Thiocyanato ligands

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

The products of reduction of Fe(NCS)2+ by Cr2+ in aqueous solution containing thiocyanate ions (equation 36), include the isomers of [Cr(NCS)(SCN)(H20)4]+, which contains both bland S-bonded thiocyanate ligands.641 These isomers undergo spontaneous decomposition by parallel aquation (loss of the S-thiocyanato ligand) and isomerization (Cr—SCN— Cr—NCS) reactions. Details of the solution visible spectra of these isomers as well as those of similar chromium(III) complexes for comparison are listed in Table 68. From the compiled data it is apparent that the S-bonded thiocyanate ligand lies very close to Br- in the spectrochemical series while the N-bonded form lies between Nj and NO. 

There are several well-defined mixed Cu(I)-Ou(II) complexes containing cyano or thiocyanato anions. These are Cu(II)Cu(I)2(NH3)4-(CN)4, its 1,2-diaminoethane analog Cu(II)Cu(I)2(en)2(CN)4 (77), and Cu(II)Cu(I)(NH3)3(NCS)3 (125). The last complex is polymeric and contains tetrahedrally coordinated copper(I) atoms which are S-bound to two thiocyanato ligands and N-bound to two further thiocyanato... 

Ligand Replacement Unidentate by Unidentate.—dissociative mechanism is proposed for the replacement of nitrito- or of thiocyanato-ligands in trans-[Co(dmgH)2(N02)2] and in rm/w-[Co(dmgH)2(NCS)2] respectively by thiourea. Thiocyanate is replaced much more rapidly than nitrite from these cobalt(m) centres. Substitution at bisdimethylglyoximatocobalt(m) complexes can be catalysed by cobalt(n) complexes. This has been demonstrated by the elucidation of the rate law for the cobalt(n)-catalysed reaction of trans-[Co(dmgH)2(PPhs)(NOa)] with pyridine ... 

Hexacoordinated salen-silicon complexes can undergo Wurtz-type coupling reactions to produce the first examples of oligosilanes and polysilanes containing hexacoordinated silicon backbones [149]. This principle has been utilized to couple salen-type complexes containing thiocyanato ligands [Si(salen )(NCS)2l to a mixture of linear oligosilanes with a hexacoordinated silicon backbone SCN-[Si(salen )] -NCS with n = 2-8 [147]. 

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