The size-dependent and shape-dependent characteristics that distinguish nanoscale materials from bulk solids arise from constraining the dimensionality of an inorganic structure1,2,3. As a consequence, many studies have focused on rationally shaping these materials to influence and enhance their optical, electronic, magnetic and catalytic properties4,5,6. Although a select number of stable clusters can typically be synthesized within the nanoscale regime for a specific composition, isolating clusters of a predetermined size and shape remains a challenge, especially for those derived from two-dimensional materials. Here we realize a multidentate coordination environment in a metal–organic framework to stabilize discrete inorganic clusters within a porous crystalline support. We show confined growth of atomically defined nickel(ii) bromide, nickel(ii) chloride, cobalt(ii) chloride and iron(ii) chloride sheets through the peripheral coordination of six chelating bipyridine linkers. Notably, confinement within the framework defines the structure and composition of these sheets and facilitates their precise characterization by crystallography. Each metal(ii) halide sheet represents a fragment excised from a single layer of the bulk solid structure, and structures obtained at different precursor loadings enable observation of successive stages of sheet assembly. Finally, the isolated sheets exhibit magnetic behaviours distinct from those of the bulk metal halides, including the isolation of ferromagnetically coupled large-spin ground states through the elimination of long-range, interlayer magnetic ordering. Overall, these results demonstrate that the pore environment of a metal–organic framework can be designed to afford precise control over the size, structure and spatial arrangement of inorganic clusters.
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Additional crystallographic information, powder X-ray diffraction data, scanning electron microscopy and energy-dispersive X-ray spectroscopy data, gas-sorption data, magnetic data, Mössbauer spectroscopy data, diffuse reflectance UV–Vis spectra, and elemental analyses are available in the Supplementary Information. Metrical data for the solid-state structures are available from the Cambridge Crystallographic Data Centre under reference numbers CCDC 1901128 to 1901144.
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This research was supported through a Multidisciplinary University Research Initiatives Program funded by the US Department of Defense, Office of Naval Research under award N00014-15-1-2681. Single-crystal X-ray diffraction experiments were performed at beamline 11.3.1 at the Advanced Light Source at Lawrence Berkeley National Laboratory. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. Powder X-ray diffraction data were collected at beamline 17-BM-B at the Advanced Photon Source, a US Department of Energy, Office of Science User Facility operated by the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. We thank the US National Science Foundation for providing graduate fellowship support for A.B.T, L.E.D. and J.O. In addition, we thank S. J. Teat, K. Chakarawet, M. Jackson and N. Masciocchi for experimental assistance and helpful discussions. We also thank K. R. Meihaus for editorial assistance.
The authors declare no competing interests.
Peer review information Nature thanks Felipe Gándara, Mohamedally Kurmoo and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
Extended Data Fig. 1 High-angle annular dark field images and energy-dispersive spectroscopy data for 1(NiBr2)15.
a, High-angle annular dark field (HAADF) image (a, top left) and energy-dispersive X-ray spectroscopy (EDS) Zr (a, top right; yellow), Ni (a, bottom left; green) and Br (a, bottom right; red) mapping of a microcrystalline powder sample of 1(NiBr2)15. b, STEM-EDS line scan analysis for Ni (red) and Zr (yellow) across the length of the crystallite plotted as normalized atom per cent. The average amount for the two elements was determined to be 72 ± 12% for Ni and 28 ± 12% for Zr, corresponding to a Ni:Zr ratio of 2.6. c, EDS spectrum for the crystallite of 1(NiBr2)15. Signals for Cu and Au originate from the space-filling washer and sample grid, respectively.
Extended Data Fig. 2 High-angle annular dark field images and energy-dispersive spectroscopy data for 1(NiCl2)15.
a, High-angle annular dark field (HAADF) image (a, top left) and energy-dispersive X-ray spectroscopy (EDS) Zr (a, top right; yellow), Ni (a, bottom left; green) and Cl (a, bottom right; red) mapping of a microcrystalline powder sample of 1(NiCl2)15. b, STEM-EDS line scan analysis for Ni (green) and Zr (yellow) across the length of the crystallite plotted as normalized atom per cent. The average amount for the two elements was determined to be 70.7 ± 11% for Ni and 29 ± 11% for Zr, corresponding to a Ni:Zr ratio of 2.4. c, EDS spectrum for the crystallite of 1(NiCl2)15. Signals for Cu and Au originate from the space-filling washer and sample grid, respectively. cps, counts per second.
Extended Data Fig. 3 High-angle annular dark field images and energy-dispersive spectroscopy data for 1(CoCl2)18.
a, High-angle annular dark field (HAADF) image (a, top left) and energy-dispersive X-ray spectroscopy (EDS) Zr (a, top right; yellow), Co (a, bottom left; violet) and Cl (a, bottom right; green) mapping of a microcrystalline powder sample of 1(CoCl2)18. b, STEM-EDS line scan analysis for Co (violet) and Zr (yellow) across the length of the crystallite plotted as normalized atom per cent. The average amount for the two elements was determined to be 75 ± 13% for Co and 25 ± 13% for Zr, corresponding to a Co:Zr ratio of 3.0. c, EDS spectrum for the crystallite of 1(CoCl2)18. Signals for Cu and Au originate from the space-filling washer and sample grid, respectively.
Extended Data Fig. 4 High-angle annular dark field images and energy-dispersive spectroscopy data for 1(FeCl2)19.
a, High-angle annular dark field (HAADF) image (a, top left) and energy-dispersive X-ray spectroscopy (EDS) mapping Zr (a, top right; yellow), Fe (a, bottom left; orange) and Cl (a, bottom right; green of a microcrystalline powder sample of 1(FeCl2)19. b, STEM-EDS line scan analysis for Fe (orange) and Zr (yellow) across the length of the crystallite plotted as normalized atom per cent. The average amount for the two elements was determined to be 77 ± 9% for Fe and 23 ± 9% for Zr, corresponding to a Fe:Zr ratio of 3.3. c, EDS spectrum for the crystallite of 1(FeCl2)19. Signals for Cu and Au originate from the space-filling washer and sample grid, respectively.
a, b, Nickel site occupancies for single-crystal structures of NiBr2-loaded (a, light to dark red) and NiCl2-loaded (b, light to dark green) 1 obtained by reaction of 1 with 1.00 equiv to excess (>50 equiv) NiX2 (X = Br, Cl) in diglyme. Error bars represent the crystallographic standard uncertainties of the Ni(ii) site occupancies. Lines are included to guide the eye.
a, b, In-phase (a) and out-of-phase (b) variable-temperature a.c. magnetic susceptibility data from 2 to 10 K for 1(FeCl2)19 under zero d.c. magnetic field and a 0.4 mT a.c. magnetic field oscillating at frequencies of 1, 5, 7.5, 10, 50, 75, 100, 500, 750 and 1,000 Hz (blue to red). Coloured lines are guides for the eye.
a, b, 57Fe Mössbauer spectra for 1(FeCl2)19 at 100 K (a) and 5 K (b). The data were fit with four high-spin octahedral Fe(ii) components (green), two high-spin four- and five-coordinate Fe(ii) components (red), and a magnetic hyperfine component (grey). Spontaneous oxidation leads to a high-spin Fe(iii) impurity (blue) visible at 5 K. Overall fits are depicted in black.
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Gonzalez, M.I., Turkiewicz, A.B., Darago, L.E. et al. Confinement of atomically defined metal halide sheets in a metal–organic framework. Nature 577, 64–68 (2020). https://doi.org/10.1038/s41586-019-1776-0
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