Construction of helical coordination polymers via flexible conformers of bis(3-pyridyl)cyclotetramethylenesilane: metal(ii) and halogen effects on luminescence, thermolysis and catalysis

Abstract

Infinite rectangular-tubular helices, [MX₂L] (M = Zn(II), Hg(II); X⁻ = Cl⁻, Br⁻; L = bis(3-pyridyl)cyclotetramethylenesilane), have been efficiently constructed via the combined effects of the potential flexible conformers of L and the tetrahedral geometry of M(II) ions. This helical molecular system affords a racemic mixture of P- and M-helices in a crystal. The helical pitches (7.8934(4)–8.1560(2) Å) that are sensitive to the nature of M(II) ions and halide anions are attributable to subtle change in the flexible dihedral angles between the two pyridyl groups around Si and the M(II) hinges. Their photoluminescence intensities, correspondingly, are in the order [ZnCl₂L] > [ZnBr₂L] ≫ [HgCl₂L] > [HgBr₂L]. Zinc(II) complexes show recyclable catalytic effects on the transesterification reaction in the order [ZnCl₂L] > [ZnBr₂L]. Calcination of [ZnCl₂L] and [ZnBr₂L] at 500 °C produces uniform hexagonal tubular spire crystals of 1.2 × 1.2 × 4.0 μm³ dimensions and spheres, respectively.