W0220

Design, Synthesis and Structural Studies of Open-Framework Materials in Niobium Oxohalide Cluster Chemistry. Ekaterina Anokhina, Michael Essig, Cynthia Day, and Abdessadek Lachgar, Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109 USA

We are using the mixed-ligand approach to modify the structural and physical properties of materials. We have applied this method to design and prepare new phases with open frameworks in niobium cluster chemistry.

The most common structural building unit in reduced niobium halides (Cl or Br) and oxides is the Nb₆X₁₈-type cluster based on an octahedral Nb₆ core surrounded by two sets of ligands: 12 inner ligands that bridge two Nb atoms; and 6 outer ligands, each bonded to one Nb.

Using the Nb₆Cl₁₈ cluster as our starting motif, we designed new cluster units in which we substituted some inner chlorines with oxide ligands. We focused our synthetic efforts on compositions in which possible ligand arrangements can lead to open cluster frameworks. We reported earlier on the synthesis and structure of Ti₂Nb₆Cl₁₄O₄,^[1] here we report the structural characterization of a layered niobium oxohalide with partially occupied nanosize pores, KTi₂Nb₆Cl₁₅O₄ (I). The layers in the novel framework of (I) are built-up from clusters connected to each other through outer-outer chlorine bridges to form large hexagonal voids where the potassium cations are located. Adjacent layers interact with each other only through potassium ions. Crystal data: space group P-3, Z = 3; a = 16.913(2)Å, c = 9.063(2)Å.

^[1] E.V. Anokhina, M.W. Essig, A. Lachgar, Angew. Chem. Int. Ed. 1998, 37, 522-525.