Synthesis of a Uranyl Persulfide Complex and Quantum Chemical Studies of Formation and Topologies of Hypothetical Uranyl Persulfide Cage Clusters

The compound Na4[(UO2)­(S2)3]­(CH3OH)8 was synthesized at room
temperature
in an oxygen-free environment. It contains a rare example of the [(UO2)­(S2)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–(S2)–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–(S2)–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 [(UO2)­(S2)­(SH)4]4– or [(UO2)­(S2)­(C2O4)4]4– into fullerene topologies
with ∼60 vertices may be favored by use of large counterions.