The investigation of compounds with meta-to-metal charge transfer (MMCT) may help to understand the ubiquitous electron transfer in chemical, physical and biological systems. Besides, such compounds may have potential applications in molecular devices such as quantum cellular automata, molecule switches, and phase-coherent logic gates.

In a recent study published in Angew. Chem. Int. Ed., Prof. SHENG Tianlu and his colleagues from Prof. WU Xintao's group at Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences have synthesized and characterized an unusual tetra-nuclear linear cyanido-bridged complex [Ru₂⁵⁺-CN-Ru₂⁵⁺]⁺.

Through the single-crystal X-ray diffraction structure analyses and electron paramagnetic resonance (EPR) spectroscopy and magnetic measurement, the researchers found that complex [Ru₂⁵⁺-CN-Ru₂⁵⁺]⁺ is the first example of mixed spin Ru₂⁵⁺-based complex, in which the electronic configurations of the cyanido-C bound Ru₂⁵⁺ and the cyanido-N bound Ru₂⁵⁺ are S=1/2 and S=3/2, respectively.

Prof. LIN Chengsheng from FJIRSM has given a theoretical explanation for the formation of the mixed spin complex.

By the analysis of Uv/vis-NIR spectra and TDDFT calculations, the researchers revealed that in complex [Ru₂⁵⁺-CN-Ru₂⁵⁺]⁺ there exists MMCT from the cyanido-N bound Ru₂⁵⁺ (S=3/2) to the cyanido-C bound Ru₂⁵⁺ (S=1/2).

This is the first report on the new type of MMCT which occurs between two same bimetallic cluster ions with same oxidation states but different spin states. This study may provide a new vision for understanding the electron transfer in the nature and in designing molecular devices.

Structure of complex [Ru₂⁵⁺-CN-Ru₂⁵⁺]⁺ and schematic MMCT in the complex (Image by Prof. WU’s group)