First- and second- sphere coordination of the uranyl ion by bis­[2-(2-hydroxy­phenoxy)­ethoxy]­ethane

Uranyl nitrate hexahydrate reacts with bis­[2-(2-hydroxy­phenoxy)­ethoxy]­ethane (C₁₈H₂₂O₆), denoted LH₂ hereafter, in the presence of triethylamine to give ­triethylammonium aqua[2,2′-(3,6-dioxaoctane-1,8-diyldioxy)diphenolato-κ²O,O′](nitrato-κ²O,O′)dioxouranium(VI), (Et₃NH)[UO₂(H₂O)L(NO₃)], which possesses a symmetry plane. The uranyl ion is coordinated to the two phenoxide O atoms, a nitrate ion and a water mol­ecule (first sphere); the water mol­ecule is itself held in the crown ether chain by hydrogen-bonding interactions, thus ensuring second-sphere coordination by the ligand L.

S1. Comment

Bis[2-(2-hydroxyphenoxy)ethoxy]ethane, LH₂, which is analogous to dibenzo-24-crown-8 less one of the -[O(CH₂)₂]₃-O– ether chains, is a unit frequently encountered, further linked in the 6-position of both aromatic rings, in macrocycles designed for metal ion complexation, such as Schiff bases (Casellato et al., 1997). The ligands thus obtained have been used in the synthesis of heterobinuclear species (see, for example: Reetz et al., 1995; Arion et al., 1998). We report herein the crystal structure of the uranyl ion complex of the dianionic ligand L, (I), which presents some interesting features. Up to now, the only structure reported for this molecule is that of its hydrate (Suh et al., 1985). The structure of the sodium isothiocyanate complex of the related dimethoxy ligand has also been described (Suh et al., 1978). We reported previously the structure of a compound with a shorter ether chain, bis[2-(2-hydroxyphenoxy)ethyl]ether as a methanol solvate (Thuéry, Nierlich & Masci, 2002), in which the methanol molecule, as the water molecule in the hydrate cited above, is hydrogen bonded to phenolic and ether O atoms.

The asymmetric unit of (I) comprises half the complex unit and its counter-ion, the whole molecular assembly being given by a symmetry plane containing the uranyl ion. The uranyl ion is bound in its equatorial plane to the doubly deprotonated ligand L by the two equivalent phenoxide O atoms, with a U—O bond length of 2.180 Å, slightly shorter than the U—O(phenoxide) bond length in uranyl calixarene complexes (Thuéry, Nierlich, Harrowfield & Ogden, 2001). The metal atom is also bound to two equivalent nitrate O atoms, with a U—O bond length of 2.521 (7) Å, as usual, and to a water molecule with a U—O distance of 2.478 (11) Å. Together with the two oxo atoms, these five donor O atoms constitute the uranium first coordination sphere, which displays the common pentagonal bipyramidal geometry, distorted due mainly to the small 'bite' of the chelating nitrate ion. The five equatorial donor O atoms define a plane with a r.m.s. deviation of 0.024 Å, the U atom being at 0.007 (5) Å from this plane. The two aromatic rings are nearly orthogonal, with a dihedral angle of 89.6 (3)°. This coordination geometry is much different from the wrapping, annular structure observed in the sodium complex of the dimethoxy derivative (Suh et al., 1978).

