We consider type II string theory in space-time backgrounds which admit eight
supercharges and can be characterized by the existence of an SU(3) x SU(3)
structure. We show that the couplings of such backgrounds strongly resemble the
couplings of four-dimensional N=2 supergravities and precisely coincide with
the N=2 couplings after an appropriate Kaluza-Klein reduction. Specifically we
show that the moduli space of metrics admits a special Kahler geometry with
Kahler potentials given by the Hitchin functionals. Furthermore we explicitly
compute the N=2 version of the superpotential from the transformation law of
the gravitinos, and find its N=1 counterpart.Comment: 62 pages, improved version, to appear in JHE
