From a Well-Defined Organozinc Precursor to Diverse Luminescent Coordination Polymers Based on Zn(II)-Quinolinate Building Units Interconnected by Mixed Ligand Systems.

Katarzyna Sołtys-Brzostek,Michał K Leszczyński,Kamil Sokołowski,Janusz Lewiński,Natalia Olejnik-Fehér,Iwona Justyniak

doi:10.3390/molecules26237402

Abstract

Introduction of photoactive building blocks into mixed-ligand coordination polymers appears to be a promising way to produce new advanced luminescent materials. However, rational design and self-assembly of the multi-component supramolecular systems is challenging from both a conceptual and synthetic perspective. Here, we report exploratory studies that investigate the potential of [Zn(q)2]2[tBuZn(OH)]2 complex (q = deprotonated 8-hydroxyquinoline) as an organozinc precursor as well as a mixed-ligand synthetic strategy for the preparation of new luminescent coordination polymers (CPs). As a result we present three new 2D mixed-ligand Zn(II)-quinolinate coordination polymers which are based on various zinc quinolinate secondary building units interconnected by two different organic linker types, i.e., deprotonated 4,4′-oxybisbenzoic acid (H2obc) as a flexible dicarboxylate linker and/or selected bipyridines (bipy). Remarkably, using the title organozinc precursors in a combination with H2obc and 4,4′-bipyridine, a novel molecular zinc quinolinate building unit, [Zn4(q)6(bipy)2(obc)2], was obtained which self-assembled into a chain-type hydrogen-bonded network. The application of the organometallic precursor allowed for its direct reaction with the selected ligands at ambient temperature, avoiding the use of both solvothermal conditions and additional base reagents. In turn, the reaction involving Zn(NO3)2, as a classical inorganic precursor, in a combination with H2obc and bipy led to a novel 1D coordination polymer [Zn2(q)2(NO3)2(bipy)]. While the presence of H2obc was essential for the formation of this coordination polymer, this ditopic linker was not incorporated into the isolated product, which indicates its templating behavior. The reported compounds were characterized by single-crystal and powder X-ray diffraction, elemental analysis as well as UV-Vis and photoluminescence spectroscopy.

Highlights

Coordination polymers (CPs), a class of crystalline porous materials made up of metal clusters or ions linked via organic ligands, represent a rapidly growing area in modern chemistry and materials science due to their wide range of applications [1,2,3,4,5]
We selected the previously reported quinoline-based zinc complex [Zn(q)2]2[tBuZn(OH)]2 (q = deprotonated 8-hydroxyquinoline) [41,42] as a model luminescent core for exploratory studies investigating the potential of organozinc precursors and a mixed-ligand synthetic strategy for the preparation of new luminescent coordination polymers (CPs)
We found that the bands related to the quinolinate ligand in the spectra of CP1–CP5 and HP4 were shifted to the higher frequencies in comparison to the free Hq ligand, which is in agreement with the spectrum of the [Zn(q)2]2[tBuZn(OH)]2 precursor [41,42]

Summary

Introduction

Coordination polymers (CPs), a class of crystalline porous materials made up of metal clusters or ions linked via organic ligands, represent a rapidly growing area in modern chemistry and materials science due to their wide range of applications [1,2,3,4,5]. One of the ligand systems known for its capability to form luminescent molecular complexes [22] and metal-organic materials [23] is 8-hydroxyquinoline (Hq) and its derivatives, which have been successfully applied in biomedicine [24] and the fabrication of optoelectronic devices such as organic light emitting diodes or solar cells [25,26]. Extended organic ligands based on the quinoline core have been applied in the development of luminescent coordination polymers, which represents an efficient strategy, albeit, often requiring multi-step preparation of organic ligand systems [27,28,29,30,31,32,33,34]. Simple quinolinate ligands could be incorporated into mixed-ligand CPs as co-ligands, an approach which has the challenge of designing and controlling the self-assembly of multicomponent supramolecular systems [35], it is not surprising that this approach has been explored to a lesser extent and only a few examples of well-defined functional quinolinate-based CPs [36,37,38], including materials with valuable luminescent properties [39,40], are reported

Methods

Results

Conclusion