Aldo Giorgetti

Complexes of lanthanoid salts with macrocyclic ligands. Part 25. Lanthanoid trifluoroacetate complexes with 12-crown-4, 15-crown-5, and 18-crown-6 ethers

Abstract The lanthanoid trifluoroacetates, Ln(TFA)3, react with 12-crown-4, 15-crown-5, and 18-crown-6 ethers to give complexes with various metal:ligand ratios, 1:1, 3:2, and 2:1. The following complexes have been isolated and characterized: Ln(CF3CO2)3· (C8He16O4), Ln = La, Ce, Pr; [Ln(CF3CO2)3]3· (C8H16O4)2, Ln = Pr, Eu, Er; [Ln(CF3CO2)3]2· (C8H16O4), Ln = Pr, Nd, Sm; [Ln(CF3CO2)3]2· (C10H20O5), Ln = LaEu; Ln(CF3CO2)3·(C12H24O6), Ln = LaEu; [Ln(CF3CO2)3]2·(C12H24O6), Ln = Y, EuEr, Yb. Thermogravimetric data show that the 2:1 complexes are usually thermally more stable. The 2:1 complexes with the 15-membered polyether undergo a slow hydrolysis in the presence of traces of water, which yields the hydroxo complex [Ln2(CF3CO2)3(OH)(C10H20O5)2] [Ln2(CF3CO2)8]. The vibrational spectra confirm the coordination of the coronands; the Δνas(CCO) shifts are not large, which point to a moderate interaction between the polyethers and the metal ions. Magnetic susceptibilities and X-ray powder diagrams have been measured. High-resolution excitation and emission spectra have been analysed for the europium-containing compounds. The spectrum of Eu(CF3CO2)3·3H2O indicates the presence of a single species with low symmetry, in agreement with the crystal structure data for the isostructural Pr-salt. The anhydrous salt Eu(CF3CO2)3 generates an emission spectrum with broad bands and probably contains several, closely related polymeric species. The spectrum of [Eu(CF3CO2)3]2(C10H20O5) is consistent with the presence of two chemically different sites for Eu(III); the emission bands are broad. The double salt AgEu(CF3CO2)4·3CH3CN has also been investigated; the observed transitions point to the presence of a species with idealized D2d symmetry. The emission spectrum of [Eu(CF3CO2)3]2(C12H24O6) displays sharp bands and reveals the presence of two different sites for the metal ion with efficient energy transfers between them. One of the species may have a relatively high symmetry. In solution, all the complexes are non-electrolytes in acetonitrile and propylene carbonate and close to 1:1 electrolytes in methanol. Some dissociation occurs in acetonitrile for the 2:1 complexes with 18-crown-6 ether. On the other hand, 1H NMR spectra of the lanthanum 1:1 complexes with 12- crown-4 and 18-crown-6 ethers indicate no dissociation of the complexed polyether. Log β1 is greater than 6 for both complexes; it is equal to 4.4 for the samarium 1:1 complex with 18-crown-6 ether.

Complexes of lanthanoid salts with macrocyclic ligands. Part 19. Sandwich complexes between lanthanide(III) ions and 15-crown-5 ether: Luminescence and structural data

Abstract The reaction of the lighter lanthanide perchlorates and hexafluorophosphates with 15-crown-5 ether gives sandwich complexes formulated as LnX3− (C10H20O5)2. Crystalline material was obtained for Nd(ClO4)3(C10H20O5)2 (1), Eu(ClO4)3(C10H20O5)2 (2), and La(PF6)3(C10H20O5)2 (3). The luminescence spectrum of a powdered sample of (2) was recorded at 77 K under high resolution. The 5D0 → 7F0 transition is extremely weak and comprises four distinct components at 578.05 nm (Site I), 579.33/579.41 nm (Site II), and 579.73 nm (Site III). Selective excitations produce spectra which strongly suggest the presence of an inversion centre at the europium ion in Site I; the coordination polyhedron of this site is close to a pentagonal antiprism. A comparison between crystallographic and luminescence data demonstrate the fluxional behaviour of the complex, four configurations of which are frozen at low temperature and give rise to different luminescence spectra. Complexes (1) and (2) are isomorphous and form tetragonal crystals with an I-centered lattice; (2) belongs to Laue group 4/m, a = 10.492(3), c = 14.917(8) A, and Z = 2. (3) forms cubic crystals with an F-centered lattice, a = 30.50(3) A and Z = 32. Both structures appear to be highly disordered.

