Development, characterisation and rapid evaluation of standard enthalpies of vaporisation and fusion of volatile Bis(N-RN-R-salicylaldimine)nickel(II) (n-R=methyln-R=methyl to pentyl) complexes for its MOCVD applications

Five volatile complexes of nickel namely bis(N-RN-R-salicylaldimine)nickel(II) (n-R=methyln-R=methyl, ethyl, nn-propyl, nn-butyl or nn-pentyl) were prepared and their complete volatilisation in an inert high purity N2N2 purge gas below 638 K was demonstrated by dynamic thermogravimetry. The congruent nature of vaporisation was verified from the molecular masses of the vapor species obtained using Fast Atom Bombardment Mass Spectrometry (FABMS). Based on the molecular masses so obtained, the equilibrium vapor pressures of the complexes over a temperature span of 50–90 K (from the respective melting points) determined by adapting a horizontal dual arm single furnace thermoanalyser as a transpiration apparatus led to the values of 111.8(±4.3)111.8(±4.3), 93.1(±6.7)93.1(±6.7), 85.7(±8.3)85.7(±8.3), 76.8(±8.5)76.8(±8.5) and 90.3(±8.4)kJmol-1, respectively, for the standard enthalpies of vaporisation (ΔHvapo). From the melting point depression in the DTA-mode, the values of 13.0(±1.0)13.0(±1.0), 15.1(±1.4)15.1(±1.4), 10.8(±0.6)10.8(±0.6), 10.8(±1.1)10.8(±1.1) and 13.9(±1.3)kJmol-1, respectively, were evaluated for the standard enthalpies of fusion (ΔHfuso) after establishing the ideal eutectic behaviour of these complexes as solvents with bis(2,4-pentanedionoato)nickel(II) as a non-volatile solute. Combining these values with the equality of the vapor pressures of the solid and liquid phases at their respective melting points, a systematic trend in the equilibrium vapor pressures of the solids could be observed without recourse to direct measurements, which were not possible due to their sluggish sublimation.