Electronic interaction of ligands with carbonyl groups in transition-metal complexes of the types LMn(CO)5 and LMo(CO)5

Abstract

The Mn 2p3/*, C Is, and 0 1s binding energies of LMn(C0)5 compounds are linearly related to each other and to the inductive constant uI and the Pauling electronegativity xp of the group L. The binding energies show little correlation with the mesomeric constant uRo. Apparently only the u-donor ability of L is important in determining the degree of back-bonding to the CO groups in LMn(C0)5. The Mo 3d5/,, C Is, and 0 1s binding energies of LMO(CO)~ compounds (L = PX3 or CO) are linearly related to each other and to the phosphorus lone-pair ionization potential of the free PX3.The data indicate that both the u-donor and ?r-acceptor abilities of PX3 are important in determining the degree of back-bonding to the CO groups in X3PMo(CO)5. The *-acceptor ability of PF3 appears to be slightly greater than that of CO. IntroductionIn recent years much attention has been given to the electronic interaction of various ligands, L, with carbonyl groups in transition-metal complexes of the type L,M(CO),.l-lo No general consensus has been reached regarding the nature of the interaction. Thus, the influence of the group L on the C-O stretching force constants has been variously explainedentirely in terms of the a-acceptor character of L,3*4 entirely in terms of the a-donor character of L,5,6 and in terms of both the a-acceptor and a-donor characters of L.132*7- 9 We have used X-ray photoelectron spectroscopy to study the problem because this technique yields information not readily obtained by any other method-that is, information about the charges of individual atoms in compounds. It has been previously shown that the carbon 1s and oxygen 1s binding energies of a carbonyl group are a good measure of the d v a * back-bonding to the carbonyl group."J2 We restricted this study to volatile LM(C0)5 compounds of manganese and molybdenum and determined gas-phase core binding energies of the metal, carbon, and oxygen atoms, as well as of the atoms in the ligands L. Only three of the 20 compounds we studied have been previously studied by other workers as gases by using X-ray photoelectron spectrosco-

Discrete trinuclear complexes of niobium and tantalum related to the local structure in niobium chloride, Nb3Cl8

“…Standard crystallographic procedures were used. 5 Lorentz and polarization corrections were applied. Empirical absorption correction based upon azimuthal scans was applied in the case of the Nb-PMe2Ph and Ta-PEt3 structures.…”

Core level photoelectron spectroscopy for polymer and catalyst characterisation

“…The potential application of ESCA to catalysis involving metal containing compounds has been known for quite some time. 25,26 Application was demonstrated to both homogeneous and heterogeneous catalysis. Correlations between acidity/basicity and XPS shifts have been reported.…”

The partnership of gas-phase core and valence photoelectron spectroscopy

“…XPS is similarly plagued by the bugaboo of relaxation energy, although one can approximately correct for the effects of this energy by restricting study to sets of similar molecules that presumably have similar relaxation energies or by actually calculating the relaxation energies. 3,4 But even when relaxation energies are corrected for, attempts to interpret core binding energies in terms of atomic charges are beset with the fundamental difficulty of defining atomic charge and the problems of dealing with lone-pair electrons. 5 Of course, both UPS and XPS have proved to be useful analytical techniques, UPS being used to detect molecules on the basis of spectral "fingerprints",6 and XPS being used to detect atoms on the basis of characteristic binding energies.7 Because of the "surface sensitivity" of these techniques (due to energy loss by scattering of photoelectrons emitted below the surfaces of solids), they are widely used as analytical probes of solid surfaces and of species absorbed on solid surfaces.…”