Vom Molekül zum Polymer: Eine quantenmechanische Studie an anorganischen Metall- und Nichtmetallverbindungen

The molecular structures of all silver halide monomers, Ag2X, AgX,
AgX2 and AgX3, (X = F, Cl, Br, I), have been calculated at the
B3LYP, MP2 and CCSD(T) levels of theory by using quasirelativistic
pseudopotentials for all atoms except fluorine and chlorine. All
silver monohalides are stable molecules, while the relative
stabilities of the subhalides, dihalides and trihalides
considerably decrease toward the larger halogens. The ground-state
structure of all Ag2X silver subhalides has C2v symmetry, and the
molecules can be best described as [Ag2]+X-. Silver dihalides are
linear molecules; AgF2 has a 2Sg ground state, while all of the
other silver dihalides have a ground state of 2Pg symmetry. The
potential energy surface (PES) of all silver trihalides has been
investigated. Neither of these molecules has a D3h symmetric
trigonal planar geometry, due to their Jahn-Teller distortion. The
minimum energy structure of AgF3 is a T-shaped structure with C2v
symmetry. For AgCl3, AgBr3 and AgI3, the global minimum is an
L-shaped structure, which lies outside the Jahn-Teller PES. This
structure can be considered as a donor-acceptor system, with X2
acting as donor and AgX as acceptor. Thus, except for AgF3, in the
other three silver trihalides, silver is not present in the formal
oxidation state 3. Hybrid density functional theory methods have
been used to examine the reactivity of hexafluoro- and
hexachlorocyclotriphosphazene with respect to single, multiple and
complete substitution with water, ammonia, phosphoric and sulfuric
acid. Geometries of both educts and all substitution products habe
been optimized and their thermodynamic properties are discussed.
Based on these results the thermodynamically most favorable
reaction pathways have been determined. Starting from a basic unit,
which consists of two phosphazene rings that are geminally linked
by two hydrazine bridges, several possibilities to form
double-stranded chains or helices containing cyclotriphosphazenes
were examined by PM3 calculations.