Synthesis and Crystal Structure of Zn(OAc)[EMIM], a Novel Ionic Compound with Isolated Homoleptic Trinuclear Metal Clusters.

We synthesized and characterized a novel anhydrous zinc(II) aceto 1-ethyl-3-methylimidazolium (EMIM) coordination compound with the simplified empirical formula Zn(OAc)[EMIM]. The title compound is structurally related to recently reported Mn(OAc)[EMIM], and Fe(OAc)[EMIM]. While in the other two ionic salts metal cations were organized in infinite chains of corner-sharing octahedra, Zn in Zn(OAc)[EMIM] assumes two different coordination environments, including Zn(OAc) octahedra and Zn(OAc) tetrahedral sites, linked together by carboxylate oxygen-sharing to form isolated [Zn(OAc)] trinuclear linear clusters. The homoleptic trinuclear cluster configuration of zinc is important because it provides a distinct coordination environment that can influence the cluster's electronic and structural properties, offering unique opportunities for designing novel materials with specific characteristics. This configuration is unique as it avoids the presence of water in the coordination shell, which can alter the behavior of the cluster, thus enabling more controlled and predictable interactions in various applications, including catalysis. Similar to the Mn and Fe compounds, in the title compound, the EMIM moieties do not interact directly with the Zn and contribute to the structure framework of the compound through hydrogen bonds with the acetate anions. Two different polymorphs of Zn(OAc)[EMIM] were crystallized and characterized, one with monoclinic symmetry (α-phase) and one with triclinic symmetry (β-phase). The α-phase has a melting temperature of 80 °C, while the β-phase melts at ∼81 °C, thus both can be considered as metal-containing ionic liquids. Both forms of the Zn(OAc)[EMIM] compound are porous and plausibly capable of accommodating other types of molecules.