Organometallic Thermochemistry Database

J. A. Martinho Simões


Standard enthalpies of formation are the building blocks of any thermochemical database. In the case of organic compounds, and, in particular, those which contain only carbon, hydrogen, oxygen, and nitrogen, the enthalpies of formation are most commonly derived from combustion calorimetry experiments. For many organic compounds this technique affords very accurate data, not only because their reaction with oxygen is well characterized and occurs with nearly 100% yield, but also because the standard enthalpies of formation of the products (e.g. carbon dioxide and water) are well known. In other words, for a large variety of organic compounds, combustion calorimetry could well be called an "absolute" method, since the enthalpy of formation of the "fuel" is the only unknown in the combustion enthalpy balance.

Unfortunately, combustion calorimetry is not suited to probe the thermochemistry of many other important classes of substances. This is due to several reasons, but perhaps the most common is that the combustion reaction is not always well characterized. For example, the combustion of an organometallic compound of formula CxHyMz may lead to non-stoichiometric metal oxides, which requires a detailed analysis of these reaction products if the enthalpy of formation of CxHyMz is to be derived. While some difficulties related to ill-defined combustion products can be overcome by using rotating-bomb combustion calorimeters, most of the available thermochemical data for organometallic substances, unlike the case of organic compounds, have not been determined from their reaction with oxygen but from their reaction with some other reactant. The drawback in using alternative experimental methods, such as reaction-solution calorimetry, is that these reactions often involve two or more species whose enthalpies of formation are not available. It will be noted that this situation is frequently met in the present database.

The Organometallic Thermochemistry Database includes thermochemical properties (enthalpies and entropies of reaction) of neutral organometallic compounds (see below), as reported in the literature. Whenever available, or appropriate, the following information is provided in each record: (1) The molecular formula of the compound (or, in the case of a reaction, the molecular formula of one of the compounds); (2) the structural formula of the compound; (3) the physical state of the compound to which the data refer; (4) the solvent, if any; (5) the reaction to which the data refer, or, in the case of a combustion reaction, the product metal oxide and other products that need to be specified; (6) the main experimental method which afforded the thermochemical data; (7) the enthalpy of the reaction, followed by the literature reference(s) where the value was reported; (8) the entropy of the reaction, followed by the literature reference(s) where the value was reported; (9) the standard enthalpy of formation in the condensed state; (10) the standard enthalpy of sublimation or vaporization of the compound, followed by the literature reference(s) where the value was reported; (11) the method used to determine the standard enthalpy of sublimation or vaporization; (12) the standard enthalpy of formation in the gas phase; (13) comments and additional information.

A systematic inventory of enthalpies of reaction is obviously more difficult to organize than a compilation based on enthalpies of formation. The approach followed in the Organometallic Thermochemistry Database, was that, whenever possible, the enthalpy of each reaction would be listed in two different records: one involving all reactants and products in their standard states and the other involving all reactants and products in solution. The former record will enable a future calculation of an enthalpy of formation value if the required auxiliary data become available. The latter is deemed to be useful to derive metal-ligand bond dissociation enthalpies in solution. Both will be helpful in estimating new values or assessing the existing data [1, 2, 3, 4, 5]. Additional enthalpies of solution may be available in the literature (including the reference(s) indicated in a given record), enabling the calculation of reaction enthalpies with the species in different physical states. At any rate, reliably estimating the contribution of enthalpies of solution to a given reaction enthalpy may not be a difficult exercise, particularly in non-polar solvents.

The physical state of many species involved in reactions in solution is not rigorously defined in the Database, reflecting the same problem in the original literature, where accurate information about the concentration of reactants and products is frequently absent. Also, there are abundant examples where substances like hydrogen, methane, etc., are described as being exclusively in solution or in the gas phase and no correction for gas/liquid partition was made. Although this lack of information is obviously unfortunate, it is believed that the uncertainties due to the ill-defined compositions are usually smaller than the uncertainties assigned to the experimental enthalpies of reaction.

