Sulfur structure studies

Structure. The thiosulfate sulfur atoms have been shown to be nonequivalent by radioactive sulfur exchange studies (1). When a sulfite is treated with radioactive sulfur and the resulting thiosulfate decomposed to sulfur and sulfite by acids, the radioactivity appears in the sulfur ... 

It is likely that the lead and sulfur atoms in most of the lead sulfarsenites and related minerals have the tercovalent argonic structures Pb—- and S y+, as in galena. Nowacki (1969) has published a valuable summary of results of structural studies of the so-called sulfosalt minerals, in relation to a system of classification of the structures that he has developed. Many structures of sulfide minerals have been determined by him and his coworkers. 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

III. Application of EPR to the Structural Study of Iron-Sulfur Proteins... 

The properties of these complexes are well studied 126,132). Although monomeric in solution 126,133), they are dimeric in the solid state and a structural study of Cu(Et2copper atom lies 0.26 A out of the plane formed by four sulfur atoms at a distance of 2.30(1) A. A fifth, long Cu—S bond (2.85 A) is approximately perpendicular to this plane, whereas a hydrogen atom of an ethyl group is situated at the other side of the S4 plane at a distance of 2.86 A from the copper atom. 

Structural Studies on Chondroitin Sulfuric Acid. I. The Nature of... 

Given the efforts in this group and others (Table 1) to form the Cd based II-VI compounds, studies of the formation of Cd atomic layers are of great interest. The most detailed structural studies of Cd UPD have, thus far, been published by Gewirth et al. [270-272]. They have obtained in-situ STM images of uniaxial structures formed during the UPD of Cd on Au(lll), from 0.1 M sulfuric acid solutions. They have also performed extensive chronocoulometric and quartz crystal microbalance (QCM) studies of Cd UPD from sulfate. They have concluded that the structures observed with STM were the result of interactions between deposited Cd and the sulfate electrolyte. However, they do not rule out a contribution from surface reconstructions in accounting for the observed structures. 

The high nucleophilicity of heterosubstituted allyllithium compounds makes them attractive reagents in synthetic organic chemistry. Structural studies of these compounds give a fundamental understanding about the control of the regioselectivity. Often, these studies are difficult due to the tendency of the compounds to form complex fluxional aggregates in solution. Piffl and coworkers have studied the dependency of the oxidation state of sulfur on the structure and electronic properties of the heterosubstituted... 

Table I lists isomorphous replacements for various metalloproteins. Consider zinc enzymes, most of which contain the metal ion firmly bound. The diamagnetic, colorless zinc atom contributes very little to those physical properties that can be used to study the enzymes. Thus it has become conventional to replace this metal by a different metal that has the required physical properties (see below) and as far as is possible maintains the same activity. Although this aim may be achieved to a high degree of approximation [e.g., replacement of zinc by cobalt(II)], no such replacement is ever exact. This stresses the extreme degree of biological specificity. The action of an enzyme depends precisely on the exact metal it uses, stressing again the peculiarity of biological action associated with the idiosyncratic nature of active sites. (The entatic state of the metal ion is an essential part of this peculiarity.) Despite this specificity, the replacement method has provided a wealth of information about proteins that could not have been obtained by other methods. Clearly, there will often be a compromise in the choice of replacement. Even isomorphous replacement that should retain structure will not necessarily retain activity at all. However, it has become clear that substitutions can be made for structural studies where the substituted protein is inactive (e.g., in the copper proteins and the iron-sulfur proteins). It is also possible to substitute into metal coenzymes. Many studies have been reported of the...

Cyclization of benzophenones having an o -thioacetic acid, ester or amide group has been used in structure studies and to synthesize 3-phenylbenzo[6 ]thiophenes with specific substituents. Thus (57) was readily converted to (58 X = OH, OEt or NH2) as precursors to a variety of benzo[6 ]thiophenes (57AC(R)705>, and as precursor to the unequivocal synthesis of 3-phenylbenzo[6 jthiophene, to demonstrate a remarkable sulfur-catalyzed rearrangement (59AJC218). 

Since the first report of the sulfur-addition reaction to 1,1-dithio complexes (156), a number of structural studies have verified the originally proposed ring expansion of the MS2C ring following this reaction. In addition, mechanistic studies on the sulfur insertion reaction and electronic spectral studies of the perthiocarboxylate Ni(II) complexes have been reported. 

Trihalosulfonium Ions. Of the parent trihalosulfonium ions, X3S+ (X = F, Cl, Br), F3S+ and C13S+ were reported first. The reaction product of SF4 and BF3 was described by Bartlett as the SF4BF3 adduct,199 but it was subsequently proved by structural studies (NMR, Raman, IR)200 201 to be the F3S 1 BF4 salt. According to crystal structure analysis,202 the ion F3S+ is of C3v symmetry and has very short S—F bonds (1.495 and 1.499 A) indicative of a substantial positive charge on sulfur. Other F3S+MF6 (M = As, P, Sb) salts were studied by Gillespie and co-workers.200... 

Shine and co-workers239,240 have reported the synthesis and full NMR characterization of a series of alkoxysulfonium ion perchlorates including ions 85 derived from cis- and fraws-substituted cyclohexanols. The X-ray structural study of four salts showed that the orientation of the S O bond is always pseudoaxial. The optically active (—)-86 ion and similar systems have been synthesized.241 1H and 13C NMR measurements indicate that sulfur has a trigonal bipyramidal geometry due to the S—O intramolecular interaction in the axial position. 

In this way it was established that both thiazone and thianthrene structures are present in all the quinoneimine sulfur dyes studied (C.L. Vat Blue 43, 53630 [1327-79-3] C.L Sulphur Black 6, 53295 [1327-16-8], C.l. Sulphur Black 7, 53300 [1327-17-9]-, C.L Sulphur Black 11, 53290 1327-14-6] and C.L. Sulphur Red 5, 53820). The thianthrene structure was also found to contribute greatly to the sub-stantivity of the dyes. 

The important point to appreciate is that the formal valency of zinc is satisfied by two bonds to sulfur so that the additional interactions are indeed hypervalent interactions. Thus, the nature of the adopted structures arises from the ability of the central element to form hypervalent, or secondary, interactions and it is proposed that this ability is moderated by steric considerations associated with the alkyl substituents. As noted from the structural studies for the uncoordinated xanthate anions summarized earlier in Section II, there are no electronic differences among the xanthate ligands that can be correlated with the nature of the oxygen-bound substituent. This conclusion is vindicated by the homogeneity of the molecular structures of the binary nickel xanthates as... 

---