Ferrocene/thiourea

At ambient temperature, ferrocene/thiourea has the conventional rhoinbohedral thiourea host structure.The Fe atoms of the fessocene guest molecules occupy the sites of 32 symmetry within the host tunnel, and the cyclopenta-dienyl rings are disordered. Heat capacity measure-ments have suggested that there are five phase transitions (at ca. 147, 160, 171, 186, and 220 K) between 13-280 K, which led to the proposal that the transitions at 147 K and 160 K are associated with reorientational order-disorder processes involving the molecular axis of ferrocene. 

Early studies of the dynamic properties focused on NMR of ferrocene/thiourea-d4, from which it was concluded that the fivefold axes of the ferrocene molecules are frozen in a number of nonequivalent orientations at low temperature, and that the phase transition at 160 K is associated with the onset of reorientational motion of these axes. Anisotropic C-NMR chemical shielding spectra,Mossbauer spectroscopy,and solid-state studies have also shed significant light... 

Thiourea forms a layered lattice able to act as host for some organometallic guest molecules. The ferrocene-thiourea inclusion compound has been investigated by spectroscopic methods (NMR, Mossbauer) and it has been shown that the thiourea host structure is preserved [492-502]. Other inclusion compounds of thiourea with organometallics such as ( /" -l,3-cyclohexadiene)Mn(CO)3, (7/ -C6H6)Cr(CO)3, (/ -l,3-cyclohexadiene)Fe(CO)3, and t/ -C(CH2)3Fe(CO)3 have been reported [503, 504]. 

C12H67FO20S, Tri-n-butylsulphonium fluoride hydrate, 27, 781 Cl 2H88Ni,026 f n-Propylamine clathrate hydrate, 39B, 466 Cl2H118N4O41, Trimethylamine clathrate hydrate, 33B, 260 Cl3H22FeN6N3, Ferrocene - thiourea clathrate, 44B, 571 Cl4H18CdN8Ni, catena-M Ethylenediaminecadmium(lI) catena-tetra-M cy-ano-nickelate(II) - bis(pyrrole), 41B, 701 ClgHigCdNeNi, Diamminecadmium tetracyanonickelate benzene clathrate, 40B, 1096... 

NMR also has been used to further elucidate the structure and dynamic state of the ferrocene-thiourea inclusion compound [21,22] previously studied by Mossbauer techniques [23], [24] and C [25] NMR. First of all, a new single crystal Mossbauer... 

Metallocenes (but only with unsubstituted cyclopentadienyl rings) also form thiourea inclusion compounds. X-ray diffraction and Mdssbauer data on the ferrocene inclusion compound show that at 295 K the guest molecules are orientationally disordered at the sites of 32 symmetry. A phase change at 162 K generates a more ordered structure78). 

When I- is titrated with Cu(Cl04)2 in AN, it is oxidized in two steps, I ->If and If ->I2. The formal potentials of the two steps are +0.396V and -0.248V vs Ag/Ag+, respectively. Many organic compounds, such as hydroquinone, ascorbic acid, ferrocene and its derivatives, allylamine, hydroxylamine, phenylhydrazine, thiourea and SH compounds, can also be titrated with Cu(II) in AN. Figure 4.9 shows the titration curves of tetramethylbenzidine (TMB) in AN [12]. In dry AN, TMB is oxidized in two steps as follows ... 

Copper(II) and cerium(IV) have been studied as oxidants in acetonitrile. The copper(II)-copper(I) couple has an estimated electrode potential of 0.68 V relative to the silver reference electrode. It has been studied as an oxidant for substances such as iodide, hydroquinone, thiourea, potassium ethyl xanthate, diphenylbenzidine, and ferrocene. Cerium(IV) reactions are catalyzed by acetate ion. Copper(I) is a suitable reductant for chromium(VI), vanadium(V), cerium(IV), and manganese(VII) in the presence of iron(III). For details on many studies of redox reactions in nonaqueous solvents, the reader is referred to the summary by Kratochvil. ... 

Hough, E. Nicholson. D.G. X-ray crystallographic studies on ferrocene included in a thiourea host lattice. J. Chem. Soc., Dalton Trans. 1948. 15. 

Clement R. Gourdji. M. Guibe, L. Molecular motions in the thiourea-r/4-ferrocene inclusion compound. Chem. Phys. Lett. 1980. 72. 466. 

Gibb, T.C. Anisotropic relaxation of the electric field gradient tensor in the Te Mossbauer spectra of a thiourea-ferrocene clathrate. J. Phys., C 1976. 9, 2627. 

Atomic absorption spectroscopy is a preferred method in clinical chemistry. However, UV/Vis spectrometry by use of chelating methods combined with photometry of chromophores offers simple and fast approaches. Examples are methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS 1990) taking ferrocene for Fe, eliminating interferences by Cu by addition of thiourea. Mg is determined by addition of xylidyl blue, Ca by use of o-cresolphthalein or arsenazo complexes. Interferences by Mg are reduced by addition of 8-hydroxyquinoline. Further chromophores and complexing agents are discussed in subsequent chapters and elsewhere [39]. 

Addition of thiourea to chalcones containing a ferrocene substituent is usually accomplished by moderate heating of the reactants. The selectivity is low, and chromatographic separation of the products is impaired by their instability. In the presence of sodium ethoxide in ethanol under sonication (Eq. 20), a rapid addition takes place and the adduct crystallizes out of the solution, thus preventing an undesired sonochemical decomposition. 125... 

Ferrocene-containing pyrimidine derivatives have been prepared by addition of thiourea to arylferrocenylpropenones. Heating the reaction components at 60 to 70 °C for 3-5 h gave complex mixtures of products. However, sonication gives the product shown in good yield [197] (Scheme 91). 

In situations where the rate of assembly demands extremely rapid cure times, or where the surfaces to be bonded are inherently unreac-tive, treatment of substrates with a primer is often necessary. Primers consist of compounds which accelerate the curing reactions. Since they would destabilize the adhesive if added directly to the formulation, they are supplied and used as a separate component. The criteria for an acceptable primer include compatibility with the adhesive, the ability to accelerate the rate of curing, and lack of any adverse effects on bond strengths. Various thiazoles, butyral-dehyde-aniline adducts and thioureas " were found to meet these criteria. Since trace levels of transition metals accelerate anaerobic adhesive cure, primers containing complexed copper have been employed successfully. In another system, acidic primers are used which react with ferrocene in the adhesive to release the required metal ions. ... 

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