The thermochemical convention on uncertainties [6] is unfortunately ignored in many current publications. Moreover, information on how the uncertainties were calculated is often omitted, which hinders the evaluation of "correct" error bars for each experimental quantity. The option taken in the Organometallic Thermochemistry Database was simply to quote the uncertainties given in the original publications.

Another important option that had to be considered concerns the use of ancillary data to derive enthalpies of formation and, in a few cases, also enthalpies of reaction. It must be stressed that parameters like enthalpies of reaction or combustion are the true experimental quantities, whereas enthalpies of formation are computed from those parameters and rely on enthalpies of formation of other compounds. Each author has preferences regarding these auxiliary values, so it may happen that two literature values for the enthalpy of formation of a given compound differ markedly only because they were derived with different ancillary data. Unless stated otherwise, all the enthalpies of formation in the Organometallic Thermochemistry Database have been recalculated on the basis of a single set of ancillary data, in order to insure that the value calculated for a given enthalpy of reaction, by using the enthalpies of formation listed in the Database, will not be affected by inconsistencies in those data. Therefore, in summary, the Organometallic Thermochemistry Database includes the experimental enthalpies of reaction, as reported in the literature, but presents recalculated values for the enthalpies of formation. The thermochemical "consistency" between the Database and the auxiliary values is better than ±1 kJ/mol. The auxiliary data records are provided, together with the literature references from which they were quoted. Estimated values are enclosed in parentheses.

A note regarding data reliability seems appropriate. It is believed, although with some optimism, that most of the enthalpy values presented are accurate within the attached error bars. Unfortunately, there are too few cases where the thermochemistry of the same organometallic compound or of the same reaction have been probed by at least two groups or by at least two different experimental techniques. Whenever comparisons are possible and the data differ noticeably, a recommendation was normally provided, although it must be stressed that "selected data" does not necessarily mean "high quality" data. In some other cases, no reason was found to decide for a given value and a simple or weighted average was recommended. Thermochemical data evaluation for organometallic compounds is still incipient [1, 2, 3, 4, 5] and it may well be possible that different selections will be made in future updates of the Database. It should, finally, be pointed out that authors sometimes make corrections of their own reported data in a later publication. Whenever this is the case, only the corrected values are given in the record, but all the literature references are indicated.

Some values included in the Database have only historical interest. For example, it has been shown that static-bomb combustion calorimetry is unsuitable to probe the thermochemistry of a variety of transition and non-transition element compounds [7]. For example, as remarked by G. Pilcher, static-bomb results for compounds of Si, Al, and Pb "should be rejected and it does not seem at all worthwhile for such measurements on compounds of these elements to be attempted in the future". This and other conclusions in the same paper should be kept in mind when using the Database, particularly when a single record, relying on static-bomb combustion calorimetry, is available for a given compound.

An additional comment regarding data from static-bomb combustion calorimetry must be made: in the case of Ge compounds, although the rotating-bomb method is clearly preferred, static-bomb experiments may afford reliable data. This depends, however, on a correct assignment of the state of the product oxide, GeO2 (amorphous, hexagonal or tetragonal) [7]. In the present Database, all the enthalpies of formation of Ge compounds derived from static-bomb experiments were recalculated by assuming that amorphous GeO2 is formed [7].

In general, the estimated enthalpies of sublimation listed in the Organometallic Thermochemistry Database are probably the most unreliable information provided. To our knowledge, there is no general method for estimating those quantities for most classes of compounds, in contrast to the variety of available procedures for predicting enthalpies of vaporization [6, 7, 8]. Usually, estimated sublimation enthalpy values are, at best, educated guesses, often based on an experimental (or an estimated!) value for a similar compound. The approach followed in the Database was merely to quote the values that have been published, unless an experimental value has been reported. A word of caution on the reliability of many gas-phase enthalpies of formation is thus in order.

Up to a certain extent, the previous remarks also apply to some enthalpies of liquid-vapor phase transitions, which have been reported at boiling temperatures instead of 298.15 K. Although the differences will usually be small, ca. less than 4 kJ/mol, a reassessment of all the available enthalpies of vaporization is clearly desirable. This task is now being undertaken and the results will be included in a future release of the Database.

