Thiocyanate linkage isomers

Electronic Effects The first thiocyanate linkage isomers were isoluled after it was noted that the struc-... 

Relative stabilities of the thiocyanate linkage isomers in solution depend upon the nature of the solvent. Thus, square-planar Pd(II) and Pt(II) complexes of type ML2(CNS)2 (L = PPh3, AsPh3, SbPh3, and other neutral ligands) adopt only the S-bonded mode in solvents such as DMF... 

Linkage isomerism This is a special type of structural isomerism in which the differences arise from a particular ligand which may coordinate to a metal ion in more than one way. In Table 1-3 we indicated that a ligand such as thiocyanate could bond to a metal through either the nitrogen or the sulfur atom, and the complex ions [Co(NH3)5(ACS)]2+ and [Co(NH3)5(5CN)]2+ are related as linkage isomers. 

The most stable structures and formation energies of zinc thiocyanate complexes have been calculated by ab initio density functional methods. The formation energies of the linkage isomers [Zn(NCS)4]2. [Zn(NCS)2(SCN)2]2, and [Zn(SCK)4]2 were determined. A comparison of the formation energies indicated that [Zn(SCN)4]2 is the most stable isomer both in water and in dimethyl sulfoxide.567... 

Identification of trace amounts of impurities and/or isomers by these techniques is a rather exhausting task. We and others find that the HPLC method is more useful for identifying linkage isomer impurities (e.g., involving N- or S-bound thiocyanate).32,112... 

The nature of the solvent may modify the mode of thiocyanate coordination of certain complexes in solution. For example, a study of the behaviour of [Pd(NCS)2(AsPh3)2] and its linkage isomer in a number of different solvents concludes that Pd—SCN bonding is promoted by solvents with high dielectric constants, whereas solvents with low dielectric constants result in a mixture of Pd—NCS, Pd—SCN and Pd—SCN—Pd bonding modes.78... 

Electronic effects become apparent in the M—NCS/M—SCN linkage switches observed in a series of Pd11 (iso)thiocyanate complexes. Ligands positioned trans to the pseudohalide and that are suited to accept electron density from the metal into empty orbitals (backbonding) stabilize the Pd—NCS linkage isomer. However, this rationale is contradicted by the trend in Co—(NCS) bonding in a series of cobalt complexes (see ref. 204b for a review). 

Scheme 1 Linkage isomers of bis(thiocyanate)(2,2,-bipyridine)platinum(II)) their interconversion, and their emission maxima and excited states at 77 K. Based on data from [48]...

The organometallic complexes of these metals with thiocyanate are important because linkage isomers have been obtained (690). Some of the relevant compounds are included in Table XXIII. The compound 7T-cpW(CO)gSCN, which was characterized by the positions of its CN and CS frequencies and by the integrated intensity of the former, resists all attempts to convert it to the A-thiocyanato isomer, unlike... 

The effect of different solvents on the type of thiocyanate coordination has been studied by dissolving the two linkage isomers (Pd-(AsPh3)2(CNS)2 in various solvents. It was found that Pd—SON bonding was promoted by solvents with high dielectric constants and a mixture of Pd—NCS, Pd—SON, and Pd—SON—Pd bonding by solvents having low dielectric constants (154, 155). These and related results will be discussed in Section V. 

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