The reported complexes formulated as [MnCl2(hppH)2] (1), [FeCl2(hppH)2] (2), and [NiCl2(hppH)2] (3) and a new theo-retically designed example, [CuCl2(hppH)2] (4), have been used for calculations at the 3LYP/LANL2DZ/6-311G (d, p)level of density functional theory (DFT). The intramolecular hydrogen bonds (HB) N H⋯Cl could followed through their physicochemical properties such as, vibrational frequency, electronic transmission in UV–Visible spectroscopy, metal–ligand donor–acceptor interactions in NBO analysis, total energy and frontier molecular orbital energy. These properties influenced by the relationship of structure and metal–ligand electron density exchange will be discussed. The computations revealed that the stronger N H⋯Cl HB exists in complexes with longer M Cl and M Nimine bonds and shorter H⋯Cl bond, and vice versa that confirms the shortest and longest HBs in 4 and 3, respectively. These results agree with the second–order perturbation energies obtained by NBO analysis within charge transfer from the proton–ac- ceptor chlorine to the p∗ orbital of the N atom. The calculated electronic absorption spectra by TD–DFT calculations show the larger Cl−to M2+ donation in 2 and 3 in comparison with 1 and 4 that confirms the stronger HB in 1 and 4compared to 2 and 3. In order to find the basis set effect on the structure, vibrational frequencies, and electronic transi-tions, we use another basis set def2-TZVP includes polarization function for Mn element in complex 1. The obtained test results showed unremarkable differences between two basis sets LANL2DZ and def2-TZVP (cf. Figs. S2, S3 and Tables S1 and S2 in Supplementary Materials)

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