Synthesis, structure, UV–Vis–IR spectra, magnetism and theoretical studies on CuII[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous CuII complex

Abstract

The ligand influenced formation of the title complexes has been discussed in the light of the structure, spectral (IR and UV–Vis), RT magnetic and theoretical studies (DFT and TDDFT). Complex 2 , for which only a structure has been reported previously, has been thoroughly studied and compared with complex 1 with respect to the structure and spectral properties. In the unit cell, the monomeric complex 1 assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ , while the octahedral complex 2 assembles into a 2-D layer in the unit cell through the H-bonding interactions between amino H and the anionic S and N3 atom. The TDDFT analysis of the absorption spectra indicate that absorption maxima are at a relatively high energy and are mainly assigned to π → π∗ transitions (in pyridine) with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. ► Synthesis and structural details of a new copper complex, CuII[(2-aminomethyl)pyridine](thiocyanate) has been presented. ► The UV–Vis and IR spectra along with the geometrical aspects have been analyzed in depth with the help of theoretical (DFT and TDDFT) calculations. ► In addition, to highlight the ligand influence on the complex formation, Cu[(2-aminomethyl)pyridine]2(SCN)2 was also synthesised, structural and spectral characteristics were fully analyzed and compared with the title complex. The title complex was synthesized under self-assembly conditions using Cu(acetate) 2 ·H 2 O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ . Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV–Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π ∗ transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp) 2 (SCN) 2 takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes.