New compounds with interesting luminescent properties
The physicochemical properties of molecules are determined by a series of external factors such as temperature, or intrinsic to the element that makes them up, such as their atomic number. The final result of the conjugation of all of them is the conformation of molecules with 1D, 2D, or even 3D structures that will have their application in the creation of new materials, in the field of biomedicine, agriculture, etc. In this article, Josefina Pons' research team explains the process by which they obtained new compounds with molecular and supramolecular structures with highly interesting luminescent properties.
The synthesis of coordination polymers (CPs) and discrete polynuclear coordination complexes has become a promising research area the last decades. These compounds have a variety of applications in catalysis, separation, gas storage, magnetism, sensing and so on. Moreover, their simple synthetic methodology in comparison with other synthesis, have stablished their study as one of the main topics in MOFs research.
For these compound, further of the coordination bonds, there are other supramolecular interactions (H-bonds, C-H···π, π···π interactions) also as a determining factor which influence in the final structural array of the crystalline materials through its cooperative effects. A family of these organic molecules are the carboxylic acid. Its carboxylate group can present different coordination modes, and can form di-, tri- and tetranuclear metal carboxylates. In addition, the presence of other factors which dictate the final structural scaffold, such as the ionic counterions, the metal/linker ratio, the temperature or the solvent polarity.
Carboxylate trinuclear compounds with formula [M3(CO2)6(L)n] (n = 2 or 4), have been used as SBUs for the synthesis of MOFs showing potential catalytic, magnetic and fluorescent properties. Furthermore, the fact that a high number of these types of arrays contain labile solvent molecules on their lateral positions, makes them appropriate for the exchange of either their lateral positions or their carboxylate moieties by polytopic linkers, and these compounds present interesting properties. Zinc carboxylate complexes have been extensively used due to the great variety of coordination numbers of their carboxylate ligands. Moreover, presenting a d10 configuration contribute to the formation of diverse geometries. All these characteristics together with their luminescent and biological applications.
Figure 1 Molecular structure of complex: a) 2·4CH3CN and b) 3·4EtOH. c) N-H···O intramolecular interactions of the ACA ligands in 2·4CH3CN and 3·4EtOH with labels assigned for complex 3·4EtOH. The phenyl and other atoms which do not participate in any of the mentioned interactions have been omitted for clarity.
Recently, our group has been studying the reactivity of a carboxylic acid (cinnamic derivative, pOHCinn) towards Cu(II). Also we have studied the reactivity of this ligand which Zn(II) and Cd(II) obtaining the compounds [M(ACA)2(H2O)2], with these compounds we have studied the reactivity 4-phenylpyridine (4-Phpy), show a different behavior between Zn(II) and Cd(II), yielding a monomeric [Zn(ACA)2(4-Phpy)2(H2O)2]·3H2O and a dimer [Cd(μ-ACA)(ACA)(4-Phpy)2]2·2EtOH complexes. To the best of our knowledge, the use of ACA as a ligand for the synthesis of coordination complexes has not been previously described in the literature.
As a continuation of our previously study, in this paper we have assayed the reaction between Zn(OAc)2·2H2O, alpha-acetamidocynnamic acid (HACA) and 4- Phpy using EtOH as solvent at room temperature, yielding the CP, [Zn2(μ-OO’-ACA)2(ACA)2(4-Phpy)2]n (1), which by recrystallization in CH3CN or EtOH forms two trinuclear complexes [Zn3(μ-ACA)6(4-Phpy)2]·4CH3CN (2) and [Zn3(μ-ACA)6(EtOH)2]·4EtOH (3), respectively. The compound 2 was also obtained by reaction between Zn(OAc)2·2H2O, HACA and 4-Phpy using CH3CN as solvent at room temperature.
These compounds were characterized by analytical and spectroscopic techniques, for three compounds the single crystals for X-ray diffraction method were resolved. The molecular and supramolecular interactions have been studied, compounds 2 and 3 present 2D and compound 1 is 3D. Finally, the supramolecular interactions for 2 and 3 have been compared using Hirshfeld surface analyses and electrostatic potential calculations.
Universitat Autònoma de Barcelona.
Chemistry Department.
Inorganic Chemistry Area.
References
Ejarque D, Calvet T, Font-Bardia M, Pons J. Construction of Zn(II) Linear Trinuclear Secondary Building Units from A Coordination Polymer Based on α-Acetamidocinnamic Acid and 4-Phenylpyridine. Molecules. 2020 Aug 9;25(16):3615. doi: 10.3390/molecules25163615
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