INORGANIC LINKAGE ISOMERISM OF SELENOCYANATE ION

Utilization of the steric hindrance created by the ligand 1,1,7,7-tetraethyldiethylenetriamine, Et4dien, when complexed with palladium(II), has resulted in the first synthesis of inorganic linkage isomers of the selenocyanate ion. The formulation of [Pd(Et4dien)SeCN][B(C6H5)4], isolated at low temperatures, as an Se-bonded complex is supported by the integrated absorption intensity of its C-N stretching band and characteristic shifts, relative to those of the free ligand, of its C-Se stretching and NCSe bending vibrations. Dissolution in a variety of solvents yields the corresponding N isomer, the first-order rate of isomerization decreasing as the dielectric constant of the solvent is decreased, thereby supporting a dissociative process. The isomerization produces characteristic band shifts in both the infrared and visible-ultraviolet spectra of the complex. The corresponding diethylenetriamine complex, [Pd(dien)SeCN][B(C6H5)4], has been found to be stable with respect to isomerization. Surprisingly, the N-bonded isomer of the Et4dien complex, once isolated, reisomerizes to the Se-bonded form at room temperature in the solid state. The tetraphenylborate salt of [Pd(Et4dien)NCS]+ behaves in an analogous manner, but the thiocyanate salt is stable with respect to isomerization, both in solution and in the solid state. This represents the first observation of the dependence of the bonding mode of an ambidentate ligand on the nature of a noncoordinated group. © 1969, American Chemical Society. All rights reserved.