Electronic absorption spectra of reduction products of pentavalent niobium and tantalum in different alkali chloride and oxychloride melts

We have studied the electronic absorption spectra of niobium chloride and oxychloride compounds in different oxidation states and of the reduction products of pentavalent niobium and tantalum in various alkali chloride melts at different temperatures up to 1000 K. Furthermore, we present spectra of the corresponding cluster compounds Na 4 Nb 6 Cl 18 and Na 4 Ta 6 Cl 18 dissolved in alkali chloride melts at elevated temperatures. It is found that these compounds decompose at these temperatures. In comparing the spectra corresponding to the different oxidation states of the niobium systems, it is concluded that reduction of NbCl 5 with excess metal yields Nb(II) or Nb(III), whereas in NbOCl 3 the oxidation state IV is stabilized