D. Saravanakumar

Macrocyclic Unsymmetrical Binuclear Copper(II) Complexes as Ligands: Spectral, Structural, Magnetic and Electrochemical Studies

A new series of macrocyclic unsymmetrical binuclear copper(II) complexes was prepared by using [CuLa,b] (La=[6,6′-piperazine-1,4-diyldimethylenebis(4-methyl-2-formyl)phenol] and Lb=[6,6′-piperazine-1,4-diyldimethylenebis(4-bromo-2-formyl)phenol]) and [Cu(oxen)](ClO4)2 or [Cu(oxpn)](ClO4)2, where oxen=N,N′-bis(2-aminoethyl)oxamide and oxpn=N, N′-bis(3-aminopropyl)oxamide. The binuclear copper(II) complexes contain three different compartments: the first compartment has two piperazinyl nitrogens and two phenolic oxygens (N2O2), the second compartment has two phenolic oxygens and two imine nitrogens (O2N2) and the third compartment has two imine nitrogens and two amide nitrogens (N4) as coordinating sites. Apart from the three compartments the complex has two oxamide oxygen atoms for further coordination. The copper(II) ion in the complex is tetracoordinated with two tertiary nitrogen atoms and two phenoxy oxygen atoms coordinated in the equatorial plane to the copper(II) ion and the geometry around the copper nuclei is distorted square planar. The binuclear copper(II) complexes were characterized by elemental and spectral analysis. Electronic spectra of the complexes show a single broad band for the d–d transition in the region around 585–635 nm. The mono- and binuclear copper(II) complexes show four-line hyperfine splitting in the ESR spectra. For the mononuclear complexes the observed g ‖ values are in the range 2.21 to 2.31, g ⊥ values vary from 2.10 to 2.11 and A ‖ values from 175 to 180 G. For the binuclear complexes the observed g ‖ values are in the range 2.20 to 2.10, g ⊥ values vary from 2.06 to 2.01 and A ‖ values from 165 to 175 G. Room temperature magnetic moments of the mono- and binuclear copper(II) complexes show a μ eff value around 1.72 BM, which is near to the spin-only value of 1.73 BM. Electrochemical studies of the mono- and binuclear copper(II) complexes are discussed. The mononuclear copper(II) complexes show one irreversible reduction wave in the region -0.54 to -0.89 V and the binuclear copper(II) complexes show two irreversible single-step one-electron transfer processes in the range , at the cathodic potential region.

Simple colorimetric fluoride sensors based on nitrophenyl derivatives

Easy to prepare fluoride ion sensors bearing OH and NH groups as binding sites and nitrophenyl group as a chromophore [2-[(4-nitrophenylimino)methyl]-4-methylphenol (1), 2-[(4-nitrophenylamino)methyl]-4-methylphenol (2), 2-[(2,4-dinitrophenylimino)methyl]-4-methylphenol (3) and 2-[(2,4-dinitrophenylamino)methyl]-4-methylphenol (4)] were synthesised and characterised. The visible colour changes, the UV–vis and 1H NMR spectral changes towards anions were studied. The sensing ability of the receptor depends on the presence of electron-withdrawing group attached to the receptors and extended conjugation in the receptor framework and the order of the sensing ability is found to be 3>1>4>2 based on binding constant.