Photochemistry of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)strontium tetraglyme solutions for eventual liquid phase photochemical deposition

Abstract

The mechanism of Sr(hfac) 2TG (hfac = 1,1,1,5,5,5,hexafluoro-2,4-pentanedionato and TG, tetraglyme = 2,5,8,11,14-pentaoxapentadecane) photodegradation was investigated in methanol and dichloromethane at 254 and 300 nm. In methanol, photodegradation led to SrF 2 through the attack of fluoride on the metal, occurring from the CF 3 group in the intraligand excited state π–π*. In dichloromethane, a mixture of SrCl 2 and SrF 2 was obtained in proportions dependent on the initial complex concentration and irradiation wavelength. SrF 2 was formed by photoexcited species of the complex with the same mechanism occurring in methanol. SrCl 2 was formed by a solvent-initiated reaction at 254 nm, involving substitution of ligand by chloride ion, coming from photochemical solvent decomposition, whereas at 300 nm it was formed by a solvent–assisted reaction, involving an electron transfer to solvent from excited ligand in triplet state. The photochemical kinetics were followed by UV spectrophotometry, the photodecomposition products were recognized by ESI-mass, XRD and XPS. The Sr(hfac) 2TG photodegradation was usefully exploited to obtain pure thin films or mixture of SrCl 2 and SrF 2 by the LPPD technique, operating in suitable experimental conditions. The films were characterized by SEM, XPS and XRD.