Thiocyanate ligand

Scheme 3.5 Norephedrine-derived amino thioacetate and thiocyanate ligands for additions of ZnEt2 to aldehydes.

The Ru redox potentials of the thiocyanate complexes were more positive (by 350 mV) than its corresponding dichloro complexes and show quasire-versible behavior. This is in good agreement with the Ligand Electrochemical Parameters scale, according to which the thiocyanate Ru wave should be 340 mV more positive than the dichloro species Ru° potential [56]. The ioJ ired peak current is substantially greater than unity due to the oxidation of the thiocyanate ligand subsequent to the oxidation of the ruthenium(II) center. 

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. 

The reaction of [MoCLt(NCMe)2] with K(SCN) in MeCN solution yields [Mo(NCS)6]2- and this anion has been isolated as its [NBu4]+ and [AsPh4]+ salts.188 Vibrational spectroscopy has indicated N-bonded rather than S-bonded thiocyanate ligands. The adduct [Mo(NCS)4(bipy)] has also been obtained.189... 

The coordination chemistry of the cyanate, thiocyanate and selenocyanate ligands has been recently reviewed.1874 Platinum(II) forms the complex ion Pt(SCN)2-, and the corresponding homoleptic platinum(IV) complex Pt(SCN)i can be prepared. Numerous mixed ligand complexes of platinum(II) are known containing the thiocyanate ligand and other ligands, although there are fewer platinum(IV) examples. 4... 

Much discussion on the coordination chemistry of the thiocyanate ligand centers on its function as an ambidentate ligand. For coordination to platinum both N-bonded and S-bonded thiocyanate ligands are found and the small energy difference between the two bonding modes leads to small effects such as steric and electronic factors, as well as solvent changes, causing conversion between S- and N-bonded thiocyanate. 

The thiocyanate ligand will also bridge two metal ions. The a and (i forms of Pt2Cl2(NCS)2(PPr3)2 initially prepared by Chatt have been shown by crystallography to have the structures (210) and (211).1883... 

Crystal structure data are available for Ag(tu)2Cl,343 Ag(tu)3C104344 and Ag(tu)2SCN.345 In the latter compound the Ag atoms were coordinated by two thiourea S atoms (Ag—S = 248.2 and 246.2 pm) and one S of a thiocyanate ligand (Ag—S = 260.8 pm). The three S atoms formed an almost planar arrangement with the central Ag atom. A fourth sulfur atom was much more weakly bound (Ag—S = 311.1 pm) and completed a highly distorted tetrahedron. In addition, it acted as a bridge to the second half of the centrosymmetric dimer (43). 

Many organometallic derivatives are known, including complexes with bridging thiocyanate ligands.530,531... 

All are based on a centred icosahedron of gold atoms with two atoms missing, and each peripheral gold is bound to either a phosphine or a halide or thiocyanate ligand.693-696 A typical skeletal structure for the [AU11X3L7] structure is (111). Some closely related derivatives of formula [AunX2L8]+ are also known.692... 

The nature of the anion can play a part in determining the mode of bonding in the solid state. Thus the complex cation [Pd(CNS)(Et4dien)]+ has an N-bonded thiocyanate ligand in its most stable form when SCN- is the counterion,73 but when PF or BPhiT are the counterions the stable isomer in the solid state has S-bonded thiocyanate ligands.75,76... 

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