Reinvestigation of tris­­odium di­hydroxido­tetra­oxidoneptunate(VII) dihydrate

The title compound, Na₃[NpO₄(OH)₂]·2H₂O, contains distorted tetra­gonal–bipyramidal centrosymmetric [NpO₄(OH)₂]³⁻ complex anions. The Np—O distances are 1.8975 (7) and 1.8891 (7) Å in the NpO₄ group and 2.3451 (7) Å to the OH group. Both Na atoms (one in a general position, the second in a special position on an inversion centre) have a distorted octahedral oxygen environment.

Related literature

The structure of Na₃[NpO₄(OH)₂]·2H₂O was investigated by photographic technique with visual estimation of reflection intensities by Tomilin et al. (1981a). Several other Np^VII compounds containing [NpO₄(OH)₂]³⁻ anions have been studied by photographic techniques, viz. Na₃[NpO₄(OH)₂] (Tomilin et al., 1981b), Na₃[NpO₄(OH)₂]·4H₂O (Tomilin et al., 1981c), K₃[NpO₄(OH)₂]·2H₂O (Tomilin et al., 1983). Diffractometric structure determinations have been made for [Co(NH₃)₆][NpO₄(OH)₂]·2H₂O (Grigor'ev et al., 1986), Cs₃[NpO₄(OH)₂]·3H₂O (Grigor'ev et al., 1993), K₃[NpO₄(OH)₂]·2H₂O (Charushnikova et al., 2007) and Na₃[NpO₄(OH)₂] (Grigoriev & Krot, 2007).

Experimental

Crystal data

• Na₃[NpO₄(OH)₂]·2H₂O

• M_r = 440.02

• Monoclinic, P 2₁ /c

• a = 7.8166 (3) Å

• b = 7.7703 (2) Å

• c = 6.8211 (2) Å

• β = 112.9139 (14)°

• V = 381.60 (2) ų

• Z = 2

• Mo Kα radiation

• μ = 13.79 mm⁻¹

• T = 100 (2) K

• 0.12 × 0.08 × 0.02 mm

Data collection

• Bruker Kappa APEXII area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 2004) T_min = 0.522, T_max = 0.770

• 16264 measured reflections

• 2357 independent reflections

• 1920 reflections with I > 2σ(I)

• R_int = 0.024

Refinement

• R[F² > 2σ(F²)] = 0.010

• wR(F²) = 0.021

• S = 1.04

• 2357 reflections

• 70 parameters

• 3 restraints

• All H-atom parameters refined

• Δρ_max = 0.75 e Å⁻³

• Δρ_min = −0.88 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

Np—O1	1.8975 (7)
Np—O2	1.8891 (7)
Np—O3	2.3451 (7)

O1—Np—O2	91.41 (3)
O1—Np—O3	90.82 (3)
O2—Np—O3	94.67 (3)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O1^i	0.815 (15)	1.976 (16)	2.7866 (10)	173 (2)
O4—H4A⋯O3	0.856 (17)	1.799 (17)	2.6538 (12)	178 (2)
O4—H4B⋯O3^ii	0.840 (16)	1.931 (16)	2.7612 (12)	169 (2)
Symmetry codes: (i) ; (ii) -x+2, -y+1, -z+1.

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL97 (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL97.

Supporting information

S1. Comment

The title compound, (I) (Fig. 1), contains centrosymmetric complex anions [NpO₄(OH)₂]^3- which are distorted tetragonal bipyramidal. The main bond lengths and angles in this anion are given in Table 1. The Np—O distances in the NpO₄ group are close to the values 1.8981 (13) and 1.9012 (12) Å found in Na₃[NpO₄(OH)₂] (Grigoriev & Krot, 2007). The Np—O distance to the OH group is a little longer than 2.3145 (11) Å in Na₃[NpO₄(OH)₂].

Principal features of structure are the same as described by Tomilin et al. (1981a).

The Na1 atom occupies a special position on an inversion centre and has a distorted octahedral oxygen environment formed by six O atoms of two [NpO₄(OH)₂]^3- anions. The Na1 atoms and [NpO₄(OH)₂]^3- anions form columns along the [001] direction, the layers of the columns are parallel to the (100) plane (Fig. 2). The Na2 atoms and crystallization water molecules occupy general positions between the layers. The Na2 atom has a distorted octahedral oxygen environment formed by O atoms of [NpO₄(OH)₂]^3- anions and water molecules.

The OH group acts as proton donor in a hydrogen bond with an O atom of NpO₄ group of a neighbouring anion (Table 2). This hydrogen bond is stronger than the bond formed by OH group in Na₃[NpO₄(OH)₂] [the O···O distance 3.0255 (17)]. Such a difference can be one of the reasons for the elongation of the Np—O3 bond in (I). Water molecule makes two hydrogen bonds with O atoms of OH groups.