The coordinated water molecule is located near the centre of the O2···O2' diameter of the semi-circle defined by the ether chain, which, if the phenolic rings are neglected, is analogous to half a 18-crown-6 moiety. The atoms O2 and O3 are located at -0.50 (1) and 0.07 (2) Å from the mean O₅ plane defined above. The distances between O8 and the ether O atoms are indicative of loose hydrogen bonds [O8···O2 3.095 (11), O8···O3 2.942 (14) Å, the O2···O8···O3' angle, 111.7 (4)°, is also compatible with a bonding of both water H atoms to these two ether O atoms]. However, the water H atoms having not been found, it appears impossible to describe more precisely the nature, possibly bifurcated, of the hydrogen bonding in this case. It may be noted that, in the hydrate of LH₂ (Suh et al., 1985), in which the H atoms have been located, the O(water)···O(ether) distances corresponding to possible hydrogen bonds are comparable to the present ones (2.916–3.039 Å). The situation is however somewhat different in the hydrate since hydrogen bonds involving the phenolic groups are also present. The conformation of the ether chain is characterized by C—O—C—C torsion angles near to 180° (anti angles), an O2—C7—C8—O3 gauche torsion angle of 65 (2)° and a more unusual O3—C9—C9'—O3' angle (0° by symmetry). The ligand L in (I) appears as a ditopic ligand: the phenoxide groups only are involved in first-sphere coordination of the uranyl ion, whereas the ether coordination site is involved in second-sphere, non-covalent, bonding via the first-sphere water ligand. Second-sphere coordination is a well documented feature (Alston et al., 1989; Atwood et al. 1991; Steed, 2001). The present case reminds second-sphere coordination via intramolecular hydrogen bonding of hydrated alkali metal cations by crown ethers (Steed, 2001 and references therein).

The triethylammonium ion in (I) is located 'above' the complex anion and is likely involved in a hydrogen bond with the oxo atom O5, with a N2···O5 distance of 3.22 (6) Å (this bond may result in the U—O5 bond length being slightly larger than the U—O4 one). Such hydrogen bonds between ammonium counter-ions and oxo atoms are very frequent in uranyl complexes (Thuéry, Nierlich, Harrowfield & Ogden, 2001 and references therein). The ammonium ion is further 'capped' by the cavity formed by the aromatic rings of the neighbouring molecule along the c axis, but no strong C—H···π interactions are to be expected, the shortest H···C(aromatic) distance being 2.736 Å.

S2. Experimental

The ligand LH₂ was prepared as reported previously (Bartsch et al., 1983). LH₂ was reacted with UO₂(NO₃)₂·6H₂O in boiling CHCl₃—CH₃CN (3:1), in presence of a large excess of NEt₃. On slow evaporation, the resulting orange solution deposited crystals suitable for X-ray crystallography.

S3. Refinement

A 180° range in ϕ was scanned during data collection, with 2° ϕ steps. Crystal-to-detector distance fixed at 28 mm.

The water H atoms, likely disordered over the four positions compatible with hydrogen bonding with the ether O atoms, as well as the proton bound to the ammonium N atom were not found on the Fourier-difference map. All other H atoms were introduced at calculated positions with C—H bond lengths of 0.93 (CH), 0.97 (CH₂) or 0.96 (CH₃) Å, and treated as riding atoms with a displacement parameter equal to 1.2 (CH, CH₂) or 1.5 (CH₃) times that of the parent atom. The methyl group in general position was refined as a rotating rigid group, whereas the one located on the symmetry plane was not allowed to rotate.

Computing details

Data collection: KappaCCD Software (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL (Bruker, 1999); PARST97 (Nardelli, 1995).

Figures

Fig. 1. The title molecule (I) with the atomic numbering scheme. H atoms are drawn as small spheres of arbitrary radii. Possible hydrogen bonds are shown as dashed lines. Displacement ellipsoids are drawn at the 30% probability level. The triethylammonium counter-ion has been omitted for clarity. Symmetry code: (i) 1 - x, y, z.

(I)

Crystal data

O5NU·H2O·C18H20O6·C6H16N	Dx = 1.817 Mg m^−3
Mr = 784.59	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pmn21	Cell parameters from 9425 reflections
a = 15.6688 (10) Å	θ = 2.6–25.7°
b = 9.6025 (5) Å	µ = 5.72 mm^−1
c = 9.5303 (7) Å	T = 100 K
V = 1433.93 (16) Å^3	Needle-like, dark red (translucent)
Z = 2	0.20 × 0.08 × 0.05 mm
F(000) = 768

Data collection

Nonius Kappa-CCD diffractometer	2768 independent reflections
Radiation source: fine-focus sealed tube	2546 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.061
Detector resolution: 18 pixels mm^-1	θmax = 25.7°, θmin = 2.6°
ϕ scans	h = −19→17
Absorption correction: empirical (using intensity measurements) program DELABS from PLATON (Spek, 2000)	k = −11→11
Tmin = 0.326, Tmax = 0.756	l = −11→11
9425 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.091	w = 1/[σ^2(Fo^2) + (0.0249P)^2 + 4.7737P] where P = (Fo^2 + 2Fc^2)/3
S = 1.20	(Δ/σ)max = 0.001
2768 reflections	Δρmax = 1.46 e Å^−3
191 parameters	Δρmin = −0.60 e Å^−3
0 restraints	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.024 (16)

