Heteroleptic poly(pyrazolyl)borate derivatives of the lanthanide ions. The synthesis of tropolonate and carboxylate complexes and the X-ray crystal structures of [Yb{HB(C3N2H3)3}2(O2C7H5)] and [Yb{HB(C3N2H3)3}2(O2CPh)]

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Abstract
The new heteroleptic hydrotris(pyrazol-1-yl)borato lanthanide complexes [Ln{HB(C3N2H3)3}2X](X = tropolonate, Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Yb, or Lu; X = benzoate, Ln = Y, Sm, Eu, Yb, or Lu; X = acetate, Ln = Y, Eu, Gd, Yb, or Lu) have been synthesised. The complexes [Ln{HB(C3N2H3)3}2(O2CMe)](Ln = Ce and Sm) were prepared but appeared to be unstable in solution, disproportionating to [Ln{HB(C3N2H3)3}3]. Crystal and molecular structures of [Yb{HB(C3N2H3)3}2(O2C7H5)] and [Yb{HB(C3N2H3)3}2(O2CPh)] have been determined by X-ray diffraction methods and are eight-co-ordinate, unsolvated monomers. They have an approximately C2 molecular symmetry with a distorted square-antiprismatic co-ordination geometry. Their steric angle sums are 0.819 and 0.814 respectively. The steric angle factors for the tropolonate and benzoate ligands in these structures are respectively 0.209 and 0.174. The steric angle factor for HB(C3N2H3)3 in [Yb{HB(C3N2H3)3}2(O2CPh)] is anomalously high (0.320 compared with an average of 0.305 for three other examples) as a result of the shorter Yb–N and longer Yb–O distances compared to those found in the related systems [Yb{HB(C3N2H3)3}2{OC(Me)CHC(Me)O}] and [Yb{HB(C3N2H3)3}2(O2C7H5)].

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