Synthesis, Characterization, and Crystal Structures of Two New Manganese Aceto EMIM Ionic Compounds with Chains of Mn2+Ions Coordinated Exclusively by Acetate

Abstract

We synthesized and determined crystal structures of two manganese(II) aceto EMIM coordination compounds with simplified empirical formulas Mn4(OAc)10[EMIM]2 and Mn4(OAc)10[EMIM]2·2H2O. Both compounds feature extended chains of Mn2+ octahedrally coordinated exclusively by acetate anions, which has been observed for the first time. The EMIM moieties and water molecules participate in hydrogen bonding with acetate anions but do not directly interact with the metal cation. Both compounds have melting temperatures around 120 °C and can be considered as (non-room-temperature) ionic liquids. The structural arrangement represented by the two title compounds is robust in terms of accommodating other types of cations and allows for tuning of physical properties of the ionic liquid by means of cation substitution. Thermal analysis results obtained using TGA-DSC and VT IR suggest melting phase transitions around 120 °C, followed by structural rearrangement in the molten state taking place around 140-160 °C. Compounds I and II have a higher thermal stability range compared to [EMIM][OAc] ionic liquid, with an onset decomposition temperature above 260 °C.