Tricarbonate complex of hexavalent Am with guanidinium: synthesis and structural characterization of [C(NH₂)₃]₄[AmO₂(CO₃)₃]·2H₂O, comparison with [C(NH₂)₃]₄[AnO₂(CO₃)₃] (An=U, Np, Pu)

Abstract

Tricarbonate complex of hexavalent Am with guanidinium: synthesis and structural characterization of [C(NHSummary. A formation of Am(VI) carbonate complexes has been observed under ozonation of Am(III) in guanidinium carbonate solutions. New [C(NH 2 ) 3 ] 4 [AmO 2 (CO 3 ) 3 ]·2H 2 O tricarbonate complex has been isolated and studied by the X-ray analysis. The Am atom has oxygen environment as distorted hexagonal bipyramid with three CO 3 2− ions in equatorial plane and oxygen atoms of the AmO 2 group in the apical positions. Averaged Am−O CO 3 bond length is 2.431(13) Å, the length of Am=O bond is 1.750(12) Å. In crystal hydrogen bonds between [C(NH 2 ) 3 ] + cations, water molecules and [AmO 2 (CO 3 ) 3 ] 4− complex anions link the fragments of structure into the three-dimensional network. To compare the peculiarities of the structure of tricarbonate complexes it was prepared [C(NH 2 ) 3 ] 4 [AnO 2 (CO 3 ) 3 ], where An = U(VI), Np(VI) and Pu(VI). In structure of [C(NH 2 ) 3 ] 4 [AnO 2 (CO 3 ) 3 ] an actinide contraction appears as a slight shortening of the bond lengths in the actinyl groups AnO 2 : 1.80 Å for U, 1.78 Å for Np 1.76 Å Pu. The An−O CO 3 bond length in the equatorial plane of hexagonal bipyramids remains almost unchanged in the series from U to Am. An analysis of the structures showed that hydrogen bonding played an important role in crystal formation.

Periodic Trends in Actinyl Thio-Crown Ether Complexes

“…[9][10][11][12][13] Published structural data reveal a smooth actinide contraction of actinyl bond lengths from R(U-O) = 180 pm to R(Am-O) = 175 pm. [14][15][16][17] The existence of CmO 2 2+ in solution has not yet been reliably demonstrated and this species is considered unimportant in curium chemistry. [18,19] The actinyl moiety is remarkable due to the fact that it is, in contrast to similar d-element compounds, linear and has very short metal-oxygen bond lengths, suggesting strong multiple bond character.…”

“…In aqueous solutions, uranium complexes exist mostly in the form of U VI O 2 2+ , whereas Np VI O 2 2+ and Pu VI O 2 2+ are substantially less stable relative to the reduced pentavalent actinyls Np V O 2 + and Pu V O 2 + . Am VI O 2 2+ is metastable. − Published structural data reveal a smooth actinide contraction of actinyl bond lengths, typically from R­(U–O) = 1.80 Å to R­(Am–O) = 1.75 Å. − The existence of CmO 2 2+ in solution has not yet been reliably demonstrated, and this species is considered unimportant in curium chemistry due to the low stability of Cm­(VI) in curinyl complexes. , The actinyl moiety is remarkable due to the fact that in contrast to similar d-element compounds it is linear and has very short metal–oxygen bond lengths suggesting strong multiple bond character. Actinyl complexes normally coordinate 4–6 monodentate ligands in their equatorial plane. − The f-elements, in contrast to many d-block transition metals, are in general hard acids and therefore have a strong affinity for hard O- and F-donor ligands.…”

Synthesis, Structural, and Electronic Properties of K4PuVIO2(CO3)3(cr): An Environmentally Relevant Plutonium Carbonate Complex

“…10 The M4[An VI O2(CO3)3] is an important class of compounds in the nuclear and reprocessing technology for the separation of the actinides along with An VI complexes with other ligands in the course of fundamental actinide science. [11][12][13][14] Transuranic compounds remain less studied since most investigations are conducted on uranium due to the availability and relatively low radiotoxicity of uranium element.…”

“…[An VI O 2 (CO 3 ) 3 ] 4– dominates exclusively in water with high carbonate content, [CO 3 2– ] ≥ 10 –3 M, where solid complexes with the composition M 4 [An VI O 2 (CO 3 ) 3 ] (M = Na, K) might potentially form . M 4 [An VI O 2 (CO 3 ) 3 ] is an important class of compounds in the nuclear and reprocessing technology for the separation of actinides along with actinide­(VI) complexes with other ligands in the course of fundamental actinide science. − …”

The actinides

“…99 In [C(NH 2 ) 3 ] 4 [AmO 2 (CO 3 ) 3 ]Á2H 2 O, Am has distorted hexagonal bipyramidal coordination. 100 Cm(III) complexes have been characterised in solution by luminescence 101 and time-resolved laser-induced fluorescence 102 methods. Claims have been made for a volatile curium(VI) oxide, CmO 3 .…”