Structure transformation from Sierpiński triangles to chains assisted by gas molecules

Chao Li; Zhen Xu; Yajie Zhang; Jie Li; Na Xue; Ruoning Li; Mingjun Zhong; Tianhao Wu; Yifan Wang; Na Li; Ziyong Shen; Shimin Hou; Richard Berndt; Yongfeng Wang; Song Gao

doi:10.1093/nsr/nwad088

Structure transformation from Sierpiński triangles to chains assisted by gas molecules

Natl Sci Rev. 2023 Mar 30;10(7):nwad088. doi: 10.1093/nsr/nwad088. eCollection 2023 Jul.

Authors

Chao Li^{1

2}, Zhen Xu¹, Yajie Zhang¹, Jie Li¹, Na Xue³, Ruoning Li¹, Mingjun Zhong¹, Tianhao Wu¹, Yifan Wang¹, Na Li¹, Ziyong Shen¹, Shimin Hou¹, Richard Berndt², Yongfeng Wang¹, Song Gao⁴

Affiliations

¹ Center for Carbon-based Electronics and Key Laboratory for the Physics and Chemistry of Nanodevices, School of Electronics, Peking University, Beijing 100871, China.
² Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel 24098, Germany.
³ Central Laboratory, Tianjin Key Laboratory of Epigenetics for Organ Development in Preterm Infants, the Fifth Central Hospital of Tianjin, Tianjin 300450, China.
⁴ Institute of Spin Science and Technology, South China University of Technology, Guangzhou 511442, China.

Abstract

Reversible transformations between fractals and periodic structures are of fundamental importance for understanding the formation mechanism of fractals. Currently, it is still a challenge to controllably achieve such a transformation. We investigate the effect of CO and CO₂ molecules on Sierpiński triangles (STs) assembled from Fe atoms and 4,4″-dicyano-1,1':3',1″-terphenyl (C3PC) molecules on Au surfaces. Using scanning tunneling microscopy, we discover that the gas molecules induce a transition from STs into 1D chains. Based on density functional theory modeling, we propose that the atomistic mechanism involves the transformation of a stable 3-fold coordination Fe(C3PC)₃ motif to Fe(C3PC)₄ with an axially bonded CO molecule. CO₂ causes the structural transformation through a molecular catassembly process.

Keywords: CO; Sierpiński triangles; fractals; metal–organic motifs; scanning probe microscopy.