Thermoanalytical study of linkage isomerism in coordination compounds. Part 5: A DSC and DFT study on the linkage isomerization of the dinitrito and dinitro isomers of cis-tetraamminecobalt(III) complexes. (8th January 2015)

• Record Type: Journal Article
• Authors: Hasani, Nahid; Eslami, Abbas
• Is Part Of: Polyhedron. Volume 85(2015)
• Page Start: 412
• Page End: 428
• Publication Date: 2015-01-08
• Subjects: Dinitro -- Dinitrito -- Tetraamminecobalt(III) -- Linkage isomerization -- DFT; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2014.08.061
• Languages: English
• ISSNs: 0277-5387

Abstract

Abstract : Graphical abstract: Thermal linkage isomerization of dinitrito cis -[Co(NH3 )4 (ONO)2 ]X and dinitro cis -[Co(NH3 )4 (NO2 )2 ]X (X = Cl −, NO3 −, ClO4 − ) complexes were investigated by DSC in the solid state. The observed DSC peak was resolved into two peaks, corresponding to two isomerization stages. A comparative experimental and DFT study was performed on the thermodynamic and kinetic isomerization. Highlights: Dinitrito/dinitro interconversion in cis -tetraamminecoblt(III) investigated by DSC. A two-stage linkage isomerization was considered in the solid state. The counterion affected on the thermodynamic and kinetic parameters of isomerization. DFT calculations employed for characterization of plausible species in isomerization. Abstract: The solid-state linkage isomerization of cis -[Co(NH3 )4 (NO2 )2 ]X (dinitro) and cis -[Co(NH3 )4 (ONO)2 ]X (dinitrito) (X = Cl −, NO3 −, ClO4 − ) was investigated by differential scanning calorimetry (DSC). All three salts of the dinitrito isomer show an exothermic peak associated with linkage isomerization, while only the chloride salt of the dinitro isomer exhibits an endothermic DSC peak. The results imply that the chloride salts of both isomers are metastable at ambient temperature and can convert to a stable equilibrium mixture of both isomers at elevated temperatures, but the NO3 − and ClO4 − salts of the dinitro isomer are in stable state even at high temperatures. The DSC peak temperature and the enthalpy changes of the dinitrito to dinitro isomerization depend upon the nature of counterion as follows: NO3 − < Cl − < ClO4 − . The stepwise enthalpy changes of the linkage isomerization of the dinitro (only for the Cl − salt) and dinitrito complexes were obtained through mathematical resolution of the observed peak into two peaks, assuming a two-stage reversible isomerization for the Cl − salt and a similar irreversible process for the NO3 − and ClO4 − salts. The nature of the counterion has little effect on the kinetics of the linkage isomerization. The electronic structures and transition states of the linkage isomers were optimized by DFT and their electronic spectra calculated by TDDFT/PCM methods.