Binding ability of chloride ion with platinum and rhodium dinuclear complex containing ethylenediamine as co-ligand

In this study, the binding capability for Cl− ion was investigated with amidate-bridged platinum–rhodium dinuclear complex axially coordinated PPh3 to the rhodium atoms containing ethylenediamine (=en) as co-ligand. Mixing [PtRhCl3(piam)2(en)]·3H2O (2Cl) with PPh3 and NaPF6 provided [PtRhCl2(piam)2(en)(PPh3)]PF6 (2(PPh3)·PF6) which can bind Cl− ion at the axial position of platinum atom to be [PtRhCl2(piam)2(en)(PPh3)]Cl (2(PPh3)·Cl), where both crystal structures were determined by single-crystal X-ray analyses. UV–vis titration demonstrated that the formation constant of 2(PPh3)·PF6 with Cl− is 1.6 × 103 M−1, significantly smaller than that with NH3 as a co-ligand, which suggests that multinucleation is necessary for effective hydrogen bonds as well as the affinity of metals.