Three-Dimensional Supermolecules Assembled from a Tris(Zn2+−cyclen) Complex and Di- and Trianionic Cyanuric Acid in Aqueous Solution (Cyclen = 1,4,7,10-Tetraazacyclododecane)

Two new three-dimensional supermolecules having closed hollow frameworks were isolated by self-assembly of a tris(Zn 2+ −cyclen) (Zn 3 L 3 ) (L 3 = 1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene) with di- (CA 2 - ) or trideprotonated cyanuric acid (CA 3 - ) in aqueous solution (cyclen = 1,4,7,10-tetraazacyclododecane). One was a very stable 2:3 complex of Zn 3 L 3 and CA 2 - formed above pH 6, which was isolated from a 2:3 mixture of Zn 3 L 3 and cyanuric acid (CA) in aqueous solution and characterized by 1 H NMR and potentiometric pH titration. The X-ray crystal structure showed that each CA 2 - is sandwiched between two Zn 2+ −cyclen moieties extended from two tris(Zn 2+ −cyclen). The crystal data: formula C 75 H 147 N 36 O 36 Cl 3 Zn 6 ((Zn 3 L 3 ) 2 −(CA 2 - ) 3 ·3NO 3 ·3ClO 4 ·6H 2 O), M r = 2627.84, monoclinic, space group P 2 1 / n (No. 14), a = 27.327(3) Å, b = 29.127(2) Å, c = 16.025(2) Å, β = 90.56(1)°, V = 12754(1) Å 3, Z = 4, R = 0.091, and R w = 0.110. The second one was an unexpected supramolecular complex by 4:4 self-assembly of Zn 3 L 3 and CA 3 -, which was isolated by allowing a 1:1 mixture of Zn 3 L 3 and CA in aqueous solution to stand at pH 11.5. Its X-ray crystal analysis showed a highly symmetric 4:4 assembling complex having an inner hollow, which was schematically represented as a truncated tetrahedron made by binding four equilateral triangles and four scalene hexagons to each other through CA 3 - −Zn 2+ bonds. Crystal data of the 4:4 supramolecular complex: formula C 144 H 344 N 72 O 88 Zn 12 ((Zn 3 L 3 ) 4 −(CA 3 - ) 4 ·12NO 3 ·40H 2 O), M r = 5277.29, cubic, space group I 4̄3m (No. 217), a = 23.430(4) Å, V = 12862(3) Å 3, Z = 2, R = 0.068, and R w = 0.086. The 2:3 supercomplex is stable in H 2 O, while the 4:4 complex is stable only in solid or in DMSO solution and tends to go back to the 2:3 complex in the presence of H 2 O. The 2:3 and 4:4 complexes were equivalent in terms of acid−base equilibrium, and direction of the disproportionation to the 4:4 complex was favored due to its insolubility.