" From Cluster-Anion to Polymer Units "

Dr. Mehmet Somer, Koç University, Chemistry Department

Abstract:

The cluster anions such as [X₇]^3–, [X₁₁]^3–, [E₄]^4–, [E₉]^4–, [E₉]^3– (X = Elements 15 = P, As, Sb; E = Elements 14 = Si, Ge, Sn, Pb) are constituents of the binary phases M₃X₇, M₃X_11, M₄E₄, M₄E₉  and M₃E₉ (M = Na, K, Rb, Cs). Several attempts have been done to make the anions mobile by dissolving the binaries in appropriate solvents - e.g. liq. NH₃, ethylenediamine, DMF- aiming to use them as building blocks for new materials.  Those “naked” and molecular mobile clusters are extremely reactive and capable of undergoing nucleophilic additions and substitutions, and furthermore, redox reactions. Of special interest is the letter type of treatment in which the negatively charged X or E atoms are partially oxidized to yield new element modifications. The route to so called allo germanium, the layered Si modification and different allotropes of phosphorus is well-known and is based on careful oxidation of the suitable precursors such as Li₇Ge₄, Ca₂Si  or K₃P₇ in aprotic and non-oxidizing solvents. Hereby, the topology of the originally anionic building blocks is more or less maintained while the structure itself is strongly disordered or completely amorphous. A more ordered transition from free anion to one-dimensional “chain units” of different lengths has been reported for [Ge₉]^4– ®  [Ge₉–Ge₉]^6–  ®  [Ge₉–Ge₉–Ge₉]^8– ®  [Ge₉–Ge₉–Ge₉–Ge₉]^10–, very recently. It seems thinkable, that the same reaction route can be adopted also by the other cluster species, finally yielding new and well-ordered 1D element modifications

Dec. 22^nd, 2004, 14:40, FENS L 063