COMPLEXES OF THALLIUM(I) AND LEAD(II) WITH THE POTENTIALLY TETRADENTATE LIGAND BIS[3-(2-PYRIDYL)-PYRAZOLYL]DIHYDROBORATE

The complexes [TIL] and [PbL2] have been prepared and crystallographic ally characterised, where L-is the potentially tetradentate ligand bis [3-(2-pyridyl)-pyrazolyl]dihydroborate containing two N,N'-bidentate c helating arms linked by a-BH2-fragment. In [TIL] the Tl(I) is coordina ted by one tetradentate chelating ligand L-, whose four N donor atoms are approximately coplanar. The Tl(I) ion lies similar to 1.4 Angstrom out of this plane, and the stereochemically active lone pair is assum ed to occupy the vacant axial site of the square pyramid. The Tl-N(pyr idyl) bonds (2.96-3.17 Angstrom) are considerably longer than the Tl-N (pyrazolyl) bonds (2.61-2.69 Angstrom). The molecules lie in a stack a long the Tl ... Tl axis. In [PbL2] there are seven Pb-N bonds in the r ange 2.588-2.817 Angstrom, which are considered as 'normal' Pb-N inter actions, and one much longer interaction (3.055 Angstrom) to a pyridyl N atom which, although rather remote, is still oriented towards the m etal. The metal ion is therefore '7 + 1'-coordinate from two tetradent ate chelating ligands. Again there is an obvious gap in the coordinati on sphere which is occupied by a stereochemically active lone pair. (C ) 1998 Elsevier Science S.A.