboxyl­ate O atoms.

S1. Comment

The carboxylic acid derivatives of pyridine are useful ligands for the synthesis of uranyl complexes and uranyl–organic frameworks. In particular, several complexes involving 2,6-pyridyldicarboxylate have been described, which are either molecular (Masci & Thuéry, 2005) or polymeric species (Immirzi et al., 1975; Harrowfield et al., 2006; Cahill et al., 2007, and references therein). This ligand chelates the uranyl ion through its O,N,O donor atoms, and it appeared interesting to investigate the possible chelation by pyridine ligands bearing longer and more flexible acid chains. The mono-acid used in this work, 2-pyridylacetic acid, has seldom been used as a ligand in structural studies, and never with f element ions. The Cambridge Structural Database (CSD; Version 5.28; Allen, 2002) contains only eight structures of complexes formed by this ligand or its 6-methyl derivative with d transition metal atoms (Ni, Cu, Zn, Pd and Pt) or with Sb; in these complexes, the ligand is generally O,N-chelating, with the exceptions of one N-bonded Pt complex (Ma et al., 2005) and one O-bonded Sb complex (Domagala et al., 1990). The present title uranyl complex, (I), has been obtained under hydrothermal conditions and is polymeric, as expected.

The asymmetric unit in (I) comprises one uranyl ion, one deprotonated 2-pyridylacetate ligand and one hydroxide ion (Fig. 1). The linear uranyl group is O,N-chelated by 2-pyridylacetate, and is also bound to one carboxylate O atom from a neighbouring complex unit and two bridging hydroxyde groups. The five equatorial donor atoms [N1, O3, O5, O4ⁱ and O5ⁱⁱ; symmetry codes: (i) x + 1, y, z; (ii) -x + 1, -y + 1, -z + 1] define a mean plane with an r.m.s. deviation of 0.13 Å, atom U1 atom being displaced by 0.0250 (12) Å. The uranium coordination geometry is thus the usual pentagonal–bipyramidal one. The N1—U1—O3 angle is rather large and precludes the equatorial six-coordinate environment that is the most frequent with 2,6-pyridyldicarboxylates. The U1—N1 and U1—O3 bond lengths (Table 1) are very close to their average counterparts in the O,N,O-chelated complexes with 2,6-pyridyldicarboxylate reported in the CSD (12 hits) [2.59 (6) and 2.42 (4) Å, respectively], although the latter are often six-coordinate. The lower coordination number in (I) is not associated with shorter bond lengths, which is probably a result of the less suitable ligand geometry. The chelating ligand and the metal atom form a six-membered ring which is in the boat conformation. Atoms N1, C5, C7 and O3 define a mean plane with an r.m.s. deviation of 0.017 Å, with atoms U1 and C6 located on the same side, at distances of 0.977 (8) and 0.668 (7) Å from the plane. The dihedral angles between the uranyl equatorial plane and the aromatic ring and O3/O4/C7 planes are 42.86 (10) and 32.3 (8)°, respectively, and that between the last two planes is 59.0 (5)°. The N1—C5—C6—C7 torsion angle of 65.4 (5)° indicates that the carboxylic acid group is tilted out of the plane of the aromatic ring, as in the previous chelate complexes with this ligand. Uranyl centrosymmetric dimers are formed by the hydroxide double bridges, the pentagonal–bipyramidal polyhedra of the two metal atoms sharing a common edge defined by the double bridge. Such an occurrence is quite frequent in uranyl complexes, either in molecularcomplexes, as in some dinuclear species with nitrate (Alcock & Flanders, 1987; Evans et al., 2002; Thuéry & Masci, 2002; Fischer & Palladino, 2005; Spencer et al., 2006) and 2,6-pyridyldicarboxylate ligands (Masci & Thuéry, 2005), or in polymeric complexes obtained under hydrothermal conditions (Thuéry, 2007). The average U1—O(hydroxide) bond length [2.33 (2) Å], the U1—O5—U1ⁱⁱ angle (Table 1) and the U1···U1ⁱⁱ separation [3.8713 (6) Å] are in perfect agreement with the average values for the analogous complexes in the CSD (20 hits), which are 2.33 (2) Å, 112 (2)° and 3.85 (6) Å, respectively.

