By using an achiral (4-carboxynaphthalen-1-yl)phosphonic acid (4-cnappH(3)), compound Co-2(4-cnapp) (OH) (H2O)(2) (1) is isolated crystallizing in orthorhomibic space group P2(1)2(1)2(1). It shows a three-dimensional framework structure in which the Delta-type chains of corner-sharing Co-3(mu(3)-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.