Silver-containing ionic liquids with alkylamine ligands

The synthesis, structure and electrochemical properties of several silver-containing liquid metal salts have been investigated. These ionic liquids comprise of a silver-containing cation with a silver centre coordinated by two or more alkylamine ligands and a bis(trifluoromethylsulfonyl)imide (Tf₂N) anion. With the monodentate amines tert-butylamine (tBuAm), iso-butylamine (iso-BuAm), sec-butylamine (sec-BuAm), 2-ethylhexylamine (2-EtHexAm), di(2-ethylhexyl)amine and piperidine (pip), compounds with the formula [Ag(L)₂][Tf₂N] are formed, several of which are room-temperature ionic liquids and all melt at or below 100 °C. In the case of [Ag(L)₂][Tf₂N] (L=tBuAm, iso-BuAm and pip), single-crystal X-ray diffraction shows that, in the solid state, the silver centres are two-fold coordinated by two amine ligands and the anion and cation exist as separated ion pairs. With ethylenediamine (en), two different compounds were formed, depending on the silver-to-ligand ratio and their structures were elucidated by X-ray diffraction. [Ag(en)][Tf₂N] has a very high melting point and is polymeric in the solid state, with en ligands coordinated to different silver(I) centres, creating one-dimensional chains. [Ag(en)₂][Tf₂N], on the other hand, is a room-temperature ionic liquid, with four-coordinate silver(I) centres, but is actually polymeric in the solid state. The electrodeposition behaviour of [Ag(2-EtHexAm)₂][Tf₂N] and [Ag(en)₂][Tf₂N] was investigated both at room temperature and at 90 °C and it was possible to achieve very high current densities in unstirred solutions and to electrodeposit closed, crackfree, silver coatings. A crystal of [Ag₂(en)Cl₂] was obtained from a solution of [Ag(en)][Tf₂N] in deuterochloroform and its structure is described.status: publishe