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Volume 67 
Part 6 
Pages m205-m207  
June 2011  

Received 22 February 2011
Accepted 5 May 2011
Online 19 May 2011

Sodium tris(acetato-[kappa]2O,O')dioxidoamericate(VI) and guanidinium tris(cyclopropanecarboxylato-[kappa]2O,O')dioxidoamericate(VI)

aA.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospekt, 119991 Moscow, Russian Federation
Correspondence e-mail: mickgrig@mail.ru

The title compounds, Na[{AmO2}(C2H3O2)3], (I), and (CH6N3)[{AmO2}(C4H5O2)3], (II), contain complex anions in which AmO22+ cations are surrounded by three bidentate-chelating carboxylate groups. The atoms of the AmO2 group and the Na atoms in (I) are situated on threefold axes. All the atoms in (II) occupy general positions. Both compounds are isomorphous with earlier studied analogous compounds of previous members of the actinide (An) series.

Comment

Linear dioxidocations AnO2+ and AnO22+ are typical of actinides (An) in oxidation states V and VI. Most of the crystal structures reported for compounds containing such cations involve UVI and NpV. The data for Pu compounds are more scarce. AmVI compounds are usually believed to be isomorphous with corresponding compounds of U, Np and Pu. Nevertheless, there are several examples of PuVI compounds that are not isomorphous with their U and Np analogues. PuVI orthophthalate {PuO2[(OOC)2C6H4]H2O}·H2O (Grigoriev et al., 2004[Grigoriev, M. S., Antipin, M. Yu., Krot, N. N. & Bessonov, A. A. (2004). Radiochim. Acta, 92, 405-409.]) is not isomorphous with {UO2[(OOC)2C6H4]H2O}·H2O (Charushnikova et al., 2004[Charushnikova, I. A., Krot, N. N. & Starikova, Z. A. (2004). Radiochemistry, 46, 556-559.]). In this case, the change in the coordination mode of the phthalate anion (seven-membered metallocycle in the U compound and four-membered metallocycle in the Pu compound) can be explained by a decrease in the ionic radius on going from U to Pu, viz. the actinide contraction (Edelstein et al., 2006[Edelstein, N. M., Fuger, J., Katz, J. J. & Morss, L. R. (2006). The Chemistry of the Actinide and Transactinide Elements, Vol. 3, edited by L. R. Morss, N. M. Edelstein & J. Fuger, p. 1798. Dordrecht: Springer.]). [(PuO2)2SiO4(H2O)2] crystallizes in a tetragonal space group whereas its U and Np analogues crystallize in an orthorhombic one (Grigor'ev et al., 2003[Grigor'ev, M. S., Bessonov, A. A., Makarenkov, V. I. & Fedoseev, A. M. (2003). Radiochemistry, 45, 257-260.]; Bessonov et al., 2003[Bessonov, A. A., Grigoriev, M. S., Ioussov, A. B., Budantseva, N. A. & Fedosseev, A. M. (2003). Radiochim. Acta, 91, 339-344.]). In the case of [PuO2(IO3)2]·H2O and [UO2(IO3)2(H2O)], even the composition of the coordination polyhedron is different (Bean et al., 2001[Bean, A. C., Peper, S. M. & Albrecht-Schmitt, T. E. (2001). Chem. Mater. 13, 1266-1272.]; Runde et al., 2003[Runde, W., Bean, A. C., Albrecht-Schmitt, T. E. & Scott, B. L. (2003). Chem. Commun. pp. 478-479.]).

Until recently, full X-ray crystallographic data for AmVI compounds have not been available. We present here two crystal structure determinations for AmVI tricarboxylate complexes, viz. sodium tris(acetato-[kappa]2O,O')dioxidoamericate(VI), Na[AmO2(OOCCH3)3], (I)[link], and guanidinium tris(cyclopropanecarboxylato-[kappa]2O,O')dioxidoamericate(VI), [C(NH2)3][AmO2(OOCC3H5)3], (II)[link].

