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)] (1 alpha, 1 beta, and 1 gamma) (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 1 alpha, 1 beta, or 1 gamma into the coordination polymer [MoO2(L)](n) (2a). The square inclusion complex [MoO2(L)](4)superset of CH2Cl2 center dot 4CH(2)Cl(2) (2b superset of CH2Cl2 center dot 4CH(2)Cl(2)) was obtained by a self-assembly reaction in dichloromethane. 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)] (1 alpha, 1 beta, and 1 gamma), [MoO2(L)](4)superset of CH2Cl2 center dot 4CH(2)Cl(2) (2b superset of CH2Cl2 center dot 4CH(2)Cl(2)), [MoO2(L)(gamma-pic)]center dot gamma-pic (3.gamma-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, thermogravimetric, and differential scanning calorimetry measurements, IR, UV-vis, one- and two-dimensional NMR spectroscopies, and the powder X-ray diffraction method.