Ytterbocene Charge-Transfer Molecular Wire Complexes

Abstract

A systematic study of the novel charge-transfer [(f)14-(pi)0-(f)14 --> (f)13-(pi)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp)2Yb](BL)[Yb(Cp)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6',6' '-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb-Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(pi)2-(f)13], cationic [(f)13-(pi)1-(f)13] and dicationic [(f)13-(pi)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(pi)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1-3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by pi-pi and pi-pi transitions, masking the f-f bands that are expected to best reflect the electronic metal-metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of pi electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(alpha)(alphabeta)Yb(beta) at approximately 13 K.

Comparative Study of f-Element Electronic Structure across a Series of Multimetallic Actinide and Lanthanoid-Actinide Complexes Possessing Redox-Active Bridging Ligands

“…33 As discussed above, the synthesis of (C 5 that in 13 (~7.6 Å). 40,41 A calculated comproportionation constant of K c ≈ 10 8.5 from this wave spacing illustrates the stability of the singly reduced species [8] -. 16 Evaluation of complexes where M = Sm or La (Scheme 1) provided additional observations.…”

“…This latter system, even with occupied π* orbitals on the tpy moieties, shows no measurable splitting of the lanthanide-based reduction waves. 41 Comparison of the lanthanum and lanthanide congeners with the heterotrimetallic U III -Th IV -U III complex 7a and homotrimetallic U III -U IV -U III complex 7b allows for assessment of the 4f-5f-4f vs. 5f-5f-5f mixed-valencies. As shown in Figure 6B, differences between these systems are immediately apparent on evaluation of their cyclic voltammograms.…”

Thermal Dihydrogen Elimination from Cp*2Yb(4,5-diazafluorene)

“…On the other hand, the spectrum from 2 displays only a set of three low intensity, yet relatively sharp, bands in the same range that are characteristic of f 13 f f transitions. 5,14,19 The disappearance of the band with a maximum at 909 nm was used to follow the time dependence and therefore the rate of reaction because it is a signature of the presence of unpaired spin 8 density in the ligand in 1 and 3 and is situated in the range in which 2 does not absorb.…”

Compounds based on cluster anion [Re4Te4(CN)12]4−, Ln3+ cations (Ln = Gd, Tb, Dy, Ho, Er) and 4,4′-bipyridine: Synthesis, structure and properties

“…This ligand was chosen as possible bridging N-donor ligand to connect lanthanide atoms and obtain coordination polymers. Analysis of literature data showed that 4,4 0 -bipyridine capable to coordinate rare-earth cations in aqueous solutions in terminal [18][19][20][21][22] and in bridging position [23][24][25][26][27]. Evaporation of reaction mixture, containing LnCl 3 and 4,4 0 -bipy in neutral and slightly acidic media resulted in precipitation of amorphous products of variable composition.…”