Whenever possible, the values listed in the Organometallic Thermochemistry Database refer to 298.15 K. However, the thermochemistry of some reactions has been studied at a different temperature, e.g. 293 or 303 K. No mention of this is made in the record, since the corrections to 298.15 K are negligible. However, in those cases where the enthalpy was determined at temperatures further from 298.15 K and no correction was possible, the experimental temperature is indicated. The temperature ranges of equilibrium experiments (leading to van't Hoff plots) are given, unless no information was found in the literature. It will be noticed that this "Second Law method" of obtaining thermochemical quantities has been used for many organometallic reactions. Unfortunately, the data have sometimes poor quality, often because the plot relies on a small number of points. Reaction entropies are particularly sensitive to the errors and may indicate that a result is, at least, questionable. Very simple methods to assess the accuracy of organometallic reaction entropies have been suggested [9].

Although the present Database attempts to be comprehensive for the elements and ligands indicated below, and it is unlikely that important data have been inadvertently missed, gaps will be corrected in future editions. Future extensions of the Database to other elements and families of molecules (e.g. coordination compounds) are envisaged. In any case, an effort to list all the available information on the energetics of neutral organometallic compounds, no matter the source or the experimental technique, has been made. Even kinetics-based data were included, whenever there was evidence that an activation enthalpy would be a good approximation (a lower or upper limit) of a reaction enthalpy. Thermochemical data derived from gas-phase ion techniques will be the subject of a different database. Only a very limited amount of values from those experiments has been included in the Organometallic Thermochemistry Database.

Elements covered in the Database

Groups 1 (except Hydrogen), 2, 3 (including lanthanides and actinides), 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 (except Boron), 14 (except Carbon and Silicon), and 15 (Antimony and Bismuth only).

Types of compounds included in the Database

All the compounds which have at least one metal-carbon bond have been surveyed, with the exception of metal carbides. Several other families of molecules of special importance to organometallic chemistry, such as metal alkoxides, have also been included.

Future additions to the Database

The Database will be updated at least yearly. Future additions will include organo- phosphorus, arsenium and silicon compounds.


  1. Martinho Simões, J.A.; Minas da Piedade, M. E. In Energetics of Organic Free Radicals, Martinho Simões, J.A.; Liebman, J.F.; Greenberg, A., Editors, Blackie: London, 1996, chapter 6.
  2. Martinho Simões, J.A. In Energetics of Organometallic Species, Martinho Simões, J.A., Ed.; NATO ASI Series C Vol. 367, Kluwer: Dordrecht, 1992, and references cited therein.
  3. Benson, S. W. Acc. Chem. Res. 1992, 25, 375.
  4. Drago, R. S.; Wong, N. M. Inorg. Chem. 1995, 34, 4004.
  5. Angelici, R. J. Acc. Chem. Res. 1995, 28, 51.
  6. Cox, J. D.; Pilcher, G. Thermochemistry of Organic and Organometallic Compounds; Academic Press: London, 1970.
  7. Pilcher, G. In Energetics of Organometallic Species Martinho Simões, J. A., Editor; NATO ASI Series C Vol. 367; Kluwer: Dordrecht, 1992.
  8. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed. McGraw-Hill: New York, 1988.
  9. Minas da Piedade, M. E.; Martinho Simões, J. A. J. Organometal. Chem. 1996, 518, 167.

Reference 1 is a survey of the methods that have been used to estimate and assess thermochemical data of organometallic compounds. References 2-5 describe additional methods and/or examples. Reference 7 is an authoritative critical review of combustion calorimetry applied to organometallic compounds. Methods of estimating enthalpies of vaporization are described in references 6 and 8. A very simple procedure for assessing or estimating reaction entropies is proposed in reference 9.

