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Method Article
We present the high-temperature synthesis of intermetallic precursors K4Ge9, their dissolution in ethylenediamine to form Ge94- deltahedral Zintl ions, and the reaction of the clusters with alkynes to form organo-Zintl ions. The latter are characterized by electrospray mass spectrometry in solutions and by single-crystal X-ray diffraction in the solid state.
Although the first studies of Zintl ions date between the late 1890's and early 1930's they were not structurally characterized until many years later.1,2 Their redox chemistry is even younger, just about ten years old, but despite this short history these deltahedral clusters ions E9n- (E = Si, Ge, Sn, Pb; n = 2, 3, 4) have already shown interesting and diverse reactivity and have been at the forefront of rapidly developing and exciting new chemistry.3-6 Notable milestones are the oxidative coupling of Ge94- clusters to oligomers and infinite chains,7-19 their metallation,14-16,20-25 capping by transition-metal organometallic fragments,26-34 insertion of a transition-metal atom at the center of the cluster which is sometimes combined with capping and oligomerization,35-47 addition of main-group organometallic fragments as exo-bonded substituents,48-50 and functionalization with various organic residues by reactions with organic halides and alkynes.51-58
This latter development of attaching organic fragments directly to the clusters has opened up a new field, namely organo-Zintl chemistry, that is potentially fertile for further synthetic explorations, and it is the step-by-step procedure for the synthesis of germanium-divinyl clusters described herein. The initial steps outline the synthesis of an intermetallic precursor of K4Ge9 from which the Ge94- clusters are extracted later in solution. This involves fused-silica glass blowing, arc-welding of niobium containers, and handling of highly air-sensitive materials in a glove box. The air-sensitive K4Ge9 is then dissolved in ethylenediamine in the box and then alkenylated by a reaction with Me3SiC≡CSiMe3. The reaction is followed by electrospray mass spectrometry while the resulting solution is used for obtaining single crystals containing the functionalized clusters [H2C=CH-Ge9-CH=CH2]2-. For this purpose the solution is centrifuged, filtered, and carefully layered with a toluene solution of 18-crown-6. Left undisturbed for a few days, the so-layered solutions produced orange crystalline blocks of [K(18-crown-6)]2[Ge9(HCCH2)2]•en which were characterized by single-crystal X-ray diffraction.
The process highlights standard reaction techniques, work-up, and analysis towards functionalized deltahedral Zintl clusters. It is hoped that it will help towards further development and understanding of these compounds in the community at large.
1. Preparing Niobium Tubes
2. Loading Niobium Tubes: Preparing K4Ge9
3. Preparing Fused Silica Tube via Glass-Blowing
4. Sealing Fused Silica Tube using a High Vacuum Line
5. Heating the Reaction Mixtures in a Furnace
6. Dissolving Precursor in Ethylenediamine
7. Reacting Ge9-clusters with Me3SiC≡CSiMe3
8. Running ES-MS of Reaction Solution
9. Crystallizing Ge9-divinyl Ions with a Sequestering Agent
10. Checking Crystals Unit Cell on a D8-Diffractometer
11. Representative Results
The unique isotope pattern of the anionic clusters allows them to be easily detected in the negative ion-mode (Fig 1). Also noteworthy is that reduced singly charged species, in addition to pairing with a potassium ion is a common phenomenon of this soft-ionization technique.59
The crystal structure with relevant bond lengths and angles of [Ge9(CH=CH2)2]2- in [K(18-crown-6)]2[Ge9(HCCH2)2]•en, 1, can be seen in Figure 2 .
Figure 1. ES-MS spectra (negative-ion mode) of ethylenediamine solutions of the reactions of Ge9 clusters with Me3SiC≡CSiMe3. Shown are also the theoretical isotope distributions below the experimental distribution. (Sevov et. al. Inorg. Chem. 2007, 46, 10953.)
Figure 2. A view of [K(18-crown-6)]2[Ge9(HCCH2)2]•en, 1. Color scheme: = Ge,
= C,
= H. Selected bond lengths and angles: Ge-C 1.961 and 1.950 Å, C=C 1.318 and 1.316 Å, Ge-C-C 123 and 127 °. (Sevov et. al. Inorg. Chem. 2007, 46, 10953.)
Figure 3. Schematic representation of Preparing Niobium Tubes: (a) cutting Nb tubes; (b) cleaning Nb tubes in a Nb acid solution; (c) using vise-grips to crimp and bend Nb tube.
Figure 4. Schematic representation of Preparing Niobium Tubes: (a) diagram of arc welder; (b) staggered Nb tubes in arc welder holder and (c) welding tip above Nb tubes.
