Bond energy-bond order relations in transition-metal bonds: vanadium

Abstract

orbitals is also consistent with the strong -accepting character of PF3. PRDDO calculations on the model complex Cr(N-H3)5(PF3) yield Cr d-orbital populations of 1.74 e for dxz and dyz and 1.98 e for dxy. The enhanced depopulation of the d, orbitals in this complex relative to Cr(NH3)5(PH3) demonstrates the greater -accepting ability of PF3 relative to PH3 even without d orbitals on phosphorus. There are several reasons for the enhanced -accepting ability via a* orbitals of PF3 compared to PH3 and PH3 relative to NH3. First, highly polar bonds, such as those between phosphorus and fluorine, characteristically have low-lying cr* orbitals and are thus better acceptors. Similarly, the P-H * orbitals in PH3 lie at lower energies than those of NH3.17 Second, because the P-F bond is highly polar toward F, the * orbital must necessarily be highly polar toward P, therefore increasing the CT*-metal d" overlap. The second argument also holds to a lesser extent for P-H as compared to N-H bonds: e.g., the N-H * orbital will be polar toward H and therefore not overlap well with the metal. Finally, the phosphine * orbitals are composed of 3s and 3p orbitals, which overlap more effectively with metal 3d orbitals than the 2s and 2p orbitals utilized by amines.Of course, a quantitative calculation of the -accepting ability of ligands such as PF3 will probably require d orbitals, but our results show that d orbitals on phosphorus are not necessary for a qualitative understanding of back-bonding effects in these systems.

Reaction of Sc+, Ti+, and V+ with CO. MC+ and MO+ bond energies

“…6 In general, the agreement of the thermochemistry obtained here with previous work ensures that the thresholds determined for reactions (3) and (4) represent the true thermodynamic limit.…”

“…Although the analysis becomes more speculative, further progress in understanding the anomalous cross-section shapes for Sc + in processes (3) and (4) can be made. As shown in Fig.…”

“…2 Aristov and Armentrout (AA) previously reported preliminary thermochemical results measured from the V + + CO system. 3 They cited values of DO(VO+) = 5.68 ± 0.22eVandDo(VC+) = 3.82 ± 0.22 eV. The former value is somewhat lower than both DO(VO+) = 6.00 ± 0.35 eV determined by collision-induced dissociation, 4 and the most precise value, DO(VO+) = 5.99 ± 0.10, obtained by using Eq.…”

“…Only in the case of VO + have such direct measurements of the metal-oxide bond energy been made previously. 3,4 These reaction systems also provide bond energies for the ionic metal carbides, species for which thermochemistry is scarce. The thermochemistry of such metal-carbide and -oxide species is of interest due to its importance to organometallic and atmosphericS chemistry, and in understanding corrosion processes.…”

Communication: State-to-state photoionization and photoelectron study of vanadium methylidyne radical (VCH)

“…We note that a value of 4.94 ± 0.09 eV for D 0 (V + -CH) was obtained in a previous collision-induced ion dissociation study. 19 The experimental apparatus and procedures used are similar to those reported previously. [12][13][14][15] Cold VCH molecules in the form of a pulsed supersonic beam (30 Hz) were prepared by using a laser ablation beam source.…”