Orientational Self-Sorting in Octahedral Palladium Cages: Scope and Limitations of the “cis Rule”

Octahedral coordination cages of the general formula Pd6L1212 were obtained by combining Pd(CH3CN)42 with heteroditopic N-donor ligands. Four different ligands were employed. These ligands have 3-pyridyl donor groups at one end and 4-pyridyl, imidazolyl, or triazolyl donor groups at the other end. According to a geometric analysis, cages with a cis configuration at the six metal centers should be preferred (“cis rule”). This prediction was corroborated by spectroscopic data and crystallographic analyses. Limitations of the “cis rule” were also encountered, and possible explanations are discussed.