Synthesis and reactivity of A14ZnGe16 (A = K, Rb)

Thomas Fässler's group have recently published a paper in JACS, in which they describe the synthesis of the A₁₄ZnGe₁₆ (A = K, Rb) intermetallic phases. These compounds were synthesised in the solid state by heating stoichiometric mixtures of the elements for several days. Both phases were found to contain fourteen A⁺ cations, one [(Ge₄)Zn(Ge₄)]^6– cluster anion, and two tetrahedral Ge₄^4– ions. 

The [(Ge₄)Zn(Ge₄)]^6– species consists of two tetrahedral Ge₄^4– clusters bridged by Zn²⁺. One Ge₄ cluster is bonded to Zn via a triangular face (η³-coordination), while the other is bonded via an edge (η²-coordination). Sevov has previously synthesised a Cs₆ZnGe₈ phase, which also features a [(Ge₄)Zn(Ge₄)]^6– cluster anion, however in this case both Ge₄ clusters are bonded to Zn in an η³-fashion.

[(Ge₄)Zn(Ge₄)]^6–.

Next, Fässler tried reacting the K₁₄ZnGe₁₆ phase with Cu(mes) (mes = 2,4,6-trimethylphenyl) in liquid ammonia and in the presence of 18-crown-6. This resulted in the formation of [((mes)Cu)₂Ge₄]^4–, which consists of a Ge₄^4– cluster coordinated to two Cu(mes) fragments via two of its triangular phases. The analogous [((mes)Cu)₂Si₄]^4– species was also synthesised by Fässler, by reacting K₆Rb₆Si₁₇ with Cu(mes).

[((mes)Cu)₂Ge₄]^4–.

These results are impressive because, although the tetrahedral E₄^4– (E = Si, Ge, Sn, Pb) cluster anions have been known about for some time, their solution chemistry has been very little studied. This is possibly because there are very few readily available, soluble precursors. The synthesis of a Ge₄^4–-containing phase that is soluble in liquid ammonia could well result in the formation of many more novel cluster anions.

Rational synthesis of [Ge9(Si(SiMe3)3)3]–

Slavi Sevov's group have recently published a paper in the journal Inorganic Chemistry. Sevov's group are one of the very few other groups in the world who study Zintl ions, however their research is mainly focussed on the group 14 Zintl ions, E₉^4– (E = Si, Ge, Sn, Pb). Some examples of Sevov's recent work with group 14 Zintl ions can be found here and here. This latest research concerns the synthesis of [Ge₉(Si(SiMe₃)₃)₃]^– from Ge₉^4– and Si(SiMe₃)₃Cl.

Schnepf has previously synthesised [Ge₉(Si(SiMe₃)₃)₃]^– by reacting GeBr with Li[Si(SiMe₃)₃], however Sevov has discovered a much simpler and more convenient method. This method involves reacting the K₄Ge₉ Zintl phase with Si(SiMe₃)₃Cl in acetonitrile and in the presence of 2,2,2-crypt. This resulted in the formation of [K(2,2,2-crypt)][Ge₉(Si(SiMe₃)₃)₃], which contains the [Ge₉(Si(SiMe₃)₃)₃]^– cluster anion.

[Ge₉(Si(SiMe₃)₃)₃]^– consists of a tricapped trigonal prismatic Ge₉^4– cluster, which is bonded to the three Si(SiMe₃)₃ groups via its three capping atoms.

[Ge₉(Si(SiMe₃)₃)₃]^–.

The synthesis of [Ge₉(Si(SiMe₃)₃)₃]^– is exciting because it was thought for a long time that only the mono- and disubstituted [Ge₉(ER₃)]^3– and [Ge₉(ER₃)₂]^2– (E = Ge, Sn; R = Me, Ph) species were accessible. This research suggests that further examples of trisubstituted Ge₉^4– clusters could be easily formed, and also that the so far elusive tetrasubstituted clusters, Ge₉R₄, might one day be synthesised.

