Intermolecular influences on M-M multiple bonds from thin-film UPS studies of Group VI M2(O2CCH3)4 complexes

Lichtenberger, Dennis L.; Kristofzski, J.G.

doi:10.1021/ja00245a046

Cited by 21 publications

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“…It should be noted that in spite of all efforts to effect some resolution of the two bands in an Mo 2 (O 2 CR) 4 compound by changing the R group, no such observation has been made. A study of the PES of solid M 2 (O 2 CCH 3 ) 4 compounds, 306 as thin fi lms deposited from the vapor phase, and a comparison of these spectra with the vapor phase spectra previously studied has provided results that in no way contradict the interpretations just discussed. Fig.…”

Section: Paddlewheel Moleculesmentioning

confidence: 91%

Physical, Spectroscopic and Theoretical Results

Cotton

2005

Multiple Bonds Between Metal Atoms

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Structural Correlations Bond orders and bond lengthsThroughout the preceding chapters of this book we have reported and in some cases discussed the lengths of the multiple bonds between metal atoms. We have reported in tabular form most of the M-M distances that have been determined crystallographically. It is now time to make some general comments on these distances in relation to our understanding of the M-M bonds.It is a general qualitative rule in chemistry that bond lengths and bond orders are inversely related. In some limited areas, particularly with the fi rst-row elements carbon, nitrogen, and oxygen, quantitative relationships expressing bond length as a single-valued function of bond order are well known. However, these quantitative relationships are based heavily on faith, as well as fact. Bond lengths are facts; bond orders are not. In the process of inferring a bond order from a bond length one is often getting out no more than what was put in to begin with.We shall not further digress into a discussion of the philosophical ambiguities of these quantitative bond order-bond length correlations because they have proven to be useful, within their own sphere of application. However, there is no a priori reason to expect that similar procedures will (or will not!) work in the very different realm of metal-to-metal bonds. Experience is the only test, and experience thus far has shown that M-M bonds cannot usefully be treated in such a way.In the realm of M-M bonds it is best to invoke only a qualitative inverse relationship between bond order and bond length and to defi ne bond order only in a qualitative or ordinal way. In this book we have used the term M-M bond order only to indicate how many electron pairs are believed, on the basis of essentially qualitative considerations, to play a signifi cant part in holding the pair of metal atoms together. We condemn as foolish and hopeless any effort to associate a unique, precise, quantitative bond order with each and every M-M internuclear distance.In principle, M-M bond lengths, like others, should be amenable to treatment by the method of molecular mechanics, and some efforts [1][2][3][4] (hampered by a dearth of necessary experimental data) to do this have been reported. In general the results are encouraging and can account for

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Section: Paddlewheel Moleculesmentioning

confidence: 91%

Physical, Spectroscopic and Theoretical Results

Cotton

2005

Multiple Bonds Between Metal Atoms

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“…A conclusive assignment of these ionizations in the gas-phase photoelectron spectra of these systems has only been realized relatively recently . The gas-phase and thin-film He I photoelectron spectra of M 2 (O 2 CCH 3 ) 4 (M = Cr, Mo, W) have been published previously by our group . In general, assignment of the M−M π and δ features (M = Mo, W) as the two bands of lowest ionization energy in these spectra is accepted.…”

Section: Introductionmentioning

confidence: 99%

Quadruple Metal−Metal Bonds with Strong Donor Ligands. Ultraviolet Photoelectron Spectroscopy of M₂(form)₄ (M = Cr, Mo, W; form = N,N‘-diphenylformamidinate)

1999

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The He I photoelectron spectra of M2(form)4 (M = Cr, Mo, W; form = N,N‘-diphenylformamidinate) and Mo2(cyform)4 (cyform = N,N‘−dicyclohexylformamidinate) are presented. For comparison, the Ne I, He I, and He II photoelectron spectra of Mo2(p-CH3-form)4 have also been obtained. The valence ionization features of these molecules are interpreted based on (1) the changes that occur with the metal and ligand substitutions, (2) the changes in photoelectron cross sections with excitation source, and (3) the changes from previously studied dimetal complexes. These photoelectron spectra are useful for revealing the effects that better electron donor ligands have on the valence electronic structure of M2(L⌒L)4 systems. Comparison with the He I spectra of the isoelectronic M2(O2CCH3)4 compounds is particularly revealing. Unlike with the more electron-withdrawing acetate ligand, several formamidinate-based ionizations derived from the nitrogen pπ orbitals occur among the metal−metal σ, π, and δ ionization bands. Although these formamidinate-based levels are close in energy to the occupied metal−metal bonds, they have little direct mixing interaction with them. The shift of the metal−metal bond ionizations to lower ionization energies for the formamidinate systems is primarily a consequence of the lower electonegativity of the ligand and the better π donation into empty metal levels. The metal−metal δ orbital experiences some additional net bonding interaction with ligand orbitals of the same symmetry. Also, an additional bonding interaction from ligand-to-metal electron donation to the δ* orbital is identified. These spectra suggest a greater degree of metal−ligand covalency than in the related M2(O2CCH3)4 systems. Fenske−Hall molecular orbital and density functional (ADF) calculations agree with the assignment and interpretation of these spectra. Calculated ionization energies are reported for M2(form)4 based on several different density functionals and with different orientations and substitutions for the phenyl rings. It is found that good estimates of the ionization energies are obtained when the truncated system M2(HN(CH)NH)4, in which the phenyl groups are replaced by hydrogen atoms, is employed.

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“…Eventually, the polymerization of the formed unsaturated α-hydroxy phosphonates or initial α-haloenals under the experimental conditions can be faster than the addition reaction itself. In fact, it is known that the alkali metal alkoxides initiate the polymerization of the α-haloenals [15,16]. So, what kind of transformations will be realized in this case?…”

Section: Resultsmentioning

confidence: 99%

Hydrophosphonylation of α‐Haloalkenals

Rulev

2013

Heteroatom Chemistry

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Intermolecular influences on M-M multiple bonds from thin-film UPS studies of Group VI M2(O2CCH3)4 complexes

Cited by 21 publications

References 0 publications

Physical, Spectroscopic and Theoretical Results

Physical, Spectroscopic and Theoretical Results

Quadruple Metal−Metal Bonds with Strong Donor Ligands. Ultraviolet Photoelectron Spectroscopy of M₂(form)₄ (M = Cr, Mo, W; form = N,N‘-diphenylformamidinate)

Hydrophosphonylation of α‐Haloalkenals

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Intermolecular influences on M-M multiple bonds from thin-film UPS studies of Group VI M2(O2CCH3)4 complexes

Cited by 21 publications

References 0 publications

Physical, Spectroscopic and Theoretical Results

Physical, Spectroscopic and Theoretical Results

Quadruple Metal−Metal Bonds with Strong Donor Ligands. Ultraviolet Photoelectron Spectroscopy of M2(form)4 (M = Cr, Mo, W; form = N,N‘-diphenylformamidinate)

Hydrophosphonylation of α‐Haloalkenals

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Quadruple Metal−Metal Bonds with Strong Donor Ligands. Ultraviolet Photoelectron Spectroscopy of M₂(form)₄ (M = Cr, Mo, W; form = N,N‘-diphenylformamidinate)