Facile synthesis and vapochromic studies of Co(II) complexes bearing NO and OO donor ligands

• Two Co(II) complexes of malonic or isonicotinic acids were prepared by a solvent-free technique.
• The compounds were characterized by elemental analysis, FT-IR, UV-vis spectroscopy and XPRD.
• Vapochromic behaviours of the two compounds were studied using colour changes and FT-IR spectroscopy.
• Heating the exposed samples at 100 °C regenerates the original material without degradation.

Two Co(II) complexes containing malonic and isonicotinic acids have been prepared by manual grinding of stoichiometric amounts of the starting materials. Elemental analysis (CHN), IR, UV-vis spectroscopic techniques, TGA-DTG investigation and X-ray powder diffraction analysis were used to characterize the two compounds. Isonicotinic acid coordinated to the metal via the pyridine ring nitrogen and one oxygen atom of the carboxylic group while malonic acid coordinated via both oxygen atoms of the carboxylate groups indicating bidentate coordination mode in the two compounds. The compounds were exposed to some volatile organic compounds (VOCs) containing nitrogen or oxygen donor atoms in the solid state and their vapochromic behaviours studied using colour changes, FT-IR and solid state UV-vis spectroscopies. Heating the samples exposed to the VOCs for a few minutes at 100 °C regenerates the original material without degradation, even after several heating cycles.