Monoclinicity tellurium

Te (tellurium, brown black, amorphous), Te02 (tellurous anhydride, white), Te02 hydr. (tellurous acid, H2Te03 or Te02-H20, white, amorphous), TeOs hydr. (orthotelluric acid, H6Te06 or Te03 3H20, colorless, cubic or monoclinic). 

NMR spectroscopy ( Se, /= 1/2, 7%) is a powerful technique for identifying cyclic selenium molecules, especially the heteroatomic ring systems that contain sulfur or tellurium in addition to selenium, for which several isomers are possible for most compositions (Section 12.1.2). Solutions of monoclinic selenium in CS2 have been shown by high-performance liquid chromatography to form an equilibrium mixture of cyclo-Seg, cyclo-Sey and cyclo-Se6. The Se NMR spectra of such solutions show two singlets that are attributable to cyclo-Seg and cyclo-Se with relative intensities that correspond to a molar ratio of ca 6 No resonance is observed for cyclo-Sey presumably as a result of the fluxional behaviour (pseudorotation) of the seven-membered ring (Section 12.1.2). 

Di-o-tolyl tellurium dichloride, (CH3.C6H4)2TeCl2,is prepared in a similar manner to the corresponding phenyl compound. It is best recrystallised from absolute alcohol, separating as small monoclinic tablets. M.pt. 183° C., readily soluble in benzene, toluene or xylene, but sparingly soluble in ligroin, methyl or ethyl alcohol. 

Di-o-tolyl tellurium oxide, (CH3.C6H4)2TeO, occurs when the dibromide is treated with 5 per cent, sodium hydroxide. It separates from toluene as small monoclinic columns, sintering at 199° C. and melting at 205° to 206° C., readily soluble in alcohols, sparingly soluble in benzene or toluene. Its aqueous solution has an alkaline reaction. 

Di-p-tolyl tellurium di-iodide, (CH3.C6H4)2TeI2, crystallises from toluene as deep red prismatic crystals of the monoclinic system, melting at 218° to 219° C. on rapid heating. 

The rickardite structure was found also in Ni8 zTe2 (218), In the nickel compound non-metallic properties are excluded already by equation (7). Above 140—250° C the occupation of the octahedral sites is random but at lower temperatures the cations order and a monoclinic superstructure is formed on the nickel-rich side while a tetragonal cell results on the tellurium-rich side of the composition range (218). 

This is very different from sulfuric and selenic acids. It consists of hydrogen-bonded octahedral molecules Te(OH)6 in both its cubic and monoclinic crystalline forms. The acid or its salts may be prepared by oxidation of tellurium or Te02 by H202,... 

Class I. ELEMENTS. A. Metals. Cubic copper, silver, gold, iron, platinum, iridium. - Tetragonal tin. - Rhombohedral and Hexagonal arsenic, antimony, bismuth, tellurium, (Os, Ir). - B. Metalloids. Cubic diamond. - Hexagonal graphite. - Orthorhombic sulfur, iodine. - Monoclinic sulfur, selenium. - Class II. SULFIDES. - Class HI. HALIDES. -Class IV. OXIDES, divided into SIMPLE OXIDES and COMPLEX OXIDES, such as CARBONATES, PHOSPHATES, SILICATES, BORATES and SULFATES. 

Fig. 6.14 (a) Molecular structure of /rans-teirachlorobis(tetramethylthiourea)tellurium(IV) in the monoclinic form. Note that the line Cl(4)—Te—Cl(2) approximates an axis for a pentagonal bipyramid if it is assumed that a lone pair occupies a position between S(l) and Cl(3) [Pg.120]

The largest molecule of oxygen is triatomic ozone, but selenium and tellurium form longer chains in the elemental state, like sulfur. The crystal structures of the two red, monoclinic (a and ff) modifications of selenium have been determined by Burbank (38) and Marsh et al. (170). In these, the molecules are Se8 rings of the same crown form as S8 sulfur, while... 

A crystalline phase of sulfur has been synthesized by workers (3, 4, 5, 6, 7) at pressures above 21 kb at temperatures in excess of 210°-240°C. This phase is insoluble in CS2. Lind and Geller (8) showed that this high pressure phase, designated fibrous sulfur, is monoclinic (P2) and consists of right and left handed helices. This helical structure resembles slightly the helicoidal zigzag chain structures of selenium and tellurium at ambient conditions. Fibrous sulfur has several properties characteristic of a modest semiconductor such as a steep negative temperature coeflBcient of resistance and a photoelectric eflFect. It shows also an EPR absorption peak and does not revert at ambient conditions (for up to 4 years) to ordinary octameric sulfur (6,7),... 

From evidence of diatomic selenium and tellurium in the vapor state and of octameric puckered rings in monoclinic selenium, as well as evidence of metallic tellurium at high pressure (23), it is suspected that in principle (if sluggish kinetics can be overcome) pressure and temperature may induce transformations in other group VI A elements comparable with those observed in sulfur. 

Figure 5 The structure of the monoclinic form of frfl i-tetrachlorobis(tetramethylthiourea)tellurium(lV) (reproduced by permission from Acta Chem. Scand., Ser. A, 1975, 29, 141)...

Figure 11 tra.ns-Dimethanethiosulphonatobis(ethylenethiourea)tellurium n), as seen normal to the TeS4 co-ordination group. Left triclinic dimorph right monoclinic dimorph. Tellurium atoms in centres of symmetry (Reproduced by permission from Acta Chem. Scand., 1973, 27, 218)... 

---