title: Conducting dimerized cobalt complexes with tetrathiafulvalene dithiolate ligands.
abstract: To obtain novel single-component molecular metals, we attempted to synthesize several cobalt complexes coordinated by TTF (tetrathiafulvalene)-type dithiolate ligands. We succeeded in the syntheses and structure determinations of ((n)Bu(4)N)(2)[Co(chdt)(2)](2) (1), ((n)Bu(4)N)(2)[Co(dmdt)(2)](2) (2), [Co(dmdt)(2)](2) (3), and [Co(dt)(2)](2) (4) (chdt = cyclohexeno-TTF-dithiolate, dmdt = dimethyl-TTF-dithiolate, and dt = TTF-dithiolate). Structure analyses of complexes 1-4 revealed that two monomeric [Co(ligand)2]- or [Co(ligand)(2)](0) units are connected by two Co-S bonds resulting in dimeric [Co(ligand)(2)](2)(2-) or [Co(ligand)(2)](2) molecules. Complex 1 has a cation-anion-intermingled structure and exhibited Curie-Weiss magnetic behavior with a large Curie constant (C = 2.02 K x emu x mol(-1)) and weak antiferromagnetic interactions (theta = -8.3 K). Complex 2 also has a cation-anion-intermingled structure. However, the dimeric molecules are completely isolated by cations. Complexes 3 and 4 are single-component molecular crystals. The molecules of complex 3 form two-dimensional molecular stacking layers and exhibit a room-temperature conductivity of sigmart = 1.2 x 10(-2) S.cm(-1) and an activation energy of E(a) = 85 meV. The magnetic behavior is almost consistent with Curie-Weiss law, where the Curie constant and Weiss temperature are 8.7 x 10(-2) K x emu x mol(-1) and -0.85 K, respectively. Complex 4 has a rare chair form of the dimeric structure. The electrical conductivity was fairly large (sigmart = 19 S.cm(-1)), and its temperature dependence was very small (sigma(0.55K)/sigma(rt) = ca. 1:10), although the measurements were performed on the compressed pellet sample. Complex 4 showed an almost constant paramagnetic susceptibility (chi(300) (K) = 3.5 x 10(-4) emu x mol(-1)) from 300 to 50 K. The band structure calculation of complex 4 suggested the metallic nature of the system. Complex 4 is a novel single-component molecular conductor with a dimeric molecular structure and essentially metallic properties down to very low temperatures.
authors.affiliation: Research Centre for Spectrochemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Emiko
authors.initials: E
authors.lastname: Fujiwara
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Hosoya
authors.forename: Akiko
authors.initials: A
authors.lastname: Kobayashi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Madoka
authors.initials: M
authors.lastname: Tokumoto
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Okano
authors.forename: Hideki
authors.initials: H
authors.lastname: Fujiwara
authors.forename: Hayao
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Fujishiro
authors.forename: Eiji
authors.initials: E
authors.lastname: Nishibori
authors.forename: Masaki
authors.initials: M
authors.lastname: Takata
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakata
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006571:Heterocyclic Compounds / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D006571:Heterocyclic Compounds; D008024:Ligands; D013438:Sulfhydryl Compounds; D003035:Cobalt; C063887:tetrathiafulvalene