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 ion towards this oxygen atom results in a noticeable lengthening of the Tl-N(pyrazolyl) bond which lies approximately trans to it (2.70 Angstrom, compared with 2.54 Angstrom for the other two Tl-N bonds). The crystal structure of [Pb(Tp(Py))(NO3)].0.5Et(2)O shows that the Pb-II ion has four strong interactions (with the pyrazolyl nitrogen atoms and one of the nitrate oxygen atoms; range of bond lengths 2.49-2.67 Angstrom) 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 only the four stronger interactions are considered, the irregular coordination sphere of the Pb-II ion has an obvious gap in it which is the site of the stereochemically active lone pair. (C) 1997 Elsevier Science Ltd.