Silver Ion-Mediated Heterometallic Three-Fold Interpenetrating Uranyl–Organic Framework

A unique
case of a uranyl-silver heterometallic 3-fold interpenetrating network
(U-Ag-2,6-DCPCA) from a multifunctionalized organic ligand, 2,6-dichloroisonicotinic
acid, in the presence of uranyl and silver ions is reported. It is
the first report of a heterometallic uranyl–organic interpenetrating
network or framework. Notably, a (4,4)-connected uranyl building unit
in U-Ag-2,6-DCPCA, which is available through combined influences
of structural halogenation and silver ion additive on uranyl coordination,
plays a vital role in the formation of a 3-fold interpenetrating network.
Halogen substitution effectively changes structural features and coordination
behaviors of isonicotinate ligand and contributes to the control of
uranyl coordination. Meanwhile, it exerts influence on the stabilization
of 3-fold interpenetrating networks by halogen–halogen interactions.
Theoretical calculation suggests that the silver ion should mainly
serve as an inductive factor of uranyl species through strong Ag–N
binding affinity, directly leading to the formation of a (4,4)-connected
uranyl building unit and finally a heterometallic 3-fold interpenetrating
network. Related experimental results, especially an interesting postsynthetic
metalation, afford further evidence of this induction effect.