Synthesis of a uranyl persulfide complex and quantum chemical studies of formation and topologies of hypothetical uranyl persulfide cage clusters

The compound Na ₄[(UO ₂)(S ₂) ₃](CH ₃OH) ₈ was synthesized at room temperature in an oxygen-free environment. It contains a rare example of the [(UO ₂)(S ₂) ₃] ^4- complex in which a uranyl ion is coordinated by three bidentate persulfide groups. We examined the possible linkage of these units to form nanoscale cage clusters analogous to those formed from uranyl peroxide polyhedra. Quantum chemical calculations at the density functional and multiconfigurational wave function levels show that the uranyl-persulfide-uranyl, U-(S ₂)-U, dihedral angles of model clusters are bent due to partial covalent interactions. We propose that this bent interaction will favor assembly of uranyl ions through persulfide bridges into curved structures, potentially similar to the family of nanoscale cage clusters built from uranyl peroxide polyhedra. However, the U-(S ₂)-U dihedral angles predicted for several model structures may be too tight for them to self-assemble into cage clusters with fullerene topologies in the absence of other uranyl-ion bridges that adopt a flatter configuration. Assembly of species such as [(UO ₂)(S ₂)(SH) ₄] ^4- or [(UO ₂)(S ₂)(C ₂O ₄) ₄] ^4- into fullerene topologies with -60 vertices may be favored by use of large counterions.