Figure 5. Schematic representation of Loading Niobium Tubes : (a) inside the drybox and (b) Nb tubes: (i) before welding, (ii) after using vise-grips to crimp one edge, (iii) after welding one edge, (iv) after loading and then welding the Nb tube closed, (v) after opening the Nb tube to take out the K4Ge9 precursor.
Figure 6. Schematic representation of Preparing Fused-Silica Tube by Glass-Blowing in (a) and (b)(i) large and small quartz tubing, (ii) body and neck sealed together, (iii) neck with ball joint, (iv) neck and ball joint sealed together, (v) Nb tubes sealed inside quartz tube, (vi) after the fused silica tube is sealed.
Figure 7. Schematic representation of Sealing Fused Silica Tubes on a High Vacuum Line in (a) and (b) after the Nb tubes is sealed showing etching of the quartz tube from Nb acid solution.
Figure 8. Schematic representation of Placing Loaded Fused Silica Tubes in Furnace.
Figure 9. Schematic representation of Reacting K4Ge9 with Me3SiC≡CSiMe3 inside the drybox (a) (i) unopened Nb tube, (ii) one edge of the Nb tube cut with the (iii) cutting pliers, (iv) crushed precursor and (b) (i) precursor dissolved in ethylenediamine, (ii) immediately after Me3SiC≡CSiMe3 is added (oily droplets on top of test-tube walls seen).
Figure 10. Schematic representation of Running ES-MS of Reaction Solution in (a) mass spectrometer syringe prepared in dry box, (b) Bruker Microtof-II.
Figure 11. Schematic representation of Crystallizing Ge9-divinyl with Sequestering Agents in (a) reverse layering and (b) several hours later.
Figure 12. Schematic representation of Checking Crystals Unit Cell on a D8-Diffractometer: (a) selecting crystals under the microscope and (b) collecting a unit cell.
It is important to clean well the partially oxidized Nb tubes. However, if the tubes are left too long in the Nb cleaning solution, this will severely compromise the thickness of the tube. Thus, 10 – 15 seconds are imperative and the tubes should be very lustrous at the end (Fig 3). After the tubes are sealed inside the fused silica jacket they should be cleaned again with a dilute Nb acid solution. This should result in mild effervescence, cleaning any oxidized areas on Nb tubes that occurred during welding o...
No conflicts of interest declared.
The authors would like to thank the National Science Foundation for the continuous financial support (CHE-0742365) and for the purchase of a Bruker APEX II diffractometer (CHE-0443233) and a Bruker Microtof-II mass spectrometer (CHE-0741793). The authors would also like to thank CEST facility for their use of the Micromass Quattro-LC mass spectrometer.
Name | Company | Catalog Number | Comments |
D8-Xray diffractometer | Bruker Corporation | Bruker APEX II | |
Electrospray mass spectrometer | Bruker Corporation | Microtof-II | |
Electrospray mass spectrometer | Micromass | Quattro-LC | triple -quadropole |
Drybox | Innovative Technology | S-1-M-DL | IT-Sys1 model |
Inert Gas/Vacuum Shielded Arc Welding Arrangement | ![]() | Special Order | |
Arc Welder Power Source | Miller | Maxstar-91 | |
Welding Rubber Gloves | Home Depot | KH643 | |
Electric Engraver | Burgess Products | 74 | Vibro-Graver |
Circular Glass Saw | Pistorius Machine Co. Inc | GC-12-B | |
Tube Furnace | Lindberg/Blue M | TF55035 | Minimite Laboratory Tube Furnace, Moldatherm (1100 °C) |
Glass Drying Oven | Fisher Scientific | 13-247-650G | |
High Vacuum Hg Schlenk-Line | Special Order | Univ Of Notre Dame | Alternative: Edwards E050/60; VWR International; Cat. No. EVB302-07-110 |
Large Torch | Victor Technologies | JT100C | Welding torch, tip: Victor 5-W-J |
Small Torch | Veriflo Co. | 3A | Blow-pipe |
Tesla Coil | VWR international | KT691550-0000 | Leak detector |
