NLO response as a function of structural water presence: A comparative experimental (UV-vis) and DFT (structural, NPA, MEP) study on Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2

Abstract

A comparative experimental (UV–vis) and theoretical (DFT) study on the nonlinear optical (NLO) response of the double salts Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2 is presented in the current paper. For that purpose, a detailed analysis on the electronic absorption behavior of the compounds under investigation in the range from 200 to 1100 nm is conducted. The position of the experimentally registered electronic transitions is compared with that of the corresponding theoretical ones (calculated by means of DFT at B3LYP/6–311+G(d,p) level of theory). A time-dependent variant of DFT is applied to calculate the oscillator strengths and absorption maxima. Moreover, structural parameters, net atomic charges and molecular electrostatic potential surface are accomplished at B3LYP/6–311+G(d,p) level of theory as well.Results showed that the NLO response depends strongly on the structural water presence. Hence, the ionic salt Cs2Ni(SeO4)2•4H2O is a good NLO material in the middle ultraviolet (MUV), near ultraviolet (NUV) and near infrared (NIR) regions, while MUV and NUV areas characterize Cs2Ni(SeO4)2. However, it was revealed that Cs2Ni(SeO4)2 possesses considerably better NLO properties within 200–400 nm than Cs2Ni(SeO4)2•4H2O. These findings were related to a different electron density rearrangement in the Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2, a consequence of the metal-oxygen interactions strength.