Aqueous nickel thiocyanato complexes

The thiocyanate ion is a widely studied ligand, mainly due to its ambidentate nature. Aside from some general reviews [75NEW2], [79GOL/KOH], a critical survey of stability constants of thiocyanate complexes has been published [97BAH/PAR]. The latter publication listed the majority of available thermodynamic data for the Ni(II) - thiocyanate system, but recommended values are given only for log, y9, (V.116) at / = 1.0 and 1.5 M. 

Several experimental values are published for log,Q (or log,g ) [64TRI/CAL], [71LAN/CUM], (or [88BJE2]). In [64TRI/CAL] there was a rather small excess of ligand ( 0.5 M), and for both ionic strengths is reported. Con- 

Method Medium /m G°C) og 0 P. reported ogioA retained Reference 

Method Medium L ICO logic A reported logic A accepted Reference 

Method Medium /m t( C) logio A reported logic A acceptedl Reference 

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Differential calorimetry has been used to measure the enthalpies of formation of the MSCN complexes (M = Mn(II), Co(Il), Ni(ll), Cu(II), Zn(ll), Cd(ll) and Pb(Il)) in aqueous solutions at 25°C. No backgroimd salt was used to attempt to maintain constant ionic strength. The concentration of nickel(ll) perchlorate varied between 5.04 and 8.9 mM, while [SCN ],ot ranged from 2.44 to 4.31 mM. Thus only the mono-thiocyanato complex was formed in the calorimeter ... 

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