Structural, spectroscopic and semiempirical characterisation of the calcium cation complexes with 14-membered macrocyclic ligand of cyclic oxaalkyl diamide of o-phthalic acid

Cyclic oxaalkyl diamide of o-phthalic acid (CPhDA) has been obtained and its ability to form complexes with calcium cation has been studied by X-ray, ESI MS, 1H and 13C NMR, FT-IR and PM5 semiempirical methods. The ESI MS measurements have proved that in gas phase the 3:1, 2:1 and 1:1 CPhDA–Ca2+ as well as 3:1 and 2:1 CPhDA–Ca(ClO4)+ complexes are formed. In the solid state a 3:1 complex between CPhDA and calcium perchlorate of the CPhDA–Ca(ClO4)2–H2O (3:1:0.5) stoichiometry crystallises as hemihydrate in centrosymmetric space group (R-3) of the rhombohedral system. In crystal, the central Ca2+ cation is coordinated by the three CPhDA ligands via the carbonyl oxygen atoms in a distorted trigonal antiprism. The cationic [Ca(CPhDA)3]2+ complex exhibits a threefold symmetry. Two [Ca(CPhDA)3]2+ cations related by an inversion centre interact with oxygen atom of water molecule that statistically occupies two positions around the inversion centre along the Ca···Ca axis. The FT-IR spectra show the characteristic changes in the frequencies of the amide I and amide II bands upon complexation. The structures of the CPhDA and its complexes with calcium cation are visualised using DFT and PM5 methods and discussed in detail.