Roger J. Irving

The standard enthalpy of sublimation of naphthalene

Abstract The standard enthalpy of sublimation of naphthalene has been determined calorimetrically at 298.15 K. The value obtained, (73.00 ± 0.25) kJ mol−1 is in agreement with the accepted value derived from vapour pressure measurements.

Standard enthalpies of formation of the bis(pentane-2,4-dionato) complexes of the Group II metals: Be, Mg, Ca, Sr, Ba, Zn, Cd, and Hg. The mean (metal-oxygen) bond-dissociation enthalpies

Abstract The standard ( p o = 101.325 kPa) molar enthalpies of formation of the following crystalline pentane-2,4-dionate complexes were determined by solution-reaction calorimetry. Using enthalpies of sublimation (literature values or estimates), the mean molar bond-dissociation enthalpies were derived based on an estimated D (OH) in the enol form of pentane-2,4-dione, Hpd, of (400 ± 20) kJ·mol −1 . Δ f H m o {m(pd) 2 , cr } 〈D〉( m-O ) Δ f H m o {m(pd) 2 , cr } 〈D〉( m-O ) Metal kJ·mol −1 kJ·mol −1 Metal kJ·mol −1 kJ·mol −1 Be −1236.4 ± 2.3 265 ± 10 Ba −1332.9 ± 3.1 232 ± 10 Mg −1263.2 ± 2.2 221 ± 10 Zn −961.8 ± 3.0 139 ± 10 Ca −1348.9 ± 2.4 246 ± 10 Cd −903.1 ± 2.4 119 ± 10 Sr −1344.9 ± 3.1 236 ± 10 Hg −723.9 ± 2.7 62 ± 10 The 〈 D 〉(m-O) values correlate well with the mean molar dissociation enthalpies of the corresponding solid oxides: mO(cr) = m(g) + O(g).

Standard enthalpies of formation of tris[bis(pentane-2,4-dionato)nickel(II)] and bis(2,2,6,6-tetramethylheptane-3,5-dionato)nickel(II) and an estimation of nickel–oxygen bond energies

Standard enthalpies of formation of the title complexes have been determined from hydrolyses in acid solution by solution calorimetry at 298.15 K as –624.0 ± 2.2 and –299.2 ± 2.0 kcal mol–l respectively. Estimates of gas-phase enthalpies of the monomeric forms of both complexes yield an average homolytic Ni–O bond energy of 50 ± 2 kcal mol–l, but in the pentane-2,4-dionate trimer the bridging oxygens have Ni–O bond energies of approximately half those of the terminal Ni–O bonds.

Enthalpies of vaporization of some β-diketones

Molar enthalpies of vaporization of six β-diketones have been measured at 298·15 K by a direct calorimetric method; for 1,1,1,5,5,5-hexafluoropentane-2,4-dione, ΔHv0= 7·31 ± 0·03 kcal mol–1, 1,1,1-trifluoropentane-2,4-dione, 8·90 ± 0·4, 2,6-dimethylheptane-3,5-dione, 13·40 ± 0·04, 2,2-dimethylheptane-3,5-dione, 13·59 ± 0·03, 2,2,6-trimethylheptane-3,5-dione, 13·80 ± 0·05, and for 2,2,6,6-tetramethylheptane-3,5-dione, ΔHv0= 14·23 ± 0·03 kcal mol–1. The relationship between the enthalpy of vaporization and the normal boiling point is briefly discussed.

Standard enthalpies of formation of bis(pentane-2,4-dionato)copper(II) and tetrakis[bis(pentane-2,4-dionato)cobalt(II)] and an estimation of the metal–oxygen bond energies

Standard enthalpies of formation of the title compounds have been determined by solution calorimetry at 298.15 K as –181.8 ± 0.5 and –826.6 ± 2.2 kcal mol–1 respectively. Estimates of the gas-phase enthalpies of the monomeric forms of the complexes lead to average bond energies of 38 kcal for Cu–O and 48 kcal for Co–O. In the solid tetramer the terminal Co–O bonds are almost twice as strong as the bridging Co–O bonds.

Thermochemistry of beryllium β-diketonates and Be–O bond energies

Enthalpies of formation of the crystalline complexes of beryllium with 2,2,6,6-tetramethylheptane-3,5-dione (dpm), 1,1,1-trifluoropentane-2,4-dione (tfac), and tropolone, have been determined at 298.15 K by solution calorimetry: ΔHf°[Be(dpm)2](c)=–386.5 ± 2.0 kcal mol–1, ΔHf°[Be(tfac)2](c)=–597.3 ± 2.0 kcal mol–1, and ΔHf°[Be(trop)2](c)=–208.56 ± 0.42 kcal mol–1. Gas phase enthalpies have been calculated and from these the Be–O bond energies have been derived.

Crystal and molecular structure of a tetranuclear cobalt(II)–tropolonate complex: [Co4(C7H5O2)8(H2O)2]

Crystals of the title compound are monoclinic, a= 13.341 (5), b= 18.634(9), c= 11.603(5)A, β= 171.43(3)°, Z= 2, space group P21/c. The structure was determined from X-ray diffractometer data by Patterson and Fourier syntheses, and refined by full-matrix least-squares calculations to R 0.067 for 2 070 observed reflections. There are two distinct cobalt atoms in the structure, both achieving a co-ordination number of six but with considerably distorted octahedral geometry. Of the four independent tropolone ligands in the asymmetric unit, three chelate and have one bridging oxygen atom while the other ligand chelates and does not bridge. A water molecule completes the co-ordination polyhedra. The Co–O distances vary from 2.051 (6) to 2.1 49(9)A, with mean distances corresponding to whether the ligand chelates (2.060 A), chelates and bridges (2.084 A), or forms a bridging bond (2.137 A). The molecules are hydrogen-bonded via the water molecules and tropolone oxygen atoms. The stability of the structure is due to efficient lattice packing and hydrogen bonding, both facilitated by the compact planar structure of the ligand.

Thermochemical study of the nickel–sulphur bond energy in bis(5-mercapto-2,2,6,6–tetramethylhept-4-en-3-onato-S)nickel(II)

The standard enthalpy of formation of the title complex has been determined at 298.15 K by solution calorimetry. The gas-phase enthalpy of formation has been calculated and a value for the Ni–S bond energy has been derived.

Thermochemistry of tri(tropolonato)- and tri(4-methyltropolonato)-aluminium(III)

Enthalpies of formation of tri(tropolonato)- and tri(4-methyltropolonato)-aluminium(III) have been determined at 298·15 K by solution calorimetry. The gas-phase enthalpies of formation have been calculated and from these the Al–O bond energies have been derived.

Thermochemistry of tris(l,1,1 -trifluoropentane-2,4-dionato)- and tris(2,2,6,6-tetramethylheptane-3,5-dionato)-aluminium(III)

Enthalpies of formation of the crystalline title complexes have been determined at 298.15 K by solution calorimetry: ΔHf⊖[Al(tfpd)3(c)]=–892.7 ± 3.1 and ΔHf⊖[Al(tmhd)3(c)]=–571.5 ± 3.1 kcal mol–1. Gas-phase enthalpies have been calculated, and from these the Al–O bond energies have been derived.