Investigation of the "bent sandwich-like" divalent lanthanide hydro-tris(pyrazolyl)borates Ln(TpiPr2)2 (Ln = Sm, Eu, Tm, Yb)12. (12th May 2015) - Kühling, Marcel
Abstract : Synthesis, luminescence and reactivity of the lanthanide(ii ) "bent sandwich-like" hydro-tris(pyrazolyl)borate complexes Ln(Tp iPr2 )2 (Ln = Sm, Eu, Tm, Yb) have been investigated. Abstract : The series of homoleptic lanthanide(ii ) "bent sandwich-like" hydro-tris(pyrazolyl)borate complexes Ln(Tp iPr2 )2 (Ln = Sm (1 ), Eu (2 ), Tm (3 ), Yb (4 ); Tp iPr2 = hydro-tris(3, 5-diisopropylpyrazolyl)borate) has been completed by the synthesis of the hitherto unknown europium and ytterbium derivatives2 and4 . Both compounds were prepared in high yields by treatment of LnI2 (THF)2 (Ln = Eu, Yb) with 2 equiv. of KTp iPr2 in a THF solution. Although the molecules are sterically highly congested, an X-ray diffraction study of bright red4 revealed a similar bent B–Yb–B arrangement (151.1° and 153.9°, two independent molecules) as in the previously investigated Sm(ii ) and Tm(ii ) complexes1 and3 . An initial reactivity study showed a very different behavior with acetonitrile. While2 and4 proved to be unreactive toward acetonitrile, the more strongly reducing Sm(ii ) complex1 yielded two new products. The major product was the dark green-black acetonitrile solvate Sm II (Tp iPr2 )2 ·CH3 CN (5 ), while the second product, the colorless (Tp iPr2 )Sm III (3, 5- i Pr2 pz)2 (NCCH3 ) (6 ) with two 3, 5-diisopropyl-pyrazolate ligands, resulted from oxidation of samarium to the trivalent state and degradation of a Tp iPr2 ligand. Disappointingly, from the most reducing Tm(ii ) complex3 only the ligand fragmentation product pyrazabole, [HB(3, 5- i Pr2 pz)2 ]2 (7 ), could be isolated and the fate of the Tm containing by-product(s) remains unknown. The new compounds4–6 were structurally authenticated through single-crystal X-ray diffraction. The europium compound2 shows an extremely bright yellow emission in solution, which can be observed also at daylight excitation, as well as in the solid state. The high intensity is even remarkable when compared to other Eu(ii ) containing materials. The photoluminescence was investigated with the conclusion that the rigidity of this complex is responsible for these outstanding luminescence properties.