By using an achiral (4-carboxynaphthalen-1-yl)phosphonic acid (4-cnappH3), compound Co2(4-cnapp)(OH)(H2O)2 (1) is isolated crystallizing in orthorhomibic space group P212121. It shows a three-dimensional framework structure in which the Δ-type chains of corner-sharing Co3(μ3-OH) triangles are cross-linked by the organic groups of the phosphonate ligands. Interestingly, the bulk sample of compound 1 is enantioenriched, thus providing a rare example of symmetry breaking upon crystallization from achiral starting materials. Slow magnetization relaxation is observed at low temperature.