Disruption of the La(III)[15-Metallacrown-5] Cavity through Bithiophene Dicarboxylate Inclusion

The inclusion of bithiophenedicarboxylate (btDC) in La(III)[15-MCCu,N,L-phenylalaninehydroximate-5] hosts (LaMC) unexpectedly results in a clathratocomplex with a completely disrupted hydrophobic cavity. Structures best formulated as {(LaMC)2(μ2-O)} are formed that dimerize across the hydrophilic parts. This dimer appears stabilized by 5 phenyl-DMF-phenyl interactions and 10 DMFamine hydrogen bonds. Electrospray ionization mass spectrometry reveals the presence of 2 : 2 LaMC-btDC complexes in solution. In the solid state, both cis- and trans-bithiophene dicarboxylate guests bridge the > 17 Å distance between LaMC hydrophobic faces. The resulting solid has over 50% void space, suggesting guest-length and solvent considerations can predictably lead to the formation of open LaMC coordination frameworks or close-packed molecular compartments.