Work

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

Year: 2026

Type: article

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.

Source: Langmuir

DOI: 10.1021/acs.langmuir.6c03586

Authors: Akalanka B. Ekanayake, Collin S. Hill, Thumini R. Dias, Leonard R. MacGillivray, Alexei V. Tivanski

Institutions: University of Iowa, Université de Sherbrooke

Language: English

Topic: Metal-Organic Frameworks: Synthesis and Applications

Subfield: Inorganic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,500

Funders: University of Iowa, Division of Materials Research