Actually, the reason it doesn't work is because 1/4 isn't an integer. If a, b are real and c is an integer, then

##e^{c(a+bi)}=e^{ac}\cdot e^{bci}=e^{ac}(\cos cb + i\sin cb)=(e^a)^c(\cos b + i\sin b)^c=(e^{a+bi})^c##

But note that we used De Moivre's law, which only holds for integers.