This work was supported by the Deutsche Forschungsgemeinschaft (DFG) within the framework of SPP 1708. GT thanks the Leopoldina Nationale Akademie der Wissenschaften for a postdoctoral scholarship.

Caution: Always be cautious when working with chemicals. Apply common safety precautions, including the appropriate utilization of gloves, goggles, and a lab coat at all times. In particular, be aware that all discussed compounds containing heavy elements, as well as their elemental sources, are of high toxicity. 1,2-diaminoethane is a corrosive liquid. Alkaline metals and ternary solid-state products may react pyrophorically with air and moisture.
Note: All manipulations are performed in an a...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dilead(II)+Chalcogenide+anions+Pb2Ch32-+(Ch+=+Se,+Te):+A+207Pb,+125Te,+and+77Se+Solution+NMR+Study.+X-ray+crystal+structure+of+(2,2,2-crypt-K+)2Pb2Se32-.">Dilead(II) Chalcogenide anions Pb2Ch32- (Ch = Se, Te): A 207Pb, 125Te, and 77Se Solution NMR Study. X-ray crystal structure of (2,2,2-crypt-K+)2Pb2Se32-.</a> Inorg. Chem. 26 (5), 741-749 (1987).</li><li>Scharfe, S., Kraus, F., Stegmaier, S., Schier, A., F&#228;ssler, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zintl+Ions,+Cage+Compounds,+and+Intermetalloid+Clusters+of+Group+14+and+Group+15+Elements.">Zintl Ions, Cage Compounds, and Intermetalloid Clusters of Group 14 and Group 15 Elements.</a> Angew. Chem. Int. Ed. 50 (16), 3630-3670 (2011).</li><li>Joannis, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Action+du+sodammonium+et+du+potassamonium+sur+quelques+m&#233;taux.">Action du sodammonium et du potassamonium sur quelques m&#233;taux.</a> C. R. Hebd. Seances Acad. Sci. 113, 795-798 (1891).</li><li>Joannis, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sur+quelques+alliages+bien+d&#232;finis+de+sodium.">Sur quelques alliages bien d&#232;finis de sodium.</a> C. R. Hebd. Seances Acad. Sci. 114, 585-587 (1892).</li><li>Diehl, L., Khodadeh, K., Kummer, D., Str&#228;hle, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anorganische+Polyederverbindungen,+III.+Zintl's+&#8222;Polyanionige+Salze&amp;#34;:+Darstellung+und+Eigenschaften+der+kristallinen+Verbindungen+[Na4&#183;7+en]Sn9,+[Na4&#183;5+en]Ge9+und+[Na3&#183;4+en]Sb7+und+ihrer+L&#246;sungen.+Die+Kristallstruktur+von+[Na4&#183;7+en]+Sn9.">Anorganische Polyederverbindungen, III. Zintl's &#8222;Polyanionige Salze&amp;#34;: Darstellung und Eigenschaften der kristallinen Verbindungen [Na4&#183;7 en]Sn9, [Na4&#183;5 en]Ge9 und [Na3&#183;4 en]Sb7 und ihrer L&#246;sungen. Die Kristallstruktur von [Na4&#183;7 en] Sn9.</a> Chem. Ber. 109 (10), 3404-3418 (1976).</li><li>Demazeau, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvothermal+Processes:+Definition,+Key+Factors+Governing+the+Involved+Chemical+Reactions+and+New+Trends.">Solvothermal Processes: Definition, Key Factors Governing the Involved Chemical Reactions and New Trends.</a> Z. Naturforsch. 65b, 999-1006 (2010).</li><li>Thiele, G., Kr&#252;ger, T., Dehnen, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=K4[PbSe4]&#8901;en&#8901;NH3:+A+Non-Oxide,+Non-Halide+Inorganic+Lead(IV)+Compound.">K4[PbSe4]&#8901;en&#8901;NH3: A Non-Oxide, Non-Halide Inorganic Lead(IV) Compound.</a> Angew. Chem. Int. 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Ed. 54 (38), 11283-11288 (2015).</li><li>Thiele, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Smallest+molecular+chalcogenidometalate+anions+of+the+heaviest+metals:+syntheses,+structures,+and+their+interconversion.">Smallest molecular chalcogenidometalate anions of the heaviest metals: syntheses, structures, and their interconversion.</a> Dalton Trans. , (2016).</li><li>Thiele, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solvothermal+and+ionothermal+synthses+and+structures+of+amine-+and/or+(poly-)chalcogenide+coordinated+metal+complexes.">Solvothermal and ionothermal synthses and structures of amine- and/or (poly-)chalcogenide coordinated metal complexes.</a> Z. 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The combination of classical high-temperature, solid-state reactions with solution-based methods allows for the generation and isolation of novel compounds that cannot be synthesized by only one of these pathways. Even though, in most cases, a clear identification and full characterization of the intermediate species is difficult or essentially impossible, the general idea is straightforward and can be applied to a variety of elemental combinations. Furthermore, the actual synthetic conditions for the generation of one s...

