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Contents 1 Thallium chalcogenides 1.1 Tl2O, Tl2S, Tl2Se, Tl2Te 1.2 Tl5Se3, Tl5Te3 1.3 Tl4O3, Tl4S3 1.4 TlS, TlSe, TlTe 1.5 Tl2O3, Tl2S3, Tl2Se3, Tl2Te3 1.6 TlS2, Tl2S5, Tl2S9 2 Gallium chalcogenides 2.1 Ga2O, Ga2S, Ga2Se 2.2 GaO, GaS, GaSe, GaTe, 2.3 Ga 4S5 2.4 Ga3Te4 2.5 Ga7Te10 2.6 Ga2O3, Ga2S3, Ga2Se3, Ga2Te3 2.7 Ga2Te5, Ga2Te3 3 Sulfur oxo compunds bonding 3.1 (Sulfur dioxide) Structure and bonding 3.2 (Sulfur trioxide) Structure and bonding 3.3 Sulfite ion structure and bonding 3.4 Dithionite Structure and Bonding 3.5 Thiosulfate Structure and Bonding 3.6 SO2 structure and bonding 3.6.1 References

[edit] Thallium chalcogenides

The thallium chalcogenides include all compounds of thallium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with thallium). Some compounds that were reported and have found their way into text books have not been substantiated by later researchers. The list of compounds below shows compounds that have been reported, and those compounds that have not had their structure determined, or whose existence has not been confirmed by the latest structural investigations, are in italics. In contrast to the indium chalcogenides the thallium(I) compounds are well characterised, there are no compounds with a Tl₂²⁺ unit, and the only genuine thallium(III) chalcogenide is the oxide, Tl₂O₃

oxide	sulfide	selenide	telluride
Tl2O	Tl2S	Tl2Se	Tl2Te
		Tl5Se3	Tl5Te3
Tl4O3	Tl4S3
	TlS	TlSe	TlTe
Tl2O3	Tl2S3	Tl2Se3	Tl2Te3
	TlS2
	Tl2S5
	Tl2S9

[edit] Tl₂O, Tl₂S, Tl₂Se, Tl₂Te

All of these compounds are thallium(I) compounds. There are all black with a metallic appearance. Tl₂S occurs as the mineral carlinite and has been used in infrared detectors. Tl₂Se has metallic conductivity, and is a semiconductor in the liquid phase.^[1] The structure of Tl₂Te has been reinvestigated and is shown to be a new structure type related to Tl₅Te₃. ^[2]

[edit] Tl₅Se₃, Tl₅Te₃

Tl₅Se₃ has the Cr₅B₃ structure. Tl₅Te₃ has a structure related to In₅Bi₃, and has been formulated as 9Tl⁺ Tl³⁺ 6Te^{2− [3]}

[edit] Tl₄O₃, Tl₄S₃

[edit] TlS, TlSe, TlTe

TlS and TlSe are both black mixed valence compounds containing thallium in oxidation states +1 and +3. For example TlS can be formulated Tl⁺ Tl³⁺ 2S²⁻. TlS has two crystalline forms, a tetragonal chain structure and a monoclinic layer structure. The room temperature monoclinic form is ferroelectric. ^[4]. TlTe on the other hand is not a mixed valence compound but is a thallium(I) polytelluride, with a complex structure. TlTe is described as semimetallic.^[5]

[edit] Tl₂O₃, Tl₂S₃, Tl₂Se₃, Tl₂Te₃

Tl₂O₃ is the mineral avicennite. Its normal form has a bixbyite, Mn₂O₃, structure ^[6] and the high pressure form has a corundum, α-Al₂O₃, structure. It is a degenerate n-type semiconductor. Tl₂S₃ and Tl₂Se₃ have both been reported in the past however they have not been confirmed. Tl₂Te₃ is a polytelluride with a complex structure ^[7]

[edit] TlS₂, Tl₂S₅, Tl₂S₉

These are all thallium(I) polysulfides.

