The Stability of Metallic Complexes of Two Dimethylphenanthrolines

Abstract

The stepwise formation constants for the complexes formed by 5,6-dimethyl-and 4,7-dimethyl-1,lO-phenanthroline with bivalent iron, cobalt, nickel, copper, and zinc were determined by a partition method. The measurements were made a t 25' C and in aqueous solutions having an ionic strength maintained a t 0.1. The enhanced basicity of the ligands compared to the parent phenanthroline is paralleled by increased stability of the metallic complexes. The abnormally, high formation constants of the cobalt complexes suggest oxidation to cobalt (111).A number of studies t o determine the stability of metal complexes of the phenanthrolines have been published (1-8), among the most complete of which are those of Irving and co-workers (2, 4). In an extension of these studies the present investigation has sought formation curves, and hence formation constants, for the complexes formed by 5,6-and 4,7-dimethyl-1,lO-phenanthroline with a selected group of ions of the first transition series.The inductive effect of substituent methyl groups in increasing the basic strength of phenanthroline is apparent from the data of the following table: From these data it is seen that the basic strength of these compounds is enhanced by the presence of each methyl group in the conjugated ring system, and that the extent of this enhancement is related to the propinquity of the methyl groups t o the nitrogen atoms. In agreement with expectations, the increased basicity of the compounds investigated is paralleled by an increase in stability of the complexes investigated except, as noted elsewhere, when steric hindrance t o coordination about the metal atom occurs (5). The experimental method used was based on partition of the ligand between an aqueous solution and a solvent immiscible with water. The principle of the method is old, but its extension to the study of formation of complexes involving stepwise equilibria was first suggested by Kolthoff et al. (9), and subsequently extended and refined by Irving and co-workers (2). A measured volume of a solution of the ligand of known concentration in a selected solvent was shaken with a measured volume of aqueous solution containing

Electrochemical Characterization of Fe(II) Complexation Reactions at an Electrified Micro Liquid‐Liquid Interface

“…Ferroin or Fe(II)phen 3 (i. e., n = 3) is a well-known, widely used iron complex with highly reversible electrochemistry. β for n = 3 is in good agreement with that determined by Brisbin and McBryde [36] with magnitudes of 10 23 for modified phenanthroline molecules, 5,6-dimethylphenanthroline and 4,7-dimethylphenathroline. Moreover, this result is in fair agreement with that determined by McKenzie [37] and more recently by Shalaby and Mohamed [38] of 2 × 10 21 for the tris-1,10-phenanthroline-iron complex itself.…”

Relative Binding Energies of Gas-Phase Pyridyl Ligand/Metal Complexes by Energy-Variable Collisionally Activated Dissociation in a Quadrupole Ion Trap

“…Pyridyl ligands, including the well-known phenanthroline compounds, are among the most extensively studied chelating agents in coordination chemistry. [1][2][3][4][5][6][7][8][9][10][11][12][13] They strongly bind transition metals possessing both low and high oxidation states, often forming bis-and tris-ligand complexes. The bidentate 1,10phenanthroline and 2,2′-bipyridine ligands are thought to participate in strong chelating interactions in part due to the possibility of d π -p π bonding from the metal to the ligand, giving some aromatic character to the resulting chelate ring.…”

“…3,4 The binding constants of many pyridyl ligands in aqueous solution have been thoroughly investigated using traditional methods such as potentiometry or spectrophotometry. [1][2][3][4][5][6][7][8][9][10][11][12][13] To date, most studies of the chelation of metal ions by phenanthroline ligands or other pyridyl ligands have involved solution environments, but mass spectrometry offers the ability to examine aspects of metal coordination in the gas phase. Intrinsic aspects of binding selectivity, binding energies, and coordination sites can be studied in a solvent-free environment.…”

Potentiometric and spectroscopic study of ternary complexes of copper(II), substituted 1,10-phenanthrolines and oxidised glutathione

“…More surprisingly, a similar trend is observed for the system with 5,6-dmphen: the ternary complexes are not stable enough to compete with the particularly stable binary copperoxidised glutathione complex. 11 The acidic strength of the ternary complexes can also be computed; the relevant pK a values are reported in Table 4.…”