Thiocyanato-complexes

The complex coordination chemistry of Pb" is also beginning to be actively explored and some unusual stereochemistries are emerging. Thus, the mononuclear ( ) -nitrato)bis(phenanthrolene)(A-thiocyanato) complex [Pb(phen)2(NCS)( ) -NO3)] has 7-coordinate Pb" with a large vacancy... 

It should be noted that, by convention, the ambidentate ligand is always written with its donor atom first, i.e. NO2 for the nitro, ONO for the nitrito, NCS for the A-thiocyanato and SCN for the 5 -thiocyanato complex. Differences in infrared spectra arising from the differences in bonding are often used to distinguish between such isomers. 

S.SxlO l.mole .sec and 2xl0 1. mole sec , respectively) (c) the Cr(II)-catalysed isomerisation of CrSCN produced in (a) (k = 42 l.mole . sec ). Rate coefficients pertain to 1 M FICIO4 solutions at 25 °C. Thus an inner-sphere mechanism is demonstrated. The S-bonded thiocyanato complex, CrSCN, is not produced when a solution of Cr -FSCN is oxidised by Fe(III). CrSCN can be prepared by the gradual addition of a 5 x 10 M solution to an equal volume of a well-stirred solution of 5.5 x 10 A/ Fe([II) and 4.5 x 10 M SCN . The product solution is green whereas CrNCS solutions are purple. 

The thermal oxidation of thiocyanate by Fe(III) in a perchlorate medium involves two thiocyanato complexes of Fe(III) . The stoichiometry is thought to be... 

The [Ni(NCS)f,]4 ion is almost perfectly octahedral, with Ni—N distances of around 209.5 pm and N—Ni—N angles around 89.5°. The Ni—N—C and N—C—S entities are practically linear.438,439 In [Ni(NCS)2L2] where L is a R-substituted pyridine, stereochemistry and spin state depend on the type and positions of R.431 While for 2-Me- and 2-Et-pyridine square planar complexes are observed, other pyridins lead to coordination polymers with pseudo-octahedral Ni11 due to N,S-bridging thiocyanate. Ni11 thiocyanato complexes have been studied quite intensively as hosts for inclusion compounds.440"442... 

But in sonicated condition hexamminenickel(II) ions did not form, because of the degassing effect of the ultrasound leading to the removal of ammonia gas during the sonication process. Because of this reason the turbidity in sonicated sample did not come to the zero value (Table 9.8). Ultrasound was also effective in the reduction of crystallization time by 50% in Ni-chloro and by 25% in Ni-thiocyanato complex, which, however, remained the same in NiSO.4 solution as shown in Table 9.10. 

The stepwise stability constants for zirconium and hafnium thiocyanato-complexes have been determined by solvent-extraction techniques. The values ) i = 12.1 2.2, = 215 11, P4. = 205 + 20 for zirconium, and Pi =... 

An interesting study with BATO compounds concerns the linkage isomerization of coordinated [NCS] in [Tc(NCS)(cdoh)2(cdo)(BMe)] (440). Both a red, N-bond isothiocyanato complex [Tc(NCS)(cdoh)2(cdo)(BMe)] and the brown, S-bond thiocyanato complex [Tc(SCN)(dmg)3(BR)] (441) were isolated from the direct synthesis from [Tc04] . The N-bound (440) was found to be thermodynamically more stable than the S-bound isomer (441) and the conversion was monitored elegantly by spectroscopic methods. The X-ray crystal structure of (440) was determined. The NCS and SCN -substituted analogues exhibited r c N stretch at 2,114-2,124 cm and at 2,055-2,079 cm , respectively. " (Scheme 59). 

O-sulfinato complex, 37 287 sulfito complexes, 37 293 sulfur, selenium, and tellurium tetrahal-ide complexes, 37 299 thiocyanato complexes, 37 264 thioether and selenoether complexes, 37 288... 

On the other hand, the reverse trends exhibited by Eu+2 and Fe+2 as reductants imply in part that we are gaining more from the increasing stability of the bond being formed as we go from Br to F than we are losing from the stability of the bond being broken. I think this is also pertinent to the question of comparison of azido and thiocyanato complexes. With Co(CN)fz as reductant, the stable form of the product complex is sulfur-bonded, so that the orientation of the ligand in the oxidant is favorable for remote attack on the sulfur end, whereas the situation is unfavorable for Cr+2 and Fe+2 as reductants. 

The deep blue solutions produced on the addition of thiocyanates to aqueous Cr2+ decompose on standing or concentration. Nevertheless, thiocyanato complexes can be... 

Figure 18 The structure of [W2CWOEt)J191 37.4.5 Thiocyanato Complexes...

A salt of a dioxoneptunium(V) thiocyanato complex, Cs4[Np02(NCS)5], has been recorded the coordination geometry of the complex anion is presumably pentagonal bipyramidal. 

Most of the bis adducts NiX2L2 (L = substituted imidazoles and pyrazoles) have pseudo-tetrahedral coordination, but some of the chloride and thiocyanato complexes can be six-coordinate in a polymeric structure. 

In aqueous solution, thiocyanato complexes of the type Agm(SCN) 2 2 have been inferred from solubility and potentiometric data. For high concentrations of thiocyanate the complex having m = 1 was predicted to be the most abundant. Thermodynamic data are collected in Table 23.140141... 

The nature of thiocyanato complexes of silver in non-aqueous solvents has recently been reassessed.145 IR and Raman spectra were used to show that when Ag+ was complexed by SCN, the species present and the equilibrium steps involved were solvent specific. Characteristic absorption bands are summarized in Table 24. In pyridine, complexation passed through [Ag2(SCN)]+ and AgSCN to [Ag(SCN)2], such that even when the [SCN ]T/[Ag+]T ratio was 0.059, 50% was present as the linear [Ag(SCN)2]- ion. 

Most thiocyanato complexes of gold(III) are S-bonded. These include [Au(SCN)4]- and the complexes (65)—(67), which are formed by oxidative addition of thiocyanogen to the corresponding gold(I) complex.295,527-529... 

Mixed halide-thiocyanate compounds Hg(SCN)X (X = Cl, Br, I) are formed from equimolar amounts of the pure components. They contain six-coordinated mercury(H) achieved by bridging X and SCN groups.234 The formation constants of the mixed thiocyanato complexes have been detected spectroscopically.233 Raman spectra of mixed halothiocyanatomercurate(U) complexes have been reported by Cooney and Hall.236 The structure of ammonium... 

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