Incorporation of cationic electron donor of Ni-pyridyltetrathiafulvalene with anionic electron acceptor of polyoxometalate

A new salt - [Ni ^II(DMSO) ₅(TTFPy)] ₂[α -SiW ₁₂O ₄₀] (1) - based on polyoxometalates was prepared by coordinating a cationic electron donor of pyridyltetrathiafulvalene (TTFPy) with Ni ^II. Although the TTFPy molecule did not form a salt with the anionic α-[SiW ^VI ₁₂O ₄₀] ^4- because of the weak charge-transfer (CT) interaction, the coordination of Ni with the pyridyl moiety permitted salt formation driven by electrostatic interaction, giving a single crystal of 1. Crystallographic analysis, UV-vis and IR spectroscopy and electrochemical characterization revealed that the fully oxidized α-[SiW ^VI ₁₂O ₄₀] ^4- was crystallized with the neutral TTFPy moiety from the acetonitrile solution because of the low electron-withdrawing ability of α-[SiW ^VI ₁₂O ₄₀] ^4-, forming a brown-orange crystal. The crystal colour quickly turned to black by immersing in methanol, due to CT from TTF moiety to α-[SiW ^VI ₁₂O ₄₀] ^4-, which was caused by the solvent effect. Increase in the solvent acceptor number from 18.9 for acetonitrile to 41.3 for methanol resulted in the enhancement of the electron withdrawing ability of α-[SiW ^VI ₁₂O ₄₀] ^4- by 0.317 V in methanol.