Ba[6]Mg[11]F[34], a new compound of the pseudobinary BaF[2]–MgF[2] system, has been synthesized by solid state techniques from stoichiometric amounts of BaF[2] and MgF[2] and its crystal structure determined by single crystal X-ray diffraction (space group P1,a=7.5084(6), b=9.9192(8), c=10.0354(8) Å, α=81.563(2), β=72.402(2), γ=71.198(1)°, 3899 structure factors, 233 parameters, R(F[2]>2σ(F[2]))=0.018, wR(F[2] all) = 0.046). It is isotypic with the copper(II) analogue, Ba[6]Cu[11]F[34]. The main features of the structure are a network of [MgF[6]] octahedra and three different [BaF[x]] polyhedra with x=12, 11+1 and 13. Ba[6]Mg[11−x]Fe[x]F[34] and Ba[6]Mg[11−x]Mn[x]F[34] solid solutions were prepared and their composition determined by single crystal structure analyses. The luminescence properties of Ba[6]Mg[11]F[34] doped with Eu[2+] were studied using fluorescence spectroscopy. The observed luminescence was pale blue with a maximum at 465 nm.