Special details

Experimental. crystal-to-detector distance 28 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 expanded by subsequent Fourier-difference synthesis. One of the CH2—CH3 chains of the triethylammonium ion is disordered around the symmetry plane. Some restraints on bond distances and displacement parameters have been applied to this badly resolved cation. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were introduced at calculated positions, except those in the disordered part and the one bound to N2, which has not been found on the Fourier-difference map. Hydrogen atoms were treated as riding atoms with an isotropic displacement parameter equal to 1.2 (CH, CH2) or 1.5 (CH3) times that of the parent atom. The highest residual density peaks are located near the badly resolved triethylammonium cation. All other peaks are lower than 1 e A-3. 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
U	0.5000	0.81788 (4)	0.83420 (9)	0.01875 (13)
N1	0.5000	0.5491 (13)	0.6879 (13)	0.035 (3)
O1	0.6362 (4)	0.8565 (7)	0.8591 (8)	0.028 (2)
O2	0.6930 (7)	1.0573 (9)	1.0227 (10)	0.040 (3)
O3	0.5919 (7)	1.2843 (8)	1.0774 (10)	0.064 (3)
O4	0.5000	0.7302 (10)	0.9987 (10)	0.026 (2)
O5	0.5000	0.8994 (11)	0.6619 (10)	0.032 (2)
O6	0.5686 (4)	0.6085 (8)	0.7213 (8)	0.0372 (17)
O7	0.5000	0.4338 (14)	0.6098 (19)	0.065 (4)
O8	0.5000	1.0467 (12)	0.9543 (11)	0.051 (3)
C1	0.6964 (6)	0.8250 (12)	0.9520 (10)	0.030 (2)
C2	0.7302 (7)	0.6932 (14)	0.9637 (12)	0.042 (3)
H2	0.7100	0.6244	0.9036	0.051*
C3	0.7941 (9)	0.6565 (17)	1.0622 (16)	0.058 (4)
H3	0.8157	0.5664	1.0679	0.069*
C4	0.8229 (7)	0.7622 (16)	1.1497 (13)	0.043 (3)
H4	0.8641	0.7418	1.2168	0.052*
C5	0.7922 (9)	0.8965 (14)	1.1402 (13)	0.034 (3)
H5	0.8138	0.9662	1.1979	0.041*
C6	0.7284 (6)	0.9264 (11)	1.0427 (10)	0.031 (2)
C7	0.7207 (12)	1.1653 (13)	1.1141 (16)	0.067 (4)
H7A	0.7824	1.1723	1.1130	0.081*
H7B	0.7024	1.1465	1.2095	0.081*
C8	0.6821 (9)	1.2947 (17)	1.063 (2)	0.067 (5)
H8A	0.7033	1.3733	1.1163	0.080*
H8B	0.6969	1.3089	0.9649	0.080*
C9	0.5484 (3)	1.4065 (14)	1.035 (2)	0.090 (6)
H9A	0.5671	1.4289	0.9407	0.108*
