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RECENT DEVELOPMENTS IN

Tristram Chivers

Department of Chemistry, University of Calgary, Calgary, Alberta, Canada

WHERE IS CALGARY? Lecture 1: Background / Introduction

Outline

(O, S, Se, Te, Po) • Elemental Forms: Allotropes • Uses • Trends in Atomic Properties • Spin-active Nuclei; NMR Spectra • as • Cation Formation and Stabilisation • Anions: Structures • Solutions of Chalcogens in Ionic Liquids • and Imides: Multiple Bonding

3 Elemental Forms: Allotropes

Sulfur

S6 S7 S8

S10

S12 S20

4 Elemental Forms: and Allotropes Selenium • Grey form - thermodynamically stable: helical structure cf. plastic sulfur.

R. Keller, et al., Phys. Rev. B. 1977, 4404.

• Red form - cyclic Cyclo-Se8 (cyclo-Se7 and -Se6 also known).

Tellurium • Silvery-white, metallic lustre; helical structure, cf. grey Se.

• Cyclic allotropes only known entrapped in -state structures

e.g. Ru(Ten)Cl3 (n = 6, 8, 9) M. Ruck, Chem. Eur. J. 2011, 17, 6382 5 Uses – Sulfur

Sulfur : Occurs naturally in underground deposits.

• Recovered by Frasch process (superheated ).

• H2S in sour (> 70%): Recovered by Klaus process:

Klaus Process: 2 H2S + SO2 3/8 S8 + 2 H2O

• Primary industrial use (70 %): H2SO4 in phosphate 6

Uses – Selenium and Tellurium

Selenium and Tellurium : Recovered during the refining of

Selenium:

• Photoreceptive properties – used in (As2Se3) • Imparts red color in

Tellurium: • As an with Cu, Fe, Pb and to harden

! Formation of Me2Te

7 Specialised Uses of Tellurides

Solar energy • and GaAs are widely used • Other promising materials: CdTe – Band gap 1.49 eV • Major manufacturer of CdTe solar cells: First Solar (Phoenix, USA) • CdTe technology expected to increase tenfold over the next 10 years • Limitation: Very low of Te (1-5 ppb)

Thermoelectric Generators

• Sb2Te 3, PbTe exhibit thermoelectric properties – band gaps ~ 0.21 eV • Low efficiency – use limited to solid-state :

e.g. Bi2Te 3 in portable food coolers • Improved efficiency could to applications in the conversion of waste heat from nuclear reactors and industrial equipment

Ibers, Nature Chemistry, 2009, 1, 508. 8

Trends in Atomic Properties

S Se Te (Å) 1.03 1.17 1.35 1.80 1.90 2.06 2.6 2.6 2.1 First Ionization Potential 999.6 941.0 869.3 (kJ mol-1) D(E-E) (kJ mol-1) 266 192 137

• Steady increase in size S • Electronegativity decrease only between Se and Te

• Heavy chalcogens more easily oxidized

• Heavy chalcogens form much weaker homoatomic bonds 9 Binary Chalcogen Halides

Monohalides, E2Cl2 • E = S, Se: Commercially available • E = Te: Dark brown, thermally unstable liquid

Cp2TiSe5 Li2Te + TeCl4 Te 2Cl2 1,2-Te 2Se5

Laitinen, Chem. Commun, 1998, 2381.

Dihalides, ECl2 • E = S: Readily disproportionates to S2Cl2 • E = Se: Disproportionates to Se2Cl2 and SeCl4 • E = Te: Unstable, but forms stable adducts e.g. TeCl2·tmtu (tmtu = tetramethylthiourea)

Tetrahalides, ECl4 • E = S: Thermally unstable • E = Se, Te: Commercially available white

10 Spin Active Nuclei - NMR Spectra

Nucleus Spin (I) Abundance (%) 33S 3/2 0.76 77Se 1/2 7.58 (123Te) 1/2 0.87 125Te 1/2 6.99

Et3P=Te 31P NMR 125Te NMR

† †

* *

† = 125Te satellites

* = 123Te satellites

20 0 -20 -850 -900 -950 11 Reactions of Selenium Dichloride

Synthesis:

Se + SO2Cl2 THF SeCl2

O 77 • Stable for 1 day at 23 C ( Se NMR: Disproportionates to Se2Cl2 + SeCl4) Chivers, Laitinen, Inorg. Chem. 1999, 38, 4093.

