New coordination modes of iminodiacetamide type ligands in palladium(II) complexes: crystallographic and DFT studies

Abstract

The reactions of N-alkyliminodiacetamide derivatives, namely N-ethyliminodiacetamide (CH3CH2N(CH2CONH2)2; Etimda) and N-isopropyliminodiacetamide (CH3)2CHN(CH2CONH2)2; i-Primda), with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Three new palladium(II) complexes, [Pd(Etimda−H)2]∙2H2O (1), [Pd(i-Primda−H)2]∙2H2O (2) and [PdCl2(i-Primda)] (3), were obtained and characterized by X-ray structural analysis, infrared spectroscopy and thermal analysis (TGA). The square planar coordination environments around the palladium(II) ions in complexes 1 and 2 consist of two N,N′-bidentate N-alkyliminodiacetamidato ligands, with imino N atoms in trans-position. The complex 3 also exhibits a square planar coordination environment around Pd(II), but with two chloride ions and one neutral N-isopropyliminodiacetamide ligand bound in an N,O′-bidentate coordination mode. The described coordination modes, as well as the presence of deprotonated amide groups in ligands in 1 and 2, are found for the first time in palladium(II) complexes with iminodiacetamide type ligands. The molecular geometries and infrared spectra of these three complexes were also modelled using DFT calculations, at the BP86-D3/def2-TZVPP/PCM level of theory. The RMSD values suggest a good agreement of the calculated and experimental geometries. A QTAIM analysis suggests a qualitative correlation between bond lengths and energy densities, also supported by an NBO analysis. The dimer interaction energy between complex units was estimated at about −15 kcal/mol for all complexes.