H9B	0.5671	1.4818	1.0955	0.108*
N2	0.5000	0.938 (2)	0.326 (6)	0.111 (12)
C10	0.4200 (3)	0.8625 (16)	0.320 (3)	0.047 (5)
H10A	0.4036	0.8659	0.2217	0.063*
H10B	0.3795	0.9213	0.3688	0.063*
C11	0.3992 (10)	0.7194 (14)	0.3652 (16)	0.077 (5)
H11A	0.3402	0.7002	0.3465	0.115*
H11B	0.4097	0.7114	0.4642	0.115*
H11C	0.4342	0.6538	0.3156	0.115*
C12	0.5000	1.0862 (16)	0.294 (3)	0.052 (4)
H12A	0.4505	1.1078	0.2389	0.063*
C13	0.5000	1.1752 (19)	0.4247 (19)	0.068 (3)
H13A	0.5000	1.2718	0.3987	0.102*
H13B	0.4500	1.1551	0.4792	0.102*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
U	0.01938 (19)	0.01855 (19)	0.01833 (19)	0.000	0.000	0.0008 (5)
N1	0.039 (7)	0.028 (6)	0.038 (7)	0.000	0.000	−0.016 (6)
O1	0.020 (3)	0.045 (3)	0.020 (6)	−0.010 (2)	0.001 (3)	−0.003 (3)
O2	0.054 (5)	0.024 (4)	0.041 (4)	−0.013 (4)	−0.019 (4)	0.003 (4)
O3	0.113 (7)	0.025 (4)	0.055 (5)	0.004 (4)	0.012 (5)	0.004 (3)
O4	0.025 (5)	0.024 (5)	0.028 (5)	0.000	0.000	0.001 (4)
O5	0.038 (6)	0.038 (6)	0.022 (5)	0.000	0.000	0.004 (4)
O6	0.027 (4)	0.040 (4)	0.044 (4)	0.008 (3)	−0.007 (3)	−0.017 (4)
O7	0.025 (6)	0.044 (8)	0.127 (13)	0.000	0.000	−0.005 (8)
O8	0.086 (9)	0.032 (6)	0.033 (6)	0.000	0.000	−0.010 (5)
C1	0.023 (5)	0.050 (6)	0.018 (4)	−0.008 (5)	0.005 (4)	−0.002 (5)
C2	0.021 (5)	0.070 (8)	0.037 (6)	0.000 (6)	0.004 (4)	−0.025 (6)
C3	0.040 (7)	0.069 (10)	0.063 (9)	0.019 (7)	−0.014 (6)	−0.032 (8)
C4	0.022 (5)	0.075 (10)	0.033 (6)	0.011 (6)	−0.002 (5)	−0.020 (6)
C5	0.036 (6)	0.041 (8)	0.026 (6)	−0.019 (6)	−0.009 (5)	−0.007 (6)
C6	0.025 (5)	0.040 (6)	0.027 (5)	−0.018 (5)	0.004 (4)	−0.005 (4)
C7	0.080 (7)	0.055 (6)	0.067 (7)	−0.023 (6)	−0.026 (6)	0.005 (6)
C8	0.087 (9)	0.046 (7)	0.067 (8)	−0.011 (6)	−0.030 (7)	0.003 (6)
C9	0.096 (9)	0.074 (8)	0.100 (9)	−0.016 (7)	−0.028 (7)	0.010 (7)
N2	0.124 (14)	0.101 (14)	0.108 (14)	0.000	0.000	−0.005 (8)
C10	0.046 (6)	0.054 (7)	0.041 (7)	0.028 (5)	0.001 (5)	0.000 (5)
C11	0.058 (6)	0.098 (7)	0.074 (9)	0.012 (6)	−0.015 (6)	−0.039 (6)
C12	0.058 (7)	0.051 (7)	0.046 (7)	0.000	0.000	0.002 (6)
C13	0.076 (7)	0.064 (6)	0.063 (6)	0.000	0.000	0.004 (5)

