Spectroscopic investigation of mixed-ligand nickel(II) chelates containing β-ketoenols and 1,2-diamines

Synthesis and Characterization of Mixed-Ligand Nickel(II) Chelates of β-Diones and α-Diimines. Crystal and Molecular Structure of [Ni(ncup)2Etacet]ClO4

“…The physicochemical data of the complexes under investigation are presented in Table 1. The proposed structures based on physiochemical and spectroscopic findings (vibrational and electronic excitations) are further supported by single crystal X-ray analysis of the complex [Ni(ncup) 2 Etacet]ClO 4 (ncup, denotes neocuproin and Etacet, the anion of the ethyl acetoacetate).…”

“…Crystallographic data and other pertinent information can be found in Table 2. A prismatic crystal of [Ni(ncup) 2 Etacet]ClO 4 was selected for the X-ray study, centered on a Philips PW 1100 single crystal diffractometer and showed to be perfectly stable in the X-ray beam over the period of data acquisition. Systematic absences led to space group Pc2 1 n.…”

“…The isolation of the octahedral chelates under investigation apparently instigated by the tendency of nickel(II) to achieve coordination numbers exceeding four. Counterions known to participate in covalent formation, e. g. ClO 4 ± , also have a stabilizing effect and in addition to the ionic [Ni(enR) 2 b]ClO 4 compounds [4], the neutral [Ni(enR)b(O 2 ClO 2 )] ones are subjected to investigation. Coordination of the anions is revealed by the change of electrical and magnetic properties and the specific absorption in the IR spectra.…”

“…The simultaneous reaction of nickel(II) with anions of b-diones (1,3-ketoenols, b) and nitrogenous bases (such as 1,2-diamines and α-diimines, enR) leads to the formation of mixed-ligand chelates, in which the ion counterbalancing the positive charge [Nib(enR)] + , may or may not coordinate [1,2]. Since nickel(II) has a tendency to achieve coordination number exceeding four and octahedral stereochemistries, it may accomplish coordination saturation [3] either by reverting the electrostatic interaction of the counterion to covalent ones, provided that no steric interference inhabits the reaction [1] or by reacting with one of the reagents, such as b-diones leading to neutral adducts [4] or α-diimines leading to cationic complexes [Nib(enR) 2 ] + [5].…”

“…Since nickel(II) has a tendency to achieve coordination number exceeding four and octahedral stereochemistries, it may accomplish coordination saturation [3] either by reverting the electrostatic interaction of the counterion to covalent ones, provided that no steric interference inhabits the reaction [1] or by reacting with one of the reagents, such as b-diones leading to neutral adducts [4] or α-diimines leading to cationic complexes [Nib(enR) 2 ] + [5]. The composition of nickel(II) chelates obtained under similar experimental conditions depends on steric and electronic effects induced by substituents within the ligands and the ability of the anions to coordinate [6].…”