[edit] Gallium chalcogenides

The gallium chalcogenides include all compounds of gallium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with gallium). Some compounds that were reported and have found their way into text books have not been substantiated by later researchers. The list of compounds below shows compounds that have been reported, and those compounds that have not had their structure determined, or whose existence has not been confirmed by the latest structural investigations, are in italics.

oxide	sulfide	selenide	telluride
Ga2O	Ga2S	Ga2Se	Ga2Te
GaO	GaS	TlSe	TlTe
	Ga4O5
			Ga3Te4
			Ga7Te10
Ga2O3	Ga2S3	Ga2Se3	Ga2Te3
			Ga2Te5
			GaTe3

[edit] Ga₂O, Ga₂S, Ga₂Se

[edit] GaO, GaS, GaSe, GaTe,

[edit] Ga ₄S₅

[edit] Ga3Te4

[edit] Ga7Te10

[edit] Ga₂O₃, Ga₂S₃, Ga₂Se₃, Ga₂Te₃

[edit] Ga2Te5, Ga2Te3

[edit] Sulfur oxo compunds bonding

[edit] (Sulfur dioxide) Structure and bonding

added around septemeber 2006 by someone unknown SO₂ is a bent molecule with C_2v symmetry point group.

In terms of electron-counting formalisms, the sulfur atom has an oxidation state of +4, a formal charge of 0, and is surrounded by 5 electron pairs. From the perspective of molecular orbital theory, most of these electron pairs are non-bonding in character, as is typical for hypervalent molecules.

One conventional covalent bond is present between each oxygen and the central sulfur atom, with two further electrons delocalised between the oxygens and the sulfur atom.

[edit] (Sulfur trioxide) Structure and bonding

Current

Gaseous SO₃ is a trigonal planar molecule of D_3h symmetry, as predicted by VSEPR theory.

In terms of electron-counting formalisms, the sulfur atom has an oxidation state of +6, a formal charge of 0, and is surrounded by 6 electron pairs. From the perspective of molecular orbital theory, most of these electron pairs are non-bonding in character, as is typical for hypervalent molecules.

New

Gaseous SO₃ consists of a monomeric SO₃ in equilibrium with the cyclic trimer, S₃O₉, ([S(=O)₂(μ-O)]₃ which is also present in the solid γ form).
As predicted by [[VSEPR theory] the monomer has a trigonal planar structure with D_3h symmetry. Using valence bond theory there are a number of resonance forms such as SO3 octet pπ-pπ bonding with formal charge of +2 on sulfur, and SO3 expande octet with formal charge zero on all atoms.

[edit] Sulfite ion structure and bonding

[edit] Dithionite Structure and Bonding

[edit] Thiosulfate Structure and Bonding

[edit] SO2 structure and bonding

In SO₂ the sulfur atom has an oxidation state of +4. In the gas phase the molecule is bent with C_2v symmetry point group and the two S-O bond lengths are identical. In the terminology of the AXE method the molecule can be classified as AX₂E and VSEPR theory predicts the bent shape correctly. It has a dipole moment as expected for a bent molecule. The comparison of SO₂ with SO and O₃ with O₂ shows that the bond in SO₂ is unusually strong and this has been taken as evidence for d orbital participation.

	SO2	SO	O3	O2
mean bond energy (kJ/mol-1)	548	524
bond length (pm)	143.1	148.1

The mean S-O bond energy (548kJ mol-1^[8] is greater than the S-O bond energy in sulfur monoxide(524kJ mol-1^[9] and the S-O bond length of 143.1pm in SO₂, is shorter than the S-O bond, 148.1pm, in SO again this can be contrasted with ozone where the mean bond energy is less than the O-O bond energy in O₂

One of the earliest descriptions of the bonding is the Lewis structure shown below. Each atom has an octet of electrons. The formal charge is +2 on the sulfur atom and −1 on each of the oxygen atoms.
"Lewis picture"

In valence bond theory the significant resonance structures are generally believed to be the following^[10]:

A,B  Lewis

C (2 X double bond)
The A & B forms are Lewis structures, whilst C involves a d orbital on sulfur. Opinions have differed on the contribution of this resonance form. At one stage it was common to assume that this was the most important, and this view is found in some textbooks^[11].

The objection to full involvement of d-orbitals was that they were of too high an energy. A pπ-dπ backbonding model was proposed by D.W.J Cruickshank^[12]. In this whilst there is electron donation from oxygen p orbitals into sulfur d orbitals the Lewis structures are the most significant. This view is corroborated by ab-initio^[13] and GVB calculations^[14]. The following are some of the arguments used to justify d orbital involvement in SO₂:). This differs from ozone where the O-O bond energy in O₃is less than that in O₂. Ozone is used for comparison as it is first row and no d orbital involvement is expected.

[edit] References