[Scheme 1]

Several structure determinations for Na[AnO2(OOCCH3)3] compounds have been reported (Zachariasen & Plettinger, 1959[Zachariasen, W. H. & Plettinger, H. A. (1959). Acta Cryst. 12, 526-530.]; Alcock et al., 1982[Alcock, N. W., Roberts, M. M. & Brown, D. (1982). J. Chem. Soc. Dalton Trans. pp. 33-35.]; Templeton et al., 1985[Templeton, D. H., Zalkin, A., Ruben, H. & Templeton, L. K. (1985). Acta Cryst. C41, 1439-1441.]; Navaza et al., 1991[Navaza, A., Charpin, P., Vigner, D. & Heger, G. (1991). Acta Cryst. C47, 1842-1845.]; Charushnikova et al., 2007[Charushnikova, I. A., Krot, N. N. & Starikova, Z. A. (2007). Radiochemistry, 49, 565-570.]). For the Am compound, only unit-cell constants have been determined and the isostructurality with other AnVI compounds has been shown (Jones, 1955[Jones, L. H. (1955). J. Chem. Phys. 23, 2105-2107.]). Only a brief description is available for the crystal structure of [C(NH2)3][NpO2(OOCC3H5)3] (Andreev et al., 2006[Andreev, G. B., Budantseva, N. A., Fedosseev, A. M. & Antipin, M. Yu. (2006). Fifth Russian Conference on Radiochemistry, Dubna, October 23-27, 2006. Abstracts, pp. 73-74.]).

Both title compounds contain complex anions in which AmO22+ cations are surrounded by three bidentate-chelating carboxylate anions (Figs. 1[link] and 2[link]). The atoms of the AmO2 group and Na atoms in (I)[link] occupy special positions 4a in the space group P213 on threefold axes. All the atoms in (II)[link] occupy general positions. The coordination polyhedra of the Am atoms in both compounds are distorted hexagonal bipyramids with the two O atoms of the AmO2 groups in apical positions and six O atoms from three carboxylate groups in equatorial positions. The main distortion of the polyhedra is the difference between O-Am-O angles for O atoms of the same carboxylate group and for O atoms of two different carboxylate groups, these values being about 53 and 67°, respectively (Tables 1[link] and 2[link]). The AmO2 groups, ideally linear in (I)[link] and almost linear in (II)[link], are almost symmetric with close average Am-O distances of 1.738 (9) and 1.745 (4) Å, respectively. The average Am-O distances in the equatorial planes of the AmO2 groups are 2.460 (5) and 2.461 (4) Å for (I)[link] and (II)[link], respectively.

The coordination polyhedron of the Na atom in (I)[link] can be described as a strongly distorted octahedron, formed by carboxylate O atoms, with three Na-O distances of 2.358 (5) Å and three distances of 2.384 (6) Å.

The guanidinium cations in (II)[link] act as proton donors in several hydrogen bonds (Fig. 3[link] and Table 3[link]) with O atoms of the carboxylate groups of the organic anions. Each cation is connected to three complex anions forming layers parallel to the (010) plane.

Both compounds are isomorphous with earlier studied analogous compounds of previous members of the actinide series. The average An-O distances in Na[AnO2(OOCCH3)3] compounds are (in AnO2 groups and in their equatorial planes, respectively) 1.758 and 2.464 Å for U (Templeton et al., 1985[Templeton, D. H., Zalkin, A., Ruben, H. & Templeton, L. K. (1985). Acta Cryst. C41, 1439-1441.]), 1.776 (7) and 2.456 (12) Å for Np (Alcock et al., 1982[Alcock, N. W., Roberts, M. M. & Brown, D. (1982). J. Chem. Soc. Dalton Trans. pp. 33-35.]), and 1.736 (8) and 2.462 (5) Å for Pu (Charushnikova et al., 2007[Charushnikova, I. A., Krot, N. N. & Starikova, Z. A. (2007). Radiochemistry, 49, 565-570.]). The An-O distances in the equatorial plane of the AnO2 groups are practically the same in all compounds. The An=O distances in the AnO2 groups differ more significantly but without any pronounced trend. In contrast, a general decrease in the An=O distances in the AnO2 groups with increasing atomic number of the An atom was found for (NH4)[AnO2(CO3)3] compounds (An = U, Np, Pu; Charushnikova et al., 2007[Charushnikova, I. A., Krot, N. N. & Starikova, Z. A. (2007). Radiochemistry, 49, 565-570.]).