Related literature

The structure of Na₃[NpO₄(OH)₂].2H₂O was investigated by photographic technique with visual estimation of reflection intensities by Tomilin et al. (1981a). Several other Np^VII compounds containing [NpO₄(OH)₂]^3- anions have been studied by photographic techniques, viz. Na₃[NpO₄(OH)₂] (Tomilin et al., 1981b), Na₃[NpO₄(OH)₂].4H₂O (Tomilin et al., 1981c), K₃[NpO₄(OH)₂].2H₂O (Tomilin et al., 1983). Diffractometric structure determinations have been made for [Co(NH₃)₆][NpO₄(OH)₂].2H₂O (Grigor'ev et al., 1986), Cs₃[NpO₄(OH)₂].3H₂O (Grigor'ev et al., 1993), K₃[NpO₄(OH)₂].2H₂O (Charushnikova et al., 2007) and Na₃[NpO₄(OH)₂] (Grigoriev & Krot, 2007).

S2. Experimental

The starting solution for the synthesis of (I) was slightly acidic (pH ~3) 0.15 M ²³⁷NpO₂(NO₃)₂. The preparation of such solutions is described by Charushnikova et al. (2007). For the synthesis of (I), 1 ml of 0.15 M NpO₂(NO₃)₂ aqueous solution was taken into a bubble flask, 1 ml of 5 M LiOH solution was added, then ozonized oxygen (10% mass of O₃) was passed through the solution over a period of 2 h. Aliquots of 0.1 ml of the solution were put into plastic containers, 0.05, 0.1 or 0.2 ml of 16.7 M NaOH was added, and the containers were placed into a desiccator with granulated KOH (to absorb CO₂ and water vapour). After four days at room temperature almost all the Np^VII was crystallized as bulk black crystals.

S3. Refinement

The H atoms of the OH-group and crystallization water molecule were located on a difference Fourier map and refined with individual displacement parameters and O—H distances restrained to 0.82 (2) and 0.85 (2) Å, respectively.

Computing details

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 1998); data reduction: SAINT-Plus (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL97 (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL97 (Sheldrick, 1997b).

Figures

	Fig. 1. A view of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented by circles of arbitrary size. Dashed line indicates the hydrogen-bonding interaction. [Symmetry code: (i) 1 - x, 1 - y, 1 - z.]
	Fig. 2. The unit cell of (I).

trisodium dihydroxidotetraoxidoneptunate(VII) dihydrate

Crystal data

Na3[NpO4(OH)2]·2H2O	F(000) = 392
Mr = 440.02	Dx = 3.829 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5517 reflections
a = 7.8166 (3) Å	θ = 3.9–40.0°
b = 7.7703 (2) Å	µ = 13.79 mm^−1
c = 6.8211 (2) Å	T = 100 K
β = 112.9139 (14)°	Plate, black
V = 381.60 (2) Å^3	0.12 × 0.08 × 0.02 mm
Z = 2

Data collection

Bruker Kappa APEXII area-detector diffractometer	2357 independent reflections
Radiation source: fine-focus sealed tube	1920 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ω and φ scans	θmax = 40.0°, θmin = 3.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −14→14
Tmin = 0.522, Tmax = 0.770	k = −12→14
16264 measured reflections	l = −12→12

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)] = 0.010	Hydrogen site location: difference Fourier map
wR(F^2) = 0.021	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0059P)^2 + 0.087P] where P = (Fo^2 + 2Fc^2)/3
2357 reflections	(Δ/σ)max = 0.001
70 parameters	Δρmax = 0.75 e Å^−3
3 restraints	Δρmin = −0.88 e Å^−3

Special details

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
Np	0.5000	0.5000	0.5000	0.00406 (1)
Na1	0.5000	0.5000	0.0000	0.00859 (9)
Na2	0.85815 (7)	0.32123 (6)	0.90540 (8)	0.01157 (8)
O1	0.65824 (10)	0.56060 (10)	0.78208 (12)	0.00757 (11)
O2	0.37890 (10)	0.71543 (9)	0.45784 (12)	0.00792 (11)
O3	0.72436 (10)	0.59020 (9)	0.37305 (12)	0.00862 (11)
H3	0.715 (3)	0.693 (2)	0.349 (4)	0.031 (6)*
O4	0.97126 (12)	0.44316 (15)	0.24784 (14)	0.01657 (15)
H4A	0.892 (4)	0.493 (2)	0.286 (5)	0.021 (6)*
H4B	1.071 (2)	0.428 (3)	0.354 (3)	0.029 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Np	0.00487 (2)	0.00387 (2)	0.00377 (2)	0.00001 (2)	0.00205 (1)	−0.00008 (1)
Na1	0.0114 (2)	0.0080 (2)	0.0080 (2)	0.0013 (2)	0.0056 (2)	0.0006 (2)
Na2	0.01207 (18)	0.01314 (18)	0.00847 (17)	0.00321 (15)	0.00287 (14)	−0.00015 (15)
O1	0.0084 (3)	0.0080 (3)	0.0059 (3)	−0.0006 (2)	0.0023 (2)	−0.0011 (2)
O2	0.0097 (3)	0.0055 (2)	0.0086 (3)	0.0015 (2)	0.0037 (2)	0.0006 (2)
O3	0.0091 (3)	0.0075 (3)	0.0102 (3)	0.0010 (2)	0.0049 (2)	0.0020 (2)
O4	0.0077 (3)	0.0293 (4)	0.0106 (3)	0.0028 (3)	0.0013 (3)	−0.0068 (3)

