Potassium Binding Adjacent to Cationic Transition-Metal Fragments: Unusual Heterobimetallic Adducts of a Calix[4]arene-Based Thione Ligand

The synthesis of
cationic rhodium and iridium complexes of a bis­(imidazole-2-thione)-functionalized
calix[4]­arene ligand and their surprising capacity for potassium binding
are described. In both cases, uptake of the alkali metal into the
calix[4]­arene cavity occurs despite adverse electrostatic interactions
associated with close proximity to the transition-metal fragment [Rh+···K+ = 3.715(1) Å; Ir+···K+ = 3.690(1) Å]. The formation
and constituent bonding of these unusual heterobimetallic adducts
have been interrogated through extensive solution and solid-state
characterization, examination of the host–guest chemistry of
the ligand and its upper-rim unfunctionalized calix[4]­arene analogue,
and use of density functional theory based energy decomposition analysis.