Thorium(IV) and uranium(IV) complexes with cucurbit[8]uril: Supramolecular structures via direct coordination and second-shell interactions

Abstract

In this work, we investigated thorium(IV) and uranium(IV) complexes of cucurbit[8]uril {Q[8]} in HCl solutions with the addition of various transition metal chlorides as structure inducers. Consequently, three complexes with similar supramolecular structures built up with both direct coordination and second-shell interactions have been synthesized and structurally characterized. In the presence of CdCl2/RuCl3, {[ThCl(H2O)6]2(Q[8])}·(Q[8])·2(CdCl4)·2Cl·6H2O (Q[8]-Th-Cd) or {[Th(H2O)7]2(Q[8])}·(Q[8])·2(RuCl5)2O·3(HCl)·22H2O (Q[8]-Th-Ru) were synthesized while {[U(H2O)7]2(Q[8])}·(Q[8])·5(ZnCl4)·8H2O (Q[8]-U-Zn) was prepared with U(IV) ions generated in situ by direct reduction of uranyl nitrate with zinc metal. All these complexes have Q[8] directly coordinated to Th(IV)/U(IV) ions, one on each side of the two Q[8] portals in bidentate mode. Subsequent second-shell interactions between (Th2-Q[8])/(U2-Q[8]) complexes and Q[8] molecules form one-dimensional polymers which are further connected through CH···Cl [Cd/Ru/Zn chloride species] interactions forming extended supramolecular networks.