Coordination polymer core/shell structures: Preparation and up/down-conversion luminescence

Coordination Polymers Constructed from an Adaptable Pyridine-Dicarboxylic Acid Linker: Assembly, Diversity of Structures, and Catalysis

4,4'-(Pyridine-3,5-diyl)dibenzoic acid (H2pdba) was explored as an adaptable linker for assembling a diversity of new manganese(II), cobalt(II/III), nickel(II), and copper(II) coordination polymers (CPs): [Mn(μ4-pdba)(H2O)]n (1), {[M(μ3-pdba)(phen)]·2H2O}n (M = Co (2), Ni (3)), {[Cu2(μ3-pdba)2(bipy)]·2H2O}n (4), {[Co(μ3-pdba)(bipy)]·2H2O}n (5), [Co2(μ3-pdba)(μ-Hbiim)2(Hbiim)]n (6), and [M(μ4-pdba)(py)]n (M = Co (7), Ni (8)). The CPs were hydrothermally synthesized using metal(II) chloride precursors, H2pdba, and different coligands functioning as crystallization mediators (phen: 1,10-phenanthroline; bipy: 2,2'-bipyridine, H2biim: 2,2'-biimidazole; py: pyridine). Structural networks of 1-8 range from two-dimensional (2D) metal-organic layers (1-3, 5-8) to three-dimensional (3D) metal-organic framework (MOF) (4) and disclose several types of topologies: sql (in 1), hcb (in 2, 3, 5), tfk (in 4), 3,5L66 (in 6), and SP 2-periodic net (6,3)Ia (in 7, 8). Apart from the characterization by standard methods, catalytic potential of the obtained CPs was also screened in the Knoevenagel condensation of benzaldehyde with propanedinitrile to give 2-benzylidenemalononitrile (model reaction). Several reaction parameters were optimized, and the substrate scope was explored, revealing the best catalytic performance for a 3D MOF 4. This catalyst is recyclable and can lead to substituted dinitrile products in up to 99% product yields. The present study widens the use of H2pdba as a still poorly studied linker toward designing novel functional coordination polymers.

Metal–organic architectures designed from a triphenyl-pentacarboxylate linker: hydrothermal assembly, structural multiplicity, and catalytic Knoevenagel condensation

Eight new metal(ii) coordination compounds driven by a triphenyl-pentacarboxylate linker were hydrothermally assembled and fully characterized. Their structural features and catalytic behavior were investigated.

Redox-Responsive Colloidal Particles Based on Coordination Polymers Incorporating Viologen Units

Colloidal particles based on supramolecular polymers are emerging as promising functional materials because of their intrinsic dynamic features and the possibility of stimuli responsivity. In this work, ≈200 nm self-assembled redox-responsive colloidal particles made of 1D-coordination polymers were readily prepared. In these metallopolymers, organic entities made of bis(viologen) groups covalently associated with terpyridine units are spontaneously bridged by Zn²⁺ cations through the formation of coordination bonds. The properties of these particles were analyzed and their redox activities investigated. Upon reduction of the viologen units, the formation of π-dimers between the reduced viologen moieties was demonstrated by spectroscopic experiments. It was shown that intermolecular π-dimers (i.e., between different polymer chains) that do not exist in homogeneous polymer solutions were, nevertheless, formed in the particle's structure because of the effects of confinement. The presence of these π-dimers allows stabilization of the charge in the colloids.

Controlled synthesis and luminescence properties of core-shell-shell structured SiO2@AIPA-S-Si-Eu@SiO2 and SiO2@AIPA-S-Si-Eu-phen@SiO2 nanocomposites

Two novel core-shell structured SiO₂@AIPA-S-Si-Eu and SiO₂@AIPA-S-Si-Eu-phen nanocomposites have been synthesized by a bifunctional organic ligands ((HOOC)₂C₆H₃NHCONH(CH₂)₃Si(OCH₂CH₃)₃) (defined as AIPA-S-Si) connected with Eu³⁺ ions and silica via covalent bond. And the corresponding core-shell-shell structured SiO₂@AIPA-S-Si-Eu@SiO₂ and SiO₂@AIPA-S-Si-Eu-phen@SiO₂ nanocomposites with enhanced luminescence have been synthesized by tetraethyl orthosilicate (TEOS) hydrolysis co-deposition method. The composition and micromorphology of the nanocomposites were characterized by means of Fourier-transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). The as-synthesized core-shell and core-shell-shell structured nanocomposites have excellent luminescence intensity and long lifetime. The nanocomposites show bright red light under ultraviolet lamp. However, the core-shell-shell structured nanocomposites have stronger luminescence intensity than the corresponding core-shell structured nanocomposites. Meanwhile, the core-shell-shell structured nanocomposites still exhibit good luminescence stability in aqueous solution. In addition, a large number of Si-OH on the surface of the core-shell-shell structured nanocomposites can be attached to many biomacromolecules. Therefore, they have potential applications in the fields of biology and luminescence.