Synthesis and characterization of sodium polyselenides in liquid ammonia solution

Abstract

Solutions of sodium polyselenides in liquid ammonia have been studied using UV-Visible spectroscopy. The results of the investigation indicate that Na2Se3, Na2Se4, Na2Se6 are isolatable, spectroscopically identifiable species. Na2Se5 was found to be a 1: 1 mixture of Na2Se4 and Na2Se6 And no evidence was found to indicate a higher polyselenide than Na2Se6. Na2Se2 could be prepared only in equilibrium with Na2Se3 and Na2Se and was not isolated in a pure state from solution. The value of the constant (K'=K_eq/K_sp) for the equilibrium 2Na2Se2 <--> Na2Se3 + Na2Se was found to be ca 5 x 10^6 M^-3. The spectra of Na2Se and H2Se in liquid ammonia were quite similar. Both spectra have a single band ca 2900Å which, in each case, shows an energy versus temperature dependence. The slope for Na2Se is -40 cal/deg and -45 cal/deg for H2Se. The spectrum of each polyselenide consisted of several overlapping bands. All spectra were submitted to curve resolution and the results are as follows: Na2Se3 (2780Å, 3170Å. 3860Å, and 5925Å), Na2Se4 (2560Å, 3040Å, 3440Å, 4160Å, 5515Å), Na2Se6 (2660Å, 3060Å, 3820Å, 4360Å, 5810Å), and Na2Se2 (, based on difference spectra, ca 2300Å, 3200Å, 4750Å, 5600Å).