Uranyl dinitrate trihydrate, UO₂(NO₃)₂(H₂O)₃

The structure of the title compound, which has been synthesized by evaporation at 294 K, consists of centrosymmetric uranyl hexagonal bipyramids that share opposite equatorial edges with two nitrate triangles, resulting in two distinct finite clusters of composition [(UO₂)(H₂O)₂(NO₃)₂]. There are two unique symmetrically independent U^VI positions and two unique nitrate groups.

S1. Comment

UO₂(NO₃)₂(H₂O)₃ was first obtained as a by-product in a synthesis experiment intended to produce uranyl carbonates by room-temperature evaporation of a solution containing uranyl nitrate with various carbonates and nitrates. Subsequently, large single crystals of UO₂(NO₃)₂(H₂O)₃ were obtained from a solution of UO₂(NO₃)(H₂O)₆, K₂CO₃ and Cu(NO₃)₂(H₂O)₃ at room temperature and pressure. The structures are known or estimated for the chemically related compounds (UO₂)(NO₃)₂(H₂O)₂ (Taylor & Mueller, 1965), (UO₂)(NO₃)₂(H₂O)₆ (Dalley et al., 1971) and (UO₂)(NO₃)₂(H₂O)₃ (Vdovenko et al., 1963). Each contains the [(UO₂)(H₂O)₂(NO₃)₂] finite cluster. These compounds crystallize in space groups Cmc2₁, P2₁/c and P1, respectively. Whereas (UO₂)(NO₃)₂(H₂O)₂ and (UO₂)(NO₃)₂(H₂O)₆ differ from UO₂(NO₃)₂(H₂O)₃ in their hydration state and space group, the structure published by Vdovenko et al. (1963) corresponds to that for UO₂(NO₃)₂(H₂O)₃. That published structure is incomplete, as only the U and O atoms were located. The refined structure, including N-atom positions, is given herein.

There are two symmetrically distinct U^VI atoms, positioned on centers of symmetry, both of which are part of linear (UO₂)²⁺ uranyl ions and which are coordinated by six equatorial atoms of O, forming hexagonal bipyramids (Fig. 1). Two opposite equatorial edges of each hexagonal bipyramid share edges with NO₃ groups, giving the [(UO₂)(H₂O)₂(NO₃)₂] cluster. Two H₂O groups correspond to equatorial ligands of the uranyl polyhedra. One H₂O group is located between the [(UO₂)(H₂O)₂(NO₃)₂] clusters (Fig. 2).

Bond-valence sums were calculated for each ion using the method of Brese & O'Keeffe (1991). The U bond-valence sums (Burns at al., 1997) are 6.18 and 6.12 for the two unique U positions. The N bond-valence sums are 5.29 and 5.07. For O-atom positions O1, O3, O4, O5, O7, O8, O9 and O10, the bond-valence sums are within the normal range (1.80–2.07). For atoms O2, O6 and O11, values consistant with H₂O were obtained (0.44, 0.46 and 0.00, respectively).

S2. Experimental

Transparent yellow crystals of UO₂(NO₃)₂(H₂O)₃ up to 1 mm in maximum dimension were synthesized from a solution containing Cu(NO₃)₂(H₂O)₃, UO₂(NO₃)₂(H₂O)₆ and K₂CO₃, in a molar ratio of 2:5:1, in solution in water (50 ml). Following evaporation in an open vessel for 14 d at 294 K and ambient pressure, crystals were recovered from the vessel walls.

S3. Refinement

The locations of the highest peak, 2.07 e Å⁻³, and deepest hole, −1.31 e Å⁻³, in the difference Fourier map are 0.79 Å from U2 and 0.86 Å from U1, respectively. H-atom positions were not included in the refinement.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SHELXTL-NT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: Microsoft Word.

Figures

	Fig. 1. Views of the two UO2(NO3)2 clusters in UO2(NO3)2(H2O)3, shown with 50% probability displacement ellipsoids.
	Fig. 2. The crystal structure of UO2(NO3)2(H2O)3 projected along [100]. Uranyl hexagonal bipyramids are shown in light grey, nitrate triangles in black and free H2O in dark grey.

Uranyl dinitrate trihydrate

Crystal data

UO2(NO3)2(H2O)3	Z = 2
Mr = 448.08	F(000) = 400
Triclinic, P1	Dx = 3.31 Mg m^−3
a = 7.0359 (15) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.1730 (15) Å	Cell parameters from 3612 reflections
c = 10.084 (2) Å	θ = 3–34.5°
α = 81.697 (4)°	µ = 18.10 mm^−1
β = 82.041 (4)°	T = 298 K
γ = 63.642 (4)°	Block-like, yellow
V = 449.64 (16) Å^3	0.12 × 0.11 × 0.10 mm

Data collection

Make Model CCD area-detector diffractometer	3614 independent reflections
Radiation source: fine-focus sealed tube	2138 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.090
ω scans	θmax = 34.5°, θmin = 2.1°
Absorption correction: empirical (using intensity measurements) (SHELXL97; Sheldrick, 1997a)	h = −10→11
Tmin = 0.098, Tmax = 0.164	k = −11→11
9093 measured reflections	l = −15→15

