Metastability of isolated platinum and palladium tetrahalide dianions and the role of electron tunneling

In the present study we have isolated MX42− (M=Pd, Pt; X=Cl, Br) in a room temperature Penning trap under virtually collision-free, ultra high vacuum conditions and have probed for metastable decay on a time scale of up to 1000 s. While PdCl42−, PdBr42− and PtBr42− do not react appreciably on this time scale, PtCl42− undergoes tunneling electron loss to form PtCl4− with a half-life of 2.5 s. We provide kinetic data and ab-initio quantumchemical calculations of relevant initial and final states as well as Coulomb barriers. All four species are metastable towards halide loss on the basis of these calculations.