Defect-Induced Acceleration of a Solid-State Chemical Reaction in Zinc Alkoxide Single Crystals

A twofold interpenetrating three-dimensional zinc-organic framework built from naphthalene-1,4-dicarboxylate and 4,4'-bipyridine ligands

A novel three-dimensional Zn(II) complex, poly[[(μ2-4,4'-bipyridine)(μ4-naphthalene-1,4-dicarboxylato)(μ2-naphthalene-1,4-dicarboxylato)dizinc(II)] dimethylformamide monosolvate monohydrate], {[Zn2(C12H6O4)2(C10H8N2)]·2C3H7NO·H2O)}n, has been prepared by the solvothermal assembly of Zn(NO3)·6H2O, naphthalene-1,4-dicarboxylic acid and 4,4'-bipyridine. The two crystallographically independent Zn atoms adopt the same four-coordinated tetrahedral geometry (ZnO3N) by bonding to three O atoms from three different naphthalene-1,4-dicarboxylate (1,4-ndc) ligands and one N atom from a 4,4'-bipyridine (bpy) ligand. The supramolecular secondary building unit (SBU) is a distorted paddle-wheel-like {Zn2(COO)2N2O2} unit and these units are linked by 1,4-ndc ligands within the layer to form a two-dimensional net parallel to the ab plane, which is further connected by bpy ligands to form the three-dimensional framework. The single net leaves voids that are filled by mutual interpenetration of an independent equivalent framework in a twofold interpenetrating architecture. The title compound is stable up to 673 K. Excitation and luminescence data observed at room temperature show that it emits bright-blue fluorescence.

Geometries, Thermodynamic Properties and Reactions of Methylzinc Alkoxide Clusters Studied by Density Functional Theory Calculations

Methylzinc alkoxide complexes are precursors for the preparation of nanosized zinc oxide particles, which in turn are catalysts or reagents in important industrial processes such as methanol synthesis and rubber vulcanization. We report for the first time the structures, energies, atomic charges, dipole moments, and vibrational spectra of more than 20 species of the type [(MeZnOR')n] with R' = H, Me, tBu and n = 1-6, calculated by density functional theory methods, mostly at the B3LYP/6-31+G* level of theory. For R' = Me, the global minimum structure of the tetramer (n = 4) is a highly symmetrical heterocubane but a ladder-type isomer is by only 70.9 kJ mol(-1) less stable. The corresponding trimer is most stable as a rooflike structure; a planar six-membered ring of relative energy 13.5 kJ mol(-1) corresponds to a saddle point connecting two equivalent rooflike trimer structures. All dimers form planar four-membered Zn2O2 rings whereas the monomer has a planar CZnOC backbone. A hexameric drumlike structure represents the global minimum on the potential energy hypersurface of [(MeZnOMe)6]. The enthalpies and Gibbs energies of the related dissociation reactions hexamer --> tetramer --> trimer --> dimer --> monomer as well as of a number of isomerization reactions have been calculated. The complexes [(MeZnOMe)n] (n = 1-3) form adducts with Lewis bases such as tetrahydrofuran (thf) and pyridine (py). The binding energy of py to the zinc atoms is about 65% larger than that of thf but is not large enough to break up the larger clusters. The bimolecular disproportionation of [(MeZnOMe)4] with formation of the dicubane [Zn{(MeZn)3(OMe)4}2] and Me2Zn is less endothermic than any isomerization or dissociation reaction of the heterocubane, but for steric reasons this reaction is not possible if R' = tBu. A novel reaction mechanism for the reported interconversion, disproportionation and ligand exchange reactions of zinc alkoxide complexes is proposed.