Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands

Abstract

(12.VIL 91) ~~~ ~The crystal structures of the La"', Eu"', and Tb'" complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La3+ c 113 C1-( = 3-La), [Tb3* c 113 C1-( = 3-Tb), and [Eu3+ c 213 C1-( = 3-Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, C1-ions or HzO molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the Eu"' and Tb"' cryptates, which indicated residual coordination of H,O molecules.Lanthanide complexes of the macrobicyclic ligand [bpy.bpy.bpy] 1 containing three 2,2'-bipyridine (bpy) units have been prepared [ 11 [2] from the corresponding NaBr complex [3]. The Eu"' and Tb"' complexes display pronounced luminescent properties [ 11 [2] [4-61. They are of particular interest for the development of luminescent materials and of labels for biological substances, as required, e.g., in immunoassay diagnostic techniques.On the basis of the structure of the starting NaBr complex and of their analytical and spectral properties, a cryptate structure has been assigned to these lanthanide complexes, in which the Ln3+ ion is contained in the intramolecular cavity of the macrobicyclic ligand. Such a structure has been confirmed for the related "a+ c phen.phen.phen] species by crystal-structure determination [7].Cation inclusion is of prime importance for the photophysical properties of the Eu3+ and Tb3+complexes, since 1 ) it makes possible an energy transfer from the three bpy units, functioning as a UV-light collector, to the bound cation, which then emits its characteristic radiation, and 2) it protects the cation from interaction with solvent molecules, in particular with H,O, thus leading to high luminescence efficiencies, even in aqueous solution, where it is known that coordination with H,O strongly decreases light emission.In order to understand the photophysical properties of these complexes and to be able to optimize them, it is necessary to obtain detailed structural information on the mode of binding of the cations in the cavity and on the ability of the cryptand 1 to shield the bound ') 2, ')

Stereochemistry of Compounds with Coordination Number Ten

“…The adoption of one or another stereochemistry depends on the mono-or bidentate nature of the ligands that complete the coordination sphere. With monodentate ligands, [42] the complexes adopt the CTC geometry with the conformation of the cryptate ligand shown in 11 b. It is clear that such a conformation is not suitable for the coordination of a bidentate ligand at the two coordination sites left unoccupied by the cryptate, hence complexes with an extra bidentate ligand [43,44] adopt a BCSAPR stereochemistry with the conformation shown in 11 c. Note that one of the members of this family [44] is better described as a sphenocorona (shape measure of 0.83) than by the BCSAPR-CTC interconversion path.…”

Application of Ultrahigh‐Field 59Co Solid‐State NMR Spectroscopy in the Investigation of the 1,2‐Polybutadiene Catalyst [Co(C8H13)(C4H6)]

“…Recrystallization of 1 from pentane at À35 8C resulted in the formation of a small quantity of X-ray quality crystals of the Co II complex [Co(EtOH) 6 ][CoCl 4 ] (2), which is isostructural to the previously reported [CoBr 4 ] 2À derivative. [17] It was thus apparent that small amounts of the paramagnetic Co II complex were interfering with the solution NMR analysis of 1. It was found that 1 was stable on silica for very short periods of time if kept under an inert atmosphere and at a reduced temperature.…”

Molecular Dynamics Study of the Complexation of Luminescent Cations by Encapsulating Ligands With Bipyridine Units

“…For instance, cryptand-type ligands containing 2,2Ј-bipyridine combine the shielding effect upon complexation and the sensitizer 'antenna' moiety of the bipyridine groups. [8][9][10] Crystal structures of these Eu 3+ and Tb 3+ cryptates are consistent with the 'antenna effect:' 11 the cation is encapsulated inside the cavity of ligand, and makes short contacts (from 2·55 to 2·90 Å) with the eight N pyridine atoms. Its coordination sphere is completed by two Cl Ϫ anions, or by one Cl Ϫ and one H 2 O molecule.…”