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The preparation of materials with structures composed of multiple metal cations that occupy specific sites is challenging owing to the difficulty of simultaneously addressing the incorporation of different elements at desired precise positions. We report how it is possible to use a metal-organic framework (MOF) built with a rod-shaped inorganic secondary building unit (SBU) to combine multiple metal elements at specific positions in a manner that is controllable at atomic and mesoscopic scales. Through the combination of four different metal elements at judiciously selected molar ratios, 20 MOFs of different compositions and the same topology have been prepared and characterized. The use of diffraction techniques, supported by density functional theory calculations, has led us to determine various possible atomic arrangements of the metal cations within the SBUs. In addition, seven of the compounds combine multiple types of atomic arrangements, which are mesoscopically distributed along the crystals. Given the large diversity and importance of rod-based MOFs, we believe that these findings offer a new general strategy to produce complex materials with required compositions and controllable arrangements of the metal cations for desired applications. ; Work at Instituto de Ciencia de Materiales de Madrid–Consejo Superior de Investigaciones Científicas (CSIC) has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) Projects MAT2013-45460-R, CTQ2014-61748-EXP, and MAT2016-78465-R. F.G. acknowledges financial support from Fundación General CSIC (Programa ComFuturo) and MINECO (Ramón y Cajal program). Computational time has been provided by the Centre de Supercomputació de Catalunya. This work, developed under the HyMAP project, has received funding from the European Research Council under the European Union's Horizon 2020 research and innovation program (grant 648319). ; We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

8 pags, 4 figs. -- The online version contains supplementary material available at https://doi.org/10.1038/s41467-021-26184-0 ; Development of sustainable processes for hydrocarbons synthesis is a fundamental challenge in chemistry since these are of unquestionable importance for the production of many essential synthetic chemicals, materials and carbon-based fuels. Current industrial processes rely on non-abundant metal catalysts, temperatures of hundreds of Celsius and pressures of tens of bars. We propose an alternative gas phase process under mild reaction conditions using only atomic carbon, molecular hydrogen and an inert carrier gas. We demonstrate that the presence of CH2 and H radicals leads to efficient C-C chain growth, producing micron-length fibres of unbranched alkanes with an average length distribution between C23-C33. Ab-initio calculations uncover a thermodynamically favourable methylene coupling process on the surface of carbonaceous nanoparticles, which is kinematically facilitated by a trap-and-release mechanism of the reactants and nanoparticles that is confirmed by a steady incompressible flow simulation. This work could lead to future alternative sustainable synthetic routes to critical alkane-based chemicals or fuels. ; We thank Jose Criado for the artwork schematics of the system, in figures 4 and S1; Funding: We thank the European Research Council for funding support under Synergy grant ERC-2013-SyG, G.A. 610256 (NANOCOSMOS). Also, we acknowledge partial support from the Spanish MINECO through grants PID2020-113142RB-C21, PID2019106315RB-I00, and PID2019-106315RB-I00, EU ERC CoG HyMAP 648319, and from the regional government through project S2018-NMT-4367 (FotoArt-CM). AM acknowledges to the Spanish Ministry of Science (RYC2018-024561-I), to the Regional Government of Aragon (DGA E13_20R), to the National Natural Science Foundation of China (NFSC-21850410448, NSFC-21835002), and to the The Centre for Highresolution Electron Microscopy (ChEM), supported by SPST of ShanghaiTech University under contract No. EM02161943. S.K. and G.H. acknowledge funding from the Turbulent Superstructures Program of the German National Science Foundation (DFG) ; Peer reviewed