Temperature-controlled synthesis and luminescent properties of two novel coordination polymers modeled by hexa-carboxylate ligand derived from cyclotriphosphazene

Abstract

Solvothermal reactions of hexakis(4-formylphenoxy)cyclotriphosphazene (H₆L1) with Cd(NO₃)₂·4H₂O in H₂O/DMF under different synthesis temperatures produced two new compounds, namely, {[Cd₃(C₄₂H₂₄O₁₈P₃N₃) (H₂O)₇]·xGuest}_n (1), and {[Cd₂(C₄₂H₂₄O₁₈P₃N₃) (H₂O)₂]·xGuest}_n (2). Compound 1 exhibits a novel 3D framework adopting 2,4,6-connected 3-nodal topology with the point (Schläfli) symbol {4⁴·6²}{4⁵·6²·8⁸}{4} constructed from the joint of neutral Cd₂ SBUs, mono-Cd ions and L1 ligands. Compound 2 reveals a 2D crystal structure exhibiting a 3,6-connected 2-nodal kgd topology with the point (Schläfli) symbol {4³}₂{4⁶·6⁶·8³} constructed from the connection of Cd centers and L1 ligands. In these two compounds, the ligands L1 are fully deprotonated, whose six extended carboxyl arms connect six different/same metallic nodes to form high dimensional frameworks. The variable reaction temperature must be responsible for the higher coordination number and versatile coordination modes of carboxylates in 1 compared to the ones in 2, resulting in the formation of a distinct crystal structure. In the solid state, both complexes are photoluminescent (LMCT) at room temperature.