Reinvestigation of tris­odium dihydroxidotetra­oxidoneptunate(VII)

The title compound, Na₃[NpO₄(OH)₂], contains complex [NpO₄(OH)₂]^3- anions, having a distorted tetra­gonal bi­pyramidal form. The Np atom occupies a special position on a twofold axis. The Np-O distances are 1.8981 (13) and 1.9012 (12) Å in the NpO₄ group and 2.3145 (11) Å to the OH groups. The main distortion of the tetra­gonal bipyramid is a shift of the O atoms of the OH groups from ideal positions, the corresponding O-Np-O angle being 173.80 (7)°. The orientation of the OH groups differs significantly from the centrosymmetric arrangement found in other compounds with [NpO₄(OH)₂]^3- anions.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](p-O) = 0.001 Å
• R factor = 0.012
• wR factor = 0.022
• Data-to-parameter ratio = 47.0

checkCIF/PLATON results

No syntax errors found



Alert level C
ABSTM02_ALERT_3_C  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.378     0.546
            Tmin and Tmax expected:      0.302     0.502
            RR =      1.152
            Please check that your absorption correction is appropriate.
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT060_ALERT_3_C Ratio Tmax/Tmin (Exp-to-Rep) (too) Large .......       1.15
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.92

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.920
            Tmax scaled      0.502 Tmin scaled      0.348
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           45.00
           From the CIF: _reflns_number_total               2442
           Count of symmetry unique reflns         1308
           Completeness (_total/calc)            186.70%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1134
           Fraction of Friedel pairs measured     0.867
           Are heavy atom types Z>Si present        yes
PLAT033_ALERT_2_G Flack Parameter Value Deviates 2 * su from zero.       0.04
PLAT794_ALERT_5_G Check Predicted Bond Valency for Np1         (7)       7.29
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          2

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   5 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

The title compound, (I) (Fig. 1), contains complex anions [NpO₄(OH)₂]^3-, having a form of distorted tetragonal bipyramid. The main bond lengths and angles in this anion are given in Table 1. The Np atom occupies a special position on a twofold axis. The main distortion of the tetragonal bipyramid is a shift of O atoms of the OH groups from ideal positions, the corresponding O—Np—O angle being 173.80 (7)°. The orientaion of the OH groups differs significantly from centrosymmetric (Fig. 1) whereas in all other compounds with [NpO₄(OH)₂]^3- anions (Tomilin et al., 1981b,c, 1983; Grigor'ev et al., 1986, 1993; Charushnikova et al., 2007) these anions occupy centrosymmetric positions. Basing on diffractometrically studied structures of Np^VII compounds with alkaline cations, one can notice that the Np—O distances to the OH groups become longer in the sequence Na–K–Cs. The corresponding distances are 2.370 (5) Å for K₃[NpO₄(OH)₂]·2H₂O (Charushnikova et al., 2007) and 2.41 (1) Å for Cs₃[NpO₄(OH)₂]·3H₂O (Grigor'ev et al., 1993). The Np—O distances in the NpO₄ groups remain practically the same.

The Na1 atom occupies a special position on twofold axis and has a distorted octahedral oxygen environment. The Na2 atom is in general position with distorted tetrahedral oxygen environment.

The OH group acts as proton donor in a weak hydrogen bond with an O atom of NpO₄ group of a neighbouring anion (Table 2). The resulting hydrogen bond net in (I) is three-dimensional (Fig. 2).

Related literature

The structure of Na₃[NpO₄(OH)₂] was investigated using the 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 using the photographic technique: Na₃[NpO₄(OH)₂]·2H₂O (Tomilin et al., 1981b), Na₃[NpO₄(OH)₂]·4H₂O (Tomilin et al., 1981c) and K₃[NpO₄(OH)₂]·2H₂O (Tomilin et al., 1983). Diffractometric structure determinations have bee carried out for [Co(NH₃)₆][NpO₄(OH)₂]·2H₂O (Grigor'ev et al., 1986), Cs₃[NpO₄(OH)₂]·3H₂O (Grigor'ev et al., 1993) and K₃[NpO₄(OH)₂]·2H₂O (Charushnikova et al., 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), 0.2 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. An 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 were 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 atom of the OH group was located on a difference Fourier-map and refined with O—H distance restrained to 0.82 (2) Å and individual isotropic displacement parameter.

Largest electron density peak on the final difference Fourier-synthesis is 1.071 e Å^-3 (1.20 Å from O2), the deepest hole is -1.490 e Å^-3 (1.67 Å from Na1).

Computing details

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: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.

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. [Symmetry code: (i) 1 - x, 1 - y, z.]
	Fig. 2. The packing of (I) showing three-dimensional net of hydrogen bonds (dashed lines).

trisodium dihydroxidotetraoxidoneptunate(VII)

Crystal data

Na3[NpO4(OH)2]	F(000) = 1408
Mr = 403.99	Dx = 4.399 Mg m^−3
Orthorhombic, Fdd2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: F 2 -2d	Cell parameters from 8824 reflections
a = 20.0791 (6) Å	θ = 4.1–45.0°
b = 5.9534 (2) Å	µ = 17.21 mm^−1
c = 10.2062 (3) Å	T = 100 K
V = 1220.04 (7) Å^3	Plate, black
Z = 8	0.20 × 0.06 × 0.04 mm

Data collection

Bruker Kappa APEXII area-detector diffractometer	2442 independent reflections
Radiation source: fine-focus sealed tube	2258 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ω and φ scans	θmax = 45.0°, θmin = 4.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 2004)	h = −39→39
Tmin = 0.378, Tmax = 0.546	k = −11→11
21081 measured reflections	l = −20→19

