Historical Perspective of Organometallic Thermochemistry

Abstract

My involvement with thermochemistry and calorimetry goes back to 1946, at which time simple organic compounds containing C, H, O and N were the main interest of thermochemists. Organometallic compounds were then of minor interest, and few such data had been measured. The development later of rotating bomb calorimetry, the use of combustion aids, advances in solution reaction calorimetry, and in particular, the adaptation of the Calvet twin-microcalorimeter, opened the door to study organometallic compounds in general, but it was well into the 60’s before this happened. from 1970 onwards, however, more laboratories became involved with organometallics in general, particularly in Portugal at Lisbon and Oporto, in Spain, and in Russia. In more recent times, non-calorimetric developments such as photoionization mass-spectroscopy are being applied to measure individual bond-dissociation energies in specific MX_n compounds. The results indicate that these, D₁, D₂…. D_n, vary considerably from the mean value,.

The main reason for variability in the individual D values in MX_n compounds is that the valence-state of the metal changes in moving along the series MX_n, MX_n-1, MX_n-2…. M. In the case of SÍH4, e.g. this change occurs at the step SÍH3 -> SÍH2; in CH4, however, the valence change occurs at the step CH₂ → CH. The analysis of these, and other examples is attempted in this paper, to indicate the complexity of the overall problem, and the need for more experimental data than is provided by thermochemical studies alone.