Lanthanoid (II) complexes of bulky aryl oxides, Ln (OC6H2But 2-2, 6-X-4)2(Ln = Yb or Eu; X = H, Me or But) have been prepared by one or more of the following methods: (i) reaction of Ln (C6F5)2with the appropriate phenol, (ii) reaction of the lanthanoid metal, Hg(C6F5)2and the phenol, and (iii) reaction of the lanthanoid metal with the corresponding thallium(I) phenolate, in tetrahydrofuran (thf), and they have been isolated as Ln (OC6H2But 2-2, 6-X-4)2thf)3complexes. Crystallization of Yb (OC6H2But 2-2, 6-X-4)2 thf)3(X = H or Me) from toluene yields Yb (OC6H2But 2-2, 6-X-4)2 thf)2. The X-ray crystal structure of [ Yb (OC6H2But 32, 4, 6)2 thf)3]. thf [monoclinic, a 10.20(1), b 32.97(2), c 16.018(4) Â, β 93.52(8)°, V 5375 Â3Z 4, 2734 'observed' data refined to R 0.070] shows distorted square pyramidal five coordination for ytterbium with an apical thf oxygen [ Yb -O 2.44(1)Â], and transoidphenolate oxygens [ Yb -O 2.21(1), 2.22(1)Â, O- Yb -O 149.0(6)°] and transthf oxygens [ Yb -O 2.47(2), 2.48(1)Â, O-Yb -O 177.3(5)°] in the square plane. Four methyl groups (Yb…C 3.89-4.15 Â) across the square plane away from the apical oxygen may block coordination of an additional ligand. X-Ray structures of Yb (OC6H2But 2-2, 6-Me-4)2thf)n showing four coordination (n = 2) and five coordination (n = 3), given in a preliminary communication,1are further discussed.