List of abbreviations

Group or molecule

(dmgBF2)2 C8H12B2F4N4O4
(Me3Si)2Cp C5H3[Si(CH3)3]2, C11H21Si2
[14]aneN4 1,4,8,11-tetraazacyclotetradecane, C10H24N4
[15]aneN4 1,4,8,12-tetraazacyclopentadecane, C11H26N4
1,1-cbdaH2 cyclobutane-1,1-dicarboxylic acid, C6H8O4
1,2-cbdaH2 cyclobutane-1,2-dicarboxylic acid, C6H8O4
1,2-O2C6Cl4 tetrachloro-1,2-benzoquinone
1,3-C4H6 1,3-butadiene
1,3-C5H8 1,3-pentadiene
1,3-cy-C6H8 1,3-cyclohexadiene
1,4-O2C6H4 p-benzoquinone
1,5-C6H10 1,5-hexadiene
1-C6H12 1-hexene
1-EtInd 1-ethylindenyl, C11H11
2,2-Me2Bu 2,2-dimethylbutyl, C6H13
2,3-Me2Bu 2,3-dimethylbutyl, C6H13
2,3-Me2C4H4 2,3-dimethyl-1,3-butadiene, C6H10
2,3-Me2C4H8 2,3-dimethylbutane, C6H14
2,4-C6H10 trans-trans-2,4-hexadiene
2,4-C7H11 2,4-dimethylpentadienyl
2,5-Me2thf 2,5-dimethyltetrahydrofuran, C6H12O
2,6-Me2py 2,6-dimethylpyridine, C7H9N
2-C4H6 2-butyne
2-C4H8 2-butene
2-C6H12 2-hexene
2-MeC3H4 2-methylallyl, C4H7
2-Phpy 2-phenylpyridine, C11H9N
3,5-Cl2py 3,5-dichloropyridine, C5H3Cl2N
3,5-Me2Pz 3,5-dimethylpyrazol-1-yl, C5H7N2
3-C6H9 3-methylpentadienyl
9,10-Me2C14H10 9,10-dihydro-9,10-dimethylanthracene, C16H16
9,10-Me2C14H8 9,10-dimethylanthracene, C16H14
9-MeAd 9-methyladenine, C6H7N4
9-MeAdH 9-methyladeninium, C6H8N4
acac 2,4-pentanedionate, C5H7O2
Ad* allyldiene, (CH2)2C5Me3, C10H13
Ado 5'-deoxyadenosyl, C10H12N5O3
anth anthracene, C14H10
Ari aristeromicyl, C11H14N5O2
arphos Ph2PCH2CH2AsPh2, C26H24AsP
B12 cobalamine, C62H88CoN13O14P
bcbd C8H4O2
bcpd C8H4O2
bda benzylideneacetone, PhCHCHCOMe, C10H10O
bipy 2,2'-bipyridyl, C10H8N2
Bu butyl, C4H9
Bz benzyl, C6H5CH2
C-meso-Me6[14]aneN4 C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-
tetraazacyclotetradecane, C16H36N4 C10H12
dicyclopentadiene C10H14O4
diethylmuconate C10H16
dipentene C10H8
naphthalene C14H12
9,10-dihydroanthracene C14H8O2
9,10-phenanthrenoquinone C18H12
triphenylene C2(DO)(DOH)pn
C13H23N4O2 C2(DO)(DOH)pnBz
C20H30N4O2 C3H3NS
thiazole C3H4N2
imidazole C3H5
allyl C3H5Pz
1-allylpyrazole, C6H8N2 C4H2F4
3,4-tetrafluorocyclobutene C4H2Ph4
1,2,3,4-tetraphenylbutadiene, C28H22 C4H4N2
pyrazine, C4H4N2 C4H4S
thiophene C4H6N2
1-methylimidazole C4H8
2-butene C4H8O2
1,4-dioxane C4H8S
tetrahydrothiophene C5H12
pentane C5H4O2
C6H14O isopropyl ether
C6H4O2BH catecholborane, C6H5BO2
C6H8S 2,5-dimethylthiophene
C7H10O2 methylsorbate
C7H16 heptane
C8H12 bicyclo[2,2,2]oct-2-ene
C8H7N indole
CH2CHCO(O)Me methyl acrylate, C4H6O2
CH2CHO(O)CMe vinyl acetate, C4H6O2
chal chalcone, PhCHCHCOPh, C15H12O
CNpy cyanopyridine, C6H4N2
Cob cobinamide, C48H71CoN11O8
cod 1,5-cycloctadiene, C8H12
cot 1,3,5,7-cyclooctatetraene, C8H8
cotBu C8H7C4H9, C12H26
Cp cyclopentadienyl, C5H5
Cp* pentamethylcyclopentadienyl, C5Me5, C10H15
CpH 1,3-ciclopentadiene, C5H6
Cy cyclohexyl, C6H11
cy-C12H18 1,5,9-cyclododecatriene
cy-C5H8 cyclopentene
cy-C5H9 cyclopentyl
cy-C5H9CH2 cyclopentylmethyl
cy-C6H10 cyclohexene
cy-C6H12 cyclohexane
cy-C7H12 cycloheptene
cy-C7H8 1,3,5-cycloheptatriene
cy-C8H12Cl2 5,6-dichlorocyclooctene
cy-C8H14 cyclooctene
dab biacetyl bis(phenylimine),
dba dibenzylideneacetone, C17H14O
dcpe Cy2PCH2CH2PCy2, C26H48P2
