Evidence for Participation of 4f and 5d Orbitals in Lanthanide Metal–Ligand Bonding and That Y(III) Has Less of This Complex-Stabilizing Ability. A Thermodynamic, Spectroscopic, and DFT Study of Their Complexation by the Nitrogen Donor Ligand TPEN

Abstract

The formation constants (log K 1 ) of lanthanide(III) (Ln) ions [except for Pm(III)] and the Y(III) cation have been measured with the ligand TPEN (N,N,N′,N′-tetra-2-picolylethylenediamine). These log K 1 values show a typical variation with ionic radius, with a local maximum at Sm(III) and a local minimum at Gd(III), with an overall increase in log K 1 from La(III) to Lu(III) as the ionic radius decreases. The log K 1 for the Y(III)/TPEN complex is much lower than expected from its ionic radius, while the literature log K 1 for Am(III) is much higher. The latter effect is thought to be due to greater covalence in the M−L (metal−ligand) bond than for Ln(III) ions: the low log K 1 for Y(III) is interpreted as being due to lower covalence. The f → f transitions in the Nd(III) and Pr(III) complexes were examined for effects that might indicate the participation of f orbitals in M−L bonding. The intensity of the f → f transitions in the Nd(III)/TPEN complex was greatly increased compared to that of the Nd 3+ aqua ion, which appeared to be due to additional sharp peaks, possibly parity forbidden transitions where parity rules were broken by covalence in the M−L bond. The Pr(III)/TPEN complex showed that all of the f → f transitions shifted to longer wavelengths by some 5 nm, with modest increases in intensity. The effects seen in the f → f transitions of Nd(III) and Pr(III) with TPEN with its six nitrogen donors were present to a much smaller extent in the EDTA and other complexes with fewer nitrogen donors. The changes in the f → f transitions of the TPEN complexes of Er(III) and Ho(III) were small, suggesting a smaller contribution of f orbitals to M−L bonding in these heavier Ln(III) ions. The intense Laporte allowed f → d transitions in Ce(III) complexes show large shifts to longer wavelengths as complexes of, for example, EDTA with increasing numbers of nitrogen donors, suggesting the participation of both f and d orbitals, or either, in M−L bonding. The nature of M−L bonding in M(III)/TPEN complexes was further investigated via density functional theory calculations.

Overlooked Effects of La-4f Orbitals in Endohedral Metallofullerenes

“…Recently, the covalency in the lanthanide bonding and the non-negligible contribution of 4f orbitals in the bonding have attracted more attention. − Different from the traditional view of lanthanides mainly forming ionic bonds, advanced spectral measurements indicate that they also can engage in covalent bonding interactions. The covalency of bonds is enhanced by the large orbital overlap and small energy difference between the metal and ligand orbitals.…”

Lanthanide Complexes (Ln=La, Nd, Dy) of Octaethyl propane‐1,1,3,3‐tetrayltetrakis(phosphonate): Multidentate Binding Competing with Monodentate DMSO Complexes

“…Moreover, it is recognized that metal‐ligand covalency can also contribute to a 4f shell splitting of lanthanides [9] . In this respect, Hancock & Lee also recently found evidence for the participation of 4f and 5d orbitals in lanthanide metal‐ligand bonding [10] . Organic chromophore‐supported lanthanide complexes show interesting PL properties due to an enhancement of the f‐f‐transition luminescence through chemical bonding via photo‐excitation of the ligand moiety (photo‐antenna effect), while the sharp metal‐centered emission bands usually occur at the same wavelengths even in case of altered ligand backbones.…”

“…[9] In this respect, Hancock & Lee also recently found evidence for the participation of 4f and 5d orbitals in lanthanide metal-ligand bonding. [10] Organic chromophore-supported lanthanide complexes show interesting PL properties due to an enhancement of the f-f-transition luminescence through chemical bonding via photo-excitation of the ligand moiety (photo-antenna effect), while the sharp metal-centered emission bands usually occur at the same wavelengths even in case of altered ligand backbones. The ligand platform functions as an energy donor resulting in the overlap of the PL band of the ligand and absorption of the f-f transition for an efficient intramolecular energy transfer.…”

Conductive MOF on ZIF-Derived Carbon Fibers as Superior Anode in Sodium-Ion Battery

“…Herein, a new cMOF is designed and fabricated with Nd (Ln atom) and 2,3,6,7,10,11-hexaaminotriphenylene (HATP) as the building block. The f-orbitals of Ln atoms participate in bonding and electronic delocalization − to enhance the electronic conductivity (delocalization and itinerant of electrons improving the conductivity) and stability. , The cMOF is prepared on the surface of ZIF-CFs with ample and flexible pores to produce Nd-hierarchical cMOF/ZIF-CFs (Figure A). ZIF-1, ZIF-3, ZIF-10, and ZIF-70 with pore diameters of 0.69, 0.82, 1.2, and 1.4 nm are mixed individually with polyacrylonitrile (PAN) to fabricate ZIF-derived carbon fibers denoted as Nd-cMOF/ZIF-1-CF, Nd-cMOF/ZIF-3-CF, Nd-cMOF/ZIF-10-CF, and Nd-cMOF/ZIF-70-CF.…”