We have recently been investigating the double perovskites Ba2LnMoO6 (Ln= Nd - Tb; Y) which exhibit fascinating structural and magnetic properties. Ba2LnMoO6 with Ln = Nd-Eu exhibit Jahn-Teller distortions accompanied by a transition from tetragonal I4/m to triclinic I-1 symmetry at low temperature. Antiferromagnetic order of the Ln3+ and/or Mo5+ spins is also detected at low temperature. Ba2GdMoO6 is ferroelastic and there is no evidence of magnetic order of the Mo5+ or Gd3+ spins down to 2 K whereas Ba2TbMoO6 exhibits spiral magnetic order of the Tb3+ spins below 8 K. In contrast Ba2YMoO6 is the first example of an exotic valence bond glass (VBG), which is a cooperative spin-singlet ground state. Here we propose to elucidate the magnetic structure of Ba2PrMoO6 which exhibits an antiferromagnetic transition below 30 K.