The synthesis of the Mn(II) phase 4H-Ba0.5Sr0.5MnO2+delta via the topotactic reduction of 4H-Ba0.5Sr0.5MnO3-x with the novel reducing agent LiH, is described. Neutron powder diffraction data show that oxide ions are deintercalated from the host structure in a disordered manner to yield "tetrahedral" MnO4 coordination sites. Magnetic susceptibility and neutron powder diffraction data show that the title phase adopts a canted antiferromagnetically ordered state below T-N = 355K, consistent with the strong magnetic coupling expected between d(5) centers.