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

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.