Li18Na2Ge17—A Compound Demonstrating Cation Effects on Cluster Shapes and Crystal Packing in Ternary Zintl Phases

Scherf, Lavinia M.; Zeilinger, Michael; Fässler, Thomas F.

doi:10.1021/ic4027046

Cited by 14 publications

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“…Types of double-bonded heavier tetrel systems and their respective E=Ebond lengths. As it does not possess covalently bonded ligands,itcan be considered as an analogue to molecular O 2 .A fter the recently discovered Li 18 Na 2 Ge 17 , [18] Li 3 NaGe 2 is only the second ternary Li/Na/Ge compound to be reported. pounds containing dumbbells are known but their electron counts never suggest atrue double bond, and the bond lengths are at least in the range of the elemental single bond.…”

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[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

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The novel ternary Zintl phase Li3NaGe2 comprises alkali-metal cations and [Ge2](4-) dumbbells. The diatomic [Ge2](4-) unit is characterized by the shortest Ge-Ge distance (2.390(1) Å) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8-N) rule. Raman measurements support these findings. The multiple-bond character is confirmed by electronic-structure calculations, and an upfield (6)Li NMR shift of -10.0 ppm, which was assigned to the Li cations surrounded by the π systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand-free dumbbell in Li3NaGe2, the π- bonding py and pz orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled π-type bands of the neat solid Li3NaGe2 cross the Fermi level, resulting in metallic properties. Li3NaGe2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.

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“…Furthermore,weshow the first Raman spectrum of as olid-state Ge = Ge double bond. As it does not possess covalently bonded ligands,itcan be considered as an analogue to molecular O 2 .A fter the recently discovered Li 18 Na 2 Ge 17 , [18] Li 3 NaGe 2 is only the second ternary Li/Na/Ge compound to be reported.…”

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[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

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“…During our investigations in the Li‐Na‐Ge system,, the new compound Na 7 LiGe 8 was frequently observed as a side phase. The Zintl phase is readily available from a stoichiometric melt of the elements.…”

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“…Product analyses by indexing of XRD powder patterns show that the greatest possible incorporation of Ge into the anionic substructure is reached for v ≈ 0.5 in both synthesis routes. Greater overall Ge contents of reactants only lead to greater amounts of more Ge‐rich side products such as Li 12 Si 7– x Ge x , Na 7 LiGe 8– z Si z and Li 18 Na 2 Ge 17 . Therefore, the purest samples of Li 3 NaSi 6– v Ge v with a maximum v were obtained with overall Ge contents of v = 0.5.…”

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Site‐Specific Substitution Preferences in the Solid Solutions Li₁₂Si_7–xGe_x, Li_12–yNa_ySi₇, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_v

Scherf

Riphaus

Fässler

2016

Zeitschrift anorg allge chemie

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[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

et al. 2015

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4À unit is characterized by the shortest GeÀGe distance (2.390(1) ) ever observed in aZintl phase and thus represents the first Ge = Ge double bond under such conditions,a sa lso suggested by the (8ÀN) rule.R aman measurements support these findings.T he multiple-bond character is confirmed by electronic-structure calculations,and an upfield 6 Li NMR shift of À10.0 ppm, whichwas assigned to the Li cations surrounded by the p systems of three Ge dumbbells,further underlines this interpretation. Fort he unperturbed, ligand-free dumbbell in Li 3 NaGe 2 ,the p-bonding p y and p z orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals.T he partially filled p-type bands of the neat solid Li 3 NaGe 2 cross the Fermi level, resulting in metallic properties.Li 3 NaGe 2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.Multiple bonds of the heavier homologues of boron, carbon, and nitrogen have been intensively investigated during the last decades.[1-3] Among those,t he heavier tetrel homologues all adopt a trans-bent structure in contrast to planar ethylene.The pyramidalization at the Eatom in R 2 E= ER 2 drastically influences the possibility of forming aclassical p bond between the two metal atoms for E = Ge,Sn, and Pb.TheC GMT model proposed by Tr inquier and Malrieu [4] traces the deviation from planarity in R 2 E=ER 2 molecules back to the relative values of the singlet and triplet energies of the monomeric units ER 2 (E S and E T ,r espectively) and the energy of the double-bonded system:F or E s+ +p > 2 DE SÀT ac lassical planar structure is obtained, whereas E s+ +p < 2 DE SÀT favors the trans-bent structure.E s+ +p < DE SÀT results in monomeric ER 2 fragments without E À Eb onding. [1,5] Theinteratomic EÀEdistance is another strong indicator for the bond order.S cheme 1g ives an overview of several homonuclear double-bonded Si and Ge species.F or secondrow elements,double bonds are considerably shorter than the sum of the covalent radii, whereas for the heavier homologues,d eviations occur owing to the strict requirements of the bulky ligands that are often used to stabilize the reactive bonds or owing to electrostatic repulsion in the case of charged systems.F or example,i nR 2 Ge = GeR 2 ,t he Ge À Ge bond lengths are in the range of 2.21 to 2.51 , [2] most of them being shorter than aG e ÀGe single bond (2.44 ), but for [RGe=GeR] 2À ,greater bond lengths are observed.[6]In general, trans-bent structures are energetically favored over planar structures.L igand-free and thus symmetrically unperturbed germanide dumbbells have been observed in Zintl phases. [7] Assuming acomplete valence electron transfer in BaMg 2 Ge 2 ,a14 valence electron [GeÀGe] 6À dumbbell should be obtained. However,t he GeÀGe bond (2.58 ) [8] is significantly longer than atypical Ge single bond, which was sketchily explained by Coulombic repulsion of the negatively charged atoms.R ecently,t he strong interaction of alkalineearth metal dstat...

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Li₁₈Na₂Ge₁₇—A Compound Demonstrating Cation Effects on Cluster Shapes and Crystal Packing in Ternary Zintl Phases

Cited by 14 publications

References 59 publications

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

Site‐Specific Substitution Preferences in the Solid Solutions Li₁₂Si_7–xGe_x, Li_12–yNa_ySi₇, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_v

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

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Li18Na2Ge17—A Compound Demonstrating Cation Effects on Cluster Shapes and Crystal Packing in Ternary Zintl Phases

Cited by 14 publications

References 59 publications

[Ge2]4− Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li3NaGe2: A Solid‐State Equivalent to Molecular O2

[Ge2]4− Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li3NaGe2: A Solid‐State Equivalent to Molecular O2

Site‐Specific Substitution Preferences in the Solid Solutions Li12Si7–xGex, Li12–yNaySi7, Na7LiSi8–zGez, and Li3NaSi6–vGev

[Ge2]4− Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li3NaGe2: A Solid‐State Equivalent to Molecular O2

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Li₁₈Na₂Ge₁₇—A Compound Demonstrating Cation Effects on Cluster Shapes and Crystal Packing in Ternary Zintl Phases

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂

Site‐Specific Substitution Preferences in the Solid Solutions Li₁₂Si_7–xGe_x, Li_12–yNa_ySi₇, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_v

[Ge₂]⁴⁻ Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li₃NaGe₂: A Solid‐State Equivalent to Molecular O₂