Heteroleptic poly(pyrazolyl)borate derivatives of the lanthanides. Structural and electronic spectral studies of some salicylaldehyde complexes

The new complexes [Ln{HB(pz)3}2L][pz = pyrazol-1-yl; L = salicylaldehydate, Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb or Lu; L = 5-methoxysalicylaldehydate (mosal), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Yb or Lu] have been synthesised and the crystal structure of [Eu{HB(pz)3}2(mosal)] determined. The europium ion is eight-co-ordinate with Eu–O distances of 2.266(5) and 2.402(5)A; polytopal analysis indicates that the co-ordination geometry is best described as dodecahedral. The solid-angle sum of 0.768 is close to the norm for eight-co-ordination. These structural parameters were compared with those calculated for the previously reported binuclear complex [{Sm[HB(pz)3]2(O2CPh)}2] and estimated for its monomeric counterpart, which is as yet unknown. The use of such data in predicting when complexes of this type will dimerise was assessed. Electronic spectra of the neodymium complexes revealed less than 1% covalency in the metal–ligand bonding and emission spectral data are reported for the europium and terbium complexes.