Infrared spectrum, DFT: pBP86/DN** and NCA vibrational calculations of 2-methylthiosemicarbazide copper(II) nitrate [Cu(2MeTSC)2(NO3)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(NO3)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 CuONO2 bonds of the nitrate groups were considered in the CS and CN tautomers of the complex. DFT calculations had revealed that the infrared spectra can be well interpreted through the CN tautomer, failing in the prediction of the –NO2 group wavenumbers. A little difference stabilization energy for the tautomers were found: for the CN tautomer was E = −3487,36376 a.u., and for the CS tautomer, E = −3473,93598 a.u. The observed combination bands at 1763.0 and at 1754.0 cm−1 are an indicative that the –NO3− groups acts as monodentate ligands. Calculations had confirmed the experimental assignment of the infrared spectrum.