Single-crystals of the new manganese hydroxide halides Mn₅(OH)₆Cl₄, Mn₅(OH)₇I₃, and Mn₇(OH)₁₀I₄ were obtained by means of high-pressure/high-temperature synthesis in a Walker-type multianvil apparatus. The chloride crystallizes in the monoclinic space group P2₁/c (no. 14) with the lattice parameters (single-crystal data) a = 592.55(8), b = 1699.7(2), c = 597.33(8) pm, and β = 112.58(1)°. The iodides crystallize in the triclinic space group P1 (no. 2) with a = 653.16(2), b = 905.98(3), c = 1242.98(4) pm, α = 114.21(1)°, β = 99.91(1)°, and γ = 94.37(1)° for Mn₅(OH)₇I₃ and a = 656.90(3), b = 906.59(4), c = 909.32(4) pm, α = 119.29(1)°, β = 97.99(1)°, and γ = 95.03(1)° for Mn₇(OH)₁₀I₄. The crystal structures consist of edge-sharing Mn(OH)₆-_nX_n (X = Cl, I; n = 1, 2, 3) octahedra arranged in stacked sheets. Adjacent layers are connected by hydrogen bonds of type O-H···X, confirmed by further characterization of single-crystals by IR-spectroscopy. The crystal chemical relationship with the aristotype Mg(OH)₂ (brucite) is discussed on the basis of Bärnighausen trees (group-subgroup relations).