New Structural Forms in Molecular Metal Phosphonates: Novel Tri- and Hexanuclear Zinc(II) Cages Containing Phosphonate and Pyrazole Ligands

The reaction of ZnCl2 with tert-butylphosphonic acid and 3,5-dimethylpyrazole in the presence of triethylamine as a hydrogen chloride scavenger affords a trinuclear molecular zinc phosphonate [Zn3Cl2(3,5-Me2Pz)4(t-BuPO3)2]. The structure of this compound contains a planar trizinc assembly containing two bicapping μ3 [t-BuPO3]2- ligands and terminal pyrazole and chloride ligands. In contrast an analogous reaction of ZnCl2 with phenylphosphonic acid and 3,5-dimethylpyrazole affords a hexanuclear zinc phosphonate [Zn6Cl4(3,5-Me2PzH)8(PhPO3)4]. The six zinc centers are arranged in a chairlike conformation. The four phosphonates in this complex also act as bridging tripodal μ3 [RPO3]2- ligands.