Enthalpy of disruption

This assumption is crucial to the development of a body of thermochemical information on compounds of the transition metals. The assumption is made that b.e.c values are transferable from one compound to another in which the formal oxidation state of the metal is unchanged. This means that, for example, the value of Z (Cr-CO) in Cr(CO)6 is assumed unchanged11 in [Cr(r -C6H6)(CO)3], or that Z)(Cr-C6H6) in the same compound is assumed unchanged from its value in Cr(77-C6H6)2. In this example, A.Hf [Cr(T -C6H6)(CO)3, q] = —352.3 kJ mol-1, from which the enthalpy of disruption, A, for the process... 

Table 1. Standard enthalpy of formation of metal carbonyls [Mm(CO) ] in the gas phase. Bond description and bond enthalpy contributions (T, M and B) to the enthalpy of disruption, AHq...

For a mononuclear carbonyl, M(CO) , the enthalpy of disruption AHD refers to the process... 

Table 5. Contributions to the enthalpy of disruption to valence state, AH kJ mol-1 of the M-CObond...

T - mean enthalpy of disruption to ground state products AHcq - valence reorganization energy of CO ... 

Table 12a. Standard enthalpy of formation, A/ff(g), enthalpy of disruption, AHjy, and metal-halogen bond enthalpy contribution, (M-X), in metal carbonyl halides (kJ mol-1)...

The standard enthalpies of formation of the gaseous compounds and the enthalpy of disruption derived therefrom are given in Table 13. An interesting problem arises as to how these results are to be evaluated. If the value of AHf [M(CO)s, g] derived15,1 ) from electron impact measurements on M2(CO)io (M = Mn, Re) is used, then as outlined earlier this will be expected to give an upper limit to the value of D(M-M). It has been shown16) that for all values of Z)(M-M) below specified upper limits the following relation holds... 

The benzoyl derivative, PhCOMn(CO)5 and related acyl derivatives have intrinsic interest because they can be prepared by alkyl group migration to coordinated CO, a formal internal nucleophilic attack. This reaction, which is often referred to as carbonyl insertion86), is reversible in certain instances to give the metal alkyl. The enthalpy of disruption for PhCOMn(CO)s (Table 13) can be divided up to give the b.e.c of the Mn-COPh bond if the values of T (Mn-CO) shown in Table 13 are used, then the Mn-COPh enthalpy lies in the range 105 10 kJ mol-1, the lower value being preferred as outlined earlier. 

Table 17. Enthalpy of sublimation/vaporization, A//sub/vac, enthalpy of disruption, A/fo, and olefin-iron bond enthalpy contribution for [Fe(CO)n(olefin),j] compounds. All values are in kJ mol-1...

Standard heat of formation and derived values of enthalpy of disruption (kJ mol-1) for dimethylamide compounds of... 

Surely it is tempting to attribute the difference to the extra enthalpy of disrupting H bonds formed by the carboxylic acid group (which contradicts the reservations we have expressed about the validity of the AH estimates given in Table 7-IV). 

If the enthalpy of formation of a particular metal carbonyl cluster compound M.v(CO). has been measured, typically by calorimetric determination of the enthalpy of combustion, one can calculate the enthalpy of disruption of that cluster in... 

Reference to Table 2 indicates the scale of increase expected for metal-ligand bond enthalpy terms as the ratio of ligand to metal decreases. Taking "(Os-CO) for Os(CO)4 units as 201 kJmol", as found for Os3(CO)i2, we estimate that a realistic value of (Os-CO) for Os(CO)3 units will be some 4% higher, i.e. 209 kJmor. Using these values, one can estimate values of the enthalpy of disruption of all the known osmium carbonyls Os.v(CO)j. into gaseous metal atoms and carbon monoxide molecules ... 

Table 4. Calculated contributions to the enthalpy of disruption of selected metal carbides. 

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