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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.

A comparison is made between the vibrational characteristics of the carbonyl and cyanide ligands. There are significant differences; the latter has a smaller dipole moment and a larger quadrupole moment associated with the bond stretch. This quadrupole moment may be linked to the observation that the totally symmetric nu(CN) mode does not lie at the highest frequency for some cyanide complexes. There are problems with the pi-bonding model commonly used to interpret the nu(CN) data. For instance, for the first transition row hexacyanoanions, the spectra are almost independent of t2g occupancy but are very sensitive to the formal charge. It is suggested that the observed nu(CN) frequency shifts on complex formation are in large measure determined by the effective charge on the cation to which the cyanide group is attached, and a new model, the Internal Vibrational Stark Effect, is suggested to account for this. The model is supported by DFT calculations. Raman spectra of some cubic cyano species are reported, along with polarization and intensity data.

The title complex is the main product of the room-temperature reaction between Co 2 (CO) 8 and sulfur. Its crystals are monoclinic, space group C2/c

The average frequency of the bands belonging to the same type of vibrations and the contribution per C-H bond to the total C-H stretching and bending intensities are evaluated and compared with the relevant values for the free alkyne. Both the frequency and intensity data provide informations on the effect induced in the alkyne (bond strengths and charge distributions) by the metal coordination and are related to the type of the metal-alkyne bond, to the nuclearity, and to the geometry of the cluster

Cristallisation dans le groupe P2 1 2 1 2 1 (Affinement jusqu'a R=0,045). Les six Co sont disposes en forme de bateau. Les quatre Co de la base forment un carre regulier, avec des liaisons Co-Co des 4 cotes. Les deux Co situes au sommet sont lies de la facon suivante: Co-C-C-Co. Les 6 Co portent des CO. Un pont sulfuro est etabli entre les 4 Co de base

Preparation et breve presentation de l'etude de radiocristallographique du complexe du titre