Thermally induced single crystal to single crystal transformation leading to polymorphism

•Single crystal to single crystal transformation.•Polymorphism.•2D homochiral and achiral supramolecular sheets.•DSC analysis.•Photoluminescence study.

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 293 K while at 100 K it shows P21/c space group with C1 molecular symmetry. Supramolecular investigation shows that at 100 K the complex forms 2D achiral sheets whereas at 293 K forms two different homochiral 2D sheets. Low temperature DSC analysis indicates that this structural transformation occurs at 246 K 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.

Graphical abstract[La(1,10-phen)2(NO3)3] undergoes ‘thermally induced reversible single crystal to single crystal transformation’ between its two polymorphic phases at 100 K and 293 K. Structural analysis shows that the complex forms 2D achiral sheets at 100 K whereas at 293 K forms two different homochiral 2D sheets. DSC analysis indicates that this structural transformation occurs at 246 K. This structural transformation proceeds through coherent movement of ligands.Figure optionsDownload full-size imageDownload as PowerPoint slide