Thermally Induced Valence Tautomeric Transition in a Two‐Dimensional Fe‐Tetraoxolene Honeycomb Network

Abstract

A novel tetraoxolene-bridged Fe two-dimensional honeycomb layered compound, (NPr ) [Fe (Cl An) ] ⋅2 (acetone)⋅H O (1), where Cl An =2,5-dichloro-3,6-dihydroxy-1,4-benzoquinonate and NPr =tetrapropylammonium cation, has been synthesized. 1 revealed a thermally induced valence tautomeric transition at T =236 K (cooling)/237 K (heating) between Fe (m=2 or 3) and Cl An (n=2 or 3) that induced valence modulations between [Fe Fe (Cl An ) (Cl An )] at T>T and [Fe Fe (Cl An )(Cl An ) ] at T<T . Even in a two-dimensional network structure, the low-temperature phase [Fe Fe (Cl An )(Cl An ) ] valence set can be regarded as a magnetic chain-knit network, where ferrimagnetic Δ and Λ chains of [Fe (Cl An )] are alternately linked by the diamagnetic Cl An . This results in a slow magnetization behavior attributed to the structure acting as a single-chain magnet at lower temperatures.

Square Grid Metal–Chloranilate Networks as Robust Host Systems for Guest Sorption

“…[22] We also notet hat slow magnetisation relaxation has recently been reported for the 2D transition metal network material(NPr 4 ) 2 [Fe 2 (can) 3 ]·2acetone·H 2 O. [23]…”

“…We have preliminary observations for similar frequency dependent AC behaviour in DC fields for lanthanoid networks such as (NBu 4 ) 2 [Gd 2 (can) 5 (Na(H 2 O) 3 ) 2 ] with maxima in χ M ′′ being clearly observed . We also note that slow magnetisation relaxation has recently been reported for the 2D transition metal network material (NPr 4 ) 2 [Fe 2 (can) 3 ]⋅2acetone⋅H 2 O …”

Chameleonic layered metal–organic frameworks with variable charge-ordered states triggered by temperature and guest molecules

“…The pristine solvated compound, (NPr 4 ) 2 [Fe 2 (Cl 2 An) 3 ]$ 2(acetone)$H 2 O (1), which is prepared in accordance with a previously reported method, 31 has a at honeycomb anionic layer [Fe 2 (Cl 2 An) 3 ] 2À that is separated by two kinds of structurally distinguished NPr 4 + cations (C 1 + and C 2 + ), forming an alternating stacking form [/(l)(C 1 + )(l)(C 2 + )/] N (l means the [Fe 2 (Cl 2 An) 3 ] 2À layer) with position-disordered water molecules located only at one side of cation layers and two acetone molecules located inside the hexagonal pores of the [Fe 2 (Cl 2 -An) 3 ] 2À layer. 31 The lattice solvent molecules in 1 can be easily removed by evacuating at room temperature for several hours to produce the desolvated compound, (NPr 4 ) 2 [Fe 2 (Cl 2 An) 3 ] (1-d), with its crystallinity remaining intact (here, it took 12 h to complete the elimination). Thermal gravimetric analysis (TGA) shows that the elimination of lattice solvents is completed by heating up to $340 K under N 2 atmosphere conditions, and the compound of 1-d is very stable up to ca.…”

“…[1][2][3] One of the most intriguing targets for SRMMs is a class of thermally driven electron transfer (TDET) systems, which can also be a strong candidate for SRMMs triggered by other external stimuli such as light, 12,14,16,19,20,23,[32][33][34][35] pressure, 6,36 and chemical guests. 26,[37][38][39] Therefore, to date, various types of TDETs, such as neutral-ionic transition (N-I transition), 5,9,18,25,27,38 valence tautomerism (VT), 4,6,8,10,11,21,22,24,28,30,31 and inter-valence electron transfer (IVET), 7,13 have been investigated using organic charge-transfer systems and metal complexes. Most of these systems have been studied using a one-step TDET that occurs at one transition temperature T 1/2 (1) , and only a few examples of two-or multi-step TDET with T 1/2 (1) , T 1/2 (2) , and T 1/2(x) (T 1/2(1) < T 1/2(2) < T 1/2(x) ) have been reported thus far: (i) discrete molecules, where two VT subunits interact electronically with each other, i.e., owing to electronic disproportionation, 10,21,<...>…”

“…Recently, we have reported one-step TDET in a D 2 A 3type honeycomb-layered compound, (NPr 4 ) 2 [Fe 2 (Cl 2 An) 3 ]$ 2(acetone)$H 2 O (1), which is composed of 2,5-dichloro-3,6dihydroxo-1,4-benzoquinonate (Cl 2 An mÀ ) and Fe n+ ions with tetrapropylammonium cations (NPr 4 + ) as well as some crystallization solvents (acetone and water) located at hexagonal pores of layers and between layers. 31 This layered compound revealed two ground states of the fully electron transferred state (as the low-temperature (LT) phase) of [(Fe 3+ ) 2 This feature of charge-ordered states made us imagine the existence of a neutral state of the high-temperature (HT) phase in 1, which comprises only DA chains at higher temperatures; practically, 1 converted itself to a solvent-free form, (NPr 4 ) 2 [-Fe 2 (Cl 2 An) 3 ] (1-d), with an elimination of its lattice solvents, and no longer changes to the HT phase within 1 upon heating. Nevertheless, 1-d afforded three TDET phases (LT / IM / HT) described in Scheme 1 with two-step TDET at T 1/2b and T 1/2c appearing continuously from the IM o phase of 1 via desolvation (T 1/2b and T 1/2c are T 1/2(1) and T 1/2(2) for 1-d, respectively) (Scheme 2).…”