Thermally induced single crystal to single crystal transformation leading to polymorphism

The robust complex [La(1,10-phen)2(NO3)3] (1,10-phen=1,10-phenanthroline) exhibits thermally induced single crystal to single crystal transformation from one polymorphic phase to another. The complex crystallizes in monoclinic C2/c space group with C2 molecular symmetry at 293K while at 100K it shows P21/c space group with C1 molecular symmetry. Supramolecular investigation shows that at 100K the complex forms 2D achiral sheets whereas at 293K forms two different homochiral 2D sheets. Low temperature DSC analysis indicates that this structural transformation occurs at 246K and also this transformation is reversible in nature. We have shown that thermally induced coherent movement of ligands changes the molecular symmetry of the complex and leads to polymorphism. Photoluminescence property of complex has been studied in both solid state and in methanolic solution at room temperature. The effect of the presence low-lying LUMO orbital of π-character in the complex is elucidated by theoretical calculation using DFT method.