Towards a New Family of Photoluminescent Organozinc 8-Hydroxyquinolinates with a High Propensity to Form Noncovalent Porous Materials

We report on investigations of reactions of tBu2Zn with 8-hydroxyquinoline (q-H) and the influence of water on the composition and structure of the final product. A new synthetic approach to photoluminescent zinc complexes with quinolinate ligands was developed that allowed the isolation of a series of structurally diverse and novel alkylzinc 8-hydroxyquinolate complexes: the trinuclear alkylzinc aggregate [tBuZn(q)]3 (13), the pentanuclear oxo cluster [(tBu)3Zn5(mu 4-O)(q)5] (2), and the tetranuclear hydroxo cluster [Zn(q)2]2[tBuZn(OH)]2 (3). All compounds were characterized in solution by 1H NMR, IR, UV/Vis, and photoluminescence (PL) spectroscopy, and in the solid state by X-ray diffraction, TGA, and PL studies. Density functional theory calculations were also carried out for these new ZnII complexes to rationalize their luminescence behavior. A detailed analysis of the supramolecular structures of 2 and 3 shows that the unique shape of the corresponding single molecules leads to the formation of extended 3D networks with 1D open channels. Varying the stoichiometry, shape, and supramolecular structure of the resulting complexes leads to changes in their spectroscopic properties. The close-packed crystal structure of 13 shows a redshifted emission maximum in comparison to the porous crystal structure of 2 and the THF-solvated structure of 3.