Thioacetamide complexes

At intermediate pH values, particularly in weakly acidic solutions (pH > 2), metal sulphide formation using thioacetamide may proceed through decomposition of a metal ion (or solid phase)-thioacetamide complex rather than through intermediate formation of sulphide [4] (see Sec. 3.3.3). Thioacetamide in pure water is fairly stable and does not readily hydrolyze at room temperature. 

Many sulphides have been deposited using thioacetamide in acidic solutions (Chapter 6 describes most of these). For depositions using thioacetamide, as with thiosulphate, there are no detailed mechanistic studies. Both H2S formation and complex decomposition are possible in acid solutions, as discussed in Section 3.2.1.3. Deposition of CdS was accomplished using thioacetamide in acidic solution by exploiting electrolytic proton reduction to increase the pH locally at the cathode (substrate), and the mechanism was believed to be a surface-catalyzed decomposition of a Cd-thioacetamide complex [80]. 

In the titration of thioacetamide with silver nitrate in distilled water and in slightly acidic or basic solution, a black precipitate of silver sulfide formed. The other products of the reaction were ammonium nitrate and acetic acid. Two reaction pathways have been suggested for the course of this reaction, Scheme 3 and equation (24).349,330 In the presence of 0.1 MHN03, the reaction proceeded similarly. However, in 0.5 M or more concentrated HN03 solutions a different reaction took place. Under these conditions a light, pearly precipitate was formed and a silver thioacetamide complex was obtained. 

The increase in electrophilicity of coordinated ligands commonly leads to more favorable hydrolysis reactions. There are many reports on hydrolysis reactions of coordinated carboxamides, halogenated alkylamines, Schiff bases, thioamides, nitriles, etc. For example, thiourea and thioacetamide complexes of platinum metals decompose on heating in basic solution with formation of the corresponding metal sulfides, Eq. 1.26 and 1.27 ... 

We could not find any study of Bi(III) ions in aqueous solutions except that Wang et al. [132] obtained nanorods of bismuth sulphide by sonicating an aqueous solution of bismuth nitrate and sodium thiosulphate in the presence of complexing agents such as ethylenediamine tetraacetic acid, triethanolamine and sodium tarta-rate. Similar results were found when thioacetamide was used in place of sodium thiosulphate as a source of sulfur. However, the results improved with higher yield... 

Bi2S3, Bi2Se3. Bismuth nitrate complexed with triethanolamine or EDTA and thioacetamide, with the addition of hydrazine hydrate, have been... 

Co2+, Cu2+, Pb2+ Na2S (sodium sulphide), CH3CSNH2 (Thioacetamide) As insoluble sulphides and complexes... 

The aldol condensation of benzaldehyde with the thioacetamide carbanion (RCHCSNRV), derived from the desilylation of the silyl-thioether with tetra-/i-buty-lammonium fluoride, is stereoselective at—80°C producing the erythro isomer of the p-hydroxy thioamide preferentially (Scheme 6.18, R = Me, erythro threo 95 5) via a conformationally mobile intermediate. However, when R is bulky, a greater amount of the threo isomer is formed. Predictably, as the reaction temperature is raised, so the stereoselectively decreases. This procedure contrasts with the corresponding condensation catalysed by titanium salts, where the complexed intermediate produces the threo isomer [47, 48],... 

Going one step beyond, the reaction of these n-donor-substituted Group 6 allenylidenes with bifunctional N,N- or W, 5-dinucleophiles opened up a fruitful route for the synthesis of an extensive family of N- or 5-heterocyclic carbenes. Thus, treatment of complex [Cr =C=C=C(NMe2)Ph (CO)5] with benzamidine, guanidine or thioacetamide has been reported to yield the a,(3-unsaturated carbenes 54 (Scheme 16) [62], arising from nitrogen attack at Cy, subsequent HNMe2... 

Mixed donor ligands. On the basis of spectral, magnetic, and conductivity data the secondary copper(i) dithizonate is assigned structure (183). " The complex CuCl(thioacetamide) is polymeric with co-ordination via the S atom of the... 

There are other bath compositions based on different sulphide-generating precursors and/or complexing agents. Thioacetamide and thiosulphate are two of the former, while ethylenediamine is a common example of a complexant that has been used instead of ammonia. The volatility of ammonia, and its gradual loss in an open deposition bath, is circumvented by using a less volatile complexant, such as ethylenediamine. 

