Self-Assembly of a Pd8 Macrocycle and Pd12 Homochiral Tetrahedral Cages Using Poly(tetrazolate) Linkers

A two-dimensional molecular square (MC) was obtained by the self-assembly of a bis(tetrazole) linker, 4,4 1 -bis(1H-tetrazol-5-yl)-1.1'-biphenyl (H2L1), with a square-planar metal acceptor M [M = (tmeda)Pd(NO3)(2), where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] in dimethyl sulfoxide (DMSO) followed by crystallization. The uncommon 2,3-binding mode through N atoms of the tetrazole rings in this assembly leads to the formation of an octanuclear molecular square. The molecular square MC [Pd-8(L-1)(4)(NO3)(8)] is unstable in DMSO and slowly converts to a dynamic mixture of a 3D tetrahedral cage T1 [Pd-12(L-1)(6) (NO3)(12)] and the macrocycle MC. A tetrahedral cage (T1) is formed by the usual 1,3-binding mode of the tetrazole rings. However, self-assembly of the T1 [Pd-12(L-1)(6)(PF6)(12)] was possible to access in the pure form in a less polar solvent like acetonitrile. The pure T1 [Pd-12(L-1)(6)(PF6)(12)] also converts to a mixture of T1 and MC in DMSO. Interestingly, when a tris(tetrazole) linker, tris(4-(1H-tetrazol-5-yl)phenyl)amine (H3L2), was treated with the acceptor M, it produced a tetrahedral nanocage T2 [Pd-12(L-2)(4)(NO3)(12)] through 1,3-binding mode of the tetrazole rings without any trace of an octahedral cage through 2,3-binding mode of the tetrazole moieties.