Large Lattice Responses in a Mixed‐Valence Prussian Blue Analogue Owing to Electronic and Spin Transitions Induced by X‐ray Irradiation

Abstract

Mixed-valence metal cyanides with general formulaIII (CN) 6 ]·n H 2 O (where A is an alkali-metal cation, and M and M' are divalent and trivalent transition-metal cations, respectively) have attracted considerable interest because of their unusual electronic and magnetic properties.[1] In addition to molecular-based ferromagnetic properties with Curie temperatures higher than room temperature, [2][3][4] the availability of degenerate or quasidegenerate electronic states has made them ideal systems with which to explore switching phenomena at the molecular level.[5] For example, in some of these materials visible-light irradiation at low temperatures can drive optically controlled phase transitions to long-lived metastable states where the optical and/or magnetic properties change dramatically, thereby raising the potential of applications in memory devices and magneto-optical switching. [6][7][8][9][10] Metal-to-metal electron transfer was also induced by X-ray irradiation at very low temperatures in the Prussian blue analogue, Rb 1.8 Co 4 [Fe(CN) 6 ] 3.3 ·13 H 2 O with the resulting phase transformation monitored by energy-dispersive synchrotron X-ray diffraction.[11] Herein, we show that X-ray irradiation can also induce interconversion between the ground and excited states in another such compound 1, over a broad temperature range (between room temperature and 10 K). Depending on the experimental conditions, a variety of internal charge-transfer processes and spin transitions are triggered resulting in either continuous or abrupt phase transformations that are accompanied by large lattice relaxations and can be accurately monitored by high-resolution angle-dispersive synchrotron X-ray diffraction. 6 e g 0 , S = 0) and is accompanied by a cubic-tetragonal phase transition, driven by the Jahn-Teller distortion of the Mn III N 6 octahedra [13,14] and the appearance of ferromagnetism at approximately 10 K.[15] Green light irradiation at low temperatures induces the reverse electron transfer and the low lying Mn II -Fe III excited state can then be populated.[16] Herein, we report on the internal redox reactions triggered by synchrotron X-ray radiation as a function of temperature and time in the related mixed-valence metal cyanide, 1. As excited metastable electronic and spin states are populated and evolve with illumination time at different temperatures, the angle-dispersive synchrotron X-ray diffraction technique allows simultaneous complete crystal structure refinements, which leads to the elucidation of the resulting rich phase diagram in unprecedented detail.We examined the synchrotron X-ray diffraction profiles of 1 collected at 295 K and at 100 and 10 K after cooling in the absence of X-ray illumination. No reflections violating facecentered cubic (fcc) extinction rules are evident and the crystal structure remains strictly cubic down to 10 K. Rietveld analysis (Figure 1 a, see Supporting Information) proceeded smoothly with the generic structural model of mixed-valence metal cyanides, [17] comprising a ...

Magnetische Molekülverbindungen: Schaltung magnetischer Eigenschaften durch externe Stimuli

“…[201] Bei tieferen Temperaturen lässt sich zudem durch einen einzelnen Laserpuls eine Entmagnetisierung erreichen. [202] [202] …”

“…[196] Wie Morgadonna et al kürzlich berichteten, kann dieser Phasenübergang auch durch Röntgenbestrahlung induziert werden. [202]…”

Elaboration of Prussian Blue Analogue/Silica Nanocomposites: Towards Tailor-Made Nano-Scale Electronic Devices

“…, compounds of which the magnetic properties change following an irradiation, are particularly interesting for the development of new electronic devices such as optical memories. At present, several works report on the study of the properties of these photoswitchable Prussian blue analogues constituted by different bimetallic pairs (CoFe [1,2,3,4,5,6], MnFe [7,8,9], FeCr [10,11,12]), and exhibiting electronic structure changes induced by different external stimuli (light [1,13,14,15], temperature [3,16,17], pressure [12,18,19,20,21]). The chemical and physical properties of these molecular materials depend on their size, shape and spatial organization.…”

Mesoporous Prussian Blue Analogues: Template‐Free Synthesis and Sodium‐Ion Battery Applications

“…[7] Prussian blue (A[Fe III Fe II (CN) 6 ], A = Na + or K + ), one of the oldest synthetic coordination compounds, has a cubic face-centered structure (space group symmetry Fm " 3m). [8] The open-framework structure consists of Fe II and Fe III ions sitting on alternate corners of corner-shared octahedra bridged by small conjugated cyanide anions (CN À ; Scheme 1 a). In this structure, the low-spin ferrous ions bond to the carbon atoms and the high-spin ferric ions bond to the nitrogen atoms with bond lengths of 1.92 and 2.05 , respectively.…”