depe Et2PCH2CH2PEt2, C10H24P2
diars Me2As(1,2-C6H4)AsMe2, C10H16As2
dmg dimethylglyoximate, C4H7N2O2
dmgH dimethylglyoxime, C4H8N2O2
dmpe Me2PCH2CH2PMe2, C6H16P2
dmpm Me2PCH2PMe2, C5H14P2
dpab Ph2AsCH2CH2CH2CH2AsPh2, C28H28As2
dpae Ph2AsCH2CH2AsPh2, C26H24As2
dpcb C15H10O
dpcp 2,3-diphenylcycloprop-2-en-1-one, C15H10O
dppb Ph2PCH2CH2CH2CH2PPh2, C28H28P2
dppbz Ph2P(1,2-C6H4)PPh2, C30H24P2
dppe Ph2PCH2CH2PPh2, C26H24P2
dppen cis-Ph2PCHCHPPh2, C26H22P2
dppm Ph2PCH2PPh2, C25H22P2
dppp Ph2PCH2CH2CH2PPh2, C27H26P2
dtfpe (4-CF3C6H4)2PCH2CH2P(4-CF3C6H4)2, C30H20F12P2
Et ethyl, C2H5
Fc ferrocenyl, Fe(Cp)C5H4, C10H9Fe
Fv* CH2C5Me4, C10H14
Hacac 2,4-pentanedione, C5H8O2
HB(3,5-Me2Pz)3 hydridotris(3,5-dimethylpyrazolyl)borate, C15H22BN6
HB(3-i-Pr-5-Me-Pz)3 hydridotris(3-iso-propyl-5-methylpyrazolyl)borate, C21H34BN6
HBPz3 hydridotris(pyrazolyl)borate, C9H10BN6
He hexyl, C6H13
hfacac hexafluoro-2,4-pentanedionate, C5HF6O2
Hmhp 2-hydroxy-6-methylpyridine, C6H7NO
Hnto 3-nitro-1,2,4-triazol-5-one, C2H2N4O3
Hp heptyl, C7H15
i-C4H8 isobutylene
i-C8H18 isooctane, 2,2,4-trimethylpentane
Ind indenyl, C9H7
L2-BINO L2-binaphtholate, L2-C20H10O2
ma maleic anhydride, C4H2O3
Me methyl, CH3
Me2C3H3 1,3-dimethylallyl, C5H9
Me2Cp 1,2-dimethylcyclopentadienyl, 1,2-Me2C5H3, C7H9
Me2phen 2,9-dimethyl-1,10-phenantroline, C14H12N2
Me2Si(C5Me4)(MenC5H3) C26H40Si
Me3Cp 1,2,3-trimethylcyclopentadienyl, 1,2,3-Me3C5H2, C8H11
Me3SiCp C5H4Si(CH3)3, C8H13Si
Me4Cp tetramethylcyclopentadienyl, Me4C5H, C9H13
Me6[14]4,11-dieneN4 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, C16H32N4
MeC3H4 1-methylallyl, C4H7
MeCp methylcyclopentadienyl, C5H4Me, C6H7
Men menthyl, C10H19
MeO2CCCCO2Me dimethyl acetylenedicarboxylate, C6H6O4
Mes mesityl, 2,4,6-Me3C6H2, C9H11
Methf methyl-tetrahydrofuran, C5H10O
morph morpholine, C4H9NO
neo-PeCN C6H11N
NH2py aminopyridine, C5H6N2
No nonyl, C9H19
nor-C7H10 norbornene
nor-C7H8 norbornadiene
nto 3-nitro-1,2,4-triazol-5-one anion, C2HN4O3
Oc octyl, C8H17
OC10H19 O-menthyl
oep 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion, C36H44N4
oetap octaethyltetraazaporphyrinato dianion, C32H40N8
OTf O3SCF3, trifluoromethane sulfonic anion, triflic anion
pcbd 3-phenylcyclobutene-1,2-dione, C10H6O2
Pe pentyl, C5H11
Ph phenyl, C6H5
phen 1,10-phenantroline, C12H8N2
phenanth phenanthrene, C14H10
pic picoline, methylpyridine, C5H4MeN, C6H7N
pip piperidine, C5H11N
Pr propyl, C3H7
PR3 any phosphine
py pyridine, C5H5N
pyO pyridine N-oxide, C5H5NO
pyr pyrene, C16H10
Pz pyrazolyl, C3H3N2
pz pyrazole, C3H4N2
saloph N,N'-bis(salicylidene)-1,2-phenylenediamine dianion, C20H14N2O2
t-BuCp tert-butylcyclopentadienyl, C5H4-t-C4H9, C9H13
tap tetraanisylporphyrinato dianion, C48H36N4O4
tempo 2,2,6,6-tetramethylpiperidine-1-oxyl, C9H18NO
thf tetrahydrofuran, C4H8O
tmeda tetramethylethylenediamine, Me2NCH2CH2NMe2, C6H16N2
tmp 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrinato dianion, C56H52N4
tmpp C53H45N4
Tol tolyl, MeC6H4, C7H7
triphos Ph2PCH2CH2PPhCH2CH2PPh2, C34H33P3
tripod MeC(CH2PPh2)3, C41H39P3
txp 5,10,15,20-tetraxylylporphyrinato dianion, C52H44N4


