On the Road to MM′X Polymers: Redox Properties of Heterometallic Ni···Pt Paddlewheel Complexes

On the quest of heterometallic mixed-valence
MM′X chains,
we have prepared two stable discrete bimetallic compounds: the reduced
(PPN)­[ClNi­(μ-OSCPh)4Pt] (PPN = bis­(triphenylphosphine)­iminium;
OSCPh = benzothiocarboxylato) and the oxidized [(H2O)­Ni­(μ-OSCPh)4PtCl] species. The role of the aqua and chlorido axial ligands
is crucial to facilitate oxidation of the {Ni­(μ-OSCPh)4Pt} core. Experimental and theoretical analyses indicate that a NiPt-Cl/Cl-NiPt
isomerization process occurs in the oxidized species. The electronic
structure of the reduced system shows two unpaired electrons, one
located in a dx2–y2 orbital
of the Ni­(II) ion and a second in the antibonding dz2–dz2 combination from the Ni­(II) and Pt­(II) centers.
Oxidation occurs by removing one electron from this second multicenter
molecular orbital. Although the mixed-valence character of the oxidized
species makes the isolation of MM′X chains very attractive,
such polymeric structure is prevented by the low Pt–Cl···Ni
interaction energy and the high tendency of Ni centers to coordinate
water molecules. Thus, this work offers valuable insights and hints
to engage the production of heterometallic mixed-valence MM′X
chains, which still is a challenging task.