The enthalpy of formation of chromium hexacarbonyl

Density Functional and Ab Initio Study of Cr(CO)n (n = 1−6) Complexes

“…The total CO binding energies for Cr(CO) 6 are summarized in Table . The experimental value corresponding to D o 298 is 153 kcal/mol . Whereas the results with GGA functionals seriously overestimate the experimental value, the B3PW91 and mPW1PW91 functionals provide reasonable values.…”

Thermochemical studies of organo-transition metal carbonyls and related compounds

“…ments of the heat of decomposition or iodination, the agreement has generally been good. For example, AH~ [Cr(CO) 6, c] = -980 (conventional bomb) 6), -982 (microcalorimeter; iodination 3)) kJ mol -I , or AH~ [Cr(r/-C6H6)2, c] = + 146 (combustionT)), + 142 (microcalorimeter; iodination 8)) kJ mol-1. These results suggest that one may be cautiously optimistic about the accuracy of measurements made on more complex comPOunds, such as those containing metal clusters or ligands which are likely to be reactive when released from the metal at high temperatures.…”

“…Instead, a kinetic argument based on the greater ability of the trifluorophosphine ligand to shield the metal from nucleophilic attack by virtue of its greater size than the rod-like carbon monoxide ligand seems appropriate. This is made clear when models of Cr(PF3) 6 and Cr(CO) 6 are considered; the former is a spherical molecule with the metal buried at the centre of a shell provided by the regularly disposed fluorine atoms. This example demonstrates some of the dangers which beset the use of mass spectroscopy to determine bond enthalpies in systems of this kind.…”

Determination of bond energies by mass spectrometry: some transition metal carbonyls

“…Least-squares bond dissociation energies (eV) for the thiocarbonyls calculated with the assumption that one M^-CO bond is weaker than the rest These energies are tabulated in Table 16. Known values for the heats of formation of gaseous Cr(CO)^ and W(CO)g, -9.42 ± 0.02 and -9.17 ± 0.04 eV, respectively [53,54], and for CO and CS, -1.146 ± 0.002 and 2,91 è 0.26 eV respectively [79], along with the average energies of the substitution reaction gives AH^°(Cr(CO)^CS,g) = -6.3 ± 0. from several such studies are summarized in Table 17. It is apparent from these data that the M-M bond energies of the hcimonuclear compounds increase in the order Mn<Tc<Re, However there is some discrepancy as to where the heteronuclear compound MnRe(CO)^Q fits into the sequence.…”