The hydroxide-bridged uranyl dimers are connected to one another along the a axis through two carboxylate bridges, thus defining a central, centrosymmetric 12-membered ring which is occupied by two hydrogen bonds involving the hydroxide groups and carboxylate O atoms [O5···O3ⁱⁱⁱ' = 3.027 (5) Å, O5—H5 = 0.89 Å, H5···O3ⁱⁱⁱ = 2.27 Å and O5—H5···O3ⁱⁱⁱ 143°; symmetry code: (iii) - x, -y + 1, -z + 1]. Planar ribbons running along the a axis are thus generated, as represented in Fig. 2, in which the central row of uranyl dimers is surrounded by two lateral rows of aromatic rings. When viewed down the a axis, the packing displays ribbons stacked so as to form double C—H···π interactions around inversion centres, which link the aromatic rings to the methylene groups of neighbouring molecules [H6B···Cg^iv = 2.77 Å, C6—H6B···Cg^iv = 128°; symmetry code: (iv) -x, -y, -z]. No π stacking interactions are present. These weak C—H···π interactions result in the formation of loosely bound sheets parallel to (011), which interact with one another by van der Waals interactions only.

Related literature

For related literature, see: Alcock & Flanders (1987); Allen (2002); Cahill et al. (2007); Domagala et al. (1990); Evans et al. (2002); Fischer & Palladino (2005); Harrowfield et al. (2006); Immirzi et al. (1975); Ma et al. (2005); Masci & Thuéry (2005); Spencer et al. (2006); Thuéry (2007); Thuéry & Masci (2002).

S2. Experimental

Uranyl nitrate hexahydrate (155 mg, 0.309 mmol) and 2-pyridylacetic acid hydrochloride (54 mg, 0.311 mmol) were dissolved in demineralized water (3 ml) and a slight excess of NEt₃ (45 mg, 0.44 mmol) was added. The solution was placed in a tightly closed glass vessel and heated at 453 K under autogenous pressure (ca 1.1 MPa), yielding crystals of (I) suitable for X-ray crystallography in 24 h. Compound (I) was then recovered and washed with water (22 mg, 0.052 mmol, 17% yield). Elemental analysis calculated for C₇H₇NO₅U: C 19.87, H 1.67, N 3.31%; found: C 19.63, H 1.54, N 3.22%.

S3. Refinement

The H atom bound to O5 was found in a difference Fourier map and introduced as a riding atom, with a U_iso(H) value of 1.2U_eq(O5). All other H atoms were introduced at calculated positions as riding atoms, with C—H bond lengths of 0.93 (CH) or 0.97 Å (CH₂) and U_iso(H) values of 1.2U_eq(C).

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL-2000 (Otwinowski & Minor, 1997); data reduction: HKL-2000 (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL (Bruker, 1999) and PLATON (Spek, 2003).

Figures

	Fig. 1. A view of part of the structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (') x + 1, y, z; ('') 1 - x, 1 - y, 1 - z; (''') x - 1, y, z.]
	Fig. 2. A view of the ribbon arrangement. The uranium coordination polyhedra are shown and the other atoms are shown as spheres of arbitrary radii. H atoms not involved in hydrogen bonds have been omitted. Hydrogen bonds are shown as dotted lines.
	Fig. 3. A view of the packing down the a axis, with ribbons viewed end-on. The uranium coordination polyhedra are shown and the other atoms are shown as spheres of arbitrary radii. The H atoms have been omitted. C—H···π interactions are shown as dotted lines.

poly[µ₂-hydroxido-κ²O:O-µ₂-2-pyridylacetato-κ³O,N:O'-dioxidouranium(VI)]

Crystal data

[U(C7H6NO2)O2(OH)]	Z = 2
Mr = 423.17	F(000) = 376
Triclinic, P1	Dx = 3.158 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.4056 (8) Å	Cell parameters from 17254 reflections
b = 8.2220 (6) Å	θ = 3.4–25.7°
c = 9.0916 (12) Å	µ = 18.23 mm^−1
α = 90.946 (8)°	T = 100 K
β = 96.487 (6)°	Irregular, translucent light yellow
γ = 110.425 (8)°	0.12 × 0.08 × 0.06 mm
V = 445.04 (9) Å^3

