Two new magnesium 2,6-naphthalenedicarboxylate (ndc) metal-organic frameworks, [Mg₃(ndc)₃(dif)₄] (1) (dif = N,N-diisopropylformamide) and [Mg₃(ndc)₃(dmf) ₂(CH₃OH)-(H₂O)](dmf) (2 = TUDMOF-3) (dmf = N,N-dimethylformamide), have been synthesised under solvothermal conditions from Mg(NO₃)₂·6H₂O and pure 2,6-naphthalenedicarboxylic acid. According to single-crystal X-ray crystallographic studies, complex 1 crystallises in the space group P2 ₁/n [a = 14.769(3) Å, b = 13.325(3) Å, c = 17.998(4) Å, β = 108.67(2)°] and complex 2 in the space group P1 [a = 11.1116(11) Å, b = 12.6229(13) Å, c = 17.800(2) Å, α = 88.568(14)°, β = 83.833(13)°, γ = 70.167(11)°]. The structures of compounds 1 and 2 consist of trinuclear magnesium clusters connected to six dicarboxylate ligands; for 2, the clusters act as distorted octahedral nodes to give a 3D network. In contrast, the trinuclear clusters in 1 act as pseudo-planar-hexagonal nodes to give a 2D network assembly. According to nitrogen and hydrogen physisorption measurements at 77 K for compounds 1 and 2, TUDMOF-3 has a permanent porosity with a Langmuir surface area of 632 m ²g^-1, a specific pore volume of 0.21 cm³g ^-1 and a hydrogen storage capacity of 1.23 wt.-% at 77 K and 1 bar, whereas compound 1 is not porous.