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Three polymorphic forms of a monomeric Mo(VI) complex: building blocks for two metal−organic supramolecular isomers. Intermolecular interactions and ligand substituent effects

Three polymorphic forms of the molybdenum(VI) complex [MoO2(L)(EtOH)] (1α, 1β, and 1γ) (L2− = 4-methoxy-2-oxybenzaldehyde isonicotinylhydrazonate) were synthesized by the reaction of H2L with the dioxobis(acetylacetonato)molybdenum(VI) complex, [MoO2(acac)2], in ethanol. Removal of the coordinated ethanol molecule upon grinding or heating led to the solid-state transformation of the polymorphs 1α, 1β, or 1γ into the coordination polymer [MoO2(L)]n (2a). The square inclusion complex [MoO2(L)]4⊃CH2Cl2.4CH2Cl2 (2b⊃CH2Cl2.4CH2Cl2) was obtained by a self-assembly reaction in dichlormethane. Standard Gibbs energies of binding for molybdenum(VI) compounds [MoO2(L)(D)] with the sixth coordination site occupied by a nitrogen or an oxygen donor D were estimated using quantum chemical calculations. Crystal and molecular structures of the molybdenum(VI) compounds [MoO2(L)(EtOH)] (α, 1β, and 1γ), [MoO2(L)]4⊃CH2Cl2.4CH2Cl2 (2b⊃CH2Cl2.4CH2Cl2), [MoO2(L)(γ-pic)]∙γ-pic (3∙γ-pic), [MoO2(L)(py)] (4) and [MoO2(L)(dmso)] (5) were determined by the single crystal X-ray diffraction method. The compounds were further characterized by chemical analysis, TG and DSC measurements, IR, UV-Vis, one- and two-dimensional NMR spectroscopies and the powder X-ray diffraction method.

Polymorphs; Molybdenum(VI); Aroylhydrazone; Coordination polymers; Square inclusion complex; Supramolecular architectures

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