Stirrer/Hot -Plate | VWR international | 12620-970 | VWR HOT PLATE STR DY-DUAL120V |
Balance | Denver Instrument | 100A | XE Series |
Centrifuge | LW Scientific, Inc. | E8C-08AV-1501 | Variable speed |
Graphite Reamer, (flaring) | ABR Imagery, Inc. | 850-523 B01 | Open holes in Glass Blowing and flaring edges |
Striker | Fisher Scientific | 12-007 | |
Vise-Grips | Home Depot | 0902L3SM | |
Pipe-Cutter | Home Depot | 32820 | |
Cutting Pliers | Home Depot | 437 | |
Plastic Beaker | VWR international | 13890-046 | |
Measuring Cylinder | VWR international | 65000-006 | Careful, HF etches glass (if using a glass one) |
Large Plastic Bottle | VWR international | 16128-542 | |
13 x 100 Test-Tubes | VWR international | 47729-572 | CULTURE TUBE 13X100 CS1000 |
Laboratory (Rubber) Stoppers | Sigma-Aldrich | Z164437-100EA | Size 00 |
Test-Tube Rack | VWR international | 60196-702 | 10-13 mm tube OD |
Stir-Bars | StirBars.com/Big Science Inc. | SBM-0803-MIC | PTFE 8x3 mm Micro |
Glass Pipettes | VWR international | 14673-043 | VWR PIPET PASTEUR 9IN CS1000 |
Rubber Bulbs | VWR international | 56311-062 | Latex, thin walled |
Glass Wool | Unifrax I LLC | 6048 | Fiberfrax Bulk Fiber Insulation, Ceramic fiber |
Glass Slides | VWR international | 16004-422 | 75x25x1mm, Microscope Slides |
Paratone-N oil | Hampton Research | Parabar 10312 | Known as: Paratone-N, Paratone-8277, Infineum V8512 |
High Vacuum Silicone Grease | VWR international | 59344-055 | Dow Corning |
Liquid Nitrogen | University of Notre Dame | ||
Argon Gas Cylinder | Praxair, Inc. | TARGHP | |
Nitrogen Gas Cylinder | Praxair, Inc. | QNITPP | |
Oxygen Gas Cylinder | Praxair, Inc. | OT | 337 cf CYL |
Hydrogen Gas Cylinder | Praxair, Inc. | HK | 195 cf CYL |
Propane Gas Cylinder/source | University of Notre Dame | UND | |
Quartz tubing, Lg | Quartz Scientific Inc. | 100020B | 20 mm id x 22mm od x 48" clear fused quart tubing |
Quartz tubing, Md | Quartz Scientific Inc. | 100007B | Clear Fused Quartz Tubing,7mm id x 9mm od x 48" |
Round Bottom Quartz Joint | Quartz Scientific Inc. | 6160189B | Ball joint |
Quartz Safety Glasses | Wale Apparatus | 11-1127 | waleapparatus.com |
Pyrex Safety Glasses | Wale Apparatus | 11-2125-B3 | For clear and color borosilicate glass |
Blow Hose Kit | Glass House | BH020 | glasshousesupply.com |
Niobium Tubes | Shaanxi Tony Metals Co., Ltd | Niobium Tube, 50 ft | Seamless Niobium Tube Outside diameter: 0.375 (±0.005) inches. Wall thickness: 0.02(±0.003) Inches Niobium should be annealed. |
PEEK Starter Kit for Mass Spect | Waters | PSL613321 | PEEK (PolyEtherEtherKetone) tubing, nuts, ferrule, fits |
Mass Spect Needle Set | VWR international | 60373-992 | Hamilton Manufacturer (81165) |
H2SO4 | VWR international | BDH3072-2.5LG | ACS Grade |
HNO3 | VWR international | BDH3046-2.5LPC | ACS Grade |
HF | VWR international | BDH3040-500MLP | ACS Grade |
Distilled Water | University of Notre Dame | UND | |
Acetone | VWR international | BDH1101-4LP | |
Ethylenediamine | VWR international | AAA12132-0F | 99% 2.5 L |
Toluene | VWR international | 200004-418 | 99.8 %, anhydrous |
Mercury | Strem Chemicals, Inc. | 93-8046 | |
Potassium (K) metal | Strem Chemicals, Inc. | 19-1989 | Sealed in glass ampoule under Ar |
Germanium (Ge) powder | VWR international | AA10190-18 | GERM PWR -100 MESH 99.999% 50G |
Bistrimetylsilylacetylene, (Me3SiC≡CCSiMe3) | Fisher Scientific | AC182010100 | |
18-crown-6 (1,4,7,10,13,16-Hexaoxacyclooctadecane) | VWR international | 200001-954 | 99%, 25 gm |
2,2,2-crypt (4,7,13,16,21,24-Hexaoxa-1,10 diazabicyclo[8.8.8]hexacosane) | Sigma-Aldrich | 291110-1G | 98% |
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