A Material Showing Colossal Positive and Negative Volumetric Thermal Expansion with Hysteretic Magnetic Transition

Abstract

It is an ongoing challenge to design and synthesize magnetic materials that undergo colossal thermal expansion and that possess potential applications as microscale or nanoscale actuators with magnetic functionality. A paramagnetic metallocyanate building block was used to construct a cyanide-bridged Fe-Co complex featuring both positive and negative colossal volumetric thermal-expansion behavior. A detailed study revealed that metal-to-metal charge transfer between 180 and 240 K induced a volumetric thermal expansion coefficient of 1498 MK accompanied with hysteretic spin transition. Rotation of the magnetic building blocks induced change of π⋅⋅⋅π interactions, resulting in a negative volume expansion coefficient of -489 MK , and another hysteretic magnetic transition between 300 and 350 K. This work presents a strategy for incorporating both colossal positive and negative volumetric thermal expansion with shape and magnetic memory effects in a material.

Effect of Intermolecular Interactions on Metal‐to‐Metal Charge Transfer: A Combined Experimental and Theoretical Investigation

“…Electron transfer (ET) is a widespread and important event in nature ranging from fundamental photosynthesis and biological systems to materials science applications, such as catalysis, energy conversion, and information processing . In particular, ET between metal ions can induce marked changes in spin state, charge distribution, and bond length, which has been utilized to tune magnetic, electric, and mechanical properties of the complexes . Typical examples of external stimuli‐tuned metal‐to‐metal charge transfer (MMCT) are cyanide‐bridged Fe/Co Prussian blue analogues (PBAs), which show interconversion between the {Fe II LS (μ‐CN)Co III LS } (LS=low spin) and the {Fe III LS (μ‐CN)Co II HS } (HS=high spin) linkages .…”

“…[1][2][3][4][5][6][7][8] In particular, ET between metal ions can induce marked changes in spin state,c harge distribution, and bond length, which has been utilized to tune magnetic, electric,a nd mechanical properties of the complexes. [2,[9][10][11][12][13][14] Typical examples of external stimuli-tuned metal-to-metal charge transfer (MMCT) are cyanide-bridged Fe/Co Prussian blue analogues (PBAs), which show interconversion between the {Fe II LS (m-CN)Co III LS }( LS = low spin) and the {Fe III LS (m-CN)Co II HS } (HS = high spin) linkages. [15][16][17][18][19][20] Thed esign of such as ystem, which undergoes reversible ET between two valence isomers, requires that the metal ions involved have appropriate redox potentials.Great efforts have been devoted to tune the redox potential of the metal ions and to control their MMCT behavior via chemical modifications of the molecular compo-sition and linkage,including ligand substitutions and tunable hydrogen-bonding linkages.…”

Steuerung des Metall‐Metall‐Charge‐Transfers zur Erzeugung schaltbarer Materialien

“…Ein weiteres Beispiel ist eine cyanidverbrückte 2D‐FeCo‐Verbindung, die eine gewaltige positive und negative volumetrische Wärmeausdehnung zeigte (Abbildung a) . Die Struktur besteht aus neutralen {[(Tp)Fe(CN) 3 ] 2 Co(Bib) 2 }‐Schichten (Bib=1,4‐Bis‐(1 H ‐imidazol‐1‐yl)benzol), bei denen die trinuklearen Fe 2 Co‐Einheiten über Bib‐Liganden zu einer unendlichen 2D‐Struktur verbunden sind.…”

“… a) Temperaturabhängigkeit des Elementarzellvolumens . b) Illustration der thermisch‐ und lichtgesteuerten MMCT‐induzierten positiven thermische Expansion.…”

Effect of Intermolecular Interactions on Metal‐to‐Metal Charge Transfer: A Combined Experimental and Theoretical Investigation

“…Electron transfer (ET) is a widespread and important event in nature ranging from fundamental photosynthesis and biological systems to materials science applications, such as catalysis, energy conversion, and information processing . In particular, ET between metal ions can induce marked changes in spin state, charge distribution, and bond length, which has been utilized to tune magnetic, electric, and mechanical properties of the complexes . Typical examples of external stimuli‐tuned metal‐to‐metal charge transfer (MMCT) are cyanide‐bridged Fe/Co Prussian blue analogues (PBAs), which show interconversion between the {Fe II LS (μ‐CN)Co III LS } (LS=low spin) and the {Fe III LS (μ‐CN)Co II HS } (HS=high spin) linkages .…”