Rational Design of the First Closed Coordination Capsule with Octahedral Outer Shape

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Abstract

The rational synthesis of an octahedral coordination capsule in which the triangular faces are covered by single ligands is described herein. Starting with tris(2-hydroxybenzylidene)triaminoguanidinium chloride [H6L]Cl, we observed an oxidative cyclization of this ligand in the presence of PPh4+ ions resulting in the complex [Pd(H2L′)(PPh3)] (1). The use of 5,5-diethylbarbiturate (bar2−) as a bridging ligand in the presence of [Co(en)3]3+ (en=ethylenediamine) leads to the formation of a rectangular box with the formula (Et4N)6[{Co{(PdCl)(Pd)L}2(μ-bar)}2] (2). The analysis of the architecture of compounds 1 and 2 enables the development of a self-assembly strategy for the synthesis of an octahedral coordination cage 3 with the formula Na4(Et3NH)12[(Pd3L)8{μ-(bar)}12]⋅x H2O. Compound 3 was characterized by 13C-MAS-NMR spectroscopy and single-crystal structure analysis.

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