Abstract
Based on solvothermal synthesis, self-assembly of the heptadentate 2,6-diacetylpyridine bis(nicotinoylhydrazone) Schiff base ligand (H2L) and Zn(II) and/or Cd(II) salts has led to the formation of three homometallic [CdL]n (1), {[CdL]∙0.5dmf∙H2O}n (2) and {[ZnL]∙0.5dmf∙1.5H2O}n (3), as well as two heterometallic {[Zn0.75Cd1.25L2]∙dmf∙0.5H2O}n (4) and {[MnZnL2]∙dmf∙3H2O}n coordination polymers. Compound 1 represents a 1D chain, whereas 2–5 are isostructural and isomorphous two-dimensional structures. The entire series was characterized by IR spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction and emission measurements. 2D coordination polymers accommodate water and dmf molecules in their cage-shaped interlayer spaces, which are released when the samples are heated. Thus, three solvated crystals were degassed at two temperatures and their photoluminescent and adsorption–desorption properties were recorded in order to validate this assumption. Solvent-free samples reveal an increase in volume pore, adsorption specific surface area and photoluminescence with regard to synthesized crystals.
Highlights
Over the years, coordination polymers (CPs) have attracted interest, due to their interesting architectures and topologies, and due to their diverse applications [1,2,3,4,5,6,7]
It is well known that CPs can be obtained by the combination of metal ions as a node and as the connecting rod can be employed by multidentate organic/inorganic ligands
The Schiff bases derived from 2,6-diacetylpyridine are good candidates for elaboration of magnetic homo- and/or heterometallic CPs [8,9,10,11,12]
Summary
Coordination polymers (CPs) have attracted interest, due to their interesting architectures and topologies, and due to their diverse applications [1,2,3,4,5,6,7]. The shifting of the absorption band ν(C=C)+ν(C=N) of the pyridine ring from 1591 cm−1 in the ligand spectrum to 1583–1578 cm−1 in CPs is observed These changes are caused by the coordination of the Schiff base through the carbonyl O atoms, azomethine and central heterocyclic N atoms [24,30,31,32,33,34], as well as by its dianionic character [31], which leads to the electron delocalization in the metallocycles. If in homometallic CPs the solvent molecules are bonded with the polymeric layers by C-H···O H-bonds (Table S2), in compounds 4 and 5, in addition to the intermolecular contact, the dmf molecule is joined by C-H···π interactions with the nicotinamide aromatic system (C-H···Cg(N1 > C4) is equal to 3.99(3) Å in both structures). Further increasing of the temperature leads to the decomposition of the organic residue, a process which ends at 560 ◦C and, as a result, the corresponding metal oxides are formed
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