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

Abstract

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