Theoretical Study of Tungsten Carbonyl Complexes (n = 1−6):  Structures, Binding Energies, and Implications for Gas Phase Reactivities

Abstract

The electronic structure and geometry of (n = 1−6) have been studied at the B3LYP and ab initio levels. We find that the ground state of W(CO)+ is linear with a sextet spin state, that a linear sextet and a bent quartet are nearly degenerate for and that doublet states are unambiguously the ground states of to Successive (CO) n -1W+−CO binding energies have been computed to be larger than any of those previously determined for other transition metals. We compare our results with available experimental data. Electron transfers are very important: (i) σ donation from the CO's to the metal is found to be more favorable when involving 5d rather than 6p leading to a preference for the bent rather than linear structures for (n = 2−4); (ii) π back-donation plays a crucial role in shaping these molecules. These effects provide the driving force for the spin changes as the number of ligands increases. Spin lowering is associated with an increasing number of doubly rather than singly occupied 5dπ metal orbitals, which enhances the back-donation ability while reducing the repulsion between σ metal electrons and CO lone pairs. On the basis of our results, we propose an interpretation of the observed differences in gas phase reactivity of with small hydrocarbons as a function of n. The rationale for this interpretation is that the initially formed (CO) n W+−(hydrocarbon) complex should either have a ground or a low-lying excited state bearing at least two unpaired electrons on the metal to be able to further activate the hydrocarbon efficiently.

Potential Energy Surfaces for Mo + CO and W + CO

“…We have calculated the equilibrium distances of 5 Table 5 shows the equilibrium geometries, spectroscopic properties, and the energy separations of the low-lying electronic states of W-CO at both CASMCSCF and MRSDCI levels. As seen from this table as well as Figure 2, although the 7 Σ + , 5 Φ, a The distance between Mo and C is 8.00 Å. b,c Relative energy at the dissociation limit from (4d 4 5s 2 )a 3 P to (4d 4 5s 2 )a 3 H. 15 has considered the ground states of cations of tungsten carbonyl complexes such as W(CO) + n (n ) 1-6) at the ab initio level without inclusion of spin-orbit coupling. For WCO + , 6 Σ + was found to be the ground state, 4 Φ was the first excited state.…”

“…Investigation of such complexes and their properties could aid not only in our comprehension of catalysis and chemisorption but also in the area of organic chemistry and biochemistry, because those complexes play an important role in these areas, too. − The Mo−CO system has been employed as an oxidation and sulfidation agent and has thus attracted great attention. , Synthesis, structure, and properties of these complexes have been the topic of several studies. − Tungsten carbonyl species such as W(CO) 2 have been characterized by using the ultraviolet photoreduction method . The ground state of W(CO) + n ( n = 1−6) species have been studied theoretically at the ab initio level . Tungsten clusters such as W 3 clusters have been considered in our laboratory …”

“…14 The ground state of W(CO) + n (n ) 1-6) species have been studied theoretically at the ab initio level. 15 Tungsten clusters such as W 3 clusters have been considered in our laboratory. 16 In addition to the above applications, the study of the potential energy surfaces of MoCO and WCO could aid in our comprehension of atop chemisorption of CO on W and Mo surfaces.…”

Competition between agostic WCH2+ and HWCH+: A joint experimental and theoretical study

“…12 Based on a theoretical study, we suggested a simple correlation between the electronic structure of the W ϩ ͑CO͒ n ions and their reactivity towards simple hydrocarbons. 13 This paper is part of a current work on the control of W ϩ reactivity towards small molecules using both experimental and theoretical approaches. Here, we essentially focus on ͓W,C,2H͔ ϩ , the primary product of methane dehydrogena-tion by W ϩ .…”

Temperature Effects in Transition Metal Ion and Cluster Ion Reactions

“…7,17 A further advantage of such systems as opposed to the bulk is that a collision complex of a metal ion or ion cluster with the reactant species is sometimes sufficiently simple to be successfully modeled by theoretical ab initio calculations. [18][19][20][21][22][23] Often overlooked in mass spectroscopic studies is the fact that even though the ions and ion clusters may initially be prepared translationally and internally cold, and the reactant pressure can be carefully measured and calibrated, in reality the effective internal temperature of a cluster-reactant collision complex in which the actual reaction takes place is usually not known, and not readily accessible to experimental measurement. This problem is particularly severe in FT-ICR work, where the collision rates (0.01-1 s -1 ) are some 7-10 orders of magnitude lower than for instance in guided ion beam or drift tube experiments.…”