If the slaves were 'taken' by the federal government, the government would 'own' the slaves. This didn't happen - the slaves were freed, not taken. No compensation necessary.
All that is required for a taking, is to deprive you of the property. They deprive you of the use of it. Other countries had compensated emancipation. Even some Northern States did. This is a great wrong that was done to the South. One day it's legal, one day it's not, and no compensation, because of a fraudulently ratified amendment. "Consent of the governed" is a concept that got lost in the transfer from the old Union to the New.