Mononuclear Lanthanide(III)-Salicylideneaniline Complexes: Synthetic, Structural, Spectroscopic, and Magnetic Studies

Abstract

The reactions of hydrated lanthanide(III) [Ln(III)] nitrates and salicylideneaniline (salanH) have provided access to two families of mononuclear complexes depending on the reaction solvent used. In MeCN, the products are [Ln(NO3)3(salanH)2(H2O)]·MeCN, and, in MeOH, the products are [Ln(NO3)3(salanH)2(MeOH)]·(salanH). The complexes within each family are proven to be isomorphous. The structures of complexes [Ln(NO3)3(salanH)2(H2O)]·MeCN (Ln = Eu, 4·MeCN_Eu, Ln = Dy, 7·MeCN_Dy; Ln = Yb, 10·MeCN_Yb) and [Ln(NO3)3(salanH)2(MeOH)]·(salanH) (Ln = Tb, 17_Tb; Ln = Dy, 18_Dy) have been solved by single-crystal X-ray crystallography. In the five complexes, the LnIII center is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms from the two monodentate zwitterionic salanH ligands, and one oxygen atom from the coordinated H2O or MeOH group. The salanH ligands are mutually “cis” in 4·MeCN_Eu, 7·MeCN_Dy and 10·MeCN_Yb while they are “trans” in 17_Tb and 18_Dy. The lattice salanH molecule in 17_Tb and 18_Dy is also in its zwitterionic form with the acidic H atom being clearly located on the imine nitrogen atom. The coordination polyhedra defined by the nine oxygen donor atoms can be described as spherical tricapped trigonal prisms in 4·MeCN_Eu, 7·MeCN_Dy, and 10·MeCN_Yb and as spherical capped square antiprisms in 17_Tb and 18_Dy. Various intermolecular interactions build the crystal structures, which are completely different in the members of the two families. Solid-state IR data of the complexes are discussed in terms of their structural features. 1H NMR data for the diamagnetic Y(III) complexes provide strong evidence that the compounds decompose in DMSO by releasing the coordinated salanH ligands. The solid complexes emit green light upon excitation at 360 nm (room temperature) or 405 nm (room temperature). The emission is ligand-based. The solid Pr(III), Nd(III), Sm(III), Er(III), and Yb(III) complexes of both families exhibit LnIII-centered emission in the near-IR region of the electromagnetic spectrum, but there is probably no efficient salanH→LnIII energy transfer responsible for this emission. Detailed magnetic studies reveal that complexes 7·MeCN_Dy, 17_Tb and 18_Dy show field-induced slow magnetic relaxation while complex [Tb(NO3)3(salanH)2(H2O)]·MeCN (6·MeCN_Tb) does not display such properties. The values of the effective energy barrier for magnetization reversal are 13.1 cm−1 for 7·MeCN_Dy, 14.8 cm−1 for 17_Tb, and 31.0 cm−1 for 18_Dy. The enhanced/improved properties of 17_Tb and 18_Dy, compared to those of 6_Tb and 7_Dy, have been correlated with the different supramolecular structural features of the two families. The molecules [Ln(NO3)3(salanH)2(MeOH)] of complexes 17_Tb and 18_Dy are by far better isolated (allowing for better slow magnetic relaxation properties) than the molecules [Ln(NO3)3(salanH)2(H2O)] in 6·MeCN_Tb and 7·MeCN_Dy. The perspectives of the present initial studies in the Ln(III)/salanH chemistry are discussed.

Filling Tricompartmental Ligands with GdIII and ZnII Ions: Some Structural and MRI Studies

“…Consequently, only some doubt could remain about the nature of the solvent molecule coordinated to the gadolinium(III) ion, which could be methanol or water, as proposed in (Scheme 2). A similar coincidence between cell parameters exist for the already mentioned isostructural compounds [Ln(H 3 L )(NO 3 )(H 2 O)](NO 3 ) 2 •complexes (Ln = Gd, Tb, Dy, Er) [16], and for other isostructural series even with different solvated molecules [48].…”

Diversity of Coordination Modes in a Flexible Ditopic Ligand Containing 2-Pyridyl, Carbonyl and Hydrazone Functionalities: Mononuclear and Dinuclear Cobalt(III) Complexes, and Tetranuclear Copper(II) and Nickel(II) Clusters

“…The absence of bands that would be indicative of the monodentate and bidentate coordinated nitrato groups (present in the structure of the cluster) is rather surprising. This suggests [29,30] that the nitrato ligands are replaced by bromides that are in excess in the KBr matrix, thus producing ionic nitrates (KNO 3 ); this replacement is facilitated by the pressure that is applied for the preparation of the KBr matrix. As expected, extra nitrato bands appear in the mull (nujol, hexachlorobutadiene) spectra of 2.…”

“…As expected, extra nitrato bands appear in the mull (nujol, hexachlorobutadiene) spectra of 2. For example, the bands at 1501 and 1300 cm −1 are assigned [28][29][30]…”

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies

“…For a given bond, the Ln-O/N bond lengths follow the Nd>Dy order ( Table 1 ) due to lanthanide contraction; this trend is also observed for the Ln III… Ln III distances. The Ln-O/N bond lengths in 1 and 5 are typical for 9-coordinate Nd(III) [ 33 , 56 , 57 ] and Dy(III) [ 35 , 38 , 41 , 54 , 58 , 59 , 60 , 61 , 62 ]. The Ln1/Ln1′ coordination geometry was evaluated using the program SHAPE [ 61 , 63 ] and is best described as muffin-type ( Figure S1, Table S2 ); an alternative description of the polyhedron could be that of a spherical-capped square antiprism.…”

“…Ln III distances. The Ln-O/N bond lengths in 1 and 5 are typical for 9-coordinate Nd(III) [33,56,57] and Dy(III) [35,38,41,54,[58][59][60][61][62]. The Ln1/Ln1 coordination geometry was evaluated using the program SHAPE [61,63] and is best described as muffin-type (Figure S1, Table S2); an alternative description of the polyhedron could be that of a spherical-capped square antiprism.…”