Arsenic molecular structures

Figure 13.17 Molecular structure of some sulfides of arsenic, stressing the relationship to the AS4 tetrahedron (point group symmetry in parentheses).

The molecular structures of diazaarsoles and thiazaarsoles known from x-ray diffraction are given in Table 1. The five-membered rings are planar and their bond lengths are in accord with a delocalized cyclic 7r-system. A peculiar feature of the 4-triazenyl-l,2,3-diazaarsole structure is a short intramolecular contact of 250(1) pm between the terminal nitrogen atom of the side chain and the arsenic atom. 

Fig. 16.38 Molecular structures of two arsenic sulfides. Defences in ptcameters...

Pankratov, A.N. and Uchaeva, I.M. (2000) A semiempirical quantum chemical testing of thermodynamic and molecular properties of arsenic compounds. Journal of Molecular Structure (Theochem), 498, 247-54. 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

Emerson, K. and D. T. Britton The Crystal and Molecular Structure of Arsenic Tricyanide. Acta Cryst. 16, 113 (1963). 

The synthesis, IR, 19F-NMR, and X-ray crystal and molecular structures of XV have been reported. It is the first well-characterized four-membered As—N ring compound with arsenic atoms of coordination number five. It has been prepared by the following reaction ... 

The crystal and molecular structures of two spiroarsoranes of type XXI (R = Ph, R = R" = CH3 and R = OH, R = R" = H) have been determined by single-crystal X-ray diffraction analyses (68, 69). The crystal data for these compounds are summarized in Table V. Both compounds have a geometry at the arsenic atom that lies on the Berry coordinate between rectangular-pyramidal and trigonal-pyramidal. These structures show close parallels between the structures of related arsenic and phosphorus systems. It has been concluded that, since the solid-state structures of these compounds lie close to the Berry coordinate, the dynamic process in solution is distortion along that coordinate (68, 69). 

The organic compounds having aggressive action usually contain atoms of halogen, sulphur or arsenic or radicles such as —NOg, —CN, etc., in their molecules. It is to these atoms or radicles as well as to the molecular structure that the physio-pathological action is nowadays attributed. 

The crystal and molecular structure of (S)-7-phenyldinaph[2,l-h T,2 -d]arsole (82), which was obtained by spontaneous resolution of the racemate from hot methanol, reveals appreciable bending of the distorted naphthyl residues away from each other (Scheme 4) . The molecule is fluctional in solution on the NMR time scale, however, with similar barriers between the conformational isomers (atropisomers) for the 7-phenyl [AG 59 1 kJ mol" (259 K)] and the 7-methyl [AG 65 1 kJmol" (287 K)] compounds. The analogous phospholes are also unsuitable for resolution because of similarly low barriers to inversion of the atropisomers - Both arsenic ligands, when coordinated to iron(II) in complexes of the type [( -C5H5) l,2-C6H4(PMePh)2 FeL]PFg,... 

Several molecular structures, including those of T1(I) nitrate," " iodate," " borate," germ-anate," sulfate, " phosphates, arsenate, chromate," and selenate," have been reported. Heterobimetallic compounds with Tl-0 interactions have been reported. Their metal-thallium bonding and their photophysical properties are of particular interest. 

The crystal and molecular structure of the 2,4,6,8-tetraoxa-l,3,5,7-tetraarsaadamantane (346) has been determined <80ICA67>. It can be considered as being structurally related to AS4O6, in which the four arsenic atoms are at the corners of a tetrahedron, with the six oxygen atoms forming an octahedron. 

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