From 0D dimer to 2D NetworkSupramolecular Assembly of Organic Derivatized Polyoxometalates with Remote Hydroxyl via Hydrogen Bonding

A series of remote hydroxyl functionalized organoimido derivatives of hexamolybdate, (Bu4N)2[Mo6O18(Cres)] (1) (Cres = 4-amino-m-cresol), (Bu4N)2[Mo6O17(Cres)2]·H2O (2), (Bu4N)2[Mo6O18(Phen)]·i-PrOH (Phen = p-aminophenol)(3), (Bu4N)2[Mo6O18(Phen)]·EtOH (4), (Bu4N)2[Mo6O17(Phen)2] (5), (Bu4N)2[Mo6O18(Naph)] (Naph = 5-amino-1-napheynyl) (6), and (Bu4N)2[Mo6O18(Chex)]·1.5H2O (Chex = trans-4-aminocyclohexanol) (7) were synthesized and characterized by single crystal X-ray diffraction, FT-IR spectra, UV−vis spectra, elemental analysis, 1H NMR, and cyclic voltammetry. X-ray structural study reveals that intermolecular and intramolecular hydrogen bonding plays an important role in their supramolecular assembly; it is found that (i) bridged oxo ligands of hexamolybdate cluster are more inclined to form hydrogen bonds as acceptors than terminal oxo ligands in this system; (ii) small solvent molecules with hydrogen bonding donor and acceptor, such as water, i-PrOH, and EtOH, usually act as hydrogen bonding bridge in their supramolecular assembly; (iii) hydrogen bonding has an important influence on their anion conformation besides cell packing; (iv) the hydrogen bonding supramolecular assembly of compounds 1−7 demonstrate an interesting change from dimer (3), to 1D infinite single chain (4), to 1D infinite double chain (2), and to 2D network (1, 5, 6, and 7) owing to the alteration of the grafting organic ligand, the substituted number, and the crystallized solvent molecule. To explore their potential application in conductivity, the optical band gap of compounds 1−7 were determined upon their solid state reflectance spectra. Our current study not only surveys systematically hydrogen bonding interaction and supramolecular assembly of remote hydroxyl functionalized organoimido-derivatized hexamolybdates but also provides some available precursors for further modification including esterification.