COMPLEXES OF MAIN-GROUP ELEMENTS CONTAINING STEREOCHEMICALLY ACTIVE LONE PAIRS - THE CRYSTAL-STRUCTURES OF [TL(TP(AN))] (TP(AN) EQUALS TRIS[3-(2-METHOXYPHENYL)PYRAZOL-1-YL]HYDROBORATE) AND [PB(TP(PY))(NO3)]CENTER-DOT-0.5ET(2)O (TP(PY) EQUALS TRIS[3-(2-PYRIDYL)PYRAZOL-1-YL]HYDROBORATE)

The new podand ligand tris[3-(2-methoxyphenyl)pyrazol-1-yl]hydroborate (Tp(An)) has been prepared and the crystal structure of [Tl(Tp(An))] determined. The metal ion is in a trigonal pyramidal geometry arising from the three pyrazolyl N-donors, with the lone pair of the Tl-1 ion in the fourth position of the tetrahedron of electron pairs. There is also a weak but significant interaction with one of the anisyl oxygen atoms (Tl ... O = 3.018 Angstrom), and the displacement of the metal i on towards this oxygen atom results in a noticeable lengthening of the Tl-N(pyrazolyl) bond which lies approximately trans to it (2.70 Angst rom, compared with 2.54 Angstrom for the other two Tl-N bonds). The cr ystal structure of [Pb(Tp(Py))(NO3)].0.5Et(2)O shows that the Pb-II io n has four strong interactions (with the pyrazolyl nitrogen atoms and one of the nitrate oxygen atoms; range of bond lengths 2.49-2.67 Angst rom) and four weak ones (with the pyridyl nitrogen atoms and the other nitrate oxygen atom; range of bond lengths 2.80-2.99 Angstrom). If on ly the four stronger interactions are considered, the irregular coordi nation sphere of the Pb-II ion has an obvious gap in it which is the s ite of the stereochemically active lone pair. (C) 1997 Elsevier Scienc e Ltd.