Bonding in lanthanide complexes

The lack of spatial extension of the 4f orbitals means that they are not available to overlap with orbitals of surrounding Ugands unlike the d-block metals where the d orbitals form the boimdary smface of the ions Lanthanides Comparison to 3d Metals ). Thus covalent bonding in lanthanide complexes in their normal oxidation states does not occm to any significant extent except in zero-valent organometallic complexes with aromatic hydrocarbons. Thus the vast majority of complexes (see Lanthanides Coordination Chemistry) are bonded by ionic/electrostatic interactions with little to no covalent interaction between the metal and bound hgands. 

Lanthanides form soluble complexes with many inorganic and organic substances however, the nature of the bonding in these complexes has not been completely determined. There is evidence for either ionic or covalent bond formation or a combination of both. Lanthanides are complexed by inorganic ions, but not as readily as are the transition elements. The inorganic complexes are not as important... 

See for further literature dealing with the ionic /covalent bonding behavior in lanthanide complexes a) Jorgensen CK, Pappalardo R, Schmidtke H-H (1963) J Chem Phys 39 1422 b) Katzin LI, Barnett ML (1964) J Phys Chem 68 3779 c) Burns CJ, Bursten BE (1989) Comments Inorg Chem 9 61... 

In lanthanide complexes, the Ln ions are hard Lewis acids, which prefer to coordinate hard bases, such as F, O, N ligands. The f-orbitals are not involved to a significant extent in M-L bonds, so their interaction with ligands is almost electrostatic in nature. Table 18.3.1 lists some examples of the various coordination... 

The first lanthanide-NHC complexes were isolated by Arduengo and coworkers in 1994.62 A stable carbene displaces THF in bis(pentamethylcy-clopentadienyl)-samarium-THF to form the samarium(II)-NHC complex 55 (Scheme 29). The addition of a second equivalent of NHC resulted in the isolation of the bis(NHC) adduct 56. Compound 56 was characterised in the solid state by single crystal X-ray diffraction and exhibits samarium-NHC bond distances of 2.837(7) A and 2.845(7) A, which are longer than the M-C bond in a-bonded alkyl lanthanide complexes. 

Lanthanide-EDTA and lanthanide-NTA complexes, where Ln = Nd, Ho, Er at various Ln L ratios in a broad pH range were studied by spectroscopy. Analysis of the data on oscillator strengths and 7 parameters provided some clues on the nature of bonding in these complexes. Further 7) and T(> parameters showed a dependence on the ligand concentration. However, these studies could identify only one species [Nd(NTA)2]3 in solution [260]. 

The addition of alkanes to Ir111 species such as [CpIr(Me)L]+ can proceed via two pathways, oxidative addition (A) or or-bond metathesis akin to that in lanthanide complexes (B). 

Zinc tetraphenylporphyrinate forms a weak complex with Of in non-aqueous solutions. The bonding in this complex appears to be essentially ionic . We have already mentioned crystal structure determinations of lanthanide and actinide compounds. There is every reason to suppose that these elements have a rich dioxygen complex chemistry and this is confirmed by two recent papers For reasons of space, however, we shall not discuss the dioxygen complex chemistry of these elements. 

A connectivity of 1 is given for side chain metal-containing polymers as 1 in which the metal complex is connected via one bond to the main chain [11]. Additional examples for other connectivities are (Fig. 1-8) connectivity 2 in metal(yne)s 2 [12] connectivity 3 in arsenic(III) sulfide 3 connectivity 4 in a polymeric methyl rhenium oxide of the formula Ho.5[(CH3)o.92Re03] co 4 [13] or polymeric phthalocyanines 5 [14] connectivity 8 in lanthanide complexes of bis(tetradendate) Schiff base bridging ligands 6 [15]. 

The lanthanides and actinides form complexes with planar cyclic C R organic species. Use Fig. 11.4 together with Fig. 10.3 to detail how the bonding in such complexes might be expected to differ from those of the corresponding transition metal complexes. 

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