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Synthesis and properties of cyclic sandwich compounds


Cyclic nanometre-scale sandwich complexes assembled from individual building blocks were synthesized. Sandwich complexes, in which a metal ion is π-coordinated by two planar aromatic organic rings belong to the foundations of organometallic chemistry. They have been successfully used in a wide variety of applications ranging from catalysis, synthesis and electrochemistry to nanotechnology, materials science and medicine1,2. Extending the sandwich structural motif leads to linear multidecker compounds, in which aromatic organic rings and metal atoms are arranged in an alternating fashion. However, the extension to a cyclic multidecker scaffold is unprecedented. Here we show the design, synthesis and characterization of an isomorphous series of circular sandwich compounds, for which the term ‘cyclocenes’ is suggested. These cyclocenes consist of 18 repeating units, forming almost ideally circular, closed rings in the solid state, that can be described by the general formula [cyclo-MII(μ-η88-CotTIPS)]18 (M = Sr, Sm, Eu; CotTIPS = 1,4-(iPr3Si)2C8H62−). Quantum chemical calculations lead to the conclusion that a unique interplay between the ionic metal-to-ligand bonds, the bulkiness of the ligand system and the energy gain on ring closure, which is crucially influenced by dispersion interactions, facilitate the formation of these cyclic systems. Up to now, only linear one-dimensional multidecker sandwich compounds have been investigated for possible applications such as nanowires3,4,5,6,7,8,9,10. This textbook example of cyclic sandwich compounds is expected to open the door for further innovations towards new functional organometallic materials.

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Fig. 1: Cyclocene synthesis.
Fig. 2: Cyclocene structures.
Fig. 3: Photoluminescence properties.
Fig. 4: Quantum chemical calculations.

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Data availability

All data are available in the main text or in the supplementary material. Correspondence and request for materials should be addressed to P.W.R.

Code availability

The TURBOMOLE quantum chemistry program suite is available from Calculations were done on a cluster consisting of 8 PCs with 24 Intel(R) Xeon(R) Gold 6212U CPUs each.


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C. Anson, M. Bodensteiner and F. Meurer are acknowledged for discussions about single-crystal X-ray diffraction data refinement. M. Dahlen is acknowledged for supporting PL measurements. Funding was provided by Fonds der Chemischen Industrie, Kekulé fellowship (grant no. 110160). We acknowledge support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the Collaborative Research Centre ‘4f for Future’ (CRC 1573 project no. 471424360, projects C1 and Q).

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Experimental work was carried out by L.M. with support from A.H., P.H. and S.G. PL measurements were carried out by S.L. Single-crystal X-ray diffraction experiments and refinement were done by M.T.G. and L.M. DOSY-NMR was done by N.D.K. and C.Z. Density functional theory calculations were performed by S.G. and F.W. Project administration was done by P.W.R. Supervision was the responsibility of F.W., M.M.K. and P.W.R.

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Correspondence to Peter W. Roesky.

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Münzfeld, L., Gillhuber, S., Hauser, A. et al. Synthesis and properties of cyclic sandwich compounds. Nature 620, 92–96 (2023).

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