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

Abstract

[eng] 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)]·3H2O (4) and [Ni(pydcH)2]·H3O·2H2O (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. 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 1-3 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 the 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), were 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