Infrared spectrum, DFT: pBP86/DN and NCA vibrational calculations of 2-methylthiosemicarbazide copper(II) nitrate [Cu(2MeTSC) 2(NO 3) 2]

To elucidate tentative assignments of metal–ligand modes of thiosemicarbazide complexes, a structural study and a assignment of the normal vibrations of 2-methylthiosemicarbazide copper(II) nitrate, [Cu(2MeTSC) 2(NO 3) 2] have been done through the ab initio DFT: pBP86/DN** procedure, and through the normal coordinate analysis (NCA). In the vibrational calculations, the elongated Cu ONO 2 bonds of the nitrate groups were considered in the C S and C N tautomers of the complex. DFT calculations had revealed that the infrared spectra can be well interpreted through the C N tautomer, failing in the prediction of the –NO 2 group wavenumbers. A little difference stabilization energy for the tautomers were found: for the C N tautomer was E = −3487,36376 a.u., and for the C S tautomer, E = −3473,93598 a.u. The observed combination bands at 1763.0 and at 1754.0 cm −1 are an indicative that the –NO 3 − groups acts as monodentate ligands. Calculations had confirmed the experimental assignment of the infrared spectrum.