Birmingham-led chemists fit 16 metals into a single metal-organic framework crystal

Order matters in this experiment. Before mixing anything, the team made 15 versions of the framework, called UoB-116, each with a single rare-earth metal, and characterized every structure ^[3]. Only then did they combine two, four, 12 and 15 metals in the same underlying structure ^[3]. Each blend could be compared with single-metal frameworks whose structures were already known ^[3].

Lanthanum did two things at once. Adding more of it progressively reduced the measured surface area ^[8]. Between the all-dysprosium and all-lanthanum ends of the series, CO2 uptake fell by 4.49 mmol/g, about 78 percent ^[11]. Porosity is what gives a MOF the internal space to interact with a target molecule ^[10], so the shrinking surface area could explain much of the lost capacity. The metal ions could also change how strongly the gas binds. The release does not separate the two effects, and both uptake figures are per gram of material, measured "under the conditions tested" ^[9].

The thing this doesn't tell you is how the 16-metal crystal itself behaves. The property measurements come from varying dysprosium against lanthanum ^[6]. Whether a 16-metal mixture has magnetism, absorption and gas uptake that follow predictably from its recipe would need its own measurements. Neil Champness, the corresponding author and a professor at Birmingham, said, "Our findings confirm a route toward 'programmable' porous materials, where scientists could choose a combination of metals to dial magnetic, optical, chemical or gas-adsorption behavior." ^[13]

The paper's title describes its compositional control as "Cationic Radius Biased" ^[2]. In other words, the size of each metal ion affects how much of it ends up in the framework ^[2][14]. Champness said, "The ability to predict how strongly particular metals will be incorporated potentially offers much finer control over future multimetal materials." ^[14] I'd expect that prediction, more than the count of 16, to decide whether properties can be chosen in advance, because a designer needs to know the crystal's composition before running the synthesis.

Champness also said, "Rather than having to invent a completely new material every time they want different properties, researchers can potentially change the metallic 'recipe' within the same underlying structure." ^[15] MOFs are already being investigated for gas storage and separation, sensing, catalysis, bioimaging and magnetic materials ^[10].