Molecular design strategies for spin-crossover (SCO) metal complexes (Fe(II) and Co(II)) for thermoelectricity

Abstract TEC are developing technology to generate electricity from thermal energy. It causes current flow when redox solution disturbs the electrochemical potential equilibrium between the electrolyte and two inert electrodes upon application of a temperature gradient. We explore the spin-crossover materials which have been shown as promising TEC candidates upon its spin-state transition by change of temperature. Particularly, we analyse the correlation of the spin-state transition, redox properties, molecular structures and consequently on TEC performance. Three complexes, [M2(CH3COO)4(L)2] and [M(L)3](BF4)2, where M = Fe(II) and Co(II), and L = extended π-conjugated bipyridyl ligand and N3-Schiff bases were successfully synthesised and characterised. The best performance recorded by Complex 2 owing to the molecular octahedral structure with high-spin which allows higher diffusion of ions. It also noted that the largest change of emax value (Complex 2) arises from spin-states transition brings an additional contribution to the entropy change that accounted for TEC performance.