Early Transition Metals Strengthen the B₂Bond in MB₂Complexes

Abstract

The bond dissociation energies of early transition metal diborides (M–B2, M = Sc, Ti, V, Y, Mo) have been measured by observation of the sharp onset of predissociation in a highly congested spectrum. Density functional and CCSD­(T) ab initio calculations, extrapolated to the complete basis set limit, have been used to examine the electronic structure of these species. The computations demonstrate the formation of bonding orbitals between the metal d orbitals and the 1πu bonding orbitals of B2, leading to the transfer of metallic electron density into the bonding 1πu orbitals, strengthening both the M–B and B–B bonds in the molecule. This runs counter to most metal–ligand π interactions, where electron density is generally transferred into π antibonding orbitals of the ligand.

Probing the Chemical Bond between Lanthanides and Carbon: CeC, PrC, NdC, LuC, and TmC2

“…For this reason, we assign the TmC 2 predissociation threshold and Tm–C 2 BDE according to the data from the delayed ionization trace, giving D 0 (Tm–C 2 ) = 38,690 ± 50 cm –1 or 4.797(6) eV. We have similarly found a delayed ionization scheme to be necessary in previous studies of the BDEs of the triatomic transition metal diborides, MB 2 …”

“…We have similarly found a delayed ionization scheme to be necessary in previous studies of the BDEs of the triatomic transition metal diborides, MB 2 . 72 The lowest trace in Figure 5, in red, deserves comment. Our thulium sample had a small amount of tantalum as an impurity, probably because the molten Tm metal had at one time been in contact with a tantalum crucible or mold.…”

“…TmC 2 is a triatomic molecule and naturally has a range of possible isomers for its global minimum geometry. Following the same procedure for our recent work on triatomic MB 2 species, TmC 2 had its global minimum geometry calculated with doublet, quartet, sextet, and octet spin multiplicities and three different chemically reasonable structural isomers: (1) a triangular, cyclic C 2v geometry, (2) a linear geometry where the two carbon atoms are bonded end-on to the Tm atom (Tm–C–C), and (3) a linear geometry where the Tm atom is intercalated between the two carbon atoms (C–Tm–C). All of the geometry optimizations for the elucidation of the TmC 2 global minimum and ground electronic configuration were performed using the unrestricted B3LYP density functional .…”

CrN, CuB, and AuB: A Tale of Two Dissociation Limits

“…15 This is an unavoidable artifact of the R2PI technique. 37 The bottom red trace shows the 158 Gd atomic transitions that were used to calibrate the wavenumber axis. natively, if the threshold in Figure 3 is assigned as AuB predissociating to its first excited SAL of Au* ( 2 D 5/2g , 6s 2 5d 9 ) + B ( 2 P 1/2u , 2s 2 2p 1 ) located 1.136 eV higher in energy than its ground SAL, 15 BDEs of D 0 ( 197 Au 11 B) = 3.725(2) eV and D 0 ( 197 Au 10 B) = 3.723(2) eV are obtained.…”

“…Also observed is a strongly allowed Cu atomic transition at 30,783.697 cm −1 that caused an artificial increase in signal for CuB 15. This is an unavoidable artifact of the R2PI technique 37. The bottom red trace shows the 158 Gd atomic transitions that were used to calibrate the wavenumber axis.…”