title: Acetonitrile-facilitated reductive dimerization of TCNE to octacyanobutanediide, [C4(CN)8]2-, by Iron(II) chloride.
abstract: The redox properties of MCl2 (M=Mn, Fe, Co) acetonitrile solvates were electrochemically and spectroscopically characterized. The three voltammogram waves at 0.86, 0.48, and 0.21 V versus SCE for FeCl(2) dissolved in MeCN are assigned as one-electron reduction potentials for [Fe(II)Cl(x)(NCMe)4-x]2-x (1<or=x<or=3), respectively, and only [Fe IICl3(NCMe)]- {and [Fe IICl4]2- (E o 1/2 =0.04 V vs. SCE), if present} has a potential sufficient for TCNE reduction. The presence in solution of [Fe II(NCMe)6]2+ was also spectroscopically confirmed. The reduction potentials of M IICl2 (M=Mn, Co) acetonitrile adducts were inadequate to reduce TCNE. FeCl2 reacts with TCNE in MeCN to form [Fe II{C4(CN)8}(NCMe)2] (4), which is composed of layers of octahedral Fe II ions equatorially bonded to the four terminal N atoms of the mu4-[C4(CN)8]2- ion, with trans-MeCN groups and with 15-membered rings. Formation of 4 requires the simultaneous presence of [TCNE]* and [Fe II(NCMe)6]2+ in solution, which is in contrast to when [(NEt4)2][Fe IICl4] was used to reduce TCNE. A reaction scheme is proposed. Paramagnetic [Fe II{C4(CN)8}(NCMe)2] exhibits substantial antiferromagnetic coupling (theta=-13.3 K), and orders as an antiferromagnet below 7.8 K. The irreversibility of zero-field and field-cooled magnetization suggests that the material exists below Tc in two magnetic states relatively close in energy, that is, the purely antiferromagnetic ground state and a slightly canted antiferromagnetic metastable state.
authors.affiliation: Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0850, USA.
authors.forename: Konstantin I
authors.initials: KI
authors.lastname: Pokhodnya
authors.forename: Michael
authors.initials: M
authors.lastname: Bonner
authors.forename: Antonio G
authors.initials: AG
authors.lastname: DiPasquale
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Joel S
authors.initials: JS
authors.lastname: Miller
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D002073:Butanes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D004563:Electrochemistry; D005030:Ethylenes / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008958:Models, Molecular; D009570:Nitriles / Q000737:chemistry*; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D000097:Acetonitriles; D002073:Butanes; D005030:Ethylenes; D005296:Ferrous Compounds; D009570:Nitriles; C527510:octacyanobutanediide; C003393:tetracyanoethylene; C029451:ferrous chloride; C032159:acetonitrile