Continuous Increase in the Framework Flexibility of ZIF-90 with Crystal-Size Reduction to the Nanoscale: Evidence for Missing Metal Nodes Using Single-Crystal Infrared Spectroscopy.
- 1Department Chemistry, University of Iowa, Iowa City, Iowa52242-1294, United States.
- 2Département Chimie, Université de Sherbrooke, Sherbrooke, QuebecJ1K 2R1, Canada.
Abstract
Here we investigate the effects of crystal size on the mechanical properties (Young's modulus, framework flexibility) of a switchable metal-organic framework (MOF): zeolitic imidazolate framework-90 (ZIF-90) individual crystals with sizes ranging from micro- to nanodimensions. Atomic force microscopy (AFM) nanoindentation measurements over individual crystals reveal a significant reduction in Young's modulus with crystal-size reduction that follows a continuous power-law relationship, where Young's modulus decreases by nearly 1 order of magnitude as crystal base size decreases from ∼5 to 0.4 μm. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses coupled with the AFM results reveal that the origin of the size-dependent framework flexibility is primarily attributed to an increased concentration of missing metal node defects for smaller crystals. The presence of missing metal node defects in ZIF-90 crystals was further confirmed by single-crystal optical photothermal infrared spectroscopy measurements. Significantly, the value of the power-law exponent in Young's modulus versus crystal-size data was related to the magnitude of the relative increase in the number of missing metal node defects, indicating that the extent of the framework flexibility change with crystal size can in part be attributed to the rate of defect accumulation with crystal downsizing at the nanoscale. These findings indicate that the power-law scaling of mechanical properties may serve as an approach to assess the size-dependent extent of point-defect evolution in switchable MOFs, potentially enabling a rational design of solids with controlled functional properties.
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BibTeX
@article{ekanayake2026continuous,
title = {{Continuous Increase in the Framework Flexibility of ZIF-90 with Crystal-Size Reduction to the Nanoscale: Evidence for Missing Metal Nodes Using Single-Crystal Infrared Spectroscopy.}},
author = {Akalanka B Ekanayake and Collin S Hill and Thumini R Dias and Leonard R MacGillivray and Alexei V Tivanski},
journal = {Langmuir : the ACS journal of surfaces and colloids},
year = {2026},
month = sep,
doi = {10.1021/acs.langmuir.6c03586},
url = {https://europepmc.org/article/MED/42918010},
note = {CC BY},
}
RIS
TY - JOUR
TI - Continuous Increase in the Framework Flexibility of ZIF-90 with Crystal-Size Reduction to the Nanoscale: Evidence for Missing Metal Nodes Using Single-Crystal Infrared Spectroscopy.
AU - Akalanka B Ekanayake
AU - Collin S Hill
AU - Thumini R Dias
AU - Leonard R MacGillivray
AU - Alexei V Tivanski
PY - 2026
DA - 2026/09/01
JO - Langmuir : the ACS journal of surfaces and colloids
DO - 10.1021/acs.langmuir.6c03586
UR - https://europepmc.org/article/MED/42918010
AB - Here we investigate the effects of crystal size on the mechanical properties (Young's modulus, framework flexibility) of a switchable metal-organic framework (MOF): zeolitic imidazolate framework-90 (ZIF-90) individual crystals with sizes ranging from micro- to nanodimensions. Atomic force microscopy (AFM) nanoindentation measurements over individual crystals reveal a significant reduction in Young's modulus with crystal-size reduction that follows a continuous power-law relationship, where Young's modulus decreases by nearly 1 order of magnitude as crystal base size decreases from ∼5 to 0.4 μm. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses coupled with the AFM results reveal that the origin of the size-dependent framework flexibility is primarily attributed to an increased concentration of missing metal node defects for smaller crystals. The presence of missing metal node defects in ZIF-90 crystals was further confirmed by single-crystal optical photothermal infrared spectroscopy measurements. Significantly, the value of the power-law exponent in Young's modulus versus crystal-size data was related to the magnitude of the relative increase in the number of missing metal node defects, indicating that the extent of the framework flexibility change with crystal size can in part be attributed to the rate of defect accumulation with crystal downsizing at the nanoscale. These findings indicate that the power-law scaling of mechanical properties may serve as an approach to assess the size-dependent extent of point-defect evolution in switchable MOFs, potentially enabling a rational design of solids with controlled functional properties.
SN - 0743-7463
SN - 1520-5827
ER -