Octacarbonyl Anion Complexes of the Late Lanthanides Ln(CO)₈⁻ (Ln=Tm, Yb, Lu) and the 32‐Electron Rule

Abstract

The lanthanide octacarbonyl anion complexes Ln(CO) 8 À (Ln = Tm, Yb, Lu) were produced in the gas phase and detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching-frequency region. By comparison of the experimental CO-stretching frequencies with calculated data, which are strongly redshifted with respectt of ree CO, the Yb(CO) 8 À and Lu(CO) 8 À complexes were determined to possess octahedral (O h ) symmetry and ad oublet X 2 A 2u (Yb) and singlet X 1 A 1g (Lu) electronic ground state, whereas Tm(CO) 8 À exhibits a D 4h equilibrium geometry and at riplet X 3 B 1g ground state. The analysis of the electronic structures revealed that the metal-CO attractivef orces come mainly from covalent orbital interactions, which are dominated by [Ln(d)]!(CO) 8 p backdonation and [Ln(d)]! (CO) 8 s donation (contributes % 77 and 16 %t oc ovalent bonding, respectively). The metal fo rbitals play av ery minor role in the bonding. The electronic structure of all three lanthanide complexes obeys the 32-electronr ule if only those electrons that occupy the valence orbitals of the metal are considered.[a] J.

Octacarbonyl Ion Complexes of Actinides [An(CO)8]+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding

“…This becomeso bviousf rom the visual inspection of the deformationd ensities and the associated fragment orbital, which are shown below.T he contribution of the uranium 5f AOs to the UÀCO bonds in [U(CO) 8 ] q is much higher than that of the 4f AOs of the lanthanide atoms in [Ln(CO) 8 ] À (Ln = Tm, Yb, Lu), which amount to < 4% of the LnÀCO bondingo rbitals. [10] The EDA-NOCV resultso fT able 3s uggest that the contribution of the uranium valence orbitals possess the trend 6d @ 5f> 7s % 7p. We want to point out that the DE orb values do not only come from genuine orbital interactions between the fragments, they also include intrafragmentp olarization.A previouss tudy of transition metal hexacarbonyls [TM(CO) 6 ] q (TM q = Hf 2À ,T a À ,W ,R e + ,O s 2 + ,I r 3 + )s howedt hat the contribution by polarization is rather small.…”

“…The EDA-NOCV methodi sw ell suited for this, because it uses the electronic structure of the molecules for an unbiased analysiso ft he pairwise orbitali nteractions without referring to ar eference system.This has been found very useful in our previous studies of metal octacarbonyl complexes of main-group atoms, [17] transition metals, [16] and late-lanthanide elements. [10] Af ocus of the present work lies on the contribution of the 5f orbitals of the metals to the metal-COb onds. Our previous bonding analysis of the lanthanide octacarbonyl anions [Ln(CO) 8 ] À (Ln = Tm, Yb, Lu) showed that the 4f orbitals of the Ln atoms provide < 4% of the total orbital interactions of the Ln À ÀCO bonds.…”

“…CO s donation, which account for > 90 %o ft he orbitali nteraction. [10] It is interesting to compare these resultsw ith the presents tudy of the octacarbonylc omplexes of the 5f elements thorium and uranium.…”

“…Splitting of the 5f,6d, 7s, and 7p valence orbitals of uranium in the cubic (O h )f ield of eight CO ligands andinteractions with the 5s and 2p* valenceMOs of (CO) 8 .The e g orbital is fully occupied (n = 1) in the quartet ( 4 A 1g )stateofthe anion[ U(CO) 8 ] À .Itiso ccupied with two unpairede lectrons (n = 0) in the sextet ( 6 A 8 ] À (Ln = Tm, Yb, Lu), in which the metal d-orbital interactions account for > 90 %o ft he metal-AO contribution to the covalentbonding. [10] Ta ble 3s hows that the orbitali nteractions that come from the [U(f)] q ! (CO) 8 p backdonation and the [U(f)] q !…”

“…In ar ecent analysis of octacarbonyl anion complexes of the late lanthanides [Ln(CO) 8 ] À (Ln = Tm, Yb, Lu), we found that the 32-electronr ule is valid in the systems that have 32-34 valence electrons when the symmetry of the orbitals is considered. [10] The energy contributiono ft he fe lectrons and the acceptors trength of the vacant fo rbitals were found to be very small. The analysiso f the electronic structures revealed that the metal-COb onding interactions in the [Ln(CO) 8 ] À anion complexes are dominated by [Ln(d)]!…”