A novel complex, [Mn(C₆H₁₂N₄)₂(H₂O)₄][Mn(H₂O)₆][SO₄]₂·6H₂O, was synthesized and hexagonal single crystals with centimeter-scale sizes were obtained by the method of solvent evaporation. It was characterized by elemental analysis, infrared spectrum, thermogravimetric analysis and X-ray single-crystal diffraction. The complex belongs to triclinic crystal system, space group P with a = 9.3390(8), b = 13.3520(13), c = 16.3207(13) Å, α = 100.7160(3)°, β = 90.1020(10)°, γ = 109.9490(5)°, V = 1874.9(3) ų, Z = 2, D_c = 1.542 g/cm³, M_r = 870.64, μ = 0.876 mm^-1, T = 293(2) K, F(000) = 916 and S = 0.990. The crystal structure determination displayed a distorted octahedral geometry around the manganese atom, which is bound to two nitrogen atoms from hexamethylenetetra- mine, acting as monodentate ligands, and to four aqua ligands. Variable-temperature magnetic measurements of the complex indicate the presence of weak antiferromagnetic interaction between manganese centers.