Tuning the Structure and Flexibility of Coordination Polymers via Solvent Control of Tritopic Triazine Conformation during Crystallization

Soft crystallization routes for the controlled growth of one- and two-dimensional Cu(II)-coordination polymers of the type [(Cu(hfa)₂)_x(3-tpt)]_n (hfa = hexafluoroacetylacetonate, 3-tpt = 2,4,6-tris(3-pyridyl)-1,3,5-triazine) are described. Three volatile solvents with different protic/aprotic characteristics were chosen as the reaction media, e.g., supercritical CO₂, chloroform, and ethanol. Five (1-5) new compounds were crystallized, with different structures and Cu(II)/3-tpt ratios. The structures of 3-tpt and five new coordination polymers were elucidated by single-crystal synchrotron X-ray diffraction. A description of the crystallization pathways followed for the synthesis of the individual compounds is given based on the protic or aprotic character of the used solvents and reagents' solubility constraints. The main novelty of the work relies in establishing the foundations of 3-tpt isomeric control during crystallization through solvent selection. From the five precipitated new compounds, 3 displays a significant framework flexibility, associated with N₂ adsorption at low temperature, presenting a stepwise adsorption isotherm. The N₂ adsorption process was followed by in situ synchrotron X-ray powder diffraction.