COMPLEXES OF SILVER(I), THALLIUM(I), LEAD(II) AND BARIUM(II) WITH BIS[3-(2-PYRIDYL)PYRAZOL-1-YL]PHOSPHINATE - ONE-DIMENSIONAL HELICAL CHAINS AND DISCRETE MONONUCLEAR COMPLEXES

Reaction of 3-(2-pyridyl)pyrazole with POBr3 in toluene-NEt3 afforded not the expected tris(pyrazolyl)phosphine oxide but the partially hydr olysed compound bis[3-(2-pyridyl)pyrazol-1-yl]phosphinate (as its trie thylammonium salt). This compound has two potentially chelating N,N'-b identate arms linked by an apical PO2- group. Reaction with AgNO3, Tl( O2CMe), Pb(NO3)(2) or Ba(NO3)(2) in dry MeCN followed by recrystallisa tion afforded crystals of the complexes [AgL]. 2H(2)O, [TlL]. MeOH, [P bL2]. H2O and [(BaL2)(3)]. 6MeCN . 2H(2)O respectively, all of which h ave been crystallographically characterised. The compound [AgL]. 2H(2) O contains infinite helical chains (AgL), in which each ligand donates one N,N'-bidentate arm to each of two metals and each metal ion is fo ur-co-ordinated by two arms from different ligands. The strands are he ld together in the crystal by a complex network of hydrogen bonds invo lving lattice water molecules and also by aromatic pi-stacking interac tions. The compound [TlL]. MeOH is likewise a one-dimensional helical polymer of TlL units, with each ligand bridging two metals and each Tl ion in a '2 + 3' co-ordination geometry with two short bonds to ligan ds (<2.71 Angstrom) and three longer, weak bonds (>2.87 Angstrom): the re is an obvious gap in the co-ordination sphere due to a stereochemic ally active lone pair. A combination of interstrand aromatic pi-stacki ng interactions and hydrogen-bonding interactions involving the lattic e MeOH molecule is present. The compound [PbL2]. H2O is in contrast a discrete mononuclear complex, four-co-ordinated just by one bidentate arm from each of the two ligands with the other bidentate arms pendant : again there is a stereochemically active lone pair. The metal geomet ry is approximately trigonal bipyramidal with the lone pair in an equa torial position. The lattice water molecule is hydrogen bonded to thre e different complex units. The compound [(BaL2)(3)]. 6MeCN . 2H(2)O co ntains mononuclear BaL2 and dinuclear Ba2L4 units: the former is ten-c oordinate, with each ligand acting as an N4O donor and a phosphinate o xygen atom participating in co-ordination, whereas in the latter each Ba-II is nine-co-ordinated and two of the ligands are bridging, donati ng their four N atoms to one metal ion and a phosphinate oxygen atom t o the other.