Trapping an Unexpected/Unprecedented Hexanuclear Ce(III) Hydrolysis Product with Neutral 4‐Amino‐1,2,4‐triazole

Abstract

Using Ce(III) as both a representative lanthanide and actinide analog, the ability of mixtures of acidic and basic azoles to allow direct access to homoleptic N‐donor f‐element complexes in one pot reactions from hydrated salts as starting materials was examined by reacting mixtures of 4‐amino‐1,2,4‐triazole (4‐NH2‐1,2,4‐Triaz), 5‐amino‐tetrazole (5‐NH2‐HTetaz), and 1,2,3‐triazole (1,2,3‐HTriaz) in 1:1 and 1:3 ratios with CeCl3•7H2O, [C2mim]3[CeCl6] ([C2mim]+ = 2‐ethyl‐1‐methylimidazolium), and Ce(NO3)3•6H2O. Although unsuccessful in our goal, single crystal X‐ray diffraction revealed that neutral 4‐NH2‐1,2,4‐Triaz is structure directing via h2m2k2 bridging, with the formation of the dinuclear complexes [Ce2Cl2(µ2‐4‐NH2‐1,2,4‐Triaz)4(H2O)8]Cl4•4H2O, [Ce2(µ2‐4‐NH2‐1,2,4‐Triaz)4(4‐NH2‐1,2,4‐Triaz)2(Cl)6], and [4‐NH2‐1,2,4‐HTriaz][Ce2(µ2‐4‐NH2‐1,2,4‐Triaz)2(µ2‐NO3)(NO3)6(H2O)2]. When the synthetic conditions favored hydrolysis, the hexanuclear Ce(III) complex [Ce6(µ3‐O)4(µ3‐OH)2(µ3‐Cl)2(Cl)6(µ2‐4‐NH2‐1,2,4‐Triaz)12]•7H2O was isolated. This unexpected hydrolysis product represents the first example of a high nuclearity lanthanide complex where all Ln atoms are pairwise connected through 12 N‐donor ligands or 12 neutral bridging ligands of any type, a rare example of incorporation of non‐oxo coordinating anions in the M6X8 core, and the first reported Ce(III) hexanuclear complex of this type.

Exploring the Role of Neutral 4-Amino-1,2,4-triazole in the Formation of Hexanuclear f-Element Hydrolysis Products

“…In order to test the generality of the experiments leading to the crystallization of [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 2 (μ 3 -Cl) 2 (Cl) 6 (μ 2 -4-NH 2 -1,2,4-Triaz) 12 ]·7H 2 O, we repeated the general synthetic scheme with variations in metal salts, azole pairs, azole-to-metal salt ratio, and water content. While many of the reactions conducted did not display only one single crystalline product from each respective mixture, crystalline material was isolated and collected directly from the respective reaction mixtures which were suitable for SCXRD analysis and whose chemical identity could only be confirmed from the structure solutions (see below) which were quite complicated by disorder.…”

“…1 crystallizes with a rhombohedral unit cell ( R 3̅, a = 19.4973(3) and c = 23.9917(5) Å, V = 7898.4(3) Å 3 , Z = 3) and is closely related to the Ce complex [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 2 (μ 3 -Cl) 2 ]­(Cl) 6 (μ 2 -4-NH 2 -1,2,4-Triaz) 12 ·7H 2 O …”

“…5−7 In our efforts to further explore the potential use of these reaction conditions to be used for coordination to Pu(III) and Pu(IV), we have examined Ce(III−IV) and Nd(III) as analogues for these species to be more informed on how our target metals might interact under these conditions. 8−10 Using our approach, we recently reported an unexpected/unprecedented hexanuclear Ce(III) hydrolysis product with neutral 4-amino-1,2,4-triazole (4-NH 2 -1,2,4-Triaz), [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 2 (μ 3 -Cl) 2 (Cl) 6 (μ 2 -4-NH 2 -1,2,4-Triaz) 12 ]•7H 2 O, 11 in which the 4-NH 2 -1,2,4-Triaz ligand seemed to be directing the hydrolysis product structure. Early density functional theory (DFT) calculations on this unique product with 12 neutral bridging azoles suggested that the core center (a putative μ 6 ligand) tends to be occupied by an anion.…”

“…Early density functional theory (DFT) calculations on this unique product with 12 neutral bridging azoles suggested that the core center (a putative μ 6 ligand) tends to be occupied by an anion. 11 Given that hydrolysis reactions involving f-block metal centers have been extensively studied due to their relevance in various fields such as nuclear waste disposal and environmental remediation, 12,13 we are working toward mapping both the reproducibility of these reactions and the scope of f-elements to which they apply. Typically, hydrolysis reactions take place by the cleavage of metal−oxygen bonds through water coordination, leading to the formation of metal oxides or hydroxide complexes.…”

“…The need for a better understanding of the interactions between f-block elements and molecules containing softer donor atoms is of high importance in the areas of nuclear waste separations as a way to utilize the selectivity of these softer donor atoms . Exploration into understanding the ways to utilize these interactions has been conducted steadily over the last 40 years and has led to the discovery of synthetic approaches and the use of efficient N-donor systems for separations of these f-elements. − As a means to study these phenomena, ionic liquids have been utilized that can act as both the reaction media as well as the coordination ligands in this reaction to help facilitate coordination of the soft donor ligands by creating a “sea of N-donors” allowing for one pot syntheses. − In our efforts to further explore the potential use of these reaction conditions to be used for coordination to Pu­(III) and Pu­(IV), we have examined Ce­(III–IV) and Nd­(III) as analogues for these species to be more informed on how our target metals might interact under these conditions. − Using our approach, we recently reported an unexpected/unprecedented hexanuclear Ce­(III) hydrolysis product with neutral 4-amino-1,2,4-triazole (4-NH 2 -1,2,4-Triaz), [Ce 6 (μ 3 -O) 4 (μ 3 -OH) 2 (μ 3 -Cl) 2 (Cl) 6 (μ 2 -4-NH 2 -1,2,4-Triaz) 12 ]·7H 2 O, in which the 4-NH 2 -1,2,4-Triaz ligand seemed to be directing the hydrolysis product structure. Early density functional theory (DFT) calculations on this unique product with 12 neutral bridging azoles suggested that the core center (a putative μ 6 ligand) tends to be occupied by an anion …”