MOLAR VOLUMES OF ZINC(II) THIOCYANATO COMPLEXES AND VOLUME CHANGES OFCOMPLEXATION IN N,N-DIMETHYLFORMAMIDE

Molar volumes of zinc(II) thiocyanato complexes have been evaluated by densitometric titration in N,N-dimethylformamide at 298.15 K. All the measurements were carried out in solution containing an inert support ing electrolyte 0.2 mol dm(-3) (C2H5)(4)NClO4 and the molar volumes of all the ionic species were assumed to be kept constant throughout tit ration. The volume changes, Delta V, thus determined for the reactions are as follows: Zn2+ + SCN- = [Zn(NCS)](+); Delta V(0-1)degrees, = 15 cm(3) mol(-1) (1) [Zn(NCS)](+) + 2SCN(-) = [Zn(NCS)(3)](-); Delta(1-3 )degrees = 77 cm(3) mol(-1) (2) [Zn(NCS)(3)](-) + SCN- = [Zn(NCS)(4)]( 2-); Delta V(3-4)degrees = -18 cm(3) mol(-1) (3) These show that the v olume changes parallel the corresponding reaction entropies. The Delta V(1-3)degrees of reaction (2) shows a relatively large value, as expe cted from the fact that the coordination geometry around the zinc(II) ion changes from octahedral six-coordination to tetrahedral four-coord ination.