The Highly Conducting Spin-Crossover Compound Combining Fe(III) Cation Complex with TCNQ in a Fractional Reduction State. Synthesis, Structure, Electric and Magnetic Properties

Abstract

Three systems [Fe(III)(sal 2 -trien)](TCNQ) n ·X (n = 1, 2, X = MeOH, CH 3 CN, H 2 O) showing spin-crossover transition, conductivity and ferromagnetic coupling were synthesized and studied by X-ray diffraction, Montgomery method for resistivity, SQUID magnetometry and X-band EPR. Spin-spin interactions between local magnetic moments of Fe(III) ions and electron spins of organic TCNQ network were discovered and discussed within the framework of intermolecular superexchange coupling.

The First Conducting Spin‐Crossover Compound Combining a MnIII Cation Complex with Electroactive TCNQ Demonstrating an Abrupt Spin Transition with a Hysteresis of 50 K

“…The electron acceptors or donors in the charge‐transfer systems must be available in fractional reduction or oxidation states to promote the enhanced conductivity. Thus, 7,7,8,8,‐tetracyanoquinodimethane (TCNQ) would be suitable for this purpose . The cross effects between conductivity and spin crossover are presumed due to the chemical pressure that the coordination compounds experience upon LS/HS transformation.…”

“…The electron acceptors or donors in the charge-transfer systems must be available in fractional reduction or oxidation states to promote the enhanced conductivity.T hus, 7,7,8,8,-tetracyanoquinodimethane (TCNQ)w ould be suitable for this purpose. [6][7][8][9][10] The cross effects between conductivity and spin crossover are presumed due to the chemical pressure that the coordinationc ompounds experience upon LS/HS transformation.T he majority of known examples that exhibit HS/LS transitions feature six-coordinated Fe II or Fe III complexes, because the spin-crossover effect is most pronouncedi nd 5 and d 6 systems in which two electrons switch between t 2g and e g orbitals. [1][2][3] Much rarer are the spin-statet ransitions in d 4 systems, represented by Mn III and Cr II complexes, in whicho ne electroni st ransferred between t 2g and e g orbitals.…”

Simultaneous Spin‐Crossover Transition and Conductivity Switching in a Dinuclear Iron(II) Coordination Compound Based on 7,7′,8,8′‐Tetracyano‐p‐quinodimethane

“…The E a value of 57 meV is the lowest yet reported for as emiconducting SCO material. [39][40][41][42][43][44][45][46][47][48][49][50][51][52] In contrast, above 330 K, the s turns down sharplyi nc onjunction with the thermal spin transition, and further decreases to reach 0.074 Scm À1 at 380 K. Therefore, the s behaviors trongly correlates with the spin state. On cooling the sample from 380 to 50 K, the s values do not coincide with the trend of the first heating process ( Figure S5, Supporting Information).…”

“…Indeed, such temperature dependence of dramatic lattice changes associated with p-p stacking distances are observed for many conducting compounds with 1D p-stacked TCNQ columns, whichc an be interpretedi nt erms of Peierls distortion. [46][47][48][49][50][51][52]73] At the same time, the [Fe 2 (bpypz) 2 ] 2 + units bridged by TCNQ Bm olecules also cause large lattice changes associated with markedlya ltered coordination bond lengths aroundt he Fe II centers upon SCO. [55][56][57][58][59][60][61][62][63][64][65] Therefore, the selfgrinding effect is likely ar esult of relatively large changes in the lattice caused by thermalS CO andP eierls transitions (see above).…”

“…[1][2][3][4][5][6][7][8][9][10][11] To date, hybrid materials of co-crystallized SCO complexes and molecular conductors have been reported; these were usually designed in Coulombs ets combining ac ationic SCO complex anda na nionic molecular conductor,n amely,i onic crystalline materials. [39][40][41][42][43][44][45][46][47][48][49][50][51][52] Amongt hese SCO conductors, the most common combinations are between cationic Fe III SCO complexes and anionic molecular conductors. However, the combination of Fe II SCO complexes and molecular conductors is still rare.…”