Selenium– and tellurium–halogen reagents

Selenium and tellurium form binary halides in which the chalcogen can be in formal oxidation states (IV), (II) or (I). They are versatile reagents for the preparation of a wide range of inorganic and organic selenium and tellurium compounds taking advantage of the reactivity of the chalcogen–halogen bond. With the exception of the tetrafluorides, the tetrahalides are either commercially available or readily prepared. On the other hand, the low-valent species, EX2 (E = Se, Te; X = Cl, Br) and E2X2 (E = Se, Te; X = Cl, Br) are unstable with respect to disproportionation and must be used as in situ reagents. Organoselenium and tellurium halides are well-known in oxidation states (IV) and (II), as exemplified by REX3, R2EX2 and REX (R = alkyl, aryl; E = Se, Te; X = F, Cl, Br, I); mixed-valent (IV/II) compounds of the type RTeX2TeR are also known. This chapter surveys the availability and/or preparative methods for these widely used reagents followed by examples of their applications in synthetic inorganic and organic selenium and tellurium chemistry. For both the binary halides and their organic derivatives, the discussion is subdivided according to the formal oxidation state of the chalcogen.

Li2GeMo3O8: a novel reduced molybdenum oxide containing Mo3O13cluster units

The crystal structure of the title compound, dilithium germanium trimolybdenum octaoxide, consists of distorted hexagonal-close-packed oxygen layers with stacking sequenceABACalong [001] that are held together by alternating lithium–germanium and molybdenum layers. The two Li+and Ge4+ions all have site symmetry 3m. and occupy, respectively, tetrahedral and octahedral sites in the ratio 2:1. The Mo atom has a formal oxidation state of +3.3 and occupies an octahedral site (site symmetry .m.) and forms strongly bonded triangular cluster units [Mo—Mo distance = 2.4728 (8) Å] involving three MoO6octahedra that are each shared along two edges, constituting an Mo3O13unit.

Structural characterization of the μ-nitrido complex {[Fe(OEP)]2N}

The molecular structure of the μ-nitrido dimer, μ-nitrido-bis(2,3,7,8,12,13,17,18-octaethylporphyrinato)iron, is reported. The axial Fe – N distances average to 1.657(11)Å and the equatorial distances average to 2.005(5)Å. Although not required by symmetry, the two iron centers appear equivalent and are consistent with an assignment of a low-spin state and a formal oxidation state of +3.5. A comparison of this structure with other nitrido-bridged species is given.

Mössbauer Spectroscopic Investigation of the Cesium Suboxoferrate(III) Cs9FeO4

57Fe Mössbauer spectroscopic studies have shown that in cesium suboxoferrate, Cs9FeO4, the iron atom has the formal oxidation state +III. The isomer shift δ = 0.10(1) is in very good agreement with that of a large number of ionic ferrates(III). The same holds for geometrical details of the [FeO4]5− anion, which shows only a small deviation from ideal tetrahedral symmetry giving rise to a quadrupole splitting of ΔEQ = 0.36(2) mm/s