[Sn@Cu12@Sn20]12–

A new paper by Thomas Fässler’s research group was published recently in JACS (Journal of the American Chemical Society). Fässler's group is one of the few others in the world that investigates Zintl ions, though as far as I know they only work with the group 14 Zintl ions, E₉^4– (E = Si, Ge, Sn, Pb), not group 15 Zintl ions. (I think they're missing out.) Some examples of Fässler's recent work with group 14 Zintl ions can be found here and here. This latest research doesn't involve E₉^4– at any point, but I still think it's pretty cool.

Fässler's group have synthesised a series of A₁₂Cu₁₂Sn₂₁ (A = Na, K, Rb, Cs) intermetallic phases, which consist of twelve A⁺ cations and a [Sn@Cu₁₂@Sn₂₀]^12– cluster anion. The first step in this process was the formation of a Cu-Sn alloy, which involved melting Cu wire and Sn granules together in an arc furnace. Stoichiometric amounts of the Cu-Sn alloy and the alkali metal were then heated in sealed niobium tubes for several days. (Incidentally this is a very similar process to the synthesis of the A₄E₉ and A₃E₇ Zintl phases - more on that in a later post.) 

[Sn@Cu₁₂@Sn₂₀]^12– consists of a single Sn atom surrounded by a Cu₁₂ icosahedron, which is itself surrounded by a Sn₂₀ pentagonal dodecahedron. Each Sn atom of the Sn₂₀ cage caps one of the faces of the Cu₁₂ icosahedron, and conversely each Sn₅ ring of the pentagonal dodecahedron is capped by a Cu atom. [Sn@Cu₁₂@Sn₂₀]^12– shows only small deviations from perfect icosahedral symmetry.

[Sn@Cu₁₂@Sn₂₀]^12–.

One of the main reasons this paper caught my eye is the similarity between [Sn@Cu₁₂@Sn₂₀]^12– and the [As@Ni₁₂@As₂₀]^3– species synthesised in 2003 by Bryan Eichhorn's research group by reacting the group 15 Zintl ion As₇^3– with Ni(COD)₂ (discussed briefly here). These two cluster anions are isoelectronic to each other and are structurally very similar, both having almost perfect icosahedral symmetry. But even if it wasn't related to my own area of Chemistry, I would still find this research fascinating simply because of its beauty. Chemistry really is amazing sometimes.

What's the point?

There's one question that I am always asked when I tell people my research area. It's asked in a variety of ways but they all mean the same thing: "What use is that?" And then I have to tell my inquisitor that trying to coordinate metals to group 15 Zintl clusters has absolutely no direct applications for the near future and I'm only doing it for interest's sake.

This question annoys me because the implication is always there that if research doesn't appear to have any specific applications, then that research must be pointless. And I just cannot understand this point of view. "Blue skies research" is vital if we are to gain a full understanding of the world. Plus just because we can't see any uses for a particular research area now doesn't mean there won't be any in the future. For example, lasers were described as "a solution looking for a problem" back in 1960 but now have a huge variety of applications: microscopy, surgery and printing to name but a few. Who's to say that in thirty years from now there won't be a problem that can only be solved with group 15 Zintl ions? And then wouldn't it look ridiculous if all research into Zintls stopped in 2011 because there were no uses for them at the time? In my opinion, no research can ever be pointless.

Pointless?