Octameric water clusters of staircase structure present in a metal-organic framework built from helical lanthanide coordination polymers

Two lanthanide-carboxylate polymeric complexes containing nine-coordinate lanthanide metal centers, {[Pr(ptc(-3))center dot 2H(2)O]center dot 2H(2)O} (1), {[Nd(ptc(-3))center dot 2H(2)O]center dot 2H(2)O} (2) have been prepared by hydrothermal. synthesis of Pr(NO3)(3)center dot 6H(2)O or Nd(NO3)(3)center dot 6H(2)O center dot with pyridine-2,4,6-tricarboxylic acid (ptcH(3)). These network structures are characterized by X-ray crystallography, powder X-ray diffraction, infrared and thermal gravimetric analyses. Both I and 2 form infinite single helical chains with large widths and pitches containing six metal ions per turn. The overall structure consists of two helices connected via discrete octameric water clusters.