P4 activation by Scandium and Yttrium arene complexes

A new paper was published in Chem. Commun. recently by Paula Diaconescu's research group. Diaconescu's group have done a lot of work with complexes of group 3 metals, examples of which can be found here and here. This latest research involved reacting white phosphorus with complexes of the group 3 metals Sc and Y.

White phosphorus was found to react with [(NN^fc)Sc]₂(μ-C₁₀H₈) to form a mixture of [(NN^fc)Sc]₄P₈ and [(NN^fc)Sc]₃P₇, and with [(NN^fc)]Y(THF)]₂(μ-C₁₀H₈) to form only [(NN^fc)Y(THF)]₃P₇. [(NN^fc)Sc]₄P₈ consists of a realgar-like P₈^4– unit in the centre and four [(NN^fc)Sc]⁺ groups at the corners, each of which is bonded to two P atoms. The structure of this species is very similar to that of [(Cp*)₂Sm]₄P₈ synthesised by Roesky.

[(NN^fc)Sc]₄P₈ (NN^fc ligands omitted for clarity).

[(NN^fc)Sc]₃P₇ features a nortricyclane-like P₇^3– cage (i.e. a group 15 Zintl ion!) and three [(NN^fc)Sc]⁺ groups, each of which is bonded to two of the bridging P atoms. [(NN^fc)Y(THF)]₃P₇ has a very similar structure except that each Y centre is also bound to one THF molecule. Wolf has previously shown that white phosphorus reacts with [Cp*Fe(η⁴-C₁₀H₈)]^– to form [Cp*FeP₇]^2–, which also features the P₇^3– Zintl ion.

[(NN^fc)Sc]₃P₇ (NN^fc ligands omitted for clarity).

So there you have it - more beautiful structures formed using phosphorus. Hopefully this and my previous post have gone some way to explaining why I find phosphorus so amazing, but if you're still not convinced, there will no doubt be more fascinating research for me to write about soon!

White Phosphorus as a ligand for Copper, Silver and Gold

A new paper by Chris Russell's research group was published recently in Chem. Commun. (Chemical Communications). Russell's group have done some pretty cool things with phosphorus recently, for example this and this. I love phosphorus, so I was excited to see this latest research.

Phosphorus can exist in several forms, or allotropes. The two most common of these are white phosphorus and red phosphorus. White phosphorus consists of tetrahedral P₄ molecules, in which each atom is bound by single bonds to the other three atoms. White phosphorus is the least stable and the most reactive allotrope. Red phosphorus has a polymeric structure and can be thought of as a derivative of P₄ where one of the P-P bonds has been broken and two additional bonds to neighbouring tetrahedra have been formed. Other allotropes of phosphorus include violet (or Hittorf's) phosphorus and black phosphorus, however these are far less commonly encountered. 

Russell's latest research involved reacting white phosphorus with MX (M = Cu, Au: X = Cl; M = Ag: X = OTf) and GaCl₃ in dicholoromethane. Interestingly, three completely different products were formed depending on which of the three metals was used.

Cu was found to form chains of CuGaCl₄ units linked by P₄ molecules to form a polymeric framework, in which each P₄ is bound to two Cu atoms in an η²-fashion.

Part of the polymeric framework formed in the reaction between P₄, CuCl and GaCl₃.

Ag also forms a polymeric structure, however in this case each P₄ is only bound to one Ag atom.

Part of the polymeric structure formed in the reaction between P₄, AgOTf and GaCl₃.

Au, on the other hand, forms [Au(P₄)₂][GaCl₄], which consists of discrete [Au(P₄)₂]⁺ cations and [GaCl₄]^– anions. [Au(P₄)₂]⁺ consists of two P₄ molecules bonded to a Au atom in an η²-fashion. This is the first time [Au(P₄)₂]⁺ has been isolated, however both [Cu(P₄)₂]⁺ and [Ag(P₄)₂]⁺ were previously synthesised by Krossing. 

[Au(P₄)₂]⁺.

Elements in the same group of the periodic table can sometimes behave very differently, a fact that is brilliantly illustrated by this research: three metals, same group, same reaction, three very different products. I also think this paper has shown that phosphorus can be used to form some really beautiful structures, something I will say more about in a later post...