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 crystallographically characterised, where L-is the potentially tetradentate ligand bis[3-(2-pyridyl)-pyrazolyl]dihydroborate containing two N,N'-bidentate chelating arms linked by a-BH2-fragment. In [TIL] the Tl(I) is coordinated 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 assumed to occupy the vacant axial site of the square pyramid. The Tl-N(pyridyl) 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 along the Tl ... Tl axis. In [PbL2] there are seven Pb-N bonds in the range 2.588-2.817 Angstrom, which are considered as 'normal' Pb-N interactions, and one much longer interaction (3.055 Angstrom) to a pyridyl N atom which, although rather remote, is still oriented towards the metal. The metal ion is therefore '7 + 1'-coordinate from two tetradentate chelating ligands. Again there is an obvious gap in the coordination sphere which is occupied by a stereochemically active lone pair. (C) 1998 Elsevier Science S.A.