RECENT DEVELOPMENTS IN CHALCOGEN CHEMISTRY
Tristram Chivers
Department of Chemistry, University of Calgary, Calgary, Alberta, Canada
WHERE IS CALGARY? Lecture 1: Background / Introduction
Outline
• Chalcogens (O, S, Se, Te, Po) • Elemental Forms: Allotropes • Uses • Trends in Atomic Properties • Spin-active Nuclei; NMR Spectra • Halides as Reagents • Cation Formation and Stabilisation • Anions: Structures • Solutions of Chalcogens in Ionic Liquids • Oxides and Imides: Multiple Bonding
3 Elemental Forms: Sulfur Allotropes
Sulfur
S6 S7 S8
S10
S12 S20
4 Elemental Forms: Selenium and Tellurium 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 solid-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 water).
• H2S in sour gas (> 70%): Recovered by Klaus process:
Klaus Process: 2 H2S + SO2 3/8 S8 + 2 H2O
• Primary industrial use (70 %): H2SO4 in phosphate fertilizers 6
Uses – Selenium and Tellurium
Selenium and Tellurium : Recovered during the refining of copper sulfide ores
Selenium:
• Photoreceptive properties – used in photocopiers (As2Se3) • Imparts red color in glasses
Tellurium: • As an alloy with Cu, Fe, Pb and to harden steel
• Toxicity! Formation of Me2Te
7 Specialised Uses of Metal Tellurides
Solar energy • Silicon 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 natural abundance 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 refrigeration:
e.g. Bi2Te 3 in portable food coolers • Improved efficiency could lead 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 Covalent Radius (Å) 1.03 1.17 1.35 van der Waals Radius 1.80 1.90 2.06 Electronegativity 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 solids
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 Ligand-Stabilized Chalcogen Dications
Electron-donor ligands, e.g. diazabutadiene (DAB) (26a,b) or N-heterocyclic carbenes (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 molecules by Se2+? Ragogna, Chem Commun., 2010, 46, 1041.
16 Anions: Polysulfides 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 trisulfur radical 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] salt • Two long S···S bonds (2.633 Å) • MO analysis and EPR spectra
•• –• indicate 2 fragments, S3 and S3
• Electron-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 atoms 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 solubility in CCl4, pyridine and toluene; 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. Carbon Disulfide: 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 Ion 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 lapis lazuli and ultramarine blue
21 •- Sensor Material Based on Occluded S3
Univalent Zinc, Zn+
Paramagnetic Zn+ incorporated into zeolite by reaction of Zn vapor (at 450 OC) with protons of two Brønsted acid 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 spectroscopy
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 orange (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 molecule
• S=O double bonds – bent structure C2v
Selenium and Tellurium Oxides • White solids with polymeric structures
• (SeO2)n : 2-D polymer – 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