Metal chalcogenides, such as SnSe or CuInSe, are versatile materials with a wide range of applications, for instance, as semiconductor, thermoelectric, or nonlinear optic materials1-6. Similar elemental compositions are found within chalcogenidometalates, where the metal is in a formally positive oxidation state and coordinated by negative (poly-)chalcogenide ligands to yield an overall anionic species. Different from the abovementioned materials, such metalates are additionally comprised of counter-ions, which are well separated from the anionic substructure. Typical cations are (solvated) alkali or alkaline earth metals, ammonium, or phosphonium ions. Most often, such salts with chalcogenidometalate anions have physical properties that are similar to their parental binary or ternary compounds, such as similar band gaps or photo- and semiconductivity properties. However, due to the broad range of possible anionic architectures within each elemental combination, ranging from isolated molecular species through strands and sheets of interconnected anions to extended three-dimensional frameworks, an even finer tuning of various properties can be achieved, ultimately aiming at the designed synthesis of compounds with the desired properties. Within the concept of dimensional reduction, it has been shown that a relative increase of counter ions per formula unit, which accompanies a reduction from 3D via 2D and 1D to 0D anionic architectures (0D representing molecular species), decreases the observed band gap7. Moreover, by the utilization of different (or mixtures of) chalcogenide ligands, it is even possible to achieve an ultra-fine adjustment of the band gap8,9.
Apart from these practical applications and visionary relevancies, chalcogenidometalates are still investigated for fundamental understanding, such as for the generation of novel anionic structure types or the discovery and interpretation of an unusual bonding, as well as for their unprecedented properties. Whereas the lighter congeners (i.e., oxidometalates, commonly referred to as oxometalates) have been extensively studied, in particular for potential catalytic applications, the heavier chalcogenidometalates are far less explored.
Our own interest has been focused on the synthesis, properties, and further reactivity of chalcogenidotetrelates (i.e., the heavier homologs of silicates)10,11. There is a broad variety of such compounds, ranging from water-stable and soluble binary anions, such as the [SnTe4]4- anion12; to organic, functionalized, and multinary cluster compounds, such as {[Ir3(cod)3(&#181;3-S)2](&#181;3-S)SnCl}2 (cod = cycloocta-1,5-diene)13. Our most recent studies deal with chalcogenidoplumbates, with lead as the central metal atom(s). In line with the inert-pair concept for heavy atoms, addressing the stabilization of the 6s orbital due to relativistic effects, lead is usually observed in the formal +II oxidation state. Exceptions like PbO2 are strong oxidizing agents, and the heavier lead(IV) chalcogenides, &#34;PbCh2,&#34; have not been discovered to date14. The same holds for the chalcogenidoplumbate(IV) anions, of which only [PbO4]4- has been reported15 until recently (see below).
Apart from a diverse group of structurally investigated oxidoplumbates(II,IV), there have been only few examples of chalcogenidoplumbates(II), namely [PbTe3]4-, with a trigonal pyramidal anion16; and [Pb2Ch3]2-, where Ch = Se or Te, with a trigonal bipyramidal anion17. These are synthesized by a route that has also been applied for the generation of Zintl ions18. Upon preparation of multinary intermetallic phases by fusion of the elements at high temperatures, subsequent extraction by solvents in the presence of a sequestering agent affords the desired products in (single-)crystalline form. In the case of the [Pb2Ch3]2- anions, for instance, a phase of the nominal composition &#34;KPbCh&#34; has been extracted with 1,2-diaminoethane (en) in the presence of 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane ([2.2.2]crypt). The cryptand is necessary both for crystallization upon increase of the effective cation radius in the {K[2.2.2]crypt}+ complex counter ion, to better match the anionic size, and for a shielding of the positive charge that suppresses an electron back-donation from the anion in solution. Such salts with encapsulated cations usually reveal high tendencies for crystallization and thus, fairly good yields when compared to the corresponding salts without sequestration agents. However, a rather cumbersome synthesis or the high prices of cryptands prevent the excessive scaling of such approaches.
In contrast, K4[PbTe3]&#183;2en is synthesized via in situ reduction in solution, as has already been used as early as 1891 for the generation of the famous Pb94- anion19,20. For the latter, elemental alkaline metals were added to suspensions of lead in liquid ammonia at low temperatures, whereas for the telluridoplumbate, an alloy of the nominal composition &#34;PbTe2&#34; was reduced at room temperature, again by the addition of elemental potassium.
Our first approach towards such metalate species to be presented herein is a combination of both pathways. Here, solid-state synthesis is followed by either reduction in solution in the presence of inexpensive sequestering agents, such as 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6), or via reduction with alkaline metals that are chelated by the solvent itself, without the need for additional sequestering agents, similar to the synthesis of [Na4(en)7][Sn9]21. Our second approach also starts with high-temperature synthesis, but it is followed by solvothermal extraction of the resulting phases (i.e., extraction at elevated temperatures and pressures)22. In the following, we will present both synthetic approaches and some of our recent results upon application of these reaction pathways.