MeO OMe MeO Cl Se Cl R SeCl 2 Se (1) (3) R R MeO

(2) NH2

SeCl Se N N + N N + Se Se SeCl Se Se Cl Cl N N Se (1) Potapov, et al., Tetrahedron Letters, 2010, 51, 89; 2009, 50, 306. (2) Chivers, Laitinen, Chem Commun. 2000, 759. (3) Bendokov, et al., J. Am. Chem. Soc., 2008, 130, 6734. 12 Stabilization of Heavy Chalcogen Dihalides

Tetramethylthiourea (tmtu) complexes

TeO2 + HClaq + tmtu TeCl2·(tmtu)n (n = 1,2)

L . . Cl N Te. . L = S Cl L N

Foss, Acta Chem. Scand., 1986, A40, 675. Bipyridyl complexes • Thermally stable

• Metathesis with RMgX (R = Ph, Bz) gives R2E (E = Se, Te)

E = Se, X = Cl, Br; E = Te, X = Cl

Ragogna, Chem. Eur. J. 2009, 39, 10263. 13 Trialkylphosphine Adducts of TeCl2

Et3P=Te + SO2Cl2 (or I2) Et3PTeX2 (X = Cl, I) + SO2

Et3PTeCl2 + Me3SiBr Et3PTeBr2

Cl Te

X d(Te-P) (Å) δ (125Te) (ppm) 1J(P-Te) (Hz) Cl 2.466(1) 766 1395 Br 2.473(1) 627 1312 I 2.490(1) 331 1248

J. Konu and T. Chivers, Dalton Trans., 2006, 3941. 14 -Stabilized Chalcogen Dications

Electron-donor , e.g. diazabutadiene (DAB) (26a,b) or N-heterocyclic (NHC) (26c) stabilize highly electrophilic chalcogen dications

E = S, Se

S, Se: Ragogna, ACIE, 2009, 48, 2210. Te: Ragogna, ACIE, 2009, 48, 4409.

15 2+ DAB Complexes as Se Transfer Agents

Se2+ complexes: - - Preparation and ligand exchange reactions (NB: CF3SO3 (OTf ) anions)

Cy = cyclohexyl

Activation of small by Se2+? Ragogna, Chem Commun., 2010, 46, 1041.

16 Anions: Dianions 2- • Unbranched chains Sx (x = 2-8) + + + • Stabilized by large cations (Cs , Na(15-crown-5)] , [PPh4] ) 2- e.g. two distinct geometries of S7 :

all-trans (++++) trans-cis-trans (++--)

M. G. Kanatzidis, et al. Inorg. Chem. 1983, 22, 290. C. Müller, P. Böttcher, Z. Naturforsch. B, 1995, 50, 1623.

Radical Anions –• • Formation of the blue anion S3 (λmax ~ 620 nm) is a

common feature of solutions of polysulfides . Chivers, Inorg. Chem. 1972, 11, 2515.

“Ubiquitous Trisulfur Radical Anion” Chivers, Nature, 1974, 252, 32. 17 –• The Stable Radical Anion Cyclo-S6

+ • Isolated as [PPh4] • Two long S···S bonds (2.633 Å) • MO analysis and EPR spectra

•• –• indicate 2 fragments, S3 and S3

-pair bond between 2b1 SOMOs of both fragments

• 3-electron bond between 1a2 of

the biradical and 1a2 of the radical Cyclo-S – • Cyclo-S anion 6 6 K. Dehnicke, Angew. Chem. Int. Ed. 2000, 39, 4580 • Cyclo-S6 has one fewer electron 18 Anions: Polyselenides and Polytellurides

Polyselenides 2- • Chain structures Sex (x = 2-8) 2- • Se also forms bicyclic and spirocyclic dianions Sex (x = 10, 11) • 3- and 4-coordinate Se participate in 3-centre 2e- bonding

2- 2- Se10 Se11

D. Fenske, Angew. Chem. 1990, 29, 390. B. Krebs, Z. Anorg. Allg. Chem., 1991, 592, 17.

Polytellurides • Charges either less or greater than 2- may be observed, 3- e.g. [Te6 ] in Cs3Te22 • Hypervalent Bonding σ* • Intra- and inter-molecular np2  σ* bonding 2 np 19 Solutions of Chalcogens in Ionic Liquids

