Novel pyrazolate coordination modes and unusual Tl center dot center dot center dot Tl or Tl-pi-(phenyl) interactions in the crystal structures of [{Tl-3(Ph(2)pz)(3)}(n)], [{Tl-4(Ph(2)pz)(4)}(n)], [{Tl-4(Ph(2)pz)(3)(OH)}(2)]and [{Tl-4(MePhpz)(3)(OH)}(n)] (Ph(2)pz=3,5-diphenylpyrazolate; MePhpz=3-methyl-5-phenylpyrazolate)

[Tl(Ph(2)pz)] (Ph(2)pz = 3,5-diphenylpyrazolate) crystallises in two forms. The first from benzene has trinuclear molecules [Tl-3(Ph(2)pz)(3)] 1 linke d by intermolecular Tl-pi-eta(6)-Ph contacts. Within 1 the three thallium a toms are different, having coordination numbers of two (but also with the T l ...eta(6)-Ph contact), three and four, whilst mu-eta(1) : eta(1), mu(3)-e ta(1) : eta(2) : eta(1) and (the new) mu(3)-eta(1) : eta(1) : eta(1) modes of Ph(2)pz coordination are observed. Crystallisation of [Tl(Ph(2)pz)] from 1,2-dimethoxyethane (dme) gives tetranuclear molecules [Tl-4(Ph(2)pz)(4)] 2 solvated by dme. Three or four coordinate Tl atoms are observed with mu(3 )-eta(1) : eta(2) : eta(1) and mu(3)-eta(1) : eta(1) : eta(1)-pyrazolate co ordination. In addition there is an intermolecular Tl-pi-eta(3)-Ph interact ion linking the tetranuclear molecules into a polymer, and sundry intramole cular Tl ... C contacts, the most important of which is an unsymmetrical Tl -pi-eta(5)-Ph(2)pz interaction. Crystallisation of [Tl(Ph(2)pz)] or [Tl(MeP hpz)] (MePhpz = 3-methyl-5-phenylpyrazolate) from dichloromethane afforded the partially hydrolysed tetranuclear cages [Tl-4(Ph(2)pz)(3)(OH)] 3 or [Tl -4(MePhpz)(3)(OH)] 4, which associate to give a dimer and a polymer respect ively owing to Tl ... Tl interactions, supported for the dimer by an interc age distant Tl-pi-eta(5)-Ph(2)pz contact. Complex 3 features three and four coordinate Tl atoms and mu(3)-eta(1) : eta(2) : eta(1) and mu(3)-eta(1) : eta(1) : eta(1)-pyrazolate binding, whilst 4 has three, four and five coord inate thallium atoms and solely mu(3)-eta(1) : eta(2) : eta(1)-pyrazolate l igands.