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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
4
S6 S7
S8
S10
S12 S20
Elemental Forms: Selenium and Tellurium Allotropes
Selenium • Grey form - thermodynamically stable: helical structure cf. plastic sulfur.
• 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) 5 M. Ruck, Chem. Eur. J. 2011, 17, 6382
R. Keller, et al., Phys. Rev. B. 1977, 4404.
Uses – Sulfur
Sulfur : Occurs naturally in underground deposits. • Recovered by Frasch process (superheated water). • H2S in sour gas (> 70%): Recovered by Klaus process: • Primary industrial use (70 %): H2SO4 in phosphate fertilizers
6
Klaus Process: 2 H2S + SO2 3/8 S8 + 2 H2O
Uses – Selenium and Tellurium
7
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
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
• Sb2Te3, PbTe exhibit thermoelectric properties – band gaps ~ 0.21 eV
• Low efficiency – use limited to solid-state refrigeration:
e.g. Bi2Te3 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
9
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 (kJ mol-1)
999.6 941.0 869.3
D(E-E) (kJ mol-1) 266 192 137
S
• Steady increase in size • Electronegativity decrease only between Se and Te • Heavy chalcogens more easily oxidized • Heavy chalcogens form much weaker homoatomic bonds
Binary Chalcogen Halides
Monohalides, E2Cl2 • E = S, Se: Commercially available • E = Te: Dark brown, thermally unstable liquid
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
Cp2TiSe5
10
Li2Te + TeCl4 Te2Cl2 1,2-Te2Se5
Laitinen, Chem. Commun, 1998, 2381.
11
Nucleus Spin (I) Abundance (%)
33S 3/2 0.76
77Se 1/2 7.58
(123Te) 1/2 0.87
125Te 1/2 6.99
Spin Active Nuclei - NMR Spectra
20 0 -20
-850 -900 -950
125Te NMR 31P NMR Et3P=Te
*
†
*
†
† = 125Te satellites * = 123Te satellites
Synthesis: • Stable for 1 day at 23 OC (77Se NMR: Disproportionates to Se2Cl2 + SeCl4)
(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
Reactions of Selenium Dichloride
Chivers, Laitinen, Inorg. Chem. 1999, 38, 4093.
Se + SO2Cl2 SeCl2 THF
SeCl 2
(2)
(3) (1)
MeO OMe
SeCl
SeCl
MeO
MeO
R
N H 2
Se Cl
R R
Cl
N
Se
Se N
Se
N Se
N
N Se
N
Se Cl
Se Cl
+ +
SeCl
(2)
(3) (1)
MeO OMe
SeCl
SeCl
MeO
MeO
R
N H 2
Se Cl
R R
Cl
N
Se
Se N
Se
N Se
N
N Se
N
Se Cl
Se Cl
+ +
E = Se, X = Cl, Br; E = Te, X = Cl
Ragogna, Chem. Eur. J. 2009, 39, 10263.
Tetramethylthiourea (tmtu) complexes
Bipyridyl complexes
• Thermally stable
• Metathesis with RMgX (R = Ph, Bz) gives R2E (E = Se, Te)
TeO2 + HClaq + tmtu TeCl2·(tmtu)n (n = 1,2)
L =
Foss, Acta Chem. Scand., 1986, A40, 675.
13
Stabilization of Heavy Chalcogen Dihalides
. .
. .
L Te
L
Cl
Cl . . Te Cl N
N
S
J. Konu and T. Chivers, Dalton Trans., 2006, 3941. 14
Trialkylphosphine Adducts of TeCl2
Et3P=Te + SO2Cl2 (or I2) Et3PTeX2 (X = Cl, I) + SO2
Et3PTeCl2 + Me3SiBr Et3PTeBr2
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
Te
Cl
Electron-donor ligands, e.g. diazabutadiene (DAB) (26a,b) or N-heterocyclic
carbenes (NHC) (26c) stabilize highly electrophilic chalcogen dications
15
Ligand-Stabilized Chalcogen Dications
E = S, Se
S, Se: Ragogna, ACIE, 2009, 48, 2210. Te: Ragogna, ACIE, 2009, 48, 4409.
Se2+ complexes: Preparation and ligand exchange reactions (NB: CF3SO3
- (OTf-) anions)
Activation of small molecules by Se2+?
16
Ragogna, Chem Commun., 2010, 46, 1041.
DAB Complexes as Se2+ Transfer Agents
Cy = cyclohexyl
Dianions • Unbranched chains Sx
2- (x = 2-8)
• Stabilized by large cations (Cs+, Na(15-crown-5)]+, [PPh4]+)
e.g. two distinct geometries of S72- :
Radical Anions • Formation of the blue trisulfur radical anion S3
–• (λmax ~ 620 nm) is a common feature of solutions of polysulfides .