The Np-O distances in [C(NH2)3][NpO2(OOCC3H5)3] (Andreev et al., 2006[Andreev, G. B., Budantseva, N. A., Fedosseev, A. M. & Antipin, M. Yu. (2006). Fifth Russian Conference on Radiochemistry, Dubna, October 23-27, 2006. Abstracts, pp. 73-74.]) are 1.744 (5) and 1.752 (5) Å in the NpO2 group and range from 2.437 (5) to 2.497 (5) Å in the equatorial plane, close to the values found in (II)[link].

Thus, this study has proved the isomorphism of (I)[link] and (II)[link] with analogous compounds of previous members of the actinide series. The main difference in interatomic distances is some shortening of An-O bonds in AnO2 groups in (I)[link] and its analogues in the U-Np-Pu-Am sequence.

[Figure 1]
Figure 1
A view of the components of (I)[link], 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) y, z, x.]
[Figure 2]
Figure 2
A view of the components of (II)[link], 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 lines indicate the hydrogen-bonding interactions.
[Figure 3]
Figure 3
The pattern of hydrogen bonding in (II)[link]. The H atoms of the cyclopropanecarboxylate anions have been omitted for clarity.

Experimental

243Am(NO3)3 with a negligible admixture of 241Am was used as the starting material for the syntheses of (I)[link] and (II)[link]. Brown-yellow crystals of (I)[link] were obtained by neutralization of AmVI (5 × 10-3 M) in NaHCO3 solution (0.1 M), prepared by ozonation of the initial AmIII suspension in NaHCO3 (0.1 M), and excess of an aqueous CH3COOH solution (1 M). Crystallization commences in such solutions within a few minutes but usually the crystals are rather small.

Light-brown-yellow crystals of (II)[link] were obtained by slow evaporation of a solution containing AmVI (5 × 10-3 M) and guanidinium cyclopropanecarboxylate (0.1 M). This solution was prepared by ozonation for about 15 min of a suspension, obtained by addition of an Am(NO3)3 solution (0.1 ml, 2 × 10-2 M) to guanidinium carbonate (0.4 ml, 0.11 M), and with subsequent addition of a freshly prepared water solution (0.05 ml) of cyclopropanecarboxylic acid (1 M).

Compound (I)[link]

Crystal data
  • Na[Am(C2H3O2)3O2]

  • Mr = 475.12

  • Cubic, P 21 3

  • a = 10.5967 (2) Å

  • V = 1189.90 (4) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 6.51 mm-1

  • T = 100 K

  • 0.04 × 0.04 × 0.04 mm

Data collection
  • Bruker Kappa APEXII area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2004[Sheldrick, G. M. (2004). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.640, Tmax = 0.810

  • 15606 measured reflections

  • 1167 independent reflections

  • 1017 reflections with I > 2[sigma](I)

  • Rint = 0.135

Refinement
  • R[F2 > 2[sigma](F2)] = 0.032

  • wR(F2) = 0.056

  • S = 1.03

  • 1167 reflections

  • 50 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 0.97 e Å-3

  • [Delta][rho]min = -0.86 e Å-3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), 502 Friedel pairs

  • Flack parameter: -0.02 (4)

Table 1
Selected geometric parameters (Å, °) for (I)[link]

Am1-O1 1.735 (9)
Am1-O2 1.742 (9)
Am1-O3 2.464 (5)
Am1-O4 2.455 (5)
O1-Am1-O2 180.00
O3-Am1-O4 52.74 (16)
O4i-Am1-O3 67.26 (16)
Symmetry code: (i) y, z, x.

