INDEX polynuclear compounds

Whereas within the family of the cubic Prussian blue analogs a large number of lattice constants have been determined, little attention has been devoted so far to polymeric cyanides not belonging to the cubic system. It must be emphasized, however, that polynuclear cyanides having unit cell symmetries other than cubic are by no means rare exceptions. Hexacyanometalates(III) of Zn2+ and Cd2+ are obtained not only in a cubic modification but also as samples with complicated and not yet resolved X-ray patterns of definitely lower symmetry than cubic (55). The exact conditions for obtaining either modification are not yet known in detail. The hexacyanoferrates(II), -ruthenates(II), and -osmates(II) of Mn2+ and several modifications of the corresponding Co 2+ salts show very complicated X-ray powder patterns which cannot be indexed in the cubic system (55). Preliminary spectroscopic studies show the presence of nearly octahedral M C6-units in these compounds, too. 

HPLC was performed with a liquid chromatograph (Waters Associates Series 6000) equipped with UV and refractive-index detectors. Asphaltene fractions were examined by using a 25- X 0.5-cm column packed with silica gel and maintained at 25 °C by an external thermostatically controlled water bath. Asphaltenes and standard polynuclear aromatic compounds were passed through the column with chloroform-isopropyl alcohol blends (90 10). 

A useful 2ilternative to the Kovats system is the Lee retention index (isotherm2il and temperature dependent), based on the polynuclear aromatic hydrocarbon (PAH) standard compounds naphthalene (/ = 200), phenanthrene (/ = 300), chrysene (/ = 400), and picene or benzo(g,h,i)perylene (/ = 500). Isothermal (and temperature-dependent) Kovats and Lee retention indices for many compounds are tabulated in the NIST Chemistry Web Book (Ref. 8). 

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