“Ubiquitous Trisulfur Radical Anion”
17
Anions: Polysulfides
M. G. Kanatzidis, et al. Inorg. Chem. 1983, 22, 290.
Chivers, Nature, 1974, 252, 32.
Chivers, Inorg. Chem. 1972, 11, 2515.
C. Müller, P. Böttcher, Z. Naturforsch. B, 1995, 50, 1623.
trans-cis-trans (++--) all-trans (++++)
• 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
anion
• Cyclo-S6 has one fewer electron K. Dehnicke, Angew. Chem. Int. Ed. 2000, 39, 4580
18
The Stable Radical Anion Cyclo-S6–•
Cyclo-S6 Cyclo-S6– •
Polyselenides • Chain structures Sex
2- (x = 2-8)
• Se also forms bicyclic and spirocyclic dianions Sex2- (x = 10, 11)
• 3- and 4-coordinate Se atoms participate in 3-centre 2e- bonding
Polytellurides • Charges either less or greater than 2- may be observed,
e.g. [Te63-] in Cs3Te22
• Hypervalent Bonding
• Intra- and inter-molecular np2 σ* bonding
19
Anions: Polyselenides and Polytellurides
Se112- Se10
2-
D. Fenske, Angew. Chem. 1990, 29, 390. B. Krebs, Z. Anorg. Allg. Chem., 1991, 592, 17.
σ*
np2
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
Carbon Disulfide: Neurotoxic, highly flammable, reactive solvent
Ionic Liquids • Safe alternative to CS2 for dissolving sulfur
• At 100 -155 OC S8 has very high solubility
• In [PiBu3Me][OTs] sulfur forms bright blue solutions → carmine red at higher concentrations
Identity of sulfur species in these solutions?
20
Solutions of Chalcogens in Ionic Liquids
J. Lu, et al., J. Mat. Chem. 2002, 12, 2755.
Seddon, Chem. Commun. 2010, 46, 716.
• 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
S3
•- is the chromophore in lapis lazuli and ultramarine blue
21
The Trisulfur Radical Ion in Ionic Liquids
S62- 2 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)
Sulfur vapour at 280 oC introduced into Zn@SAPO cage and S3 is trapped in
the cavity and then reacts with Zn+ to produce blue S3•-
Li and Chen, JACS, 2003, 125, 6622; J. Mater. Chem., 2010, 20, 3307.
22
Sensor Material Based on Occluded S3•-
Sensoring Mechanism • Occluded S3
•- is a sensitive detector for H2O in air or organic solvents
• 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
Occluded S3•- as a Sensor for Water
S3•- + H2O S3 + H2O•-
• 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
Solutions of Se and Te in Ionic Liquids
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
25
Binary Chalcogen Dioxides: Multiple Bonding
n
SOO
O
Te
OO
OOSe
On
SOO
O
Te
OO
OOSe
O
TeN
TeN
RN
R
R
NR
Sulfur and Selenium Diimides • Monomeric: Cis, trans isomer usually preferred
Tellurium Diimides • Dimeric: Two known conformations
E = Se, R = Ad:
T. Maaninen, R. Laitinen, T. Chivers, Chem Commun. 2002, 1812.
Chivers, et al. JACS, 1995, 117, 2519; Inorg. Chem., 1996, 35, 9.
(cis, cis)
E
N N
RR
EN N
R
R
EN N
RR
(cis, trans) (trans, trans)
26
Chalcogen Diimides - Structures
trans, exo, exo (R = nOct, R’ = PPh2NSiMe3) cis, endo, endo (R = tBu)
TeN
TeN
R
N
RR
N
R
Tuononen, Laitinen, Inorg. Chem., 2004, 43, 2097; Inorg. Chem., 2005, 44, 443
E = S, Endothermic; E = Se, ~ Thermoneutral; E = Te, Exothermic
27
Chalcogen Diimides – Dimerization Energies
(R = Me)
tBuNSO O=Se(μ-NtBu)2Se=O Monomeric liquid Dimeric, white solid
[(μ-O)Te(μ-NtBu)Te]n: Polymeric structure disrupted by adduct formation
T. Maaninen, R. Laitinen and T. Chivers, Chem. Commun., 2002,1812.
Schatte, Chivers, Tuononen, Suontamo, Laitinen, Valkonen, Inorg. Chem. 2005, 44, 443. 28
Hybrid Chalcogen Imide Oxides
Se
N
Se
NO O
N
N
NS
O
L
L N
Te
N
Te
O
O
Te
O
N
Te
N
O
N L
L N
Te
N
Te
O
O
Te
O
N
Te
N
O
N
L = B(C6F5)3
