Synthesis and characterisation of lanthanide(II) aryloxides including the first structurally characterised europium(II) compound [Eu(OC6H2But2-2,6-Me-4)2(thf)3]·thf (thf = tetrahydrofuran)

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Abstract
The lanthanide(II) aryloxide complexes [Yb(OC6H2But 2-2,6-Me-4)2(OEt2)2]1, [Yb(OC6H3But 2-2,6)2(thf)3]2, [Yb(OC6H2But 3-2,4,6)2(thf)3]3, [Sm(OC6H2But 2-2,6-Me-4)2(thf)3]4, [Eu(OC6H2But 2-2,6-Me-4)2(thf)3]·thf 5, [Yb(OC6H2But 2-2,6-Me-4)2(thf)3]6 and [Yb(OC6H2But 2-2,6-Me-4)I(thf)x]7(thf = tetrahydrofuran) have been synthesized. Each of the complexes 1–3 was prepared by the reaction of 2 equivalents of the appropriate potassium aryloxide with Ybl2 in diethyl ether (1) or thf (2 or 3). Complexes 4–6 were prepared by the reaction of 2 equivalents of K(OC6H2But 2-2,6-Me-4) with Lnl2(thf)2(Ln = Sm, Eu or Yb) in thf. Reacting Ybl2 with 1 equivalent of K(OC6H2But 2-2,6-Me-4) in thf yielded complex 7 as the main product, but 171Yb-{1H} NMR spectroscopy showed that 6 and [Ybl2(thf)4]8 were also formed. The crystal structure of complex 5 reveals that it adopts a distorted trigonal-bipyramidal conformation with (i) apical thf oxygens [O(4)–Eu–O(5) 178.6(2)°, Eu–O(4) 2.590(5) and Eu–O(5) 2.573(5)Å]; (ii) the equatorial O(1), O(2) and O(3) thf coplanar; and (iii) Eu–O(1) 2.321(5), Eu–O(2) 2.337(5) and Eu–O(3) 2.515(6)Å. The crystal structure of complex 8 showed there to be an octahedral arrangement around the metal, the molecule lying on a crystallographic inversion centre, with angles I–Yb–O(1) 90.1(2), I–Yb–O(2) 91.4(2) and O(1)–Yb–O(2) 88.9(3)°, and bond lengths Yb–I 3.103(1), Yb–O(1) 2.399(9) and Yb–O(2) 2.373(8)Å.

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