Naphthoquinone based Chemosensor 2-(2′-aminoethylpyridine)-3-chloro-1,4-naphthoquinone: Detection of metal ions, X-ray -crystal structures and DFT studies

• Metal binding studies of naphthoquinone based chemosensor is discussed.
• X-ray structure of Chemosensor and its Ni2+ complex is presented.
• Chemosensor can be used for naked eye detection of Cu2+ in methanol-water.
• Stoichiometry and binding constant has been determined.
• Neutral and anionic form of chemosensor in solution supported by TD-DFT.

Naphthoquinone based Chemosensor 2; 2-(2′-aminoethylpyridine)-3-chloro-1,4-napthoquinone have been synthesized and characterized. Chemosensor 2 crystallizes in the orthorhombic space group Pbcn and shows extensive intramolecular as well as intermolecular hydrogen bonding interactions. Each molecule of Chemosensor 2 showed interaction with five neighboring molecules via C–H⋯N, N–H⋯N, C–H⋯Cl and C–H⋯O interactions. Slipped π–π stacking interaction was observed in adjacent quinonoid and benzenoid rings. Chemosensor abilities of Chemosensor 2 ligand have been evaluated with metal ions viz. Cu2+, Ni2+, Zn2+, Co2+, Fe3+, Mn2+, Cr3+, Hg2+, La3+ and Cd2+ in methanol, methanol-water mixture and in presence of mild base triethylamine. Stoichiometry of Chemosensor 2 with metal ions such as Cu2+, Ni2+, Zn2+and Co2+ ions was determined by Jobs method in methanol and were found as 1:1 for Cu2+and 2:1 for Ni2+, Zn2+ Co2+. The variation in the metal ligand ratio is observed in aqueous media for Cu2+. Chemosensor 2 can be used selectively for naked eye detection of Cu2+ ions. The association constant obtained in methanol shows the trend Cu2+>Ni2+>Co2+. Cu2+ and two (Ni-1 and Ni-2) Ni2+ complexes were synthesized. Ni-2 complex showed coordination of Chemosensor 2 ligands was through pyridine nitrogen's only. The Chemosensor 2 and its deprotonated forms in methanol, water and triethylamine were also studied by TD-DFT studies.

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