Mg(II) Coordination Polymers Based on Flexible Isomeric Tetracarboxylate Ligands: Syntheses, Structures, Structural Transformation and Luminescent Properties.

Xiang-Kai Yang,Jhy-Der Chen,Kedar Thapa

doi:10.3390/polym10040371

Abstract

By using a new flexible tetracarboxylic acid, bis(3,5-dicarboxyphenyl) adipoamide, H4L1, and its isomer, bis(2,5-dicarboxyphenyl)adipoamide, H4L2, three Mg(II) coordination polymers, {[Mg2(L1)(H2O)2]·2EtOH·3H2O}n, 1, [Mg2(L1)(H2O)8]n, 2, and {[Mg2(L2)(H2O)6]·H2O}n, 3, have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1 and 2 are the solvent ratio-dependent hydrothermally stable products. The tetracarboxylate ligand of complex 1 connects eight Mg(II) ions through nine oxygen atoms, resulting in a three-dimensional (3D) 5-connected uninodal net with a rare non-interpenetrating (44.66)-pcu-5-Pmna topology, whereas those of 2 and 3 link four Mg(II) ions through four oxygen atoms and six Mg(II) ions through six oxygen atoms, forming a 1D linear chain and a 3,6-connected 2-nodal 3D net having {4.62}2{42.610.83}-rtl topology, respectively. Complex 1 shows a series of structural transformations on heating to 200 °C and almost reversible structural transformation when the activated products were immersed in a mixture of ethanol and water or on hydrothermal. Likewise, complex 2 exhibits a reversible structural transformation on heating/hydrothermal, while 3 exhibits irreversible structural transformations. All three complexes exhibit blue light emissions, with that of complex 3 being much more intense.

Highlights

The investigation of coordination polymers (CPs) continues to be an intense area of research activity due to their intriguing structural topologies and promising potential applications as multifunctional materials [1,2,3,4,5,6,7,8]
The construction of CPs from s-block metal centers has been explored to a lesser extent than in transition metals (TMs), and their coordination ability is inferior compared with that of TMs; they are lighter and bigger in size, and are filled shell orbitals in ionic form, which makes them difficult incorporate into CPs [11,12,13]
We have successfully synthesized a new tetracarboxylic acid H4 L1, and its isomer H4 L2 has been prepared in a modified version

Summary

Introduction

The investigation of coordination polymers (CPs) continues to be an intense area of research activity due to their intriguing structural topologies and promising potential applications as multifunctional materials [1,2,3,4,5,6,7,8]. The structural transformations of CPs can be induced by various methods, including external stimuli like heat, light and mechanical forces, removal and uptake of solvents, exposure to reactive vapors, and exchange of solvents and guest molecules, which are rare due to the breaking and forming of coordinate and/or covalent bonds in multiple directions [9,10]. The applications of such phenomena observed in CPs are significant for sensors and switches. Among the alkali-earth metals, Polymers 2018, 10, 371; doi:10.3390/polym10040371 www.mdpi.com/journal/polymers

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