Data collection

Nonius–Kappa CCD area-detector diffractometer	1674 independent reflections
Radiation source: fine-focus sealed tube	1595 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.062
two ϕ and ten ω scans with 2° steps	θmax = 25.7°, θmin = 3.4°
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997)	h = −7→7
Tmin = 0.208, Tmax = 0.335	k = −10→10
17254 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.019	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.039	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + 0.1322P] where P = (Fo^2 + 2Fc^2)/3
1674 reflections	(Δ/σ)max = 0.001
127 parameters	Δρmax = 0.78 e Å^−3
0 restraints	Δρmin = −1.23 e Å^−3

Special details

Experimental. crystal-to-detector distance 40 mm

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Structure solved by direct methods and subsequent Fourier-difference synthesis. All non-hydrogen atoms were refined with anisotropic displacement parameters. The H atom bound to O5 was found on a Fourier-difference map and all the others were introduced at calculated positions. All were treated as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
U1	0.32099 (2)	0.28619 (2)	0.385816 (14)	0.01602 (8)
O1	0.3227 (5)	0.1625 (6)	0.5438 (3)	0.0201 (10)
O2	0.3107 (5)	0.3965 (6)	0.2201 (3)	0.0193 (9)
O3	−0.0761 (4)	0.2450 (5)	0.3768 (3)	0.0181 (8)
O4	−0.4319 (4)	0.1776 (5)	0.2749 (3)	0.0237 (9)
O5	0.3165 (4)	0.5211 (5)	0.5263 (3)	0.0208 (9)
H5	0.1939	0.5445	0.5384	0.025*
N1	0.0855 (5)	−0.0154 (6)	0.2496 (3)	0.0177 (10)
C1	0.1555 (7)	−0.1490 (8)	0.2801 (4)	0.0229 (13)
H1	0.2917	−0.1262	0.3396	0.027*
C2	0.0362 (7)	−0.3174 (8)	0.2277 (4)	0.0249 (13)
H2	0.0919	−0.4058	0.2496	0.030*
C3	−0.1693 (7)	−0.3528 (9)	0.1413 (4)	0.0257 (13)
H3	−0.2551	−0.4658	0.1056	0.031*
C4	−0.2443 (7)	−0.2177 (8)	0.1095 (4)	0.0216 (13)
H4	−0.3812	−0.2386	0.0515	0.026*
C5	−0.1116 (6)	−0.0479 (8)	0.1655 (4)	0.0178 (12)
C6	−0.1882 (7)	0.1002 (8)	0.1334 (4)	0.0208 (12)
H6A	−0.3235	0.0603	0.0627	0.025*
H6B	−0.0737	0.1888	0.0885	0.025*
C7	−0.2358 (7)	0.1793 (7)	0.2722 (4)	0.0182 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
U1	0.01239 (9)	0.01882 (17)	0.01675 (9)	0.00566 (9)	0.00117 (6)	−0.00059 (9)
O1	0.0173 (14)	0.024 (3)	0.0175 (13)	0.0059 (16)	−0.0004 (11)	0.0033 (15)
O2	0.0177 (14)	0.020 (3)	0.0174 (13)	0.0043 (16)	−0.0010 (11)	0.0003 (15)
O3	0.0137 (13)	0.025 (3)	0.0152 (13)	0.0059 (15)	0.0015 (10)	−0.0006 (15)
O4	0.0114 (14)	0.028 (3)	0.0314 (15)	0.0064 (15)	0.0023 (11)	−0.0025 (17)
O5	0.0138 (13)	0.027 (3)	0.0220 (14)	0.0084 (15)	0.0029 (11)	−0.0006 (16)
N1	0.0166 (17)	0.024 (3)	0.0176 (16)	0.0123 (19)	0.0062 (13)	0.0033 (18)
C1	0.018 (2)	0.027 (4)	0.023 (2)	0.007 (2)	0.0034 (16)	0.006 (2)
C2	0.029 (2)	0.026 (4)	0.023 (2)	0.013 (3)	0.0045 (18)	0.006 (2)
C3	0.026 (2)	0.023 (4)	0.024 (2)	0.003 (2)	0.0078 (17)	0.000 (2)
C4	0.017 (2)	0.028 (4)	0.021 (2)	0.009 (2)	0.0037 (16)	−0.003 (2)
C5	0.0145 (19)	0.021 (3)	0.0167 (19)	0.004 (2)	0.0071 (15)	0.001 (2)
C6	0.019 (2)	0.027 (4)	0.019 (2)	0.012 (2)	−0.0004 (15)	−0.003 (2)
C7	0.020 (2)	0.014 (3)	0.021 (2)	0.007 (2)	0.0043 (16)	0.000 (2)

