Structure and stability range of a hexanuclear Th(iv)–glycine complex

Abstract

A hexanuclear Th(IV)-glycine complex was observed by Th L(3)-edge EXAFS measurements in an aqueous solution. Within the stability range of this complex the positively charged hexanuclear species [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)(H(2)O)(6)(Gly)(6)(HGly)(6)](6+) was preserved in a crystal with the composition [Th(6)(μ(3)-O)(4)(μ(3)-OH)(4)(H(2)O)(6)(Gly)(6)(HGly)(6)]·(NO(3))(3)(ClO(4))(3)(H(2)O)(3). This complex appears as a result of a competing reaction between hydrolysis and ligation by glycine. At a pH value below the stability range of the hexanuclear complex, crystals with the composition [Th(H(2)O)(3)(HGly)(3)]·(ClO(4))(4)H(2)O were obtained from the solution. Three water molecules in the thorium coordination sphere indicate that this complex occurs prior to the onset of Th(IV) hydrolysis.

Coordination of Tetravalent Actinides (An=ThIV, UIV, NpIV, PuIV) with DOTA: From Dimers to Hexamers

“…This coordination number (CN) is lower than the usual value reported for this kind of actinide polynuclear cluster (CN = 9) [29] and was described only once before for uranium(IV). This coordination number (CN) is lower than the usual value reported for this kind of actinide polynuclear cluster (CN = 9) [29] and was described only once before for uranium(IV).…”

“…The amine group deprotonation is probably due to the cluster high charged ensity,c lose to their nitrogen atoms.T he distance between the protonated amine group and the cluster is indeed rationally longer( 5.22 )t han for the three other nitrogen atoms( average of 4.64 ). [29,30] To summarize, along the actinides eries, with the decrease of the ionic radii, the overall [An 6 (O) 4 (OH) 4 (H 2 O) 8 ]c oret rends to be congruently contracted. [46] Whatever the distances, An-m 3 -O 2À ,A n-m 3 -OH À ,A n-H 2 O, An-An, An-O carboxylate and the kind of carboxylate arms, the evolution is linearly relatedw ith the ionic radii.…”

“…Nevertheless, the www.chemeurj.org spectralf eatures correspond to the spectra of the clusters. [29] The wide domain suggestst hat one or severalD OTAf unctions are likely involved in potential protonation or deprotonation reactions that buffer the pH and stabilizet he hexanuclear core. For ura-nium, for pH > 6, in addition to baselined eviation, am odification of the absorption bands is witnessed with the appearance of as ignificant band around4 50 nm characteristic of U VI .T here is thus ap artial oxidation of U IV to U VI .T he UV/Vis spectrum of neptunium recorded at pH > 7.2 shows ab aselined eviation and ac hange of absorption bands,w hich has not been attributed yet, but that is consistentw ith am odification of the complex nature.P lutonium(IV) shows, at pH 6.9, as trong absorption and af eatureless spectrum.I na ddition, ab rown precipitate, characteristic of plutonium hydroxide Pu(OH) 4 ·x H 2 Oa ppears.…”

“…One compoundwith ten uranium cations presenting a[ U 10 (OH) 6 O 8 ]f rame was reported. [29,30] Uncommon structures with a[ An 6 (O) 4 (OH) 4 ] 12 + core, stabilized by aromaticl igands connected to the actinide through p-p interactions, werea lso described. [18] Another clusterw ith 12 uranium cations,[ U 12 (OH) 8 O 12 ], synthesized in presenceo ft riflate and iodate, was isolated.…”

“…[19] Overall, the most represented families of the oxo-hydroxoc lusters are the hexanuclear species, [An 6 (OH) 4 O 4 ] 12 + ,s tabilized by small organic ligandss uch as triflate, [19] phosphate, [20] sulfate, [21] isocyanurate, [22] carboxylic acids, [23][24][25][26][27][28] or small amino acids. [23,24,28,29] Recently,T akao [17] et al have providede videncef or aw ater-soluble hexanuclear cluster with neptunium(IV) stabilized by amino acids, but without af ull crystallographic structure. [31,32] One study reports an example of a5fe lement hexanuclear compound [Cp 4 (bpy) 2 ][U 6 O 13 ]( bpy = bipyridine) with 13 oxo bridges insteado ft he common eight oxygen atoms bridging the actinidecations.…”