J. Schaubroeck

A THERMODYNAMIC STUDY OF THE PROTONATION OF SOME SULPHIDE-CONTAINING PYRIDINES AND AMINO-PYRIDINES IN AQUEOUS SOLUTION

Abstract The protonation properties of pyridines with general formula (R = CH 3 , C 2 H 5 , CH 2 CH 2 OH; x = 1,2) and ( x, y = 1,2; 1,3; 2,2; 2,3) have been investigated by potentiometry and calorimetry at 25°C in 0.5 mole dm −3 K&{;NO 3 } solution. The protonation constants and the corresponding enthalpy and entropy changes are reported. The obtained values for the thermodynamic functions are discussed.

A thermodynamic study of the protonation of some sulphur-containing α,ω-diamines in aqueous solution

Abstract The protonation equilibria in aqueous solution of α,ω-thiadiamines of general formula (R)(R′)N(CH 2 ) n ,S(CH 2 ) m NH 2 (R,R′= CH 3 or H) have been investigated potentiometrically and calorimetrically at 25° C in 0.5 mole dm −3 KNO 3 solution. The enthalpy and entropy changes are discussed in terms of intrinsic proton affinities and solvation effects.

Calorimetric determination of the thermodynamic properties involved in the complex formation of silver(I) with some sulphur-containing pyridines

Abstract The enthalpy changes involved in the complex formation of Ag + with several sulphur-containing pyridines of general formula where R = Ch 3 , C 2 H 5 and CH 2 CH 2 OH and x =1,2 have been determined by direct calorimetric measurements at 25°C in 0.5 M KNO 3 solution. From the Δ H values obtained and from the free energy changes reported in an earlier publication, the corresponding entropy changes Δ S have been calculated. Changes in Δ H and Δ S are discussed in terms of inductive and steric effects. It is shown that enthalpy values are linearly correlated with the Taft σ * parameters of the substituents on the ligand.

The thermodynamics of complexation between Ag(I) and some sulphur-containing α,ω-diamines

Abstract The enthalpies of the reactions between Ag(I) ions and a number of sulphur-containing α,ω-diamines of general formula NH2(CH2)nS(CH2)mNH2 (n,m = 2,2; 2,3; 2,4; 3,3; 3,4 and 4,4) in 0.5 M (K)NO3 at 25°C have been determined by means of direct calorimetric titrations. By use of the ΔG values reported elsewhere, the corresponding ΔS values have been calculated. It has been shown that in the dimeric Ag2L2+ and Ag2L2+2 species the ligands are coordinated through all three available donor atoms, whereas in the AgL+2 species each ligand is coordinated through only two donors.

Sulphur-nitrogen chelating agent—II. Mixed-metal binuclear (Cu2, Ag+) and mononuclear (Cu2+) solid state complexes of 1,4-diazo-7-thiaoctane and 1,5-diazo-8-thianonane. An infrared and reflectance spectral analysis

Abstract A series of CuLX 2 , CuL 2 X 2 , CuLYZ and AgCuL 2 Z 3 {X − = Cl − , Br − , NO − 3 ; Y − = OAc − ; Z − = NO − 3 or ClO − 4 ; L = 1,4-diaza-7-thiaoctane [2,2-NNS(Me)] or 1,5-diaza-8-thianonane [3,2-NNS(Me)]} have been prepared and characterized by means of elementary analysis, i.r. and electronic spectroscopy. All 1 : 1 complexes containing polyanions (NO − 3 , OAc − , ClO − 4 ) are five-coordinated species with the meridionally arranged thiadiamine acting as a tridentate. The remaining coordination positions are occupied by an asymmetric bidentate nitrate or acetate group. In contrast, in the 1 : 2 complexes, the thiadiamines are incompletely coordinated leaving one or even two sulphur donors free. These free sulphide-groups readily coordinate with the Ag(I) ions to form mixed-metal AgCuL 2 Z 3 -compounds.

