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

Sun L, Hendon CH, Minier MA, Walsh A, Dincă M - J. Am. Chem. Soc. (2015)

Bottom Line: 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, DOBDC(4-) = 2,5-dihydroxybenzene-1,4-dicarboxylate).Because the metals are of the same formal oxidation state, the increase in conductivity is attributed to the loosely bound Fe(2+) 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.

View Article: PubMed Central - PubMed

Affiliation: †Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

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, DOBDC(4-) = 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 Mn(2+) 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 Fe(2+) 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.

No MeSH data available.


Calculatedenergy bands and projected density of states (DOS) ofM2(DEBDC)(DMF)2 (M = Fe, Mn; E =S, O). The work function, Φ, and the absolute energy scale arealigned to vacuum according to ref (19). Gray curves represent total DOS. Blue, teal,yellow, red, and black curves represent projected DOS of Fe, Mn, S,O, and C, respectively.
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fig3: Calculatedenergy bands and projected density of states (DOS) ofM2(DEBDC)(DMF)2 (M = Fe, Mn; E =S, O). The work function, Φ, and the absolute energy scale arealigned to vacuum according to ref (19). Gray curves represent total DOS. Blue, teal,yellow, red, and black curves represent projected DOS of Fe, Mn, S,O, and C, respectively.

Mentions: Density functional calculations were used to further probe thedifferences in electronic structure of M2(DEBDC)(DMF)2, and the significance of the additional d electron associatedwith the Fe2+ ions. The electronic density of states andionization potentials of the guest-free system are presented in Figure 3, and detailed in the SupportingInformation. Because Fe2(DOBDC)and Mn2(DOBDC) are structurally analogous,while Fe2(DSBDC) and Mn2(DSBDC) differ in the number of metal ions in their asymmetricunits, the comparison between Fe2(DOBDC) and Mn2(DOBDC) illustrates bestthe difference between Mn2+ and Fe2+. Most importantly,the valence band maximum of Mn2(DOBDC)is composed of C-p, O-p, and Mn-d states, while in Fe2(DOBDC) the Fe-d states dominate the valence band, with negligiblecontribution from ligand orbitals. This difference is attributed tothe low binding energy of the filled β-spin d band of Fe2+, which is empty for the d5 high-spin Mn2+ ions.20 Furthermore, because the lowerconduction band in both MOFs is dominated by ligand-based orbitals,the band gaps are narrowed owing to a decreased work function. Asa result, the calculated work functions and band gaps of Fe2(DOBDC) are 0.91 and 1.01 eV smaller than thoseof Mn2(DOBDC), respectively.


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

Sun L, Hendon CH, Minier MA, Walsh A, Dincă M - J. Am. Chem. Soc. (2015)

Calculatedenergy bands and projected density of states (DOS) ofM2(DEBDC)(DMF)2 (M = Fe, Mn; E =S, O). The work function, Φ, and the absolute energy scale arealigned to vacuum according to ref (19). Gray curves represent total DOS. Blue, teal,yellow, red, and black curves represent projected DOS of Fe, Mn, S,O, and C, respectively.
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getmorefigures.php?uid=PMC4442594&req=5

fig3: Calculatedenergy bands and projected density of states (DOS) ofM2(DEBDC)(DMF)2 (M = Fe, Mn; E =S, O). The work function, Φ, and the absolute energy scale arealigned to vacuum according to ref (19). Gray curves represent total DOS. Blue, teal,yellow, red, and black curves represent projected DOS of Fe, Mn, S,O, and C, respectively.
Mentions: Density functional calculations were used to further probe thedifferences in electronic structure of M2(DEBDC)(DMF)2, and the significance of the additional d electron associatedwith the Fe2+ ions. The electronic density of states andionization potentials of the guest-free system are presented in Figure 3, and detailed in the SupportingInformation. Because Fe2(DOBDC)and Mn2(DOBDC) are structurally analogous,while Fe2(DSBDC) and Mn2(DSBDC) differ in the number of metal ions in their asymmetricunits, the comparison between Fe2(DOBDC) and Mn2(DOBDC) illustrates bestthe difference between Mn2+ and Fe2+. Most importantly,the valence band maximum of Mn2(DOBDC)is composed of C-p, O-p, and Mn-d states, while in Fe2(DOBDC) the Fe-d states dominate the valence band, with negligiblecontribution from ligand orbitals. This difference is attributed tothe low binding energy of the filled β-spin d band of Fe2+, which is empty for the d5 high-spin Mn2+ ions.20 Furthermore, because the lowerconduction band in both MOFs is dominated by ligand-based orbitals,the band gaps are narrowed owing to a decreased work function. Asa result, the calculated work functions and band gaps of Fe2(DOBDC) are 0.91 and 1.01 eV smaller than thoseof Mn2(DOBDC), respectively.

Bottom Line: 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, DOBDC(4-) = 2,5-dihydroxybenzene-1,4-dicarboxylate).Because the metals are of the same formal oxidation state, the increase in conductivity is attributed to the loosely bound Fe(2+) 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.

View Article: PubMed Central - PubMed

Affiliation: †Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

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, DOBDC(4-) = 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 Mn(2+) 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 Fe(2+) 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.

No MeSH data available.