THE CRYSTAL STRUCTURE OF TRIAMMONIUM HEXATHIOCYANATE MOLYBDATE （Ⅲ）——（NH4）3Mo（NCS）6·H2O·HCl

<正> It is well known that the thiocyanate ion (NCS~-) is an ambidentate ligand, and it can coordinate to metal atom either through its nitrogen end or its sulfur end. In view of the hard and soft acids and bases theory, the nitrogen atom is 'harder' than the sulfur atom and tends to bond to a 'hard' metal ion. The tendency of a metal atom to coordinate to a certain terminal atom of thiocyanate seems to be a good criterion for determining its relative hardness. The present work is a further investigation about the structure of molybdenum (Ⅲ) thiocyanate complexes.