Unusual co-ordination numbers

Further work has been carried out on the Raman spectra of solutions of simple salts in liquid ammonia. Polarized low-frequency bands were assigned to metal-nitrogen symmetric stretching vibrations, and suggest unusual co-ordination numbers for Zn2+, Hg2+, and Ag+. Also, ion-association... 

There is a consensus from both theoretical and experimental studies that small particles may have unusual physical, chemical, and catalytic properties. Both in terms of numbers of sites of different co-ordination and with regard to electronic effects small means particles having diameters less than about 2 nm. For very small particles, sites having a particular co-ordination may be important, but the calculation of the number and distribution of such sites is subject to serious errors and requires assumptions about particle shapes, etc., which are difficult to confirm, and which may vary from one system to another. Although particles having unusual five-fold symmetry have been detected in certain circumstances, the large majority of small metal particles have conventional cubic symmetry. However, the difference in energy between two alternative structures is small - much smaller than typical heats of... 

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