<table border="0" cellpadding="0" cellspacing="0" width="655">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Ethan-1,2-diamine</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td style="width:136px;">E26266-2.5L</td>
			<td style="width:191px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Calcium hydride</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>213268-100G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Tetrahydrofuran</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>401757-1L</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Sodium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>71172-1KG</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Potassium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>244864-50G</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Tris-triphenylphosphine rhodium chloride</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>199982-5G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Lead</td>
			<td style="width:81px;">Acros</td>
			<td align="right">222625000</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Selenium</td>
			<td style="width:81px;">Sigma-Aldrich</td>
			<td>209643-50G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">18-crown-6</td>
			<td style="width:81px;">Acros</td>
			<td align="right">181561000</td>
			<td></td>
		</tr>
	</tbody>
</table>

combining solid-state and solution-based techniques: synthesis and reactivity of chalcogenidoplumbates(ii or iv)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]2- or [Pb2Ch3]2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a &#181;-PbSe ligand (i.e., the heaviest-known CO homolog).
In contrast, the solid-state synthesis of a phase of the nominal composition &#34;K2PbSe2&#34; by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]2- or [BiSe3]3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route.
All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by 205Pb and 77Se or 127Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the &#181;-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]4- anion is mainly due to a suitable stabilization within the crystal lattice.

The existence of an ortho-selenidoplumbate anion [PbSe4]4-23 (see Figure 1, top right) has been confirmed by single crystal diffraction experiments, elemental analysis, and quantum chemical calculations. The crystal structure refinement confirms the almost-perfect tetrahedral coordination geometry, as would be expected for a lead(IV) ion, whereas DFT calculations rationalize the energetically stabilized a1...

Watch this Scientific Journal Video about Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV at JoVE.com

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV

The synthesis of chalcogenidoplumbates(II,IV) via the in situ reduction of nominal "PbCh2" (Ch = Chalcogen) and via a solid-state reaction and subsequent solvothermal reactions is presented. Additionally, reactivities of plumbate(II) solutions are portrayed, which yield the heaviest-known CO homolog known to date: the &#181;-PbSe ligand.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica ...

