Chromium is a metal and has a complex-valued refractive index. The value that you are quoting is about right for the real part, but there is also an imaginary part of similar size: https://refractiveindex.info/?shelf=main&book=Cr&page=Johnson
Cr-(VI) is an oxide of Chromium, i.e., Cr2O3. There is not much data available on the optical properties of this material, but you can find some measurements here:
Article Optical properties of thermally evaporated Cr2O3 thin films
The refractive index seems to be about 1.5, and it's real-valued.