Uranyl peroxide pyrophosphate cage clusters with oxalate and nitrate bridges

Abstract

Two complex cage clusters built from uranyl hexagonal bipyramids and multiple types of bridges between uranyl ions, U₃₀Py₁₀Ox₅ and U₃₈Py₁₀Nt₄, were crystallized from aqueous solution under ambient conditions. These are built from 30 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and five oxalate bridges in one case, and 38 uranyl hexagonal bipyramids, 10 pyrophosphate groups, and four nitrate groups in the other. The crystal compositions are (H₃O)₁₀Li₁₈K₂₂[(UO₂)₃₀(O₂)₃₀(P₂O₇)₁₀(C₂O₄)₅](H₂O)₂₂ and Li₂₄K₃₆[(UO₂)₃₈(O₂)₄₀(OH)₈(P₂O₇)₁₀(NO₃)₄](NO₃)₄(H₂O)_n for U₃₀Py₁₀Ox₅ and U₃₈Py₁₀Nt₄, respectively. Cluster U₃₀Py₁₀Ox₅ crystallizes over a narrow range of solution pH that encourages incorporation of both oxalate and pyrophosphate, with incorporation of oxalate only being favored under more acidic conditions, and pyrophosphate only under more alkaline conditions. Cluster U₃₈Py₁₀Nt₄ contains two identical lobes consisting of uranyl polyhedra and pyrophosphate groups, with these lobes linked into the larger cluster through four nitrate groups. The synthesis conditions appear to have prevented closure of these lobes, and a relatively high nitrate concentration in solution favored formation of the larger cluster.