Construction of diverse CdII/ZnII coordination polymers based on 5-(quinolyl)tetrazolate generated via in situ hydrothermal synthesis

Abstract

By variation of reaction parameters such as metal salts and secondary ligands, a series of new coordination polymers, [Cd(QTZ)₂] (1), [Cd(QTZ)N₃·H₂O] (2), [Zn(QTZ)Cl] (3), [Cd₂(QTZ)₂(INA)₂]·0.25H₂O (4), [Cd₂(QTZ)(btrc)·2(H₂O)]·1.67H₂O (5), 2[Cd₃(QTZ)₂(btec)·H₂O]·H₂O (6) (QTZ = 5-(quinolyl)tetrazole; HINA = isonicotinic acid; H₃btrc = 1,3,5-benzenetricarboxylic acid; H₄btec = 1,2,4,5-benzenetetracarboxylic acid) were successfully synthesized under hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. The QTZ ligands in these compounds are in situ generated from a [2 + 3] cycloaddition reaction of 3-quinolinecarbonitrile and NaN₃ in water with the acid of Cd^II/Zn^II salt. Compound 1 displays a three-dimensional (3D) 2-fold interpenetrating diamond network with Schläfli symbol 6⁶. Compound 2 represents a two-dimensional (2D) coordination framework constructed of infinite Cd–N₃⁻ chains and QTZ ligands. Compound 3 exhibits a 4-connected 2D (4,4) net built up by interconnection of Zn₂(QTZ)₂Cl₂ subunits. Compound 4 is a 2D framework constructed by interconnection of Cd₂(QTZ)₂(INA)₂ subunit and Cd₂(QTZ)₂ subunit. Compound 5 exhibits a 2D layered structure with the Cd₂–QTZ chain extended by btrc ligands. In compound 6, trinuclear Cd^II clusters link each other by pairs of QTZ ligands to form an infinite zigzag Cd₃–QTZ chain; furthermore the adjacent Cd₃–QTZ chains are extended by the btec ligands to form a 3D network. These results indicate that QTZ is a powerful functional ligand and the nature of secondary ligands and transition metal ions also play significant roles in dominating molecular self-assembled structure. In addition, the luminescent properties of all compounds have been investigated in the solid state at room temperature.