Interfacial effects of crystal surface through free quinolinyl groups on crystal organization and catalysis

Abstract

Reaction of MX₂ (M = Cu(II), Hg(II); X⁻ = Cl⁻, Br⁻) with C₃-symmetric tris(6-quinolyl)trimesic ester (L) produces crystals consisting of C₂-symmetric metallacyclodimeric species with two free quinolinyl N-donors, [MX₂L]₂. The crystals self-aggregate in aqueous media. Furthermore, the reaction with cotton-threads and glass-fibers forms unique crystal organization on and with cotton-threads and glass-fibers, respectively. Such crystal aggregation and organization are ascribed to the hydrogen-bonding interactions between the free quinolinyl N-donors on the crystal surface and the hydroxyl (–OH) groups of water, cotton-threads, or glass-fibers. The composite organization of crystals on or with glass-fiber, [CuX₂L]₂@glass, is an effective recyclable heterogeneous catalytic system in catechol oxidation, which indicates the significant role played by the free quinolinyl N-donors. The treatment of [CuX₂L]₂ crystals with K₂PdCl₄ produces, via Pd(II)–N interactions, conceptually advanced PdCl₂@[CuX₂L]₂ composite materials that are useful for Suzuki–Miyaura C–C coupling reactions.