Thorium(IV) and Uranium(IV) Complexes with Cucurbit[8]Uril : Supramolecular Structures Via Direct Coordination and Second-Shell Interactions

With the increase of portal size and cavity, cucurbit[n]urils {Q[n]s, n = 5-8} tend to have richer host-guest chemistry and less affinity for metal complexation. As such no any tetravalent actinide complex of Q[8] has ever been reported. In this work, we studied thorium(IV) and uranium(IV) complexes of 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 three complexes have Q[8] directly coordinated to Th(IV)/U(IV) ions, one on each side of the two 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