The new three-co-ordinated lanthanide complexes [Ln{N(SiMe,),),],where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Ho, Yb, and Lu, and [Y{N(SirneJ2),], have been prepared and their l H n.m.r. and electronic spectra are reported and discussed. The magnetic susceptibility of the Gd complex a t 98 and 298 K is reported.College, Mile End Road, London E l 4NS THE chemistry of the lanthanide elements is characterized by a tendency to exhibit high co-ordination numbers (Le. >6) in their compounds, which are predominantly ionic in nature, Typical co-ordination numbers for these large ions are 8, 9, and 10, though 6, 7 , and 12 are also known. Even six-co-ordination, so common for &transition metals, is quite rare for lanthanides; an example is provided by the hexahalide complex [LnXJ3-(X = C1, Br, or I ) . l 7 , Co-ordination polyhedra are often of quite low symmetry, which hinders interpretation of electronic spectra, though Oh six-coordination , D,, nine-co-ordination , and near-lh twelveco-ordination are known.Recent X-ray crystallographic work has shown that the tris(bis(trimethylsilyl)amido}chromium and iron compounds [M(N(SiMe,),},] (I) (M = Cr or Fe), originally prepared by Burger and Wannagat: are authentic three-co-ordinated complexes with D, molecular symmetry. Other transition metal derivatives (I; M = Sc, Ti, or V) have since been isolated5 and crystal-field cause they might have low and (for these elements) otherwise unknown co-ordination numbers. Reaction (1) involving the anhydrous lanthanide chloride and the LnCl, + 3LiN(SiMe,), ---+ theoretical amount of LiN(SiMe,), proved successful * and we now present a full account of the preparation and properties of a number of three-co-ordinated lanthanide complexes (I; M = La, Ce, Pr, Nd, Sm, Eu, Gd, Ho, Yb, and Lu) and the corresponding yttrium complex.The new compounds are readily hydrolysed, soluble in organic solvents, and crystallize as needles from pentane. The cerium compound is exceedingly readily oxidised by even minute traces of air. The m.p.s all lie within the range 149-170

The new compounds M[N(SiMe,),], (M = La, Pr, Sm, Eu, Gd, Lu) have been isolated and shown to be the first examples of 3-co-ordinated lanthanides.

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The preparation, properties, and n.m.r. spectra of 1 : 1 triphenylphosphine oxide adducts of [M{N(SiMe,),),] ( M = La, Eu, or Lu) and dimeric peroxo-species [M2(N(SiMe,)2),( 02)(PPh,0)2] ( M = La, Pr. Sm. Eu. or Lu) are described. The crystal and molecular structures of [La{N(SiMe,),),( PPh,O)] (1 ) and [La,{N(SiMe,),),-(0,) (PPh,O),](2) have been determined bysingle-crystal X-ray diffraction methodsfrom data measured on a manual diffractometer and refined by least-squares to R 0.1 16 for 2 770 observed reflections for (1 ) and to R 0.1 1 3 for 2 153 data for (2). Both species crystallise in space group P i with cell parameters : ( 1) ; a = 19.92, b = 12.64, c = 12.48& a = 120.5, (3 = 87.3, y = 102.7O.Z = 2; (2) ; a = 13.55, b = 1 8 . 5 4 , ~ = 12.54A, a = 90.8, f3 = 121.7, y = 115.3", Z = 1. Complex ( 1) is monomeric and the lanthanum atom has slightly distorted LaN,O tetrahedral geometry. TheLa-O-P unit is almost linear, with La-0 2.39(2) A ; La-N distances are 2.38(2)-2.41(2) A.Complex ( 2) is a peroxo-bridged centrosymmetric dimer in which the peroxo-function acts as a symmetrical doubly bidentate bridge linking two La{N(SiMe,),}, (PPh,O) units. The metal atom can again be considered to have distorted tetrahedral co-ordination if the 0, function is assumed to occupy one co-ordination site. The La-O(0,) distances are both 2.33(3) 8. whilst La-O(PPh,O) is 2.42(2) and La-N 2.37(2) and 2.49(3) A. The 0-0 separation is 1.65(4) 8, but this may be artificially lengthened by the effects of crystal decomposition.

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