Ad hoc in English is not a synonym of "this" or "such", so you'd be changing the meaning of the sentence if you used "such" and "ad hoc" interchangeably.
Look at the definition you quoted: "Created or done for a particular purpose as necessary." If you wanted to rewrite this sentence without using the Latin phrase, but still preserving its meaning, you'd write something like:
...a tuple is always a custom-built structure...
So, while using ad hoc is good professional English, make sure you're using it in its proper sense of "built as necessary for a particular purpose," not as a replacement for "such a [thing]."
As @eques comments below, ad hoc has a slightly different connotation than custom-built. Ad hoc implies that the thing is built on-the-fly without much careful planning, while custom-built could mean something that is very deliberately planned and carefully designed. Sometimes ad hoc can even have a negative meaning (as something that's slapped together quickly as a temporary solution, but is probably badly designed and should be replaced), but that isn't the case in this particular example.
Here's an example of ad hoc in the more negative sense:
We cut a hole in the wall and put a fan in it as an ad hoc cooling system for the server room, but eventually management will have to replace the air conditioning unit with a more powerful one.