The overall goal of this combinational approach of solid-state and solution-based chemistry is to synthesize novel materials with intrinsic semi-conducting properties. This method can help answer key questions in the inorganic and materials chemistry field, such as how to synthesize compounds not accessible via traditional synthetic methods or access compounds with uncommon oxidation states, coordination modes, or ligands. The main advantage of this technique is that it is high-yielding and provides access to reactive, pure metallate and iron solutions to be used as precursors or for further reactivity studies.Though this method can provide insight into the chemistry of metalloid compounds of the heaviest metal atoms, it can also be applied to other metallates. Generally, individuals new to this method will struggle because all manipulations have to be performed under strict exclusion of air, moisture and, in some cases, light. To prepare the dry solvents for synthesis, first add one liter of freshly-purchased one-two diaminoethane to 25 grams of calcium hydride.Heat the mixture under reflux until hydrogen is no longer generated, than distill the mixture under ambient pressure. Add one liter of tetrahydrofuran, THF, to 10 grams of sodium-potassium alloy. Heat the mixture under reflux for at least twelve hours, then distill the mixture at ambient pressure.Make a saturated solution of Wilkinson's catalyst by adding 20 milliliters of THF to 300 milligrams of the catalyst. After stirring overnight at room temperature, filter the mixture with an inert gas filter frit of low porosity. Place 3.81 grams of elemental selenium in a silica ampule and add five grams of elemental lead.Heat the solids with an oxygen-methane burner until optical homogeneity of the melt is achieved, which is approximately ten minutes. Knock the ampule gently with a cork ring throughout the synthesis to detach sublimed selenium from the ampule wall, which will then drop back into the reaction mixture. After allowing the reaction mixture to cool to room temperature, break the ampule with a pestle and a mortar.Manually remove all remaining splinters of the ampule, then pestle the crude lead selenide thoroughly. Next, place 0.95 grams of elemental potassium and five grams of elemental lead in a thick-walled silica ampule. Slowly heat the solids with an oxygen-methane burner until optical homogeneity of the melt is achieved, which is approximately 20 minutes.Carefully add 1.9 grams of elemental selenium pellets to the molten alloy. Upon complete addition, increase the temperature until the reaction mixture emits bright yellow-white radiation, and hold the temperature for 10 minutes. Decrease the reaction temperature slightly if the radiation color turns to pure, bright white.After allowing the reaction mixture to cool to room temperature, break the ampule with a pestle and a mortar. Manually remove all remaining splinters of the ampule and the regulus of elemental lead, then pestle the crude potassium lead selenide thoroughly. Place one gram of lead selenide, 1.55 grams of 18 crown 6 and a large stir bar in a round-bottom nitrogen flask.Transfer the flask onto a stir-plate and add 125 milliliters of one two diaminoethane. Stir vigorously at room temperature, and then add 0.23 grams of elemental potassium. The freshly-cut potassium is very sticky.Here it was covered in the lead selenide powder prior to its addition. Zero moisture must absolutely not enter the flask during the addition of the diverse chemicals. We apply counter-flow technique with the inert gas blowing out of the flasks such that air cannot go in.After stirring overnight at room temperature, fill the solution with an inert gas filter frit of low porosity. Now, place 0.5 grams of potassium lead selenide and two milliliters of one two diaminoethane in a five milliliter glass vial. Place the glass vial in a 15 milliliter PTFE vial and place the PTFE vial in a standard stainless steel autoclave, Close the autoclave tightly, and heat in a oven at 150 degrees Celsius for five days.After five days, turn off the oven and allow it to slowly cool to room temperature for one day, then transfer the reaction mixture into paratone oil and manually select crystals of the product under a standard-light microscope at 15 to 40 fold magnification. Place ten milliliters of the crown ether solution in a 50 milliliter flask. Add ten milliliters of the saturated Wilkinson's catalyst solution and stir overnight.Once the reaction is complete, filter the solution with an inert gas filter frit of low porosity and remove the solvent under dynamic vacuum slowly over 24 hours. After transferring the crude reaction product into paratone oil, manually select crystals of the Chevrel type cluster under a standard-light microscope at 15 to 40 fold magnification. Following this, place ten milliliters of the crown ether solution in a Schlenk tube and carefully layer it with ten milliliters of the saturated Wilkinson's catalyst solution.Cover the Schlenk tube with aluminum foil and leave it undisturbed for four weeks. After four weeks, transfer the resulting solid into paratone oil and select single crystals under a light microscope. The existence of an ortho-selenidoplumbate anion was confirmed by single crystal diffraction experiments, elemental analysis, and quantum chemical calculations.The crystal structure refinement confirms the almost-perfect tetrahedral coordination geometry, whereas DFT calculations rationalize the energetically stabilized A-one representation contributing to the overall stability of the anion. Other metallate materials can be obtained by this protocol, such as potassium two mercury two selenium three, which is a semi-and photo-conductor material with a polyanionic substructure. As it exhibits a too-large band gap, the band gap can be decreased by synthesizing the heavier tellurium homologue, which increases the photo-conductivity.High-yield impurity metallate anions can be utilized for further reactivity studies yielding molecular Chevrel-type compounds. The phosphine-saturated species include mixed-valence rhodium ions, and as the charge is highly de-localized, the structure determined by single crystal diffraction does not allow for formal oxidation state assignment. The telluridopalladate cluster is electron-precise, and palladium ions adopt a distorted square planar geometry.Similar synthetic procedures afford compounds with trirhodium disalinide units, adopting a trigonal, biparametal shape with selenium at the apical positions and rhodium in the basal plane. These units represent the core of different anionic cluster complexes. They can be isolated by the addition of counter-ion sequestering agents.Once mastered, this technique can be done in a day to obtain high-purity metallates in high yield. While attempting this procedure, it's important to remember that the compounds are highly sensitive to air and moisture, and in the case of heavy-element metallates, like telluridoplumbates, also to light. Following this procedure, other metallate materials that contain, for instance, light or early transition metal atoms, should accessible, too.This extends the library of known compounds and enables fine-tuning of desired properties. After watching this video, you should have a good understanding of how to synthesize novel metallate materials with a combination of solid-state and solution-based techniques. Don't forget that working with heavy elements and their compounds can be extremely hazardous, and precautions, such as wearing appropriate lab attire and having sand readily available for fire-extinguishing purpose, should always be taken while performing this procedure.

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10.6K visualizações.  University of California, Berkeley. The overall goal of this combinational approach of solid-state and solution-based chemistry is to synthesize novel materials with intrinsic semi-conducting properties. This method can help answer key questions in the inorganic and materials chemistry field, such as how to synthesize compounds not accessible via traditional synthetic methods or access compounds with uncommon oxidation states, coordination modes, or ligands. The main advantage of this technique is that it is high-yielding and p...