Geometric parameters (Å, º)

U1—O1	1.775 (4)	C1—C2	1.373 (8)
U1—O2	1.778 (3)	C1—H1	0.9300
U1—O3	2.438 (3)	C2—C3	1.388 (6)
U1—O4^i	2.374 (3)	C2—H2	0.9300
U1—O5	2.308 (4)	C3—C4	1.378 (9)
U1—O5^ii	2.348 (3)	C3—H3	0.9300
U1—N1	2.612 (4)	C4—C5	1.408 (7)
U1—U1^ii	3.8713 (6)	C4—H4	0.9300
O3—C7	1.274 (4)	C5—C6	1.485 (8)
O4—C7	1.254 (5)	C6—C7	1.519 (6)
O5—H5	0.8892	C6—H6A	0.9700
N1—C5	1.338 (5)	C6—H6B	0.9700
N1—C1	1.346 (8)
O1—U1—O2	176.08 (14)	C5—N1—U1	123.7 (4)
N1—U1—O3	71.53 (12)	C1—N1—U1	117.3 (3)
O3—U1—O5	75.56 (10)	N1—C1—C2	123.4 (4)
O5—U1—O5^ii	67.49 (12)	N1—C1—H1	118.3
O5^ii—U1—O4^i	74.80 (11)	C2—C1—H1	118.3
O4^i—U1—N1	71.53 (11)	C1—C2—C3	118.6 (6)
U1—O5—U1^ii	112.51 (12)	C1—C2—H2	120.7
O1—U1—O5	92.37 (15)	C3—C2—H2	120.7
O2—U1—O5	91.17 (15)	C4—C3—C2	118.9 (6)
O1—U1—O5^ii	90.30 (13)	C4—C3—H3	120.5
O2—U1—O5^ii	92.61 (12)	C2—C3—H3	120.5
O1—U1—O4^i	92.84 (15)	C3—C4—C5	119.4 (4)
O2—U1—O4^i	85.40 (15)	C3—C4—H4	120.3
O5—U1—O4^i	141.94 (10)	C5—C4—H4	120.3
O1—U1—O3	93.75 (12)	N1—C5—C4	121.2 (6)
O2—U1—O3	85.50 (12)	N1—C5—C6	118.2 (5)
O5^ii—U1—O3	142.97 (12)	C4—C5—C6	120.6 (4)
O4^i—U1—O3	141.49 (10)	C5—C6—C7	112.2 (4)
O1—U1—N1	83.98 (15)	C5—C6—H6A	109.2
O2—U1—N1	92.13 (15)	C7—C6—H6A	109.2
O5—U1—N1	146.54 (10)	C5—C6—H6B	109.2
O5^ii—U1—N1	145.47 (12)	C7—C6—H6B	109.2
C7—O3—U1	129.5 (3)	H6A—C6—H6B	107.9
C7—O4—U1^iii	148.2 (3)	O4—C7—O3	124.1 (4)
U1—O5—H5	124.9	O4—C7—C6	117.1 (3)
U1^ii—O5—H5	122.3	O3—C7—C6	118.8 (4)
C5—N1—C1	118.6 (5)
C5—N1—C1—C2	0.8 (6)	C3—C4—C5—C6	−179.8 (4)
U1—N1—C1—C2	173.5 (3)	N1—C5—C6—C7	−65.4 (5)
N1—C1—C2—C3	−1.3 (7)	C4—C5—C6—C7	114.2 (4)
C1—C2—C3—C4	1.0 (6)	U1^iii—O4—C7—O3	15.1 (11)
C2—C3—C4—C5	−0.3 (6)	U1^iii—O4—C7—C6	−163.9 (4)
C1—N1—C5—C4	0.0 (6)	U1—O3—C7—O4	−173.8 (4)
U1—N1—C5—C4	−172.2 (3)	U1—O3—C7—C6	5.2 (7)
C1—N1—C5—C6	179.6 (4)	C5—C6—C7—O4	−119.7 (5)
U1—N1—C5—C6	7.3 (5)	C5—C6—C7—O3	61.3 (6)
C3—C4—C5—N1	−0.3 (6)

Symmetry codes: (i) x+1, y, z; (ii) −x+1, −y+1, −z+1; (iii) x−1, y, z.