Abstract
Materials with negative compressibility can enable transformational technological advances spanning sensing, shielding, and optoelectronics. Virtually all materials exhibiting such expansion under pressure do so in one or two spatial directions, yet thermodynamics only forbid three-dimensional compression-induced expansion within the elastic regime absent of phase transitions. We show that a class of layered hybrid organic–inorganic metal oxides isolable through mild self-assembly reactions exhibits multiphase behavior under pressure, producing microscopic negative volume compressibility of their crystallographic unit cells. This phenomenon is only observed when molecular species bridge two-dimensional metal oxide layers. Chemical reduction─yielding mixed-valence hybrid bronzes─diminishes the effect. Evidence suggests that compression surmounts the boundary of elasticity via intermolecular carbon–carbon bond formation and structural distortion, driving interlayer expansion while liberating proton and electron equivalents.
| Original language | English |
|---|---|
| Pages (from-to) | 25931-25939 |
| Number of pages | 9 |
| Journal | Journal of the American Chemical Society |
| Volume | 147 |
| Issue number | 29 |
| DOIs | |
| State | Published - Jul 23 2025 |
Funding
This material is based upon work supported by the National Science Foundation under Award No. DMR-2338086. Portions of the synchrotron X-ray diffraction studies were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge Dr. Changyong Park for his assistance at APS with XRD studies. Synchrotron X-ray diffraction studies were also carried out at Beamline 12.2.2 at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The high-pressure facilities at the ALS are supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 11-57758. We gratefully acknowledge Dr. Martin Kunz and Dr. Bora Kalkan for assistance with XRD studies at the ALS. Neutron scattering measurements and PE compression synthesis were carried out at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The beam time was allocated to the Spallation Neutron and Pressure (SNAP) Diffractometer on proposal numbers IPTS-33088 and IPTS-32380. We acknowledge Jamie Molaison and Dr. Chris Ridley for their assistance with the PE synthesis. Single-crystal and powder X-ray diffraction studies were performed at the Notre Dame Molecular Structure Facility. We thank Dr. Allen Oliver for assistance with X-ray studies. We thank the ND Energy Materials Characterization Facility (MCF) for the use of the UV–visible spectrometer and X-ray photoelectron spectrometer to acquire diffuse reflectance and XPS measurements, respectively. The MCF is supported by Notre Dame Research. LC–MS and MALDI measurements were collected using instruments at the Notre Dame Mass Spectrometry & Proteomic Facility. We thank Dr. William Boggess and Dr. Mijoon Lee for their assistance in mass spectrometry experimentation and data analysis. Solid-State MAS NMR was collected on a Bruker 300 MHz solid-state NMR instrument at the Notre Dame Magnetic Resonance Center (MRRC). We gratefully acknowledge Wei-Kuo Li and Dr. Steven Corcelli for assistance with setting up calculations in VASP. We also thank Dr. William Schneider for useful discussions. This research was supported in part by the Notre Dame Center for Research Computing (CRC). This manuscript has been coauthored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://www.energy.gov/doe-public-access-plan ).