Type of structural isomerism
According to Wikipedia, this type of isomerism is known as Isotopomerism


  Isotopomers or isotopic isomers are isomers with isotopic atoms, having the same number of each isotope of each element but differing in their positions. The result is that the molecules are either constitutional isomers or stereoisomers solely based on isotopic location. For example, $\ce{CH3CHDCH3}$ and $\ce{CH3CH2CH2D}$ are a pair of constitutional isotopomers of propane


For a different source, you can also check out the IUPAC Gold book's definition of an isotopomer.