Single-component Magnetic Molecular Conductor [Fe(dmdt)2] (dmdt: dimethyltetrathiafulvalenedithiolate)

Abstract

Molecular metal complexes with interactions between localized spins and conduction electrons are expected to show interesting electronic and magnetic properties. We prepared magnetic molecular conductors of iron complexes with extended TTF ligands and investigated their crystal structures and electronic and magnetic properties, from which we concluded that the single-component molecular iron complex has the dimeric form of [Fe(dmdt) ) and a coupled electric and antiferromagnetic phase transition near 95 K. 5,6 The three-dimensionally arranged spin 1/2 moments embedded in the "sea of ³-conduction electrons" of [Cu(dmdt) 2 ] cannot be realized in D 2 X-type conventional molecular conductors. Molecular alloys with diluted magnetic moments [Ni 1¹x Cu x (tmdt) 2 ] (x µ 0.0980.18) were synthesized, where magnetic moments (S = 1/2) are considered to exist at the central {CuS 4 } part of the [Cu(tmdt) 2 ] molecule and to have large coupling between the magnetic moments and the ³-conduction electrons. 7 We observed evidence that these mixed alloy systems are a molecular Kondo system, which cannot be realized in conventional D 2 X-type molecular metals. Recently, systems comprising iron arsenide superconductors and those comprising biomaterials with iron active centers have been attracting considerable interest. The next target of magnetic molecular metals with localized magnetic moments on the central transition-metal atom is a single-component molecular iron complex. Here, we present iron complexes with dmdt ligands, [Fe(dmdt) 2 ] n¹ (n = 0, 1, and 2). We succeeded in obtaining the unstable [Fe(dmdt) 2 ] 2¹ dianionic complex as (TPP) 2 [Fe(dmdt) 2 ] (TPP: tetraphenylphosphonium) and determined the crystal structure before electrochemical oxidation. However, after electrochemical oxidation, we noted that the central metal Fe 2+ was oxidized to Fe 3+ . All synthetic procedures were carried out under a strictly inert atmosphere using Schlenk techniques.8 Synthesis of the ligand moieties with a cyanoethyl-protecting group was performed according to the reported method. The synthesis of neutral [Fe(dmdt) 2 ] is described in the following procedures and shown in Scheme 1.The synthesis of (Me 4 N) 2 [Fe(dmdt) 2 ] was performed as follows: The dmdt ligand (121.0 mg, 0.30 mmol) was dissolved in dry THF (10.0 mL), and the solution was hydrolyzed with a 25 wt % MeOH solution of tetramethylammonium hydroxide (Me 4 NOH) (510 mg, 1.40 mmol) at room temperature in an argon atmosphere. The solution was stirred for 30 min, and the color of the solution changed from orange to reddish. After cooling to ¹78°C in a dry ice/MeOH bath, a solution of (Me 4 N) 2 [FeCl 4 ] (52.0 mg, 0.150 mmol) in dry MeOH (5.0 mL) was added dropwise to the reaction mixture. In the present synthesis, purified (Me 4 N) 2 [FeCl 4 ] was used instead of FeCl 3 as an iron source, with the expectation of synthesizing a neutral complex with Fe 2+

Structural Diversity of Compounds Based on Iron-Dithiolene with Sodium or Potassium Complexes

“…All the Fe–S distances and angles are in the range found in other similar compounds (Fe–S equatorial : 2.20–2.25 Å and Fe–S apical : 2.45–2.50 Å (Table )). ,− On the other hand, the dicationic Na 2 2+ entities linked to the anionic ones as well as the outer monocationic [Na­(thf) 6 ] + exhibit a pseudo-octahedral geometry. The Na–O distances agree with similar complexes previously reported. , …”

Measurement of the Ligand Field Spectra of Ferrous and Ferric Iron Chlorides Using 2p3d RIXS

“…However, deviations from tetrahedral symmetry produced by the Jahn− Teller effect in Fe(II) can split this transition, giving rise to multiple features, and the crystal structure does show deviation from a perfect tetrahedron. 35 Inspection of Figure 2 clearly shows that differences in the 2p3d RIXS spectra can be observed due to changes in both local site symmetry and oxidation state. It is instructive to first compare the T d and O h and ferric complexes, shown in Figure 2a,b (top).…”

“…This choice was made because, as discussed below, in T d symmetry there should only be the spin-allowed 5 E → 5 T transition. However, deviations from tetrahedral symmetry produced by the Jahn–Teller effect in Fe­(II) can split this transition, giving rise to multiple features, and the crystal structure does show deviation from a perfect tetrahedron …”

The quest for single component molecular metals within neutral transition metal complexes

“…The [Zn(dmdt) 2 ] displays a behaviour similar to [Zn(tmdt) 2 ], 44 while the [Fe(dmdt) 2 ] and [Co(dmdt) 2 ] complexes are dimerised and revealed lower conductivities and semiconducting behaviours. 44,48 In turn, the [Pt(dmdt) 2 ] measured in a compressed pellet, revealed a s RT of 150 S cm À1 , with a temperature-independent resistivity, showing a semimetallic behaviour, but a temperaturedependent magnetic susceptibility. The band calculations indicate that [Pt(dmdt) 2 ] is an ambient-pressure molecular Dirac electron system, also described as a nodal line semimetal.…”

“…14,45 Single crystal resistivity measurements revealed a s RT (110 S cm À1 ) and a weak metallic behaviour around room temperature, with a transition to an insulating state around 95 K. However, this transition is supressed at 3.3 GPa. 46 Other [M(dmdt) 2 ] complexes were also studied, such as palladium, 20,47 platinum, 32 iron, 48 zinc 44 and cobalt 49 analogues. The [Zn(dmdt) 2 ] displays a behaviour similar to [Zn(tmdt) 2 ], 44 while the [Fe(dmdt) 2 ] and [Co(dmdt) 2 ] complexes are dimerised and revealed lower conductivities and semiconducting behaviours.…”