Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation

Two new mixed ligand metal-organic frameworks of Zn(II) with disodium 5-hydroxyisophthalate and 4,4'-azobispyridine (azbpy) ligands, {[Zn(azbpy)(HO-1,3-bdc)(H2O)]center dot(azbpy)}(n) (1) and {[Zn(azbpy)(0.5)(HO-1,3-bdc)(C2H5OH)]center dot(H2O)}(n) (2) have been synthesized by changing the reaction medium (methanol to ethanol) and structurally characterized by elemental analysis, IR, PXRD, TG and single crystal X-ray diffraction. Compound 1 exhibits a 2D sheet network structure with free azbpy ligands in its void space, and is stabilized by pi-pi and C-H center dot center dot center dot pi interactions, whereas 2 has a 2D layered architecture with lattice water molecules in its void space. Compound 2 has a flexible structure and shows gated adsorption (gas and solvent) behavior, while framework 1 is nonporous. These two MOFs exhibit remarkable electrical conductivity values at room temperature and their comparison is discussed carefully. Theoretical calculations suggest that both the compounds are p-type semiconductors and correlate the structure-property relationship. Schottky barrier diode electronic devices have been fabricated by using these two semiconductor materials with aluminium (Al) and indium tin oxide (ITO) in sandwich configuration, ITO/MOF-1 or 2/Al, and both the devices exhibit sound rectification behavior. The photoluminescent properties of both the compounds in the solid state are also investigated in detail.