125Te and 57Fe nuclear resonance vibrational spectroscopies (125Te NRVS measured at PETRA III) of a [2Fe-2Te]+ cluster with a key low energy vibration highlighted that is best observable in the 125Te NRVS experiment. The vertical axis shows the partial vibrational density of states (PVDOS). (Credit: George Cutsail, figure partly from original publication)
Replacing a heavy element to an iron–sulfur molecular cluster has allowed scientists to observe a previously inaccessible magnetic spin state. An international team from Max Planck Institute for Chemical Energy Conversion (MPI CEC) and DESY, the SETI Institute (US) and SPring-8 (Japan) used intense X-ray beams from PETRA III at DESY to probe the cluster’s atomic vibrations. The researchers found that swapping the cluster’s usual sulfur atoms, similar to what is typically observed in biology, for larger chalcogen elements like selenium or tellurium dampens the atomic vibrations. This simple change stabilises an intermediate spin state that is not seen with lighter elements. Their study was published in Nature Communications.
For their experiments, the team, led by George Cutsail, formerly MPI CEC and now professor of chemistry at the LMU Munich (Germany), synthesised iron-based dimers bridged by sulfur (S), selenium (Se) or tellurium (Te). They then employed nuclear resonance vibrational spectroscopy (NRVS) to examine motions of the iron-57 (57Fe) and tellurium-125 (125Te) isotopes in the compounds. The measurements, combined with computational modeling, revealed that heavier atoms like Te weaken the vibrational coupling with iron. In effect, the heavier atoms effectively “calm” certain vibrations, allowing the easier sharing of electrons by the pair of iron centres and ultimately maintaining the unusual intermediate spin states that the sulfur-bridged molecules cannot typically achieve.
This finding provides new insight into iron-sulfur clusters which have many vital roles in biology by shuttling electrons in many enzymes and metabolic processes. By demonstrating how substituting the bridging atoms in diiron clusters (fundamental unit: [2Fe-2S]) can tune their electronic and magnetic behaviour, their work highlights the delicate interplay between atomic vibrations and electron configuration in these systems. The study also demonstrates the value of using heavy-atom isotope labels like 125Te, as spectroscopic probes, something that is uniquely possible at the PETRA III beamline P01.
The insights gained here could enhance our understanding of larger iron–sulfur enzyme cofactors and inform the design of new materials that exploit tailored spin states.
Reference:
Aleksa Radović, Justin T. Henthorn, Hongxin Wang, Deepak Prajapat, Ilya Sergeev, Nobumoto Nagasawa, Yoshitaka Yoda, Stephen P. Cramer and George E. Cutsail III, 125Te and 57Fe nuclear resonance vibrational spectroscopic characterization of intermediate spin state mixed-valent dimers, Nature Communications (2025), DOI: 10.1038/s41467-025-62118-w