Compound (II)[link]

Crystal data
  • (CH6N3)[Am(C4H5O2)3O2]

  • Mr = 590.33

  • Monoclinic, P 21 /n

  • a = 9.5421 (3) Å

  • b = 13.2830 (4) Å

  • c = 14.2737 (4) Å

  • [beta] = 92.927 (2)°

  • V = 1806.80 (9) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 4.29 mm-1

  • T = 100 K

  • 0.14 × 0.06 × 0.02 mm

Data collection
  • Bruker Kappa APEXII area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2004[Sheldrick, G. M. (2004). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.712, Tmax = 0.924

  • 26314 measured reflections

  • 5218 independent reflections

  • 3801 reflections with I > 2[sigma](I)

  • Rint = 0.088

Refinement
  • R[F2 > 2[sigma](F2)] = 0.034

  • wR(F2) = 0.065

  • S = 1.00

  • 5218 reflections

  • 226 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 1.27 e Å-3

  • [Delta][rho]min = -1.16 e Å-3

Table 2
Selected geometric parameters (Å, °) for (II)[link]

Am1-O1 1.749 (4)
Am1-O2 1.740 (4)
Am1-O11 2.421 (4)
Am1-O12 2.488 (4)
Am1-O21 2.461 (4)
Am1-O22 2.451 (4)
Am1-O31 2.464 (4)
Am1-O32 2.483 (3)
O1-Am1-O2 178.85 (18)
O11-Am1-O12 53.09 (12)
O21-Am1-O22 52.93 (12)
O31-Am1-O32 52.55 (12)
O11-Am1-O32 66.94 (12)
O22-Am1-O31 66.72 (12)
O21-Am1-O12 68.81 (13)

Table 3
Hydrogen-bond geometry (Å, °) for (II)[link]

D-H...A D-H H...A D...A D-H...A
N1-H1A...O22i 0.88 2.19 2.922 (6) 140
N2-H2A...O21 0.88 2.04 2.874 (6) 157
N2-H2B...O32ii 0.88 2.04 2.876 (6) 159
N3-H3A...O12 0.88 2.03 2.904 (6) 171
N3-H3B...O31i 0.88 2.12 2.977 (6) 164
Symmetry codes: (i) [x+{\script{1\over 2}}, -y+{\script{3\over 2}}, z+{\script{1\over 2}}]; (ii) [x-{\script{1\over 2}}, -y+{\script{3\over 2}}, z+{\script{1\over 2}}].

The H atoms of the CH3 group in (I)[link] were located in a difference Fourier map and refined as an idealized group with displacement parameters constrained to 1.5Ueq of their parent atom. The orientation of this group was refined. The H atoms in (II)[link] were placed in calculated positions with displacement parameters constrained to 1.2Ueq of their parent atoms.

The largest electron-density peak in the final difference Fourier synthesis for (I)[link] is 0.90 Å from atom Am1 and the deepest hole is 1.72 Å from O4. The largest electron-density peak in the final difference Fourier synthesis for (II)[link] is 0.80 Å from Am1 and the deepest hole is 0.56 Å from H34B.

For both compounds, data collection: APEX2 (Bruker, 2006[Bruker (2006). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-Plus (Bruker, 1998[Bruker (1998). SAINT-Plus. Version 6.01. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); software used to prepare material for publication: SHELXTL.


Supplementary data for this paper are available from the IUCr electronic archives (Reference: YF3001 ). Services for accessing these data are described at the back of the journal.


References

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Acta Cryst (2011). C67, m205-m207   [ doi:10.1107/S010827011101701X ]