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.012	All H-atom parameters refined
wR(F^2) = 0.022	w = 1/[σ^2(Fo^2) + 2.58P] where P = (Fo^2 + 2Fc^2)/3
S = 1.25	(Δ/σ)max = 0.001
2442 reflections	Δρmax = 1.07 e Å^−3
52 parameters	Δρmin = −1.49 e Å^−3
2 restraints	Absolute structure: Flack (1983), with 1136 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.039 (12)

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
Np1	0.5000	0.5000	0.53211 (2)	0.00494 (1)
Na1	0.5000	0.5000	0.86871 (10)	0.00964 (14)
Na2	0.65942 (4)	0.75441 (14)	0.45853 (8)	0.01332 (11)
O1	0.55153 (7)	0.6409 (2)	0.66461 (14)	0.01161 (19)
O2	0.55254 (6)	0.6438 (2)	0.40181 (13)	0.00956 (17)
O3	0.42959 (5)	0.80708 (19)	0.51985 (14)	0.00980 (16)
H3	0.3955 (13)	0.777 (6)	0.483 (4)	0.025 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Np1	0.00478 (2)	0.00542 (2)	0.00464 (2)	−0.00093 (4)	0.000	0.000
Na1	0.0127 (3)	0.0077 (3)	0.0085 (4)	0.0009 (3)	0.000	0.000
Na2	0.0175 (3)	0.0125 (3)	0.0100 (3)	−0.0028 (3)	−0.0028 (2)	−0.0007 (2)
O1	0.0122 (4)	0.0120 (5)	0.0106 (5)	−0.0027 (4)	−0.0039 (4)	−0.0019 (4)
O2	0.0098 (4)	0.0091 (4)	0.0097 (4)	0.0009 (3)	0.0041 (3)	0.0017 (3)
O3	0.0087 (3)	0.0089 (3)	0.0118 (5)	0.0011 (3)	0.0007 (3)	−0.0018 (3)

Geometric parameters (Å, º)

Np1—O1	1.8981 (13)	Na1—O1	2.4725 (17)
Np1—O1^i	1.8981 (13)	Na2—O3^iv	2.2653 (16)
Np1—O2^i	1.9012 (12)	Na2—O2^v	2.2723 (15)
Np1—O2	1.9012 (12)	Na2—O2	2.3183 (15)
Np1—O3^i	2.3145 (11)	Na2—O1^vi	2.3451 (16)
Np1—O3	2.3145 (11)	O1—Na2^v	2.3451 (16)
Na1—O3^ii	2.3870 (14)	O2—Na2^vi	2.2723 (15)
Na1—O3^iii	2.3870 (14)	O2—Na1^vii	2.3924 (13)
Na1—O2^ii	2.3924 (13)	O3—Na2^viii	2.2653 (16)
Na1—O2^iii	2.3924 (13)	O3—Na1^vii	2.3870 (14)
Na1—O1^i	2.4725 (17)	O3—H3	0.800 (18)
O1—Np1—O1^i	89.13 (9)	O2^ii—Na1—O2^iii	163.77 (8)
O1—Np1—O2^i	178.96 (7)	O3^ii—Na1—O1^i	162.86 (5)
O1^i—Np1—O2^i	89.82 (5)	O3^iii—Na1—O1^i	97.66 (4)
O1—Np1—O2	89.82 (5)	O2^ii—Na1—O1^i	103.60 (5)
O1^i—Np1—O2	178.96 (7)	O2^iii—Na1—O1^i	90.16 (5)
O2—Np1—O2^i	91.22 (8)	O3^ii—Na1—O1	97.66 (4)
O1—Np1—O3^i	93.13 (5)	O3^iii—Na1—O1	162.86 (5)
O1^i—Np1—O3^i	91.29 (5)	O2^ii—Na1—O1	90.16 (5)
O2^i—Np1—O3^i	86.87 (5)	O2^iii—Na1—O1	103.60 (5)
O2—Np1—O3^i	88.79 (5)	O1^i—Na1—O1	65.19 (6)
O1—Np1—O3	91.29 (5)	O2^ii—Na1—Na2^ii	38.73 (3)
O1^i—Np1—O3	93.13 (5)	O2^iii—Na1—Na2^ii	135.15 (4)
O2^i—Np1—O3	88.79 (5)	O3^iv—Na2—O2^v	119.80 (6)
O2—Np1—O3	86.87 (5)	O3^iv—Na2—O2	95.39 (5)
O3^i—Np1—O3	173.80 (7)	O2^v—Na2—O2	129.18 (6)
O3^ii—Na1—O3^iii	99.48 (7)	O3^iv—Na2—O1^vi	103.59 (6)
O3^ii—Na1—O2^ii	75.13 (4)	O2^v—Na2—O1^vi	112.99 (6)
O3^iii—Na1—O2^ii	94.25 (5)	O2—Na2—O1^vi	89.98 (5)
O3^ii—Na1—O2^iii	94.25 (5)	Np1—O3—H3	112 (3)
O3^iii—Na1—O2^iii	75.13 (4)

Symmetry codes: (i) −x+1, −y+1, z; (ii) −x+1, −y+3/2, z+1/2; (iii) x, y−1/2, z+1/2; (iv) x+1/4, −y+7/4, z−1/4; (v) −x+5/4, y+1/4, z+1/4; (vi) −x+5/4, y−1/4, z−1/4; (vii) x, y+1/2, z−1/2; (viii) x−1/4, −y+7/4, z+1/4.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O1^ix	0.80 (2)	2.25 (2)	3.0255 (17)	164 (4)

Symmetry code: (ix) x−1/4, −y+5/4, z−1/4.