A research found out that the presence of other ligands in a
complex apparently affects the mode of thiocyanate
coordination.
The ambidentate nature of SCN may be interpreted in terms of sulfur being a “soft”
base and nitrogen being a “hard” base.
The thiocyanate ion is the only ligand present in a
complex, its mode of bonding generally follows the
hard (M-NCS) or soft (M-SCN) pattern throughout
the periodic table
For example, the pentaamminecobalt(II1) ion forms theCo -NCS linkage,whereas the pentacyanocobaltate-
(111) ion exhibits soft behavior in forming the Co-SCN
bond.
Steric factors in bulky ligands also may alter the
nature of thiocyanate coordination.
Burmeister and Basolo5 used Turco and Pede’s4
a-bonding explanation to synthesize the first thiocyanate linkage isomers.
The S-bonded complex [Pd- (Ph3As)r(SCN)a] is isolated at low temperature, butit is isomerized to the N-bonded species [Pd(Ph3As)z- (NCS)!J when the solid is heated or dissolve.
They noticed that both thiocyanate groups in the palladium complex of diphenyl(o-diphenylarsinopheny1)phosphine sulfide were coordinated via sulfur,this result was unexpected on the basis of pi-bonding consideration.
Moreover, the palladium thiocyanate complex of the parent phosphine-arsine, was
only the second example known at that time that contained both N-bonded and S-bonded nonbridging thiocyanato groups.