Geometric parameters (Å, º)

Np—O1	1.8975 (7)	Na2—O2^i	2.4655 (9)
Np—O2^i	1.8891 (7)	Na2—O2^vii	2.5150 (9)
Np—O2	1.8891 (7)	Na2—O4^viii	2.6263 (13)
Np—O1^i	1.8975 (7)	Na2—O4^ix	2.7033 (12)
Np—O3	2.3451 (7)	O1—Na1^vi	2.3223 (7)
Np—O3^i	2.3451 (7)	O2—Na1^x	2.3783 (7)
Na1—O1^ii	2.3223 (7)	O2—Na2^i	2.4655 (9)
Na1—O1^i	2.3223 (7)	O2—Na2^xi	2.5150 (9)
Na1—O2^iii	2.3783 (7)	O3—H3	0.815 (15)
Na1—O2^iv	2.3783 (7)	O4—Na2^ii	2.3510 (10)
Na1—O3	2.5626 (8)	O4—Na2^xii	2.6263 (13)
Na1—O3^v	2.5626 (8)	O4—Na2^ix	2.7033 (12)
Na2—O4^vi	2.3510 (10)	O4—H4A	0.856 (17)
Na2—O1	2.3633 (9)	O4—H4B	0.840 (16)
O1—Np—O2	91.41 (3)	O2^iii—Na1—O3	87.25 (2)
O1—Np—O3	90.82 (3)	O2^iv—Na1—O3	92.75 (2)
O2—Np—O3	94.67 (3)	O1^ii—Na1—O3^v	75.46 (2)
O2^i—Np—O2	180.0	O1^i—Na1—O3^v	104.54 (2)
O2^i—Np—O1	88.59 (3)	O2^iii—Na1—O3^v	92.75 (2)
O2^i—Np—O1^i	91.41 (3)	O2^iv—Na1—O3^v	87.25 (2)
O2—Np—O1^i	88.59 (3)	O3—Na1—O3^v	180.00 (3)
O1—Np—O1^i	180.0	O4^vi—Na2—O1	88.70 (4)
O2^i—Np—O3	85.33 (3)	O4^vi—Na2—O2^i	152.85 (4)
O1^i—Np—O3	89.18 (3)	O1—Na2—O2^i	66.37 (3)
O2^i—Np—O3^i	94.67 (3)	O4^vi—Na2—O2^vii	79.02 (3)
O2—Np—O3^i	85.33 (3)	O1—Na2—O2^vii	84.77 (3)
O1—Np—O3^i	89.18 (3)	O2^i—Na2—O2^vii	87.77 (3)
O1^i—Np—O3^i	90.82 (3)	O4^vi—Na2—O4^viii	131.72 (4)
O3—Np—O3^i	180.0	O1—Na2—O4^viii	138.70 (3)
O1^ii—Na1—O1^i	180.00 (2)	O2^i—Na2—O4^viii	74.89 (3)
O1^ii—Na1—O2^iii	91.16 (3)	O2^vii—Na2—O4^viii	108.07 (3)
O1^i—Na1—O2^iii	88.84 (3)	O4^vi—Na2—O4^ix	93.44 (4)
O1^ii—Na1—O2^iv	88.84 (3)	O1—Na2—O4^ix	71.74 (3)
O1^i—Na1—O2^iv	91.16 (3)	O2^i—Na2—O4^ix	88.88 (3)
O2^iii—Na1—O2^iv	180.0	O2^vii—Na2—O4^ix	155.55 (3)
O1^ii—Na1—O3	104.54 (2)	O4^viii—Na2—O4^ix	94.370 (16)
O1^i—Na1—O3	75.46 (2)	H4A—O4—H4B	110 (3)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, y, z−1; (iii) x, −y+3/2, z−1/2; (iv) −x+1, y−1/2, −z+1/2; (v) −x+1, −y+1, −z; (vi) x, y, z+1; (vii) −x+1, y−1/2, −z+3/2; (viii) x, −y+1/2, z+1/2; (ix) −x+2, −y+1, −z+1; (x) −x+1, y+1/2, −z+1/2; (xi) −x+1, y+1/2, −z+3/2; (xii) x, −y+1/2, z−1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O1^iii	0.82 (2)	1.98 (2)	2.7866 (10)	173 (2)
O4—H4A···O3	0.86 (2)	1.80 (2)	2.6538 (12)	178 (2)
O4—H4B···O3^ix	0.84 (2)	1.93 (2)	2.7612 (12)	169 (2)

Symmetry codes: (iii) x, −y+3/2, z−1/2; (ix) −x+2, −y+1, −z+1.