SYNTHESIS AND COORDINATION CHEMISTRY OF THE TETRADENTATE CHELATING LIGAND 1,3-BIS[3-(2-PYRIDYL)PYRAZOL-1-YL]PROPANE - CRYSTAL-STRUCTURES OFCOMPLEXES WITH FE-II, CU-II, ZN-II, AG-I AND PB-II

The new ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L) was prepa red by reaction of 3-(2-pyridyl)pyrazole with 1,3-dibromopropane under phase-transfer conditions, and contains two bidentate chelating pyrid yl/pyrazolyl fragments linked by a flexible trimethylene chain, which permits the angle between the chelating fragments to vary in its compl exes. It acts as a tetradentate chelate to a single metal ion, forming a variety of mononuclear complexes which have been structurally chara cterised. The complex trans-[FeL(dmf)(2)][ClO4](2) is a high-spin d(6) complex in which L co-ordinates equatorially. In [CuL][BF4](2) the [C uL](2+) cations have a significant tetrahedral distortion arising from the inability of the ligand to be planar; chains of [CuL](2+) cations are bridged by [BF4](-) anions, with each bridging anion forming semi -co-ordinate interactions with the axial sites of the two [CuL](2+) fr agments on either side of it and also hydrogen bonds to the methylene protons of each of the two metal fragments. The complex [(ZnL)(3)(CO3) ][ClO4](4) contains a rare example of the symmetric mu(3)-bridging mod e of carbonate, which has arisen from efficient fixation of atmospheri c CO2 by a solution containing L and zinc(II) acetate. Complexes conta ining the [AgL](+) cation, with either nitrate or perchlorate as the a nions, form columnar stacks in the crystal because of weak intermolecu lar Ag Ag interactions; the basic geometry of the [AgL](+) cations is very similar to that of [CuL](2+), despite the different stereoelectro nic preferences of Ag-I and Cu-II. The complex [PbL(NO3)(2)] is eight- co-ordinate with two bidentate nitrate ligands in addition to L; the l one pair of Pb-II is stereochemically active, and results in a clear d istortion of one square face of the approximately square antiprismatic geometry.