The affinity and selectivity of terdentate nitrogen ligands towards trivalent lanthanide and uranium ions viewed from the crystal structures of the 1 ∶ 3 complexes

Abstract

Treatment of LnI 3 (Ln = La, Ce) or [UI 3 (py) 4 ] with 3 equivalents of terpy in acetonitrile gave the tris(terpy) complexes [M(terpy) 3 ]I 3 . Addition of 3 equivalents of Rbtp (2,2,pyridine) to MX 3 (X = I or OSO 2 CF 3 ) in pyridine or acetonitrile afforded the tris(Rbtp) compounds [M(Rbtp) 3 ]X 3 . By comparison with terpy, the Rbtp ligand has a better affinity for the 4f and 5f ions and is more selective for U() than for Ce() or La(). This trend has been revealed by 1 H NMR competition experiments and X-ray crystallographic studies which show that in the [M(terpy) 3 ] 3ϩ and [M(Rbtp) 3 ] 3ϩ cations, the M-N(Rbtp) bond lengths are shorter than the M-N(terpy) bond lengths, and the U-N bond lengths are shorter than the corresponding Ce-N or La-N bond distances. DALTON

‘Lanthanide contraction’ in [Ln(BTP)3](CF3SO3)3 complexes

“…complex cations are in good agreement with literature reports on BTP [28], BTP derivative complexes [7,29,30] or complexes with comparable structural motifs arising from ligands which are related to BTP in terms of symmetry and coordination behaviour [5,[31][32][33][34][35][36][37][38][39][40][41][42]. Selected geometrical parameters from our (La, Pr, Nd, Eu) and literature (Sm, Tm, Yb) [28] X-ray studies and from our computations are compared in Table 2.…”

“…The key element in these ligands is the soft donor nitrogen atom in an aromatic environment. From the large number of heterocyclic N-donor extractants tested [4], 2,6-bis([1,2,4]-triazin-3-yl)pyridines (BTPs) proved to be a most effective and convenient option [5]. The main factor for the efficient binding of trivalent actinides likely lies in the smaller steric demands of the [1,2,4]-triazin-3-yl ring with respect to the 2-pyridinyl ring, allowing the nitrogens to approach more closely to the metal.…”

Lanthanide(III)/Actinide(III) Differentiation in the Cerium and Uranium Complexes [M(C5Me5)2(L)]0,+ (L=2,2′‐Bipyridine, 2,2′:6′,2′′‐Terpyridine): Structural, Magnetic, and Reactivity Studies

“…Concomitantly, the N2-U-N2' angle of 131.59 (18)8 is larger than the N2-Ce-N3 angle of 125.1(3)8. The difference of about 0.2 between the CeÀN and UÀN distances in 3 a and 3 b is the greatest so far observed in analogous cerium(iii) and uranium(iii) complexes with aromatic nitrogen bases, [4][5][6] together with that of 0. 3 + [M = Ce, U; Rbtp= 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine].…”

“…3 + [M = Ce, U; Rbtp= 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine]. [5] The UÀN distances in 3 b are in fact intermediate between amido U IV À NR 2 bond lengths, which are typically 2.15-2.30 , [23][24][25] and UÀN(terpy) bond lengths, which average 2.62 and 2.58 in uranium(iii) [4][5][6] and uranium(iv) compounds, [6] respectively. The shortening of the U À N distances in 3 b strongly suggests Bond bipy [22] [Yb(Cp*) 2 (bipy)]…”

“…[13] Such 5f element complexes with azine ligands seem to have been neglected since the reports of the uranium bipyridine compounds [U(bipy) 4 ] [14] and [U(COT)(Cp*)(Me 2 bipy)] (COT = h-C 8 H 8 , Me 2 bipy = 4,4'-dimethyl-2,2'-bipyridine), [15] in which the metal oxidation state is questionable. Following our studies on the differentiation of trivalent lanthanide and uranium ions, especially those concerning the coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium [16,17] and the selective complexation of uranium(iii) over lanthanide(iii) triflates or iodides by bipy, [3] phen [18] and terpy, [4][5][6] we speculated that the distinct electronic behavior of the 4f and 5f ions, in particular the easier oxidation and better p-donating ability of the actinide, should emerge and lead to significant differences in the structures and reactions of the electron-rich complexes [Ce(Cp*) 2 …”