The vibrational spectra of the cyanide ligand revisited. Bridging cyanides

The nu(CN) vibrational spectra of cyanide groups bridging two metal atoms present a confused picture. Factors relevant to the interpretation of the available data are reviewed. Some mechanisms for frequency change, relative to the corresponding terminal species, are made more quantitative than previously described, and others are highlighted for the first time. The kinematic effect is much less important than previously assumed. It seems that an effect responsible for the major part of the frequency increase upon bridging commonly observed is the cation electric field, together with concomitant relaxation (the IVSE model). However, a contribution may well come from the change in the sigma bonding in the CN unit.     

Tolubalsam

Ohne Zusammenfassung     

Longitudinal optical-transverse optical (L.O.-T.O.) splitting on internal modes in the Raman spectra of noncentric crystals

A qualitative, but detailed, account of the phenomenon of L.O.-T.O. splitting in the Raman spectroscopy of noncentrosymmetric crystals is given. Tables are provided which give predictions for 45°, 90°, and 180° scattering geometries for all such crystals.     

A topological equivalent-orbital approach to the bonding in some tetrahedral molecules

The electronic structures of the tetrahedral molecules P₄, Be₄(OAc)₆O, [PtMe₃Cl]₄, [Cu I As Me₃]₄, [Tl OR]₄, [Li Me]₄ and B₄ are discussed using a simple topological equivalent(-)orbital approach.

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Zusammenfassung Die Elektronenstrukturen der tetraedrischen Moleküle P₄, Be₄(OAc)₆O, [PtMe₃Cl]₄, [Cu I As Me₃]₄, [Tl OR]₄, [Li Me]₄ und B₄ werden diskutiert unter Benutzung einer einfachen Näherung topologisch äquivalenter Orbitale.

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Résumé Les structures électroniques des molécules tétraédriques P₄, Be₄(OAC)₆O, [PtMe₃Cl]₄, [Cu I As Me₃]₄, [Tl OR]₄, [Li Me]₄ et B₄ sont discutées en usant d'une approche simple par des orbitales équivalentes topologiques.

     

A speculation concerning the origin of long-range crystallographic order in polytypic and related crystals

It is suggested that long-range crystallographic order may be mediated by acoustic vibrations which have their origin in thermoacoustic phenomena and on which structural details exert a filter effect.