AS2S3 was deposited at room temperature (27°C) from an acidic (pH 2) thioacetamide bath containing AS2O3 dissolved in concentrated HCl (and in some cases complexed with EDTA) [16]. The terminal thickness (which reached a maximum and then decreased with time) was studied as a function of various deposition parameters. Well-defined XRD peaks were obtained showing the monoclinic structure (notable since this compound has a tendency to be amorphous or nearly so as deposited). A direct bandgap of 2.42 eV (similar to the standard value for AS2S3) was estimated from the optical spectrum. The resistivity was ca. 10 H-cm. 

A fairly strongly acidic thioacetamide bath (pH between 1 and 2) was described in Ref 23, both with and without EDTA (sodium salt) as a complexant While some structural differences as well as variations in film thickness were noted between the films deposited from baths with and without EDTA, they were not highly significant. As with most other acidic baths, the films were clearly crystalline, showing defined XRD peaks that allowed a crystal size of the order of 10 nm to be estimated. 

CoS was deposited at room temperature from a triethanolamine/ammonia-complexed solution of C0CI2 using thioacetamide as sulphur source [36]. Both compositional analysis (CoS 1.035) and XRD analysis showed the formation of CoS. From the optical spectrum, a direct bandgap of 0.62 eV was found. The films were p-type with a resistivity of ca. 10 fl-cm. 

A study of the species present in these solutions and the mechanism of the deposition has been presented [71]. Under the conditions of the depositions, the main solution indium species (in the absence of thioacetamide) are In-Cl (mainly [InCU] ) complex species. Only ca. 1% of the total In content is present as free In. No ln(OH)3 or hydroxy-complexes were calculated to be present if acetic acid was present (in the absence of acetic acid, the hydroxide could form). From a kinetic analysis of the deposition reaction, it was concluded that the deposition occurred by direct reaction between the thioacetamide and the chloro-indium complexes. It was noted that thioacetic acid was the main by-product and that no acetamide was detected (see 8ec. 3.2.1.3 for a description of the possible mechanisms and by-products of thioacetamide hydrolysis). Acetonitrile (CH3CN), a less common by-product, was also detected at the higher pH values (these depositions took place between a pH of 2 and 3) but not at the lower ones. 

MnS was deposited from a room-temperature solution of Mn(II) acetate complexed with triethanolamine and buffered with NH4CI [73]. Thioacetamide was used as a sulphur source, and hydrazine was also used (it was not specified whether the reaction proceeded in its absence). No XRD pattern was seen in the as-deposited (grey-pink) film annealing at 500°C in an inert atmosphere gave a pattern corresponding to MnS. A bandgap (indirect) of 3.25 was measured from the optical spectrum. The film was p-type with a resistivity of ca. 10 O-cm. 

In this case, thioacetamide was used as the sulphur source, instead of thiourea as for the previous mixed sulphides-selenides (selenosulphate, as before, was used as the Se source) [56]. Bi(N03)3 was complexed with triethanolamine and the pH adjusted with ammonia to 8.2. The deposition was carried out at 55°C. The composition was varied by varying the thioacetamide/selenosulphate ratio. Although it is not clear what the elemental compositions of the various films were, from the limited XRD data given, it seems that solid solution did occur. The crystal sizes increased from 6 nm (pure sulphide) to 13 nm (pure selenide), and bandgap values decreased over the same range from ca. 1.9 to 1.0 eV. 

Nickel(II) complexes with thioacetamide (310) are similar to the corresponding ones with thiourea and were synthesized in a similar way. 

Thioacetamide, MeC(=S)NH2 (taa), is isoelectronic with thiourea which it resembles by acting as a unidentate S-donor ligand. Thiobenzamide, PhC(=S)NH2 (tba), behaves similarly. Both thioamides form stable complexes with (b) class and borderline metals. Thioacetamide forms the tetrahedral complexes [MX2(taa)2] (M = Fe, Co, Zn X = Cl, Br, I, NCS).47,153-157 The v(M—S) frequency is rather low, ranging from 255 to 230cm, .14s The Mossbauer spectra of FeX2(taa)2 PC = Cl, Br) are consistent with a tetrahedral configuration.158... 

---