The Chalcogens as Reagents

Sulfur: Poor in CCl4, pyridine and ; dissolves well in CS2

Selenium: Slightly soluble in CS2

Tellurium: In ethylenediamine → Nanotubes of Te and Se J. Lu, et al., J. Mat. Chem. 2002, 12, 2755. : Neurotoxic, highly flammable, reactive solvent

Ionic Liquids

• Safe alternative to CS2 for dissolving sulfur O • At 100 -155 C S8 has very high solubility i • In [P Bu3Me][OTs] sulfur forms bright blue solutions → carmine red at higher concentrations

 Identity of sulfur species in these solutions? Seddon, Chem. Commun. 2010, 46, 716. 20

The Trisulfur Radical in Ionic Liquids

• UV-Vis spectrum shows an isosbestic point • Dilute solutions are blue (617 nm) and concentrated solutions are red • Equilibrium between hexasulfide and trisulfur radical anion

2- -• S6 2 S3

•- S3 is the chromophore in and blue

21 •- Material Based on Occluded S3

Univalent , Zn+

Paramagnetic Zn+ incorporated into by reaction of Zn vapor (at 450 OC) with of two Brønsted sites → Zn@SAPO (Si Al Phosphate)

o Sulfur vapour at 280 C introduced into Zn@SAPO cage and S3 is trapped in the cavity and then reacts with Zn+ to produce blue S •- 3

Li and Chen, JACS, 2003, 125, 6622; J. Mater. Chem., 2010, 20, 3307. 22 •- Occluded S3 as a Sensor for Water

Sensoring Mechanism •- • Occluded S3 is a sensitive detector for H2O in air or organic solvents

•- •- S3 + H2O S3 + H2O • Monitored by visible and EPR

Colorimetric cards estimate ppm water based on amount of sensor material used (3.0, 6.3, 9.0 mg)

23 Solutions of Se and Te in Ionic Liquids

• Se and Te also dissolve in ionic liquids at elevated temps to give (Se at 50 oC) and purple (Te at 170 OC) solutions

•- • Orange colour may be Se3 ; identity of purple species unknown

• Reactivity of chalcogen solutions in ionic liquids demonstrated by reactions with PPh3 to give Ph3PE ( E = Se, Te)

24 Binary Chalcogen Dioxides: Multiple Bonding

Sulfur Dioxide • A monomeric gaseous

• S=O double bonds – bent structure C2v

Selenium and Tellurium Oxides • White solids with polymeric structures

• (SeO2)n : 2-D – Both Se–O and Se=O bonds

• (TeO2)n : 3-D polymer - Only Te–O single bonds

O S O O O O Se O Te n O O

25 Chalcogen Diimides - Structures

Sulfur and Selenium Diimides • Monomeric: Cis, trans isomer usually preferred

R E E N N N N R E R N N R R R (cis, cis) (cis, trans) (trans, trans) E = Se, R = Ad: T. Maaninen, R. Laitinen, T. Chivers, Chem Commun. 2002, 1812. Tellurium Diimides • Dimeric: Two known conformations

R R R R R N R R N N N N Te Te Te Te N N R N t n cis, endo, endo (R = Bu) trans, exo, exo (R = Oct, R’ = PPh2NSiMe3)

Chivers, et al. JACS, 1995, 117, 2519; Inorg. Chem., 1996, 35, 9. 26 Chalcogen Diimides – Dimerization Energies

(R = Me)

E = S, Endothermic; E = Se, ~ Thermoneutral; E = Te, Exothermic

Tuononen, Laitinen, Inorg. Chem., 2004, 43, 2097; Inorg. Chem., 2005, 44, 443 27 Hybrid Chalcogen Imide Oxides t t BuNSO O=Se(μ-N Bu)2Se=O Monomeric liquid Dimeric, white solid

O N O S Se Se O N N

T. Maaninen, R. Laitinen and T. Chivers, Chem. Commun., 2002,1812. t [(μ-O)Te(μ-N Bu)Te]n: Polymeric structure disrupted by adduct formation

L O N O N Te Te Te Te L = B(C6F5)3 N O N O L

Schatte, Chivers, Tuononen, Suontamo, Laitinen, Valkonen, Inorg. Chem. 2005, 44, 443. 28