Construction of Bimetallic and Trimetallic Aggregates with a [Y(COT)2]− Building Block: Solid-State Structures and Solution Behavior

Several new bimetallic and trimetallic complexes containing the [Y­(COT)2]− unit in different coordination environments are synthesized and fully characterized using X-ray crystallography and NMR spectroscopy. These complexes include [K([2.2.2]­cryptand)]­[Y­(COT)2] (1), [K­(18-crown-6)­(THF)]­[Y­(COT)2] (2), [Y2K2(COT)4(THF)4] (3), and [YKCa­(COT)3(THF)3] (4). In the presence of secondary ligands, bimetallic ionic pairs that comprise a [Y­(COT)2]− sandwich and a solvent-wrapped K+ ion are formed in 1 and 2. In contrast, 3 represents a bimetallic tetradecker oligomer with two [Y­(COT)2]− units bridged by a K+ ion and a terminal [K­(THF)4]+ moiety. Complex 4 is a heterotrimetallic triple-decker with an axial arrangement of three metal centers to form [Y­(COT)2K­(COT)­Ca­(THF)3]. Structural analysis shows the Y–COTcentroid distances in the [Y­(COT)2]− sandwich are equidistant (1.884(6) Å) in 1 but become asymmetric in 2–4 (1.857(3)–1.952(3) Å), reflecting additional external coordination. The two COT rings are parallel in 1 and become increasingly tilted from 0.8 to 27.5° in 2–4, respectively. Multinuclear NMR spectroscopy measurements reveal the solution behavior of the sandwich and heterometallic multidecker COT-based products. The observed NMR spectroscopic trends corroborate with weak interactions between the [Y­(COT)2]− unit and cationic moieties persisting in solutions of 2–4.