Investigation on structures, luminescent and magnetic properties of LnIII–M (M = FeIIHS, CoII) coordination polymers

Abstract

The structures, luminescent and magnetic properties of three series of coordination polymers with formulas-{[Fe₃Ln₂(L¹)₆(H₂O)₆]·xH₂O}_n (Ln = Pr-Er; 1–9), {[Co₃Ln₂(L¹)₆(H₂O)₆]·yH₂O}_n (Ln = Pr-Dy, Yb; 10–17) and {[Co₂Ln(L²)(HL²)₂(H₂O)₇]·zH₂O}_n (Ln = Eu-Yb; 18–25) (H₂L¹ = pyridine-2,6-dicarboxylic acid, H₃L² = 4-hydroxyl-pyridine-2,6-dicarboxylic acid) were systematically explored in this contribution. [Fe^II_HS–L¹–Ln^III] (1–9) and [Co^II–L¹–Ln^III] (10–17) series are isostructural, and display 3D porous networks with 1D nanosized channels constructed by Fe/Co-OCO-Ln linkages. Furthermore, two types of “water” pipes are observed in 1D channels. [Co^II–L²–Ln^III] (18–25) series exhibit 2D open frameworks based on double-stranded helical motifs, which are further assembled into 3D porous structures by intermolecular hydrogen bonds between hydroxyl groups. The variety of the resulting structures is mainly due to the HO-substitution effect. These 3D coordination polymers show considerably high thermal stability, and do not decomposed until 400 °C. The high-spin Fe^II ion in [Fe^II_HS–L¹–Ln^III] was confirmed by X-ray photoelectron spectroscopy, Mössbauer spectroscopy and magnetic studies. The luminescent spectra of coordination polymers associated with Sm^III, Eu^III, Tb^III and Dy^III were systematically investigated, and indicate that different d-metal ions in d-f systems may result in dissimilar luminescent properties. The magnetic properties of [Fe^II_HS–L¹–Ln^III] (3, 6, 7, 9, 13), [Co^II–L¹–Ln^III] (15–17) and [Co^II–L²–Ln^III] (19–24) coordination polymers were also studied, and the χ_MT values decrease with cooling. For the single ion behavior of Co^II and Ln^III ions, the magnetic coupling nature between Fe^II_HS/Co^II and Ln^III ions cannot be clearly depicted as antiferromagnetic coupling.