Tensor products over Ring of Integers

Question

I am having trouble computing the following tensor product(s): $$\mathcal {O}_{Q} \otimes _\mathbb {Z} \mathbb {C} = $$ Where in this case we use the ring of integers of the field of rationals, or how it generalizes where $\mathcal {O}_{K}$ is the ring of integers of a finite extension $\mathbb {Q}$≤K.