Preparation and characterization of diamine intercalation compounds of misfit layer sulfides

Abstract

Polycrystalline (PbS)_1.18(TiS₂)₂ , a composite misfit layer sulfide, reacts directly with ethylenediamine (en) and propylenediamine (pn) to form intercalation complexes of compositions (PbS)_1.18(TiS₂)₂(en)_0.44 and (PbS)_1.18(TiS₂)₂(pn)_0.37 , respectively. Attempts at preparing pure intercalate phases with n-alkyldiamines of longer chains failed. These novel intercalation compounds were examined by various techniques including XRD, FTIR, XPS, TG and TPD measurements. The XRD results are consistent with an intercalation model where the organic molecules are present at every TiS₂–TiS₂ interface, as monolayers with the alkyl chain almost parallel to the sulfur layers. Deintercalation of the diamines occurs at about 250 °C and releases H₂S simultaneously. The formation of H₂S has been associated to a direct attack on the lattice by water molecules since the complexes, as revealed by IR and XPS, readily absorb water under ambient conditions. Moreover, N 1s spectra of intercalated samples, prepared either bringing the host into contact with the liquid diamine or by dosing with diamine vapors in the spectrometer′s preparation chamber, revealed the presence of two types of organic molecules differently bound to the chalcogenide. This behavior departs from that observed in the in situ deposition of diamine vapors onto an oxidized aluminium surface. In this case, the N 1s spectrum exhibits a single peak of lower binding energy indicative that the amine molecule is weakly bound to the surface.