IDENTIFICATION OF ISOMERIC HETEROLIGAND COMPLEXES IN THE NICKEL(II)/COPPER(II) - SALICYLIC/ISONICOTINIC ACID HYDRAZIDE - L-HISTIDINE - WATER SYSTEMS
Rubrics: 1. CHEMISTRY
Authors:
1.
Kazan National Research Technological University
2.
KNITU; Kazan National Research Technological University
Type:
Article
Pages:
from 31
to 36
Status:
Published
Received:
22.12.2025
Accepted:
23.12.2025
Published:
23.12.2025
Language:
Russian
Keywords:
NICKEL(II), COPPER(II), SALICYLIC ACID HYDRAZIDE, ISONICOTINIC ACID HYDRAZIDE, L-HISTIDINE, HETEROLIGAND COMPLEXES, STABILITY OF COMPLEXES, ISOMERIC COMPLEXES
Abstract (English):
In cases where coexistence of isomeric complex forms in solution is permitted, an adequate description can only be given for one isomer, the most stable from a thermodynamic and kinetic point of view. Such a situation arises when carrying out mathematical modeling of the parameters of complexation equilibria in heteroligand systems of nickel(II) or copper(II) with aromatic acid hydrazide (salicylic or isonicotinic) and L-histidine in an aqueous environment. In this paper, a combined approach is proposed and successfully applied to identify heteroligand complexes formed under experimental conditions. It includes (a) establishing coordination models for complex forms in isomeric pairs based on quantum chemical calculations and (b) establishing the pH range of existence of protonated, neutral, and deprotonated forms of the ligands in solution based on the values of the corresponding dissociation constants. The paper presents the results of pH-metric titration of ligands and the dissociation constants of salicylic and isonicotinic acid hydrazides, as well as L-histidine, in an aqueous solution in the presence of 0.1 mol/l potassium nitrate at 25 °C. Heteroligand systems were also studied under the same conditions using spectrophotometry. The coordination model for each complex form was established by optimizing the geometry and comparing the calculated energies of its isomers, which differ in the mode of ligand coordination. Based on the ligand dissociation constants, it was established which forms of hydrazides and L-histidine are capable of being simultaneously present in solution under the experimental conditions. The performed analysis allowed one to refute the coexistence of isomeric complex forms in solution and, therefore, to unambiguously identify the heteroligand complexes formed under the experimental conditions.
In cases where coexistence of isomeric complex forms in solution is permitted, an adequate description can only be given for one isomer, the most stable from a thermodynamic and kinetic point of view. Such a situation arises when carrying out mathematical modeling of the parameters of complexation equilibria in heteroligand systems of nickel(II) or copper(II) with aromatic acid hydrazide (salicylic or isonicotinic) and L-histidine in an aqueous environment. In this paper, a combined approach is proposed and successfully applied to identify heteroligand complexes formed under experimental conditions. It includes (a) establishing coordination models for complex forms in isomeric pairs based on quantum chemical calculations and (b) establishing the pH range of existence of protonated, neutral, and deprotonated forms of the ligands in solution based on the values of the corresponding dissociation constants. The paper presents the results of pH-metric titration of ligands and the dissociation constants of salicylic and isonicotinic acid hydrazides, as well as L-histidine, in an aqueous solution in the presence of 0.1 mol/l potassium nitrate at 25 °C. Heteroligand systems were also studied under the same conditions using spectrophotometry. The coordination model for each complex form was established by optimizing the geometry and comparing the calculated energies of its isomers, which differ in the mode of ligand coordination. Based on the ligand dissociation constants, it was established which forms of hydrazides and L-histidine are capable of being simultaneously present in solution under the experimental conditions. The performed analysis allowed one to refute the coexistence of isomeric complex forms in solution and, therefore, to unambiguously identify the heteroligand complexes formed under the experimental conditions.
Keywords:
NICKEL(II), COPPER(II), SALICYLIC ACID HYDRAZIDE, ISONICOTINIC ACID HYDRAZIDE, L-HISTIDINE, HETEROLIGAND COMPLEXES, STABILITY OF COMPLEXES, ISOMERIC COMPLEXES
NICKEL(II), COPPER(II), SALICYLIC ACID HYDRAZIDE, ISONICOTINIC ACID HYDRAZIDE, L-HISTIDINE, HETEROLIGAND COMPLEXES, STABILITY OF COMPLEXES, ISOMERIC COMPLEXES
