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The structure of the heptacyanovanadate(III) ion, V(CN)74-, has been shown to be a pentagonal bipyramid from a singlecrystal X-ray crystallographic study of K4V(CN)7-2H20.1,2 Although this anion had been prepared in a number of studies,3-11 its structure, frequently presumed to be octahedral,,had never been explicitly determined. The possibility of seven-coordination, however, had indeed been recognized by several groups of workers.6-11 Since this same material was 'most likely prepared by Alexander and Gray7 (although they formulated it as a hexacyanide, their analytical results are essentially perfect for K4V(CN)7-2H20) and since they reported difficulty in repeating the synthesis, a separate and detailed elaboration of the synthesis and properties of K4V-(CN)7-2H20 appears warranted. Further impetus stems from reports that anhydrous10 and monohydrated9 forms of the same material have been prepared. The V(CN)74-anion need not necessarily have the same structure in these several com-