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)] = 0.043	H-atom parameters not refined
wR(F^2) = 0.109	w = 1/[σ^2(Fo^2) + (0.022P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
3614 reflections	Δρmax = 2.08 e Å^−3
130 parameters	Δρmin = −1.34 e Å^−3
0 restraints

Special details

Experimental. psi-scan absorption correction in XPREP

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. 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	0.5	0.5	0.5	0.02672 (13)
U2	0.5	0.0	0.0	0.02345 (13)
N1	0.7299 (13)	0.7396 (12)	0.5443 (8)	0.0317 (17)
N2	0.1821 (12)	0.3840 (11)	0.1100 (7)	0.0290 (16)
O1	0.6923 (11)	0.2816 (10)	0.5820 (7)	0.0379 (16)
O2	0.2872 (11)	0.5974 (10)	0.7145 (6)	0.0381 (16)
O3	0.7583 (12)	0.6536 (11)	0.4372 (7)	0.0425 (18)
O4	0.5901 (12)	0.7177 (12)	0.6281 (7)	0.0461 (19)
O5	0.3921 (10)	0.0888 (9)	−0.1553 (6)	0.0323 (15)
O6	0.2587 (11)	−0.1640 (11)	0.0681 (7)	0.0427 (18)
O7	0.1515 (10)	0.2201 (10)	0.1133 (7)	0.0355 (15)
O8	0.3585 (10)	0.3756 (9)	0.0545 (6)	0.0346 (15)
O9	0.8370 (13)	0.8224 (12)	0.5642 (8)	0.053 (2)
O10	0.0494 (12)	0.5377 (10)	0.1591 (8)	0.0455 (19)
O11	−0.0687 (10)	−0.0235 (10)	0.2683 (7)	0.0347 (15)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
U1	0.0220 (3)	0.0269 (3)	0.0279 (3)	−0.0078 (2)	0.0013 (2)	−0.0049 (2)
U2	0.0212 (3)	0.0219 (2)	0.0275 (3)	−0.0092 (2)	0.0034 (2)	−0.0075 (2)
N1	0.023 (4)	0.023 (4)	0.020 (4)	−0.011 (3)	0.002 (3)	−0.005 (3)
N2	0.021 (4)	0.016 (3)	0.021 (4)	−0.007 (3)	0.007 (3)	−0.006 (3)
O1	0.027 (4)	0.030 (3)	0.048 (4)	−0.006 (3)	−0.008 (3)	0.001 (3)
O2	0.039 (4)	0.037 (4)	0.034 (4)	−0.014 (3)	0.011 (3)	−0.007 (3)
O3	0.039 (4)	0.045 (4)	0.045 (4)	−0.019 (4)	0.005 (4)	−0.008 (4)
O4	0.041 (5)	0.057 (5)	0.046 (5)	−0.026 (4)	0.014 (4)	−0.016 (4)
O5	0.037 (4)	0.028 (3)	0.027 (3)	−0.010 (3)	−0.006 (3)	−0.006 (3)
O6	0.041 (4)	0.043 (4)	0.052 (5)	−0.027 (4)	0.015 (4)	−0.020 (4)
O7	0.029 (4)	0.037 (4)	0.043 (4)	−0.018 (3)	0.008 (3)	−0.012 (3)
O8	0.031 (4)	0.029 (3)	0.047 (4)	−0.015 (3)	0.007 (3)	−0.012 (3)
O9	0.056 (6)	0.051 (5)	0.066 (6)	−0.031 (5)	−0.001 (4)	−0.015 (4)
O10	0.042 (4)	0.032 (4)	0.054 (5)	−0.015 (3)	0.019 (4)	−0.021 (3)
O11	0.030 (4)	0.037 (4)	0.035 (4)	−0.013 (3)	0.002 (3)	−0.009 (3)

Geometric parameters (Å, º)

U1—O1	1.738 (6)	U2—O8	2.539 (6)
U1—O2	2.453 (6)	N1—O9	1.198 (10)
U1—O3	2.485 (7)	N1—O4	1.255 (10)
U1—O4	2.490 (7)	N1—O3	1.269 (10)
U2—O5	1.745 (6)	N2—O10	1.203 (9)
U2—O6	2.440 (7)	N2—O8	1.269 (9)
U2—O7	2.473 (7)	N2—O7	1.281 (9)
O1^i—U1—O1	180.0	O5—U2—O7	89.8 (3)
O1—U1—O2	90.6 (3)	O6—U2—O7	64.0 (2)
O2^i—U1—O2	180.0	O7—U2—O7^ii	180.0
O1—U1—O3	90.4 (3)	O5—U2—O8	89.7 (2)
O2—U1—O3	114.6 (2)	O6—U2—O8	115.5 (2)
O3—U1—O3^i	180.0	O7—U2—O8	51.4 (2)
O1—U1—O4	87.6 (3)	O8—U2—O8^ii	180.0
O2—U1—O4	64.4 (2)	O9—N1—O4	124.4 (9)
O3—U1—O4	50.2 (2)	O9—N1—O3	121.9 (9)
O4—U1—O4^i	180.0	O4—N1—O3	113.6 (8)
O5—U2—O5^ii	180.0	O10—N2—O8	121.8 (8)
O5—U2—O6	89.9 (3)	O10—N2—O7	121.1 (8)
O6^ii—U2—O6	180.0	O8—N2—O7	117.1 (7)

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