[Ga6R8]2- (R = SiPh2Me): Eine metalloide Clusterverbindung mit einem unerwarteten Ga6-Gerüst

Abstract

Inhaltsu È bersicht. Aus der Reaktion einer metastabilen GaBrLo È sung mit einer Lo È sung von LiSiPh 2 Me in Toluol/THF entstanden orangefarbene Kristalle von [Ga 6 (SiPh 2 Me) 8 ] 2±2 [Li(THF) 4 ] + (1). Die unerwartete planare Struktur des Ga 6 -Geru È sts (C 2h ) konnte auch mit Hilfe von DFT-Rechnungen verifiziert werden. Die DFT-Rechnungen zeigen auûerdem, dass 1 gegenu È ber einem oktaedrischen Ga 6 R 6 2± -Anion und R 2 favorisiert ist. Dagegen zeigen Rechnungen fu È r entsprechende Al-und B-Verbindungen, dass hier die oktaedrischen Spezies bevorzugt sind. Diese Ergebnisse weisen darauf hin, dass die Wade-Regeln fu È r die Vorhersage analoger Strukturen von B, Al und Ga zu allgemein und daher nicht ausreichend sind. Da die Struktur des Ga-Geru È sts in 1 einem Ausschnitt aus der allotropen b-Ga-Struktur entspricht, mo È chten wir Cluster dieses Typs als metalloid oder allgemeiner elementoid bezeichnen. [Ga 6 R 8 ] 2± (R = SiPh 2 Me): A Metalloid Cluster Compound with an Unexpected Ga 6 -Frame Abstract. The reaction of a metastable solution of GaBr with a solution of LiSiPh 2 Me in a toluene/THF mixture results in orange coloured crystals of [Ga 6 (SiPh 2 Me) 8 ] 2±´2 [Li(THF) 4 ] +(1). The unexpected structure of the planar Ga 6 frame (C 2h ) could also be realized with the help of DFT calculation. DFT calculations furthermore show that 1 is energetically favoured against an octahedral Ga 6 R 6 2± species and R 2 . In contrast calculations for the similar Al and B species show that in these cases the octahedral entities are favoured. These results demonstrate that even for similar compounds of B, Al, and Ga Wade rules are too general and that they cannot predict the correct structure. Moreover the atomic arrangement within 1 shows that a structure is preferred which is also present in allotropic b-Ga and that therefore clusters of this type should be called metalloid or more general elementoid.

Metalloid Aluminum and Gallium Clusters: Element Modifications on the Molecular Scale?

“…After removal of two R − groups the formation of an octahedral [Ga 6 R 6 ] pre‐ closo unit, analogue to the tetrahedral [Ga 4 R 4 ] cluster mentioned in Section 4.3.1, could be assumed. Model calculations have shown, however, that a rhomboid Ga 6 unit with two naked Ga atoms would be favored over the pre‐ closo cluster 72. Similar calculations for the corresponding B 6 and Al 6 compounds—for which the octahedral units are favored—show that the Ga 6 cluster 8 is a special case.…”

“…We recently reported on the [Ga 6 R 8 ] 2− cluster compound ( 8 , R=SiPh 2 Me; Figure 18)72 in which the mean oxidation state of the gallium atoms is +1. After removal of two R − groups the formation of an octahedral [Ga 6 R 6 ] pre‐ closo unit, analogue to the tetrahedral [Ga 4 R 4 ] cluster mentioned in Section 4.3.1, could be assumed.…”

Synthesis and Structures of Polyhedral Hexa‐ and Octagallium Cluster Compounds

“…Other Ga 6 compounds show structures, which are not polyhedral. [Ga 6 (SiPh 2 Me) 8 ] 2– has a planar Ga 6 ‐core and GaCp* forms a hexamer in solid state, where no Ga–Ga bonding interactions are on work, but the hexamer is stabilized by CH/HC dispersive interactions. This is obvious from the long Ga–Ga distances (d GaGa = 407.3–417.2 pm), whilst those in cluster compounds are in the range from 247–296 pm.…”

“…Polyhedral cluster compounds (Scheme 1) include Ga 4 (R x ) 4 10 (R x = R 1 , [11] R 2 , [12] R 3 , [7b] C(SiMe 3 ) 3 , [13] tmp, [14] N(SiMe 3 )dipp) [14] ), trigonal bipyramidal Ga 4 Si core cluster [(Me 3 SiSi){Ga(R 1 )} 3 (GaSiMe 3 )] -11, [15] distorted octahedral Ga 6 R 4 6 [R 4 = SiMe(SiMe 3 ) 2 ] 12, [16] closo-[Ga 6 {Si(CMe 3 ) 3 } 4 -(CH 2 Ph) 2 ] 2-13 [16] and closo-[Ga 6 Mes 4 (L) 2 ] (L = C{iPrNC(Me)} 2 ) 14, [17] square antiprismatic [Ga 8 (fluorenyl) 8 ] 2-15 [18] and capped-trigonal prismatic [Ga 9 tBu 9 ] 0,1-16. [19] Other Ga 6 compounds show structures, which are not polyhedral.[Ga 6 (SiPh 2 Me) 8 ] 2has a planar Ga 6 -core [20] and GaCp* forms a hexamer in solid state, [21] where no Ga-Ga bonding interactions are on work, but the hexamer is stabilized by CH/HC dispersive interactions. This is obvious from the long Ga-Ga distances (d GaGa = 407.3-417.2 pm), [22] whilst those in cluster compounds are in the range from 247-296 pm.Preparation of those cluster compounds requires sources for gallium in low oxidation state.…”

Ga10Br10(4‐tert‐Butylpyridine)10: A Mixed‐Valent Gallium(I) Subhalide as an Intermediate during the Formation of Elemental Gallium?

“…Thus, while for halides, kinetically simple insertion reactions (e.g. 4 GaX+GaX 3 → Ga 5 X 7 ) lead to their rapid disproportionation even at low temperatures and consequently to an extremely difficult isolation of the subhalides, further reactions are blocked for similar clusters protected by bulky ligands: for example, the gallium( I ) compound [Ga 6 (SiPh 2 Me) 8 ] 2− 17 with a Ga 6 framework similar to that in β‐gallium does not decompose to metal even above room temperature 18…”