The mean enthalpy of the lanthanide-oxygen bond in 2,2,6,6-tetramethyl-3,5-heptanedione chelates of praseodimium and holmium

Standard molar enthalpies of formation of eight lanthanide(III) 2,2,6,6-tetramethyl-3, 5-heptanedione chelates in the crystalline and gaseous states: mean Ln–O bond dissociation enthalpies

“…The value for the holmium chelate is in good agreement with that reported in this paper, were determined as −(85.50 ± 1.37) kJ · mol −1 (22) and −(70.18 ± 0.77) kJ · mol −1 (21) , respectively, which according to the above statement, seem to be very high. On the other hand, the enthalpy of dissolution of HoCl 3 · 6.00H 2 O in HCl · 26.64H 2 O was found to be more reasonable: −(27.56 ± 0.18) kJ · mol −1 (21) and comparable with the enthalpies of dissolution of hexahydrated trichlorides of Nd, Sm, Gd and Er. (37,38) The main purpose of this thermochemical investigation is the determination of the energetics of metal-ligand bonds in the complexes examined.…”

“…These values not only differ considerably from those of Sicre's et al (17) but also vary in the opposite direction. Another value of the enthalpies of sublimation for La(DPM) 3 : (156.0 ± 4.6); (22) and Pr(DPM) 3 : (163.0 ± 3.6) (21) and Ho(DPM) 3 : (131.0 ± 2.9) (21) estimated from differential scanning calorimetry data, are in accordance with the values reported by Sicre et al (17) For sake of comparison among the different metal complexes, the values of Sicre were used in this paper, since they are the only ones available for all the lanthanide dipivaloylmethanates by the same experimental technique. The standard molar enthalpy of formation of gaseous dipivaloylmethane radical may be calculated from the molar enthalpy of dissociation of the enolic hydrogen in the dipivaloylmethane ligand, D m (O-H, HDPM, enol, g):…”

“…The literature values for the standard molar enthalpies of formation of the crystalline La(III), Pr(III), and Ho(III) dipivaloylmethanates are: −(2442.2 ± 11.8) kJ · mol −1 (22) −(2434.3 ± 11.5) kJ · mol −1 (21) and −(2384.8 ± 11.5) kJ · mol −1 (22) , respectively. The value for the holmium chelate is in good agreement with that reported in this paper, were determined as −(85.50 ± 1.37) kJ · mol −1 (22) and −(70.18 ± 0.77) kJ · mol −1 (21) , respectively, which according to the above statement, seem to be very high.…”

“…shift reagents for a large number of organic molecules, (19) etc. Despite the importance of the applications of these lanthanide-β-diketonates, very little thermochemistry has been reported for them: we reported the standard molar enthalpies of formation of La(III) acetylacetonate and benzoylacetonate, (20) Airoldi et al (21) reported the standard molar enthalpies of formation of dipivaloylmethanates of Pr(III) and Ho(III), and more recently Santos Jr et al (22) reported the same property for these chelates with Sc(III), Y(III) and La(III).…”

Thermochemical studies of 2,2,6,6-tetramethyl-3,5-heptanedione chelates of scandium group elements

“…(7) On the other hand, our calculated values using the previous application of the above procedure gave values very close to the vapour pressure determinations of other lanthanide chelates. (17) In the case of Y(thd) 3 chelate, three enthalpies of sublimation have been recently published as (119.7 2 2.5) kJ·mol −1 ,…”