Crystallographic elucidation of an aluminium-bound amido Schiff base chemosensor: a selective turn-on fluorescent chemosensor for Al3+ ions

We have synthesized a biphenyl-derived two arm-containing amido Schiff base, bis((2-hydroxynaphthalen-1-yl) methylene)-[1,1 '-biphenyl]-2,2 '-dicarbohydrazide (sensor 1), having hard donors to facilitate chelation with hard metal centers. The crystal structure of sensor 1 reveals that it crystallizes in the monoclinic system with the space group I2/a and shows several types of intra/inter-molecular H-bond interactions, which stabilized the crystal lattice. The sensing property of sensor 1 towards different metal ions has been demonstrated using different analytical techniques. In fact, sensor 1 shows high fluorescence selectivity and sensitivity towards Al3+ ions in aqueous DMF media. Importantly, we have reported the first structurally characterized six-coordinate dinuclear Al3+ complex ([Na(Al2L2)center dot 2H(2)O center dot 4DMF], complex 1 (where ligand, L = sensor 1). Complex 1 crystallizes in the space group P (1) over bar. X-ray single crystal diffraction studies for complex 1 reveal that each Al3+ ion is hexa-coordinated by four oxygen and two nitrogen atoms from each arm of the two ligands. The sodium ion has penta-coordination in a highly distorted trigonal bipyramidal geometry, surrounded by two mu-bridging naphtholate oxygen atoms and three solvent DMF oxygen atoms. Upon addition of Na2EDTA to complex 1, no spectral change or naked-eye colour change was observed. Furthermore, '' test kits '' coated with sensor 1 showed successful selective detection of Al3+ ions under UV light.

Automated summary

We synthesized a biphenyl-derived amido Schiff base, sensor 1, which has hard donors for chelating with hard metal centers. The crystal structure of sensor 1 shows various types of H-bond interactions that stabilize the crystal lattice. Sensor 1 exhibits high selectivity and sensitivity towards Al3+ ions in aqueous DMF media. We also reported the first structurally characterized six-coordinate dinuclear Al3+ complex, complex 1, in which each Al3+ ion is hexa-coordinated and the sodium ion is penta-coordinated in a highly distorted trigonal bipyramidal geometry. Sensor 1-coated test kits successfully detected Al3+ ions under UV light.