The modular building principle of metal− organic frameworks (MOFs) presents an excellent platform to explore and establish structure−property relations that tie microscopic to macroscopic properties. Negative thermal expansion (NTE) is a common phenomenon in MOFs and is often ascribed to collective motions that can move through the structure at sufficiently low energies. Here, we show that the introduction of additional linkages in a parent framework, retrofitting, is an effective approach to access lattice dynamics experimentally, in turn providing researchers with a tool to alter the NTE behavior in MOFs. By introducing TCNQ (7,7,8,8-tetracyanoquinodimethane) into the prototypical MOF Cu 3 BTC 2 (BTC = 1,3,5-benzenetricarboxylate; HKUST-1), NTE can be tuned between α V = −15.3 × 10 −6 K −1 (Cu 3 BTC 2 ) and α V = −8.4 × 10 −6 K −1 (1.0TCNQ@ Cu 3 BTC 2 ). We ascribe this phenomenon to a general stiffening of the framework as a function of TCNQ loading due to additional network connectivity, which is confirmed by computational modeling and far-infrared spectroscopy. Our findings imply that retrofitting is generally applicable to MOFs with open metal sites, opening yet another way to fine-tune properties in this versatile class of materials.
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic‐scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer‐like atomic‐scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III‐V, or II‐VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
The zeolitic imidazolate framework ZIF‐4 has recently been shown to exhibit large structural flexibility as a response to hydrostatic pressures, going from an open pore phase (ZIF‐4(Zn)‐op) to a closed pore phase (ZIF‐4(Zn)‐cp). The use of diamond anvil cell (DAC) setups has so far restricted thorough experimental insight into the evolution of lattice parameters at pressures below p < 0.1 GPa. Here we revisit the high‐pressure properties of ZIF‐4(Zn) by applying a new high‐pressure powder X‐ray diffraction setup that allows for tracking the evolution of lattice parameters in pressure increments as small as Δp = 0.005 GPa in the pressure range p = ambient – 0.4 GPa; a pressure resolution that cannot be achieved by using traditional DACs. We find ZIF‐4(Zn) has a bulk modulus of K(ZIF‐4(Zn)‐op) = 2.01 ± 0.05 GPa and K(ZIF‐4(Zn)‐cp) = 4.39 ± 0.20 GPa, clarifying and confirming some ambiguous results that have been reported previously.
We provide an update on the current state of the tolerance factor concept for hybrid organic–inorganic perovskites, reviewing the different improvements that have been made over the past few years.
Please cite only the published version using the reference above. This is the citation assigned by the publisher at the time of issuing the AAM. Please check the publisher's website for any updates. This is the author's final, peer-reviewed manuscript as accepted for publication (AAM). The version presented here may differ from the published version, or version of record, available through the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.