and weighed again to determine the mass of sample. The tube was then
transferred back to the analysis port of the gas adsorption instrument.
The outgas rate was again confirmed to be less than 3 μbar min−1. For all
isotherms, warm and cold free space correction measurements were
performed using ultra-high purity He gas (UHP, 99.999% purity); N 2
isotherms at 77 K were measured in liquid N 2 baths using UHP-grade gas
sources. Oil-free vacuum pumps and oil-free pressure regulators were
used for all measurements to prevent contamination of the samples
during the evacuation process or of the feed gases during the isotherm
measurements. Langmuir and Brunauer–Emmet–Teller (BET) surface
areas were determined from N 2 adsorption data at 77 K.
Magnetic measurements
Samples were prepared by adding crystalline powder compound
to a 5 mm I.D. (7 mm O.D.) quartz tube containing a raised quartz
platform. Solid eicosane was added to cover the sample to prevent
crystallite torqueing and provide good thermal contact between the
sample and the cryostat. The tubes were fitted with Teflon sealable
adapters, evacuated on a Schlenk line, and flame-sealed under static
vacuum. Following flame sealing, the solid eicosane was melted in a
water bath held at 40 °C. Magnetic susceptibility measurements were
performed using a Quantum Design MPMS2-XL SQUID magnetom-
eter. d.c. magnetic susceptibility measurements were collected in the
temperature range 2–300 K under applied magnetic fields of 0.01 T,
0.1 T and 1 T. Magnetic hysteresis measurements were performed
at a sweep rate of 9 mT s−1. Diamagnetic corrections were applied to
the data using Pascal’s constant to give χD = −0.00177772 emu/mol
( 1 (NiCl 2 ) 15 ), χD = −0.00207772 emu/mol ( 1 (NiBr 2 ) 12 ), χD = −0.00205272
emu/mol ( 1 (FeCl 2 ) 19 ), χD = −0.00196972 emu/mol ( 1 (CoCl 2 ) 18 ), and
χD = −0.00024306 emu/mol (eicosane).
The Mydosh parameter was calculated by extracting the slope of the
Tf vs log(ν) plot, normalized against Tf(0). The freezing temperature,
Tf, is defined as the peak maximum in χ′ at each frequency. The freez-
ing temperature Tf(0) is calculated by extrapolating the peak in χ′ to
log(ν) = 0 (ref.^23 ).
Electron microscopy
Transmission electron microscopy (TEM) was performed on an FEI
Titan 80–300 kV microscope operating at 300 kV at the National Center
for Electron Microscopy. Annular dark field scanning TEM images and
energy dispersive X-ray spectroscopy (EDS) maps were acquired using
a beam current of 100–300 pA at room temperature. The four EDS sili-
con drift detectors had a collection solid angle of ~0.7 sr. Images were
acquired before and after the EDS map to confirm that the sample did
not damage visibly due to the electron beam.
Scanning electron microscopy (SEM) was performed on an FEI
Quanta Dual Beam FIB 0.5–30 kV microscope operating at 20 kV at
the Biomolecular Nanotechnology Center at UC Berkeley. Energy-
dispersive X-ray spectroscopy (EDS) maps were obtained at room tem-
perature using an Oxford EDS detector attached to the SEM.
Mössbauer spectral measurements
The Mössbauer spectra of 1 (FeCl 2 ) 19 were obtained between 5 and 295 K
with a SEE Mössbauer spectrometer equipped with a Co-57 in Rh source.
The isomer shifts are given relative to α-iron at 295 K. The spectral
absorbers were prepared in an N 2 atmosphere glove box by packing
the powder sample into a 2.54 cm diameter polypropylene washer that
was sealed with three layers of packing tape. The samples where then
transferred to the spectrometer, where the absorber was maintained
in a He atmosphere in order to prevent oxidation or decomposition.
General procedure for metal content analysis via ICP-OES
Roughly 10 mg of activated material was placed in a 20 ml plastic vial
and digested with 10 μl of concentrated HF in 2 ml of dimethylsulfoxide
and diluted with 18 ml of 5% HNO 3 in Millipore water. The resulting solu-
tion was transferred to a 100 ml volumetric flask and diluted to mark
with 5% (v/v) aqueous HNO 3 in Millipore water to give a stock solution
that contained roughly 25 ppm Zr from the sample. The stock sample
solution (10.0 ml) and 2.50 ppm Y (1.00 ml) were added to a 25.0 ml
volumetric flask and diluted to mark with 5% (v/v) aqueous HNO 3 to
give sample solution that is ~10 ppm Zr with 0.100 ppm Y as an internal
standard. Standard solutions with 0.100, 1.00, 5.00, 10.0 and 15.0 ppm
Zr, Ni, Fe and Co with 0.100 ppm Y as an internal standard were prepared
for the calibration curve.Data availability
Additional crystallographic information, powder X-ray diffraction data,
scanning electron microscopy and energy-dispersive X-ray spectros-
copy 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
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Acknowledgements 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.Author contributions M.I.G., A.B.T. and J.R.L. formulated the project. M.I.G. and A.B.T.
synthesized the compounds. M.I.G. collected and analysed the single-crystal X-ray diffraction
data, with the assistance of A.B.T. J.O. collected and analysed the powder X-ray diffraction
data. A.B.T. and L.E.D. collected and analysed the magnetic susceptibility data. A.B.T. and K.B.
collected and analysed the electron microscopy data. A.B.T. collected the Mössbauer spectra,
and F.G. and G.J.L. analysed the spectra. M.I.G. collected and analysed the gas adsorption data.
M.I.G., A.B.T. and J.R.L. wrote the paper, and all authors contributed to revising it.Competing interests The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at https://doi.org/10.1038/s41586-019-
1776-0.
Correspondence and requests for materials should be addressed to J.R.L.
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.
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