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]+=1-ethyl-2-methylimidazolium), and Ce(NO3)3 ⋅ 6H2O. Although unsuccessful in our goal, structural analysis revealed that neutral 4-NH2-1,2,4-Triaz is structure directing via η2μ2κ2 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.We describe a straightforward pathway to obtain lanthanide hydroxo polynuclear clusters from lanthanide salt hydrates and a combination of azoles. 4-NH2-1,2,4-triazole was found to play an important role both as a reaction medium and the structure-forming agent leading to multiple clusters with various nuclearity including the first example of a high nuclearity lanthanide complex where all Ln atoms are pairwise connected through 12 N-donor ligands.