Geometric parameters (Å, º)

U—O1	2.180 (6)	C4—H4	0.9300
U—O4	1.779 (9)	C5—C6	1.395 (17)
U—O5	1.819 (9)	C5—H5	0.9300
U—O6	2.521 (7)	C7—C8	1.47 (2)
U—O8	2.478 (11)	C7—H7A	0.9700
U—O1^i	2.180 (6)	C7—H7B	0.9700
U—O6^i	2.521 (7)	C8—H8A	0.9700
N1—O6	1.257 (9)	C8—H8B	0.9700
N1—O6^i	1.257 (9)	C9—C9^i	1.516 (10)
N1—O7	1.335 (18)	C9—H9A	0.9700
O1—C1	1.328 (13)	C9—H9B	0.9700
O2—C6	1.387 (14)	N2—C10	1.448 (9)
O2—C7	1.422 (9)	N2—C10^i	1.448 (9)
O8—O2	3.095 (11)	N2—C12	1.46 (3)
O3—C9	1.415 (9)	C10—C11	1.478 (10)
O3—C8	1.423 (10)	C10—H10A	0.9700
O8—O3	2.942 (14)	C10—H10B	0.9700
N2—O5	3.22 (6)	C11—H11A	0.9600
C1—C2	1.376 (16)	C11—H11B	0.9600
C1—C6	1.395 (14)	C11—H11C	0.9600
C2—C3	1.417 (18)	C12—C13	1.51 (3)
C2—H2	0.9300	C12—H12A	0.9600
C3—C4	1.389 (19)	C13—H13A	0.9600
C3—H3	0.9300	C13—H13B	0.9600
C4—C5	1.38 (2)
O1—U—O6	76.4 (2)	C5—C6—C1	121.8 (11)
O6^i—U—O6	50.4 (3)	O2—C7—C8	106.7 (13)
O1—U—O8	78.40 (18)	O2—C7—H7A	110.4
O1^i—U—O1	156.7 (4)	C8—C7—H7A	110.4
O4—U—O5	177.3 (5)	O2—C7—H7B	110.4
O1^i—U—O8	78.40 (18)	C8—C7—H7B	110.4
O4—U—O1^i	89.1 (2)	H7A—C7—H7B	108.6
O5—U—O1^i	91.4 (2)	O3—C8—C7	108.5 (13)
O4—U—O1	89.1 (2)	O3—C8—H8A	110.0
O5—U—O1	91.4 (2)	C7—C8—H8A	110.0
O4—U—O8	90.7 (4)	O3—C8—H8B	110.0
O5—U—O8	92.0 (4)	C7—C8—H8B	110.0
O4—U—O6^i	89.9 (3)	H8A—C8—H8B	108.4
O5—U—O6^i	87.6 (4)	O3—C9—C9^i	118.8 (6)
O1^i—U—O6^i	76.4 (2)	O3—C9—H9A	107.6
O1—U—O6^i	126.8 (2)	C9^i—C9—H9A	107.6
O8—U—O6^i	154.77 (17)	O3—C9—H9B	107.6
O4—U—O6	89.9 (3)	C9^i—C9—H9B	107.6
O5—U—O6	87.6 (3)	H9A—C9—H9B	107.0
O1^i—U—O6	126.8 (2)	C10—N2—C10^i	119.8 (13)
O8—U—O6	154.77 (17)	C10—N2—C12^i	118.6 (9)
O6—N1—O6^i	117.4 (11)	C10—N2—C12	118.6 (9)
O6—N1—O7	121.2 (5)	N2—C10—C11	130.0 (14)
O6^i—N1—O7	121.2 (6)	N2—C10—H10A	104.8
C6—O2—C7	117.0 (10)	C11—C10—H10A	104.8
C9—O3—C8	113.1 (9)	N2—C10—H10B	104.8
O1—C1—C2	122.4 (9)	C11—C10—H10B	104.8
O1—C1—C6	120.6 (10)	H10A—C10—H10B	105.8
C2—C1—C6	117.0 (10)	C10—C11—H11A	109.3
C1—C2—C3	123.7 (11)	C10—C11—H11B	108.9
C1—C2—H2	118.2	H11A—C11—H11B	109.5
C3—C2—H2	118.2	C10—C11—H11C	109.1
C4—C3—C2	116.4 (13)	H11A—C11—H11C	109.5
C4—C3—H3	121.8	H11B—C11—H11C	109.5
C2—C3—H3	121.8	N2—C12—C13	112 (3)
C5—C4—C3	122.1 (12)	N2—C12—H12A	109.1
C5—C4—H4	119.0	C13—C12—H12A	109.2
C3—C4—H4	119.0	C12^i—C13—H13A	109.5
C4—C5—C6	119.1 (11)	C12—C13—H13A	109.5
C4—C5—H5	120.5	C12^i—C13—H13B	109.5
C6—C5—H5	120.5	C12—C13—H13B	109.5
O2—C6—C5	124.4 (9)	H13A—C13—H13B	109.5
O2—C6—C1	113.8 (9)

Symmetry code: (i) −x+1, y, z.