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Journal of Coordination Chemistry

Year: 2008  |  Volume: 61  |  Issue: 19  |  Page No.: 3066 - 3079

Synthesis, spectroscopy, thermodynamics and structure of [ZnCl23-dpktch)] (η3-dpktch = N,N,O- di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone)

Mohammed Bakir, Rebecca R. Conry, Orville Green and Willem H. Mulder

Abstract

When dpktch was reacted with ZnCl2 in refluxing acetonitrile in air [ZnCl23-dpktch)] was isolated in good yield. Infrared spectra suggest weaker binding of dpktch in [ZnCl23-dpktch)] than in [CdCl23-dpktch)]. 1H-NMR studies in non-aqueous media show that [ZnCl23-dpktch)] is sensitive to changes in its environment and exchanges its amide proton. Electronic absorption spectral measurements confirmed the sensitivity of [ZnCl23-dpktch)] to changes in its surroundings and show inter-conversion between two intra-ligand-charge-transfer transitions (ILCT) at 330 ± 2 nm and 404 ± 2 associated with [ZnCl23-dpktch)] and its conjugate base. Thermo-optical measurements in non-aqueous dmf and dmso show facile inter-conversion between [ZnCl23-dpktch)] and its conjugate base, respectively. Also, it is shown that protonation of dmf by [ZnCl23-dpktch)] is exothermic (standard enthalpy of protonation ΔHθ = -40.7 ± 1.8 kJ mol-1), but endothermic for dmso (ΔHθ = +8.3 ± 1.5 kJ mol-1). Chemical stimuli in concentrations as low as 5.0 times 10-7 M can be detected and determined using [ZnCl23-dpktch)] in non-aqueous media. X-ray crystallographic studies on a monoclinic, P21/n single crystal of [ZnCl23-dpktch)] confirmed the N,N,O-coordination of dpktch and revealed interdigitated units of [ZnCl23-dpktch)] connected via a web of hydrogen bonds.

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