Transformation of a Mother Crystal to a Daughter Crystal through Amorphous Phase: De-assembly of Coordination Helices upon Heating and Re-assembly through Aquation

The nonlinear optical active chiral complex 1 [{Co(2,5-pdc)(H2O)2}H2O]n (2,5-pdc = 2,5-pyridine dicarboxylate) has been synthesized via a solvothermal technique using the achiral 2,5-pdc ligand. Complex 1 (phase 1), a two-dimensional coordination polymer, undergoes crystalline to amorphous (phase 2) transformation upon deaquation, which under reaquation generates a new microcrystalline phase (phase 3). The crystal structure of phase 3 has been determined by powder X-ray diffraction analysis (PXRD), which reveals that the resultant microcrystalline phase 3 is an achiral complex consisting of one-dimensional coordination chains. Phase 3 undergoes reversible structural transformation via amorphous phase (phase 2) upon dehydration and subsequent rehydration. This amorphous phase shows selective adsorption of water from a water–DMF mixture and water–CCl4 mixture. Phase 1 to phase 3 structural transformation proceeds through selective bond breaking. The magnetic studies of the two crystalline and the amorphous ...