A flexible and hydrolytically stable metal-organic framework [Mn(H₂O)₂(Fc(PHOO)₂)·2H₂O]_n has been synthesized using ferrocene-based ligand bearing phosphinic groups (Fc(PHOOH)₂ = 1,1′-ferrocenediyl-bis(H-phosphinic acid)). In this compound manganese atoms are bound by phosphinate fragments to give infinite chains, and the latter are interconnected by ferrocene groups to form two-dimensional coordination polymer. The elimination of both coordinated and lattice water molecules during heating up to 150 °C produced the compound, which is nonporous for nitrogen, but can selectively adsorb water over methanol and other solvents at 298 K. The reversible structural transformation during adsorption/desorption of water is also reflected in a change of magnetic properties of the metal-organic framework.