Organoamido- and Aryloxo-lanthanoids. X. Tris(η2-3,5-di-t-butylpyrazolato)lanthanoid(III) Complexes and the X-Ray Crystal Structure of Er(η2-But2pz)3(thf)2

The complexes Ln (But2pz)3( thf )2 ( Ln = Y, La, Pr, Nd , Sm, Gd, Dy , Er , Yb, Lu; But2pz- = 3,5-di-t-butylpyrazolate; thf = tetrahydrofuran ), and [ Ln (But2pz)3(OPPh3)2].( dme )n ( Ln = La, n = ? ; Ln = Er , n = 1; dme = 1,2-dimethoxyethane) have been prepared by reaction of the lanthanoid metal with bis ( pentafluorophenyl )mercury and the corresponding pyrazole in either thf , or in dme in the presence of triphenylphosphine oxide. The X-ray crystal structure of Er (?2-But2pz)3( thf )2 [monoclinic, space group P21 (No. 4), a 9.738(4), b 19.602(4), c 11.636(4) ?, ß 99.42(3)°, R 0.0374 for 3667 observed reflections] shows the complex to be an eight-coordinate monomer with three chelating But2pz ligands . The arrangement of centres ( Cen ) of the N-N bonds of the But2pz ligands [< Er -N> 2.336 ?; Cen-Er-Cen 140.1(4)°, 110.3(4)° and 109.6(4)°] and the thf oxygen atoms [< Er -O> 2.351 ?; O- Er -O 140.1(4)°] is intermediate between trigonal bipyramidal and square pyramidal. The other Ln (But2pz)3( thf )2 complexes and Ln (But2pz)3(OPPh3)2 are considered to have similar structures.