We report the first bromine-bridged dinuclear [Dy(Cy3PO)2(μ-Br)(Br)2]2·2C7H8 single-molecule magnet with an effective energy barrier of 684 K and magnetic hysteresis below 3 K. The asymmetric DyIII centres present two unique stereoisomeric octahedral coordination environments depending on the cis/trans disposition of the Cy3PO ligands, leading to the orthogonality of the easy magnetic axes that annihilates the dipolar interactions.