Million-Fold Electrical Conductivity Enhancement in Fe₂(DEBDC) versus Mn₂(DEBDC) (E = S, O)

Abstract

Reaction of FeCl2 and H4DSBDC (2,5-disulfhydrylbenzene-1,4-dicarboxylic acid) leads to the formation of Fe2(DSBDC), an analogue of M2(DOBDC) (MOF-74, DOBDC4– = 2,5-dihydroxybenzene-1,4-dicarboxylate). The bulk electrical conductivity values of both Fe2(DSBDC) and Fe2(DOBDC) are ∼6 orders of magnitude higher than those of the Mn2+ analogues, Mn2(DEBDC) (E = O, S). Because the metals are of the same formal oxidation state, the increase in conductivity is attributed to the loosely bound Fe2+ β-spin electron. These results provide important insight for the rational design of conductive metal–organic frameworks, highlighting in particular the advantages of iron for synthesizing such materials.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…(105) m 2 /g, from a fit to N 2 adsorption data, at 77 K, confirming the presence of permanent microporosity. This value is the second highest reported for a porous magnet, overcome only with a value of 1050 m 2 /g reported for a lactate-bridged Co II material [202]. Finally, the structural distortion is fully reversible and similar "breathing" behavior has been previously observed in MOFs [203][204][205].…”

Coordination-induced reversible electrical conductivity variation in the MOF-74 analogue Fe2(DSBDC)

“…26 Owing to the sensitivity of this material to both water and air, all subsequent manipulations were performed in a dry, oxygen-free atmosphere. Thermogravimetric analysis (TGA) of this material revealed two consecutive weight loss events at 210-335°C and 320-560°C, respectively (Fig.…”

“…Therefore, to remove all solvent and produce completely activated MOF, Fe 2 (DSBDC)(THF) 2 ·x(THF) was heated at 170°C under dynamic vacuum (<3 mTorr) for 36 h. This yielded a dark red powder whose elemental microanalysis revealed a 2 were determined by single-crystal XRD and supported by DFT simulations, respectively. 26 The structure of the activated Fe 2 (DSBDC) is proposed based on its PXRD pattern. Green, yellow, red, blue, grey, and white spheres represent Fe, S, O, N, C, and H atoms, respectively.…”

“…We hence conjecture that the major charge transport mechanism in activated Fe 2 (DSBDC) is hole hopping between Fe and S within the (-Fe-S-) ∞ chains, similar to the situation proposed in Fe 2 (DSBDC) (DMF) 2 . 26,36 Because the skeletons of Fe 2 (DSBDC)(DMF) 2 and the DCMsoaked Fe 2 (DSBDC) are isostructural, DMF likely does not affect charge mobility. Instead, it modulates charge density in the skeleton of the framework.…”

Intrinsically conducting metal–organic frameworks

“…Clearly, the strategy of redox matching between donor and acceptor components can be exploited to modulate CT, leading to conducting behavior. Dinc ă and co-workers developed analogues of the MOF-74 series of frameworks in which the oxygen donor atoms were replaced with sulfur donors, [ 35 Redox matching has also been implicated in an iron 1,2,3-triazolate framework, [Fe(C 2 N 3 H 2 ) 2 ] (C 2 N 3 H 2 = 1 H -1,2,3-triazole), which showed a room-temperature conductivity of 0.77 × 10 -4 S·cm -1 ; however, the origins of this behavior were not elucidated.…”