UC Santa Barbara

The reaction of UCl₄ or ThCl₄(DME)₂ (DME = dimethoxyethane) with 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetic acid (H₄DOTA), and 6 equiv of triethylamine, in dimethyl sulfoxide (DMSO) results in the formation of [An^IV(κ⁸-DOTA)(DMSO)] (1, An = U; 2, An = Th), which can be isolated in moderate yields after workup. Complexes 1 and 2 are the first structurally characterized actinide-DOTA complexes to feature the κ⁸ binding mode for the DOTA ligand. In addition, we isolated a few crystals of [U(κ⁴-H₂DOTA)(DMSO)₄][Cl]₂ (3). Crystallographic characterization of this material reveals that the [H₂DOTA]^2- ligand in 3 is only coordinated to U⁴⁺ by its four carboxylate arms, generating an overall κ⁴ binding mode. Similar complexes have been previously proposed as intermediates along the H₄DOTA complexation pathway, but this intermediate had not been structurally characterized until now.