We have used electronic spectroscopy in the 160-1100 nm range to study the polyvinyl alcohol-nickel(II) chloride system. Based on the results obtained, we hypothesize formation of mixed-ligand complexes of the type [Ni(H 2 O) 6-n Cl n ] 2-n (n = 0, 1, ..., 5) in the polyvinyl alcohol matrix. Transformation of the coordination sphere as the NiCl 2 concentration changes is apparent both in the region of the d-d transition bands (350-1100 nm) and in the region of the charge transfer bands (160-250 nm). We propose assigning the absorption bands separated by mathematical treatment to complexes of specific compositions.Introduction. The electronic absorption spectra and structure of nickel complexes have been studied rather thoroughly in aqueous solutions [1-3], salt melts [4,5], and in crystals [6,7]. Study of the structure of the nickel complexes and complexation processes in organic media, in particular polymers, is certainly of interest.The aim of this work was to study the electronic absorption spectra of nickel (II) chloride in a polyvinyl alcohol (PVA) matrix, as a function of the concentration of the added salt and heat treatment of the samples. We chose polyvinyl alcohol as the matrix because of its solubility in water and the fact that thin layers of polyvinyl alcohol have a broad window of transparency: from the vacuum UV to the near IR region.Objects and methods of investigation. The objects of investigation were polyvinyl alcohol films containing different concentrations of nickel chloride. The liquid composition subsequently used to fabricate the films were obtained by mixing an aqueous solution of c.p. grade NiCl 2 ⋅6H 2 O with an aqueous solution of polyvinyl alcohol. Then the composition was poured onto the substrate and dried at room temperature. The film formed was removed from the substrate and used for the measurements. The NiCl 2 concentration in the samples was set by varying the weight of nickel chloride per gram of dry PVA.The absorption spectra in the 160-280 nm region were measured on an apparatus including a VM-1 vacuum monochromator as its main component. An open hydrogen flow lamp was used as the source of UV radiation. The absorption spectra in the 250-1100 nm region were recorded on an SF-26 spectrophotometer.We processed the spectra by bandpass filtering of the signal, with the aim of revealing hidden structure in the spectra.The bandpass filter was synthesized based on a low-frequency filter described in [8]. The calculation formula has the form
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