Self-assembly of 2,5-diformylpyrrole, tris(2-aminoethyl)amine, and Cd(II) or Hg(II) affords homobimetallic cryptates. In contrast, the synthesis of heterobimetallic Zn(II)-Cd(II) and Cd(II)-Hg(II) cages requires a stepwise approach involving a monocadmium(II) precursor. The bis-mercury(II) cryptate exhibits a pronounced mercurophilic interaction, as evidenced by a short Hg···Hg separation of 3.0549(7) Å. Notably, a similarly close intracavity contact is observed for the Cd(II)-Hg(II) system, with a M···M distance of ca. 3.1 Å. The participation of the metal centers in the attractive interaction─enforced by confinement within the iminopyrrole cage─was verified through the density functional theory (DFT) calculations of bond indices and was further corroborated by QTAIM analysis.
Sarwa et al. (Thu,) studied this question.