Molecular mechanics of low bond order interactions in tetrakis(carboxylato)dimetal systems

Boeyens, Jan C. A.; Cotton, F. Albert; Han, SangHyeok

doi:10.1021/ic00206a007

Cited by 32 publications

(86 citation statements)

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“…The W-C axial bonds do not form in direct competition with the W-W -bond (as would normally be expected) because considerable 6s (and even some 6p) character is introduced. The molecular orbital mainly responsible for W-W bonding in W 2 (O 2 CR) 4 is scarcely affected by the axial ligation in this case.…”

Section: Axial Ligandsmentioning

confidence: 83%

“…There are, however, many homologous pairs that exhibit considerable similarity, viz. the M 2 (mhp) 4 One generalization that clearly emerges from all of the above facts is that for the dinuclear species as well as for the conventional mononuclear complexes, higher oxidation states are favored for the third transition series as compared to the second. Among the reasons for this is the much greater magnitude of relativistic effects on ionization energies and spin-orbit coupling in the third series atoms.…”

Section: Comparison Of Second and Third Transition Series Homologsmentioning

confidence: 88%

“…The fact that the strength of the -bond is greatest for = 0 does not necessarily mean that this is the preferred angle when all factors are taken into account, however. The bond is a relatively weak one, and the minimization of nonbonded repulsions, operating between the sets of ligands at the two ends of an L 4 M ML 4 unit, may favor a rotation away from the eclipsed ( = 0) conformation. The value of where these two forces are balanced may be expected, in general, to be other than zero.…”

Section: Internal Rotationmentioning

confidence: 99%

“…More recently, DFT calculations have been reported on Mo 2 Cl 4 (PH 3 ) 4 type molecules, both the 1,3,6,8 and 1,2,7,8 isomers. [14][15][16] While such calculations are less rigorous electronically, they have the advantage of allowing for structural relaxation.…”

Section: Internal Rotationmentioning

confidence: 99%

“…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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confidence: 99%

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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: Axial Ligandsmentioning

confidence: 83%

Section: Comparison Of Second and Third Transition Series Homologsmentioning

confidence: 88%

Section: Internal Rotationmentioning

confidence: 99%