Donor-Site-Directed Rational Assembly of Heteroleptic cis-[Pd₂ L₂ L'₂ ] Coordination Cages from Picolyl Ligands.

ABSTRACT: A donor-site engineering approach facilitates the formation of heteroleptic [Pd₂ L₂ L'₂ ]⁴⁺ cage structures through a favored cis-'in₂ /out₂ ' spatial configuration of the methyl groups of 5- and 3-substituted bis-monodentate picolyl ligands with flat acridone and bent phenothiazine backbones. The heteroleptic cages were confirmed by ESI-MS and 2D NMR experiments as well as DFT calculations, which pointed toward a cis-configuration being energetically favored. This was further supported by the synthesis and X-ray structure of a previously unreported cis-[Pd(2-picoline)₄ ]²⁺ complex. The formation of homoleptic structures, however, was met with considerable steric hindrance at the Pd^II centers, as observed by the formation of [Pd₂ L₃ (solvent)₂ ]⁴⁺ and [Pd₂ L₂ (solvent)₄ ]⁴⁺ species when only one type of acridone-based ligand was offered. In contrast, bent phenothiazine ligands with outside-pointing methyl groups showed the ability to form interpenetrated double-cages, as revealed by X-ray crystallography. The general route presented herein enables the assembly of uniform cis-[Pd₂ L₂ L'₂ ]⁴⁺ coordination cages, thus furthering the possibility to increase structural and functional complexity in supramolecular systems.

SUBMITTER: Zhu R 

PROVIDER: S-EPMC6174927 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature