Pfeiffer effect in tetrahedral and negatively charged octahedral coordination compounds

Abstract

57) The computation was simplified by truncating the orbitals 3S36, which carry small contributions on the ligands, to that part which is on the metal alone. This truncated wave function was renormalized and then transformed to the local coordinate system (x', y', 2') appropriate for the calculation of the overlap integrals.The Pfeiffer effect can be utilized to study the optical rotatory and related properties of dissymmetric complexes which are difficult or impossible to resolve because of their optical lability. Most Pfeiffer-active systems are based upon optically active (racemic) six-coordinate complex cations. Examples of Pfeiffer-active systems based upon optically active (racemic) four-coordinate, tetrahedral complexes and negatively charged, octahedral complex anions are reported here, in which both optically active organic compounds and complex inorganic compounds are utilized as environment substances. AIC605464 Reactions ofCp2NbC12 and (MeCp),TaBrz (Cp = ?r-C5H5 and MeCp = ?r-C5H4Me) with MeLi in ether give the paramagnetic alkyls CpzNbMe2 and (MeCp),TaMe2 as red crystalline solids. Magnetic moments and ESR spectral data are given. The niobium complex violently decomposes at -130 OC liberating 1.3-1.5 mol of methane/mol of complex. Convenient preparations of NbC14 and NbC14(THF)2 (THF = tetrahydrofuran) are described. Reactions of the tetrahydrofuran complex with triethyland trimethylphosphine give NbC14L2. Using chelating phosphines the eight-coordinate complexes NbCld(R2PCH2CH2PR2)2 (R = Me, Et) are isolated as magnetically dilute, blue crystalline solids.

Stabilization of uranium(IV) in heteropoly anions*

“…Assuming the ground state to be F 6, six electronic transitions are possible. It is not possible to distinguish with certainty between optical activity resulting from displacemcnt of a racemate equilibrium (a Pfeiffer effect) (19) and optical activity induced in a nonchiral species by, e.g., ionpairing (20). The remaining four transitions may be represented by the four bands between 6510 and 10000 cm -l .…”