Sublimation Study of Six 5-Substituted-1,10-Phenanthrolines by Knudsen Effusion Mass Loss and Solution Calorimetry.

Bruno Brunetti,Andrea Lapi,Aleksey V Buzyurov,Ruslan N Nagrimanov,Mikhail A Varfolomeev,Andrea Ciccioli,Stefano Vecchio Ciprioti

doi:10.3390/e24020192

Abstract

The vapor pressures of six solid 5-X-1,10-phenanthrolines (where X = Cl, CH3, CN, OCH3, NH2, NO2) were determined in suitable temperature ranges by Knudsen Effusion Mass Loss (KEML). From the temperature dependencies of vapor pressure, the molar sublimation enthalpies, ΔcrgHm0(⟨T⟩), were calculated at the corresponding average ⟨T⟩ of the explored temperature ranges. Since to the best of our knowledge no thermochemical data seem to be available in the literature regarding these compounds, the ΔcrgHm0(⟨T⟩) values obtained by KEML experiments were adjusted to 298.15 K using a well known empirical procedure reported in the literature. The standard (p0 = 0.1 MPa) molar sublimation enthalpies, ΔcrgHm0(298.15 K), were compared with those determined using a recently proposed solution calorimetry approach, which was validated using a remarkable amount of thermochemical data of molecular compounds. For this purpose, solution enthalpies at infinite dilution of the studied 5-chloro and 5-methylphenantrolines in benzene were measured at 298.15 K. Good agreement was found between the values derived by the two different approaches, and final mean values of ΔcrgHm0(298.15 K) were recommended. Finally, the standard molar entropies and Gibbs energies of sublimation were also derived at T = 298.15 K. The volatilities of the six compounds were found to vary over a range of three orders of magnitude in the explored temperature range. The large difference in volatility was analyzed in the light of enthalpies and entropies of sublimation. The latter was tentatively put in relation to the rotational contribution of the substituent group on the phenanthroline unit.

Highlights

The melting temperatures and the enthalpies of fusion of the six 5-X-1,10-phenanthroline derivatives are reported in Table 2, along with the associated uncertainties
The Knudsen Effusion Mass Loss (KEML) technique was used for the first time to determine the vapor pressures of the six 5-substituted 1,10-phenanthrolines
The molar sublimation enthalpies at the corresponding average temperature 〈T〉, were calculated from the temperature dependencies of vapor pressure. These values were adjusted to 298.15 K using a well known empirical procedure reported in the literature, and the standard (p0 = 0.1 MPa) molar sublimation enthalpies ∆cr g Hm 0 (298.15 K) were compared with those determined using solution calorimetry, according to a procedure recently proposed for validation purpose

Summary

Introduction

The aromatic heterocyclic compound 1,10-Phenanthroline is formed by three condensed rings (Figure 1), and is well known for its pronounced metal-ion complexing properties [1,2,3,4,5,6]. The aromatic heterocyclic compound 1,10-Phenanthroline is formed by three condensed rings (Figure 1), and is well known for its pronounced metal-ion complexing prop of 14 erties [1,2,3,4,5,6]. 1. Molecular structure of 5-substituted the 5-substituted. 1. Molecular structure of the Several years the molar capacities and some thermodynamic properties

Objectives

Results

Conclusion