Using alkaline-earth metal ions to tune structural variations of 1,3,5-benzenetricarboxylate coordination polymers

Abstract

Alkaline-earth metal ions were used to tune four new heterometallic frameworks, {[Cd_2.07Mg_0.93(BTC)₂(H₂O)₄]·2H₂O}_n (1), {[Cd₂Ca(BTC)₂(H₂O)₄]·2H₂O}_n (2), {[Cd₂Sr(BTC)₂(H₂O)₅]·H₂O}_n (3) and [Cd₆Ba₃(BTC)₃(H₂O)₁₀]_n (4) (H₃BTC = 1,3,5-benzenetricarboxylic acid), synthesized from H₃BTC and the corresponding metal salts. Single-crystal X-ray analysis shows that compound 1 is a three-dimensional (3D) framework based on heterometallic Cd–O–Cd–O–Mg inorganic chain subunits, compounds 2 and 3 are basically isostructural and feature a 3D framework based on Ca(II) or Sr(II) polyhedrons decorated with Cd–O–Cd inorganic chains. Compound 4 is a 3D framework templated by disordered inorganic hydrate Ba(II) ions, and also features inorganic Cd–O–Cd chains, which are connected together through corner sharing with the {Cd₁O₆} polyhedrons by {Ba₁O₆} polyhedrons, giving rise to a rare heterometallic 3D inorganic skeleton. Moreover, the solid-state fluorescence of compounds 1–4 and NLO properties of compounds 2–4 have also been investigated at room temperature.