Mixed anionic and inclusion complexes of nickel(II) with nitroaromatics showing selectivity in oxygen-π interactions

• 4-Nitrophenol form inclusion complex with [Ni(phn)3](NO3)2·2H2O; which is fluorescent.
• 2,4-Dinitrophenol or 3-nitrobenzoic acid forms mixed anionic complex with [Ni(phn)3](NO3)2·2H2O.
• Mixed anionic complexes are non-fluorescent.
• Oxygen-π interactions observed in mixed anionic complexes are attributed to fluorescence quenching.

From reaction of tris-(1,10-phenanthroline)nickel(II) nitrate (1) with different nitroaromatics, inclusion complex of 4-nitrophenol [Ni(phn)3](NO3)2·(Hnp)·2H2O (2) and mixed anionic nitro-aromatic complexes [Ni(phn)3]2(dnp)3(NO3)·11H2O (3) and [Ni(phn)3](nba) (NO3)3·11H2O (4) where (phn = 1,10-phenanthroline, Hnp = 4-nitrophenol, dnp = 2,4-dinitrophenolate, nba = 3-nitrobenzoate) are prepared and characterized. 2,4-Dinitrophenolate in complex 3 as well as 3-nitrobenzoate in complex 4, have oxygen-π interactions involving oxygen atom/s of nitro groups with the π-cloud of 1,10-phenanthroline rings and the complexes are non-fluorescent but complex 1 and inclusion complex 2 are weakly fluorescent. Complexes 3 and 4 are examples of mixed anionic complexes having odd numbers of dissimilar uni-negative anions distributed over two complex di-positive cations. Isothermal calorimetric titrations have shown that association constants of 4-nitrophenol, 2,4-dinitrophenol, 3-nitrobenzoic acid with the complex 1 at 27 °C are 514 M−1, 924 M−1, 1040 M−1 respectively.

Tris-(1,10-phenanthroline)nickel(II) nitrate (1) reacts with different nitroaromatics, 4-nitrophenol form inclusion complex [Ni(phn)3](NO3)2·(Hnp)·2H2O (2) whereas 2,4-dinitrophenol, 3-nitrobenzoic acid form mixed anionic nitro-aromatic complexes [Ni(phn)3]2(dnp)3(NO3)·11H2O (3) and [Ni(phn)3](nba) (NO3)3·11H2O (4) where (phn = 1,10-phenanthroline, Hnp = 4-nitrophenol, dnp = 2,4-dinitrophenolate, nba = 3-nitrobenzoate). The complex 1 and 2 are weakly fluorescent whereas the complex 3 and 4 are non-fluorescent.Figure optionsDownload as PowerPoint slide