Why is ["Mo"("H"_2"O")_6]^(3+) paramagnetic?

${\left[M o {\left(O {H}_{2}\right)}_{6}\right]}^{3 +}$ is a paramagnet due to the electronic configuration of the metal ion.
The $M {o}^{3 +}$ is a ${d}^{3}$ ion. Coordination chemistry would predict that the $d$ electrons were all unpaired, and therefore give rise to paramagnetism. Even if only 1 of the electrons were unpaired (which is a necessity!) the complex would still be a paramagnet).