Long-chain PdIICoII paddle wheel carboxylate complexes: Synthesis, thermal analysis and electrochemistry

Mixed-metal carboxylate complexes were synthesized by reacting one equivalent of [Pd₃^II(μ-OOC(CH₂)_nCH₃)₆] with three equivalents of [Co^II(OOC(CH₂)_nCH₃)₂] where n = 4, 6, 8, or 10. This reaction resulted in the formation of [Pd^IICo^II(µ-OOC(CH₂)_nCH₃)₄] where n = 4, 6, 8, or 10. Characterisation via ATR-FTIR revealed that mixed-metal complexes exhibit multiple coordination modes, including unidentate, bidentate, tridendate, and bridging (syn-syn) binding modes. The single crystal X-ray structure of [Pd^IICo^II(μ-OOC(CH₂)₈CH₃)₄] (Z = 2, space group P2₁/c) confirmed the binding modes observed in the ATR-FTIR studies.

Cyclic Voltammetry of [Pd₃^II(μ-OOC(CH₂)_nCH₃)₆] and [Pd^IICo^II(µ-OOC(CH₂)_nCH₃)₄] where n = 4, 6, 8, or 10 demonstrated that the redox process for Pd⁰ → Pd^II were both chemically and electrochemically irreversible. Furthermore, [Pd^IICo^II(µ-OOC(CH₂)_nCH₃)₄] did not exhibit an oxidation wave. Additionally, a progressive decrease in negative reduction of the Pd was observed with increasing carbon chain length.

TGA-MS analysis identified volatile decomposition products such as methane, hydroxide ions, water, carbon monoxide, oxygen, methanol, propyne, carbon dioxide and other species. The non-volatile decomposition residues consisted of metal oxides.