A series of mono/bimetallic isostructural hybrid tetraborates of the general formula [ZnxCo(1-x)(1,3-dap)B4O7] has been prepared using a solvothermal method. Their adsorption/desorption curves for H2O and D2O demonstrate that these materials have a stronger affinity for H2O than for D2O and enrich the D2O content of D2O/H2O mixtures.