CC-RB Combustion Calorimetry (Rotating Bomb)
CC-SB Combustion Calorimetry (Static Bomb)
DSC Differential Scanning Calorimetry
DTA Differential Thermal Analysis
EChem Electrochemical Methods
EIMS Electron Impact Mass Spectrometry
EqG Equilibrium in the Gas Phase
EqS Equilibrium in Solution
EST Thermochemical Estimate or Assessment of Literature Data
FA-SIFT Flowing Afterglow – Selected Ion-Flow Tube
HAL-HFC Halogenation – Heat-Flux Calorimetry
ICR Ion Cyclotron Resonance Mass Spectrometry
KC Knudsen Cell
KC-MS Knudsen Cell – Mass Spectrometry
KinG Kinetics in the Gas Phase
KinS Kinetics in Solution
LPHP Laser-Powered Homogeneous Pyrolysis
LPS Laser Photoelectron Spectroscopy
MBPS Molecular Beam Photofragment Spectroscopy
PAC Photoacoustic Calorimetry
PC Photocalorimetry
PES Photoelectron Spectroscopy
PIMS Photoionization Mass Spectrometry
RSC Reaction-Solution Calorimetry (Batch or Titration)
TD-HFC Thermal Decomposition – Heat-Flux Calorimetry
TD-HZC Thermal Decomposition – Hot-Zone Calorimetry
VLPP Very Low Pressure Pyrolysis

Method (Vaporization)

C Calorimetry
E Estimate
V Vapor pressure versus temperature measurements


ai aqueous, infinite dilution
am amorphous
aq aqueous
cr crystalline
g gas
l liquid
sln solution
sur surface

NIST, National Institute of Standards and Technology Material Measurement Laboratory Standard Reference
Data Program