Complexes of lanthanoid salts with macrocyclic ligands. Part 21. Sandwich complexes between lanthanoid(III) ions and unsubstituted 15-crown-5 and 18-crown-6 ethers☆☆☆

Abstract Lanthanoid hexafluorophosphates react with 15-crown-5 and 18-crown-6 ethers to give sandwich complexes Ln(PF 6 ) 3 (C 10 H 20 O 5 ) 2 (Ln ≡ La — Sm, Gd) and Ln(PF 6 ) 3 (C 12 H 24 O 6 ) 2 (Ln ≡ Ce, Nd). These complexes have a limited thermal stability and their decomposition temperature ranges from 40 to 100 °C. The Ln(PF 6 ) 3 (C 10 H 20 O 5 ) 2 complexes present two isostructural series: Ln La — Nd , and Ln ≡ Sm, Gd. The two sandwich complexes with 18-crown-6 ether are also isostructural. Vibrational spectra confirm these findings and indicate the coordination of both polyethers while the anions remain uncoordinated. The magnetic moments of the Ln(III) ions in the complexes are slightly smaller than those of the free ions (1–7%). A solution study has also been carried out for the complexes with 15-crown-5 ether. In acetonitrile, the complexes appear to be 1:1 electrolytes, with molar conductivities between 160 and 170 Ω cm 2 mol −1 . The 1 H NMR spectra have been recorded for 2–5 × 10 −2 M solutions in anhydrous acetonitrile. For Ln ≡ La, the complexed polyether displays only one singlet, well separated from the free ligand resonance. For the paramagnetic ions, two AA′XX′ multiplets of the same intensity are observed, whereas the 13 C NMR spectrum displays only one singlet. The apparent formation constants could be evaluated from the NMR data: log β 2 is equal to 7.4 (La), 4.4 (Pr), 3.8 (Nd), and 3.2 (Sm) at 25 °C.

Complexes of lanthanoid salts with macrocyclic ligands. Part 17. Synthesis and crystal and molecular structure of a hydroxide-bridged praseodymium trifluoroacetate complex with 15-crown-5-ether, [Pr2(CF3CO2)3(OH)(C10H20O5)2][Pr2(CF3CO2)8]

The reaction of praseodymium trifluoroacetate with 15-crown-5 ether in acetonitrile-methanol (3 : 1) gave a complex formulated as [ Pr(CF3CO2)3]2(C10H20O5). This compound was recrystallised and the X-ray crystal structure determined by the heavy-atom method and refined by least-squares methods to a final R value of 0.075. The recrystaliised complex turned out to have a different formula, as indicated in the title. It crystallises in the monoclinic space group P21/m, with lattice parameters a= 9.124(1), b= 31.607(4), c= 13.006(2)A, β= 99.55(1)°, and Z= 2. There are two praseodymium sites. One metal ion is nine-co-ordinate and is bonded to the macrocycle [mean Pr–O(crown) 2.58(2)A], three bridging trifluoroacetate groups [mean Pr–0 2.45(2)A], and a bridging hydroxide ion [ Pr–OH 2.31(1)A] which lies in the mirror plane y=¼ This gives rise to dimeric cations [Pr2(CF3CO2)3(OH)(C10H20O5)2]2+, the co-ordination polyhedron of which may be regarded as arising from distortion of a square antiprism by addition of a ninth ligand. The second praseodymium is eight-co-ordinate with a fairly regular square-antiprismatic co-ordination polyhedron consisting of one bidentate trifluoroacetate and three bridging bidentate trifluoroacetates [mean Pr–O 2.46(2)A] that give rise to infinite polymeric zigzag chains parallel to a.

Choosing a coordination number for Ln(III): 1:1, 1:2, 2:1, 3:2 and 4:3 complexes with crown ethers

The stoichiometry of the complexes between rare earth salts and crown ethers depends on the nature of both the macrocycle and the counteranion, as shown in the Table (1).