Charge transfer phase transition with reversed thermal hysteresis loop in the mixed-valence Fe9[W(CN)8]6·xMeOH cluster

Abstract

A bimetallic pentadecanuclear cyanido-bridged {Fe9[W(CN)8]6 (MeOH)24}·xMeOH cluster of an Fe(II/III)-W(IV/V) mixed valence nature, reveals a reversible single-crystal-to-single-crystal transformation, concomitant with metal-to-metal charge transfer between Fe and W ions. The dominance of (HS)Fe(II)-NC-W(V) units at a high temperature, and (HS)Fe(III)-NC-W(IV) units at a low temperature, leads to an unprecedented reversed thermal hysteresis loop in magnetic measurements.

Rapid and reversible photoinduced switching of a rotaxane crystal

“…Phase transitions in the crystals of molecular compounds have been extended to spin-crossover transition-metal complexes12, mixed valence compounds3 and stimulus-responsive organic materials45. A recent application of crystalline phase transition involves positive or negative thermal expansion based on an anisotropic change of the crystal shape caused by a change in temperature678.…”

FeII Spin‐Crossover Phenomenon in the Pentadecanuclear {Fe9[Re(CN)8]6} Spherical Cluster

“…[34] Among such materials, bimetallic [M(CN) 8 ]-based clusters have great potential, [35] as demonstrated by a family of {M 9 M' 6 } pentadecanuclear clusters {M II 9 [M' V (CN) 8 ] 6 (MeOH) 24 } (M= 3d metal; M ' = Mo, W; MeOH = methanol) which show a diverse range of magnetic functionalities, including high spin, [36][37][38] SMM, [39,40] and thermally induced charge transfer. [41,42] In this regard, the application of the spin-crossover (SCO) effect to polynuclear molecules is rare. SCO was broadly investigated for mononuclear complexes, based mainly on the Fe II ion, [43,44] and coordination polymers offering efficient intramolecular interactions giving thermal hysteresis loops, crucial for applications such as memory devices.…”

“…Our previous attempt with [W V (CN) 8 ] 3À resulted in the formation of {Fe 9 W 6 } molecule showing an iron(II)-tungsten(V) to iron(III)-tungsten(IV) charge-transfer (CT) process instead of an SCO effect. [41] We next used a rare [Re V (CN) 8 ] 3À molecule which was reported by J. R. Long et al [56,57] as a product of thermal decomposition of [Re IV (CN) 7 ] 4À in the presence of KIO 4 and MnCl 2 . Its voltammetry suggested that [Re V (CN) 8 ] 3À has an accessible Re VI instead of a Re IV oxidation state.…”

“…Figure 1 and Table 1 and Figures S2-S3 and Tables S1-S3 in the Supporting Information). [36][37][38][39][40][41][42] This molecule comprises one [Fe II The average FeÀN/O bond lengths at high (1 HT ) and low temperature (1 LT ) are given in Table 1. In 1 HT , the average Fe À N distance for Fe1 is close to 2.06 , whereas for the Fe2-Fe5 centers the mean lengths of Fe À N/O bonds are in the range 2.13-2.14 .…”

“…These lengths are in good agreement with values measured in octahedral high-spin Fe II centers ( HS Fe II ) in CN À -bridged systems. [14,41] In 1 LT , the FeÀN/O distances for Fe2-Fe5 atoms decrease gradually because of a standard thermal contraction. On the contrary, the Fe1ÀN bond lengths change by approximately 6 % to give a mean value of 1.93 which can be assigned to a low-spin Fe II center ( LS Fe II ).…”