A new Cu(II)-complex of 3-aminopyridine, [CuCl(3-AP) 4 ][Cu(3-AP) 4 (H 2 O)]Cl 3 AE 2H 2 O (1), containing two contrasting complex cations has been synthesized and structurally characterized by single crystal X-ray diffraction and solid-state linear-dichroic infrared (IR-LD) spectral analysis. In both cations four 3-AP molecules coordinate the Cu(II) atom in a monodentate fashion through their endocyclic (N py ) nitrogens, thereby generating a squareplanar coordination geometry for the CuN 4 chromophor. Perpendicular to the N 4 plane, the metal ion is coordinated by a chloride anion in the first cation and a water ligand in the second cation. One of three additional water molecules of crystallization occupies the vacant octahedral site of the second cation and participates in a weak CuÁ Á ÁOH 2 interaction. An IR-LD spectral analysis of the samples, oriented as a suspension in a nematic liquid crystal confirmed the crystallographic data and the retention of the pyridine ring aromatic character after coordination. The presented results are additionally supported by UV, 1 H-NMR, EPR and MS analysis and by thermogravimetric and calorimetric data.

The self-association of 2- and 3-(acetylamino)pyridines in a condensed phase was investigated by conventional and linear-polarized IR spectroscopy. Interpretation of spectra of the monomer and associated forms was carried out by the reducing-difference procedure. Theoretical quantum chemical calculations at the B3LYP level of theory and with 6-31±G** basis set were performed in order to obtain the electronic structure and vibrational characteristics of both compounds.

The aromatic character, distortion, and stabilization as a result of single and double protonation of 3-aminopyridine like three different complex salts were studied by infrared-, ultraviolet spectral analysis, proton nuclear magnetic resonance, and quantum chemical ab initio calculations. Linear-dichroic infrared spectroscopy was applied for identification of the infrared bands. The correlation structure-spectroscopic properties of the model systems are determined: bis(3-aminopyridinium) tetrachlorocuprate (II) salt, where the ring nitrogen atom participates in protonation; 3-ammoniumpyridinium tetrachlorocuprate (II) salt, where both nitrogen atoms are protonated; and a complex with copper (II) bis(3-aminopyridinium) hexachlorodicuprate (II), where the metal ion is coordinated through amino group.