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Crystal engineering with coordination compounds of NiII, CoII, and CrIII bearing dipicolinic acid driven by different nature of the noncovalent interactions

Five new proton transfer compounds, (Hapy)[Cr(pydc)2]∙5H2O∙[pydcH2](1), (Hacr)[Cr(pydc)2]∙2H2O(2), (H9a-acr)[Cr(pydc)2]∙4.27H2O (3), [Co(pydc)(pydcH2)]∙H2O (4) and [Ni(pydcH)2]∙3H2O (5) (where pydcH2 = pyridine-2, 6-dicarboxylic acid ; apy = 2-aminopyridine ; acr = acridine and 9a-acr = 9-aminoacridine) have been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction techniques. The crystallographic analysis revealed that compounds 1-5 have distorted octahedral geometries with pydc2- and pydcH− ions or pydcH2 coordinated as tridentate ligands to each metal ion through one oxygen atom of each carboxylate group and the nitrogen atom of the pyridine ring. Compounds 1, 2 and 3 consist of cationic complexes where the dipicolinic acid is coordinated to the metal ion in the dianionic form, whereas 4 and 5 are neutral complexes. In 4 the acid is coordinated to metal ion in the neutral form, which is quite rare. In the crystal structures of the different complexes extensive O–H∙∙∙O, N–H∙∙∙O and C–H∙∙∙O hydrogen bonds as well as other noncovalent interactions involving aromatic rings (C–H∙∙∙π, C–O∙∙∙π and π∙∙∙π stacking) are described and analysed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks.

crystal engineering ; coordination compounds ; dipicolinic acid ; intermolecular interactions

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