Lanthanide Contraction within a Series of Asymmetric Dinuclear [Ln₂] Complexes

Abstract

A complete isostructural series of dinuclear asymmetric lanthanide complexes has been synthesized by using the ligand 6-[3-oxo-3-(2-hydroxyphenyl)propionyl]pyridine-2-carboxylic acid (H3L). All complexes have the formula [Ln2(HL)2(H2L)(NO3)(py)(H2O)] (Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), Y (15); py = pyridine). Complexes of La to Yb and Y have been crystallographically characterized to reveal that the two metal ions are encapsulated within two distinct coordination environments of differing size. Whereas one site maintains the coordination number (nine) through the whole series, the other one increases from nine to ten owing to a change in the coordination mode of an NO3(-) ligand. This series offers a unique opportunity to study in detail the lanthanide contraction within complexes of more than one metal. This analysis shows that various representative parameters proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. Slater's model for the atomic radii has been used to extract, from these decays, the shielding constant of 4f electrons. The average of O⋅⋅⋅O distances within the coordination polyhedra shared by both metals and of the Ln⋅⋅⋅Ln separations follow also a quadratic decay, therefore showing that such dependence holds also for parameters that receive the contribution of two lanthanide ions simultaneously. The magnetic behavior has been studied for all nondiamagnetic complexes. It reveals the effect of the spin-orbit coupling and a weak antiferromagnetic interaction between both metals. Photoluminescent studies of all the complexes in the series reveal a single broad emission band in the visible region, which is related to the coordinated ligand. On the other hand, the Nd, Er, and Yb complexes show features in the near-IR region due to metal-based transitions.

Thermodynamic Stability of Heterodimetallic [LnLn′] Complexes: Synthesis and DFT Studies

“…The unit cell contains four asymmetric units, each composed of one metal complex, one pyridinium cation hydrogen atom bonded to the latter, and five lattice pyridine molecules. The complex moiety (Figure ) shows the structure observed consistently for this family of compounds; it is anionic and composed of two Ln III metal ions (one Ce and one Gd) bridged and chelated by three HL 2− ligands. The latter show two opposite orientations with respect to the Ce⋅⋅⋅Gd vector.…”

“…The average of the Ln−O bonds (Table ), <Ln−O>, (O from HL 2− ligands) were 2.524 (Ce) and 2.406 Å (Gd), which gives a ΔO value of 0.12 Å (Figure ). In the previously reported homodimetallic [Ce 2 ] analogue, the <Ce−O> values were 2.524 and 2.481 Å (ΔO=0.043 Å), whereas the corresponding parameters for the [Gd 2 ] derivative were 2.430 and 2.404 Å (ΔO=0.026 Å) . The intermetallic Ce⋅⋅⋅Gd separation was 3.8780(3) Å, compared with 3.9286(5) and 3.8038(11) Å for the [Ce 2 ] and [Gd 2 ] compounds, respectively.…”

“… Plot of <Ln−O> values for various (Hpy)[Ln 2 (HL) 3 (NO 3 )(py)(H 2 O)] complexes (Ln=La, Ce, Pr, Sm, Gd, Er, Yb), together with the values for 1 ([LaEr]), 2 ([CeEr]), 3 ([CeGd]), 4 ([PrSm]), and 5 ([LaYb]). Red and black symbols are values for the large and small positions, respectively (Ln1 and Ln2 in Scheme ).…”

“…[33] We previously reported an exhaustive, quasi-isostructural series of homometallic dinuclear lanthanide complexes with the formula (Hpy)[Ln 2 (HL) 3 (NO 3 )(py)(H 2 O)] from the asymmetric ligand H 3 L( H 3 L = 6-(3-oxo-3-(2-hydroxyphenyl)propionyl)pyridine-2-carboxylic acid, py = pyridine;S cheme 1). [34][35] Within these molecules, each metal exhibits ac ompletely distinct coordination environment. Ac omprehensive structural analysisc learly shows the expected contraction as the Ln atomic number increases across the series.…”

Luminescence, magnetocaloric effect and single-molecule magnet behavior in lanthanide complexes based on a tridentate ligand derived from 8-hydroxyquinoline

“…The magnetic susceptibilities of complexes 26 were measured on powder samples in an applied magnetic field of 1000 Oe over the temperature range 2300 K. The χ M T vs T (χ M being the molar magnetic susceptibility) and χ M 1 vs T are shown in Fig. 26 As the temperature decreases, the χ M T value decreases slowly and almost remains constant until ca. S8 (ESI).…”