Raman spectroscopy has been used to study the liquid system CsCl-NbCl5-NbOCl3 at temperatures between 340 and 650 degrees C, Molten NbOCl3 shows Raman bands typical of bridging and terminal oxygen. In the basic regions of the system the ions NbCl6-, NbOCl52-, and NbOCl4- have been identified, In the acidic region, polymeric ions with bridging oxygen probably coexist with ions with terminal oxygen. The structure of NbCl6-, NbOCl52-, and NbOCl4- have been verified by and the interpretation of their spectra assisted with ab initio SCF and CASSCF calculations. SCF calculations have also been performed for NbCl5 and NbOCl3 and VOCl3, VOCl4-, and VOCl52- for comparison. In the binary CsCl-NbOCl3, when x(CsCl) > 0.5, the equilibrium NbOCl4- + Cl- = NbOCl52- is established. This is also verified by quantum chemical calculations.