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

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 [H 6 L]Cl, we observed an oxidative cyclization of this ligand in the presence of PPh 4 + ions resulting in the complex [Pd(H 2 L′)(PPh 3 )] ( 1 ). The use of 5,5‐diethylbarbiturate (bar 2− ) 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 (Et 4 N) 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 Na 4 (Et 3 NH) 12 [(Pd 3 L) 8 {μ‐(bar)} 12 ]⋅ x  H 2 O. Compound 3 was characterized by 13 C‐MAS‐NMR spectroscopy and single‐crystal structure analysis.