Thermochemical study of the stepwise protonation of 1,10-diaza-4,7-dithiadecane, and its complex formation with copper(II) and nickel(II) ions in aqueous solution

Abstract The behaviour of 1,10-diaza-4,7-dithiadecane (2,2,2-NSSN) in aqueous solution in equilibria with protons, Cu 2+ or Ni 2+ ions has been investigated potentiometrically and calorimetrically. The protonation constants for the ligand, and the stability constants for its complexes at 25°C in 0.5 mole dm −3 (K)NO 3 are reported, together with the corresponding thermodynamic parameters Δ G , Δ H and Δ S . The results are compared with those for 1-aza-4-thiapentane and 1,7-diaza-4-thiaheptane. The ligand 2,2,2-NSSN forms complexes of formula ML 2+ and MHL 3+ with both Cu 2+ and Ni 2+ . It is found that in the non-protonated 1:1 complexes the ligand acts as a tetradentate. In the CuHL 3+ complex, the ligand is bound through one nitrogen and two sulphur donors, whereas in the NiHL 3+ complex the ligand is probably bound through only one nitrogen and one sulphur donor. Explanations are suggested.

Thermochemical study of the complex formation of ag(I) with some sulphur-containing aminopyridines

Abstract The enthalpies of formation of the complexes between the silver(I) ion and some sulphur-containing aminopyridines of general formula N(CH2)n−1-S-(CH2)m-NH2 where n = 1, and m = 1,2; 1,3; 2,2; 2,3 have been determined by direct calorimetric titration at 25°C in 0.5 M (K)NO3 solution. The corresponding entropy terms, ΔS, have been calculated using the obtained enthalpy values and the previously reported ΔG values. In acid medium (pH ; 3) additional chelation through the pyridine nitrogen is obvious by a marked increase in the enthalpy of formation of the complexes AgL2H4+3, AgL2H3+2 and AgLH2+. The last complex dimerizes into a cyclic dimer Ag2L, H4+2. At still higher pH values (pH &>; 6) the participation of the amino group in the dimeric chelates Ag2L2H3+ and Ag2L2+2 is revealed again by a marked increase in the heat of complexation.

A thermodynamic and spectrophotometric study of the complex formation of copper(II) ions with sulphide-containing α,ω-aminopyridines in aqueous solution

Abstract The complexation in aqueous solution of ligands of the type (CH 2 ) n−1 S(CH 2 ) m NH 2 ( n and m = 2 or 3) with Cu(II) has been investigated. The thermodynamic functions Δ G , Δ H and Δ S of complex formation have been determined at 25°C in 0.5 M KNO 3 solution by means of potentiometric and direct calorimetric titrations. They revealed that the ligands studied act as tridentates towards Cu(II). It was found that the CuL 2+ complexes having one or two six-membered chelate rings are more distorted than their analogues with only five-membered chelate rings. The CuL 2+ 2 complex with L = CH 2 SCH 2 CH 2 NH 2 was found to be a strong covalent complex, in which both ligand molecules were completely coordinated.

A calorimetric and carbon-13 NMR spectral analysis of the protonation in asymmetric α,ω-thiadiamines

Abstract Enthalpies of protonation and 13C-NMR chemical shifts are used to calculate the fractional protonation at each basic site in α,ω-thiadiamines. Results are discussed in terms of the inductive effects exercised by the central thioether group on both terminal aminofunctions.

An ESCA study on the structure of sulphur-nitrogen chelating agents and their metal complexes

Abstract The ESCA spectra of eight 1:1 and 1:2 transition metal complexes and three hydrochloric salts of ligands containing amine and thioether donor sites were measured. Fine structure in the C 1 s peaks is discussed in comparison with 13 C NMR data and estimated partial atomic charges. The anticipated difference in chelating behaviour of these ligands towards Cu 2+ ions in 1:1 and 1:2 complexes is confirmed fully by the binding energy shifts in the S 2 p levels.