Spectral analysis and crystal structure of a new mononuclear copper(II) complex of 3-aminopyridine

A new Cu(II)-complex of 3-aminopyridine, [CuCl(3-AP)(4)][Cu(3-AP)(4)(H2O)]Cl-3 center dot 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 square-planar coordination geometry for the CuN4 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 Cu center dot center dot center dot OH2 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, H-1-NMR, EPR and MS analysis and by thermogravimetric and calorimetric data.