The molecular conductors [M(tmdt)2] (M=Ni, Pt) consisting of single molecular species are investigated with 13 C NMR and 1 H NMR. The temperature dependences of 13 C NMR shift and relaxation rate provide microscopic evidences for the metallic nature with appreciable electron correlations. Both compounds exhibit an anomalous frequency-dependent enhancement in 1 H nuclear spin-lattice relaxation rate in a wide temperature range. These observations signify the presence of extraordinary molecular motions with low energy excitations.

Crystals of the single-component molecular conductor [Cu(dmdt)(2)] (dmdt = dimethyltetrathiafulvalenedithiolate) were prepared as a molecular system, with three-dimensionally arranged magnetic moments embedded in "sea" of π conduction electrons. [Cu(dmdt)(2)] had fairly large room-temperature conductivity (110 S cm(-1)) and exhibited weakly metallic behavior near room temperature. Below 265 K, the resistivity (R) increased very slowly with decreasing temperature and then increased rapidly, indicating a transition from a highly conducting state to an insulating state near 95 K. The magnetic susceptibility showed Curie-Weiss behavior at 100-300 K (C = 0.375 emu/mol, Θ = 180 K). The Curie constant and the high-temperature resistivity behavior indicate that conduction electrons and three-dimensionally arranged magnetic moments coexist in the crystal. The ESR intensity increased down to about 95 K. The ESR signal was broadened and decreased abruptly near 95 K, suggesting that electric and antiferromagnetic transitions occurred simultaneously near 95 K. The crystal structure was determined down to 13 K. To examine the stability of the twisted conformation of Cu complex with dithiolate ligands, the dihedral angle dependence of the conformational energy of an isolated M(L)(2)(n-) molecule was calculated, which revealed the dihedral angle dependence on the ligand (L) and the oxidation state of the molecule (n). High-pressure four-probe resistivity measurements were performed at 3.3-9.3 GPa using a diamond anvil cell. The small resistivity increase observed at 3.3 GPa below 60 K suggested that the insulating transition observed at ambient pressure near 95 K was essentially suppressed at 3.3 GPa. The intermolecular magnetic interactions were examined on the basis of simple mean field theory of antiferromagnetic transition and the calculated intermolecular overlap integrals of the singly occupied molecular orbital (SOMO) of Cu(dmdt)(2).

[Ni(1-x)Cu(x)(tmdt)(2)] (tmdt = trimethylenetetrathiafulvalenedithiolate) was prepared for realizing molecular Kondo systems. Magnetic moments (S = (1)/(2)) are considered to exist at the central {CuS(4)} parts of Cu(tmdt)(2) molecules. The χT-versus-T curve of the system with x ≈ 0.15 showed a broad peak at ~10 K. The decrease in the χT value below 10 K is consistent with a singlet ground state, as expected for a Kondo system. However, in the system with x ≈ 0.27, the χT value decreased when the temperature was lowered to 2 K, indicating antiferromagnetic interactions between magnetic moments through π-d interactions. Although the susceptibility anomaly suggested that the π-d interactions become important at T < 20 K, the observed resistivity (ρ(obs)) showed no resistivity minimum characteristic of a Kondo system down to 4.2 K. However, the differential resistivity Δρ(T) = ρ(obs) - ρ(L)(T) showed a logarithmic resistivity increase at 8-20 K with decreasing temperature, where ρ(L)(T) is a fitted function of ρ(obs) obtained at T > 50 K that is considered to represent approximately the temperature dependence of the resistivity without spin scattering of the conduction electrons.

A single-component layered molecular conductor, [Au(ptdt) 2 ] (ptdt: propylenedithiotetrathiafulvalenedithiolate) was prepared. Unlike the single-component molecular metal, [Au(tmdt) 2 ] (tmdt: trimethylenetetrathiafulvalenedithiolate) exhibiting three-dimensional compact molecular packing and antiferromagnetic transition at 110 K, the compressed pellet of the microcrystals of [Au(ptdt) 2 ] exhibited fairly high conductivity and small temperature-independent paramagnetic susceptibility.In 1999, the crystal structure and electrical properties of a single-component molecular conductor, [Ni(ptdt) 2 ] (Chart 1), were reported.1 Although [Ni(ptdt) 2 ] did not exhibit metallic properties, it exhibited high conductivity. This high conductivity of the crystal convinced us of the validity of our idea regarding the design of a single-component molecular metal.2 Two years later, the first single-component molecular metal, [Ni(tmdt) 2 ], was realized by using an analogous extended-TTF-type (TTF: tetrathiafulvalene) dithiolate ligand, tmdt.3 The observation of de Haasvan Alphen oscillations at very high magnetic fields and low temperatures as well as ab initio band structure calculations proved the existence of the three-dimensional (3D) Fermi surfaces (FSs). 4,5 To date, various single-component molecular metals including a series of isostructural [M(tmdt) 2 ] (M = Ni, Cu, Pd, Au, and Pt) systems have been reported. 6 The high controllability of the electronic band structure achieved by exchanging the central metal atom (M) for another transition metal is an important characteristic of the single-component molecular conductor. The electronic band structure of [M(tmdt) 2 ] near the Fermi level is determined mainly by three molecular orbitals, namely, sym-L³, asym-L³(d), and pd·(¹) orbitals (Figure 1). 8 The sym-L³ and asym-L³(d) orbitals form 3D stable metal bands in the Ni, Pd, and Pt complexes with an even number of total electrons. On the other hand, the asym-L³(d) orbital becomes the singly occupied molecular orbital (SOMO) of Au(tmdt) 2 with an odd number of total electrons, and [Au(tmdt) 2 ] becomes a magnetic metal exhibiting antiferromagnetic transition at 110 K (in this paper, [M(tmdt) 2 ] and M(tmdt) 2 represent the crystal of a singlecomponent molecular conductor and the constituent molecule, respectively). 9 In the case of [Cu(tmdt) 2 ], pd·(¹) becomes the SOMO and an antiferromagnetic chain coexists with ³ conduction electrons. 10In addition to the frontier molecular orbital properties, the mode of molecular arrangement, which is controllable to a certain extent by the type of ligand (L) used, plays a crucial role in the determination of the band structure of a single-component molecular conductor [M(L) 2 ]. A variety of electronic structures can be realized by using different combinations of M and L. However, the role of L, especially the bulkiness of the terminal alkyl group of L has not been investigated sufficiently. In this work, [Au(ptdt) 2 ] was prepared in order to study the effect of the terminal alk...

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+