Free tetra- and hexa-coordinated platinum-cyanide dianions, Pt(CN)42- and Pt(CN)62-: A combined photodetachment photoelectron spectroscopic and theoretical study

Two doubly charged transition metal complexes, Pt(CN)42- and Pt(CN)62- commonly found in the condensed phases, are produced as isolated species from solutions to the gas phase using electrospray ionization. Their stability and electronic structures are investigated by photodetachment photoelectron spectroscopy and density functional theory (DFT) calculations. The adiabatic electron detachment energies for the dianions to monoanions are measured to be 1.69 and 3.85 eV for Pt(CN)42- and Pt(CN)62-, respectively. The magnitude of the repulsive Coulomb barrier is estimated to be ∼2.5 eV for Pt(CN)42-, and ∼1.7 eV for Pt(CN)62-. Well-resolved and distinct peaks are observed in the spectra, yielding rich electronic structure information for these complexes. DFT calculations including scalar relativistic and spin-orbit effects are carried out to determine the geometries and to interpret the observed spectral features. The calculations show that the frontier occupied molecular orbitals are largely metal-based for Pt(CN)42- and ligand-based for Pt(CN)62-, in contrast to the standard ligand field theory description.