SYNTHESES, PROPERTIES AND STRUCTURAL CHARACTERISTICS OF SEVERAL NEW (POLYPYRAZOLYLBORATO)SAMARIUM(III) COMPLEXES - AGOSTIC INTERACTION OF THE BH2 PROTON WITH SAMARIUM

(Polypyrazolylborato)samarium(III) complexes [SmCl(BHpz(3))(2)(L)] (pz = 1-pyrazolyl) (1, L = Hpz; 2, L = N-CH(3)pz) were prepared from SmCl . 6H(2)O, and treated with several sodium beta-diketonates to give [S m(BHpz(3))(2)(A-B)] (3, 4, and 5) with acetylacetonate (acac), trifluo roacetylacetonate (tfa), and hexafluoroacetylacetonate (hfa) ligands a s A-B respectively. H-1 NMR spectroscopy of the BHpz(3) moieties in th ese five complexes showed stereochemically non-rigid motions. In contr ast to the Hpz complex 1 with a square-antiprismatic coordination geom etry, the structure of [Sm(BHpz(3))(2)(BH(2)pz(2))] (6), obtained from [SmCl(BHpz(3))(2)(L)] and K[BH(2)pz(2)], was found to be bicapped tri gonal prismatic with additional agostic interaction between the samari um atom and one of the BH2 protons. The interaction was confirmed by t he close interatomic distance between them and also by the upheld shif t in H-1 NMR signal for the agostic BH2 proton. (C) 1998 Elsevier Scie nce S.A. All rights reserved.