Structural and Magnetic Characterization of Electron-Transfer Salts of Hexacyanotrimethylenecyclopropanide, {C3[C(CN)2]3},_and [Fe(C5Me5)2]*+(1:1; Two Phases) and [Fe(C6H3Me3)2]2+(1:2). Evidence for 1-D Antiferromagnetic Behavior in Segregated [Fe(C5Me5)2],+Chains

Joel S. Miller, Jian H. Zhang, William M. Reiff, Michael D. Ward

Research output: Contribution to journalArticle

Abstract

The reaction of S = ½hexaeyanotrimethylenecyclopropanide, {C3[C(CN)2]3}·-, acceptors (A−) with organometallic cation donors (D·+) results in the formation of extended linear chain compounds. Reaction of A− with [Fe(C5Me5)2]·+ results in the formation of at least two 1:1 phases of [Fe(C5Me5)2]·+ {Cjf.C(CN)2]3}·− and reaction with [Fe(C6Me3H3)2]2+ leads to the 1:2 phase [Fe-(C6Me3H3)2]2*|C3[C(CN)2]3)22−. One of the 1:1 phases crystallizes in the centrosymmetric monoclinic C2/c space group [a = 15.207 (3) Å, b = 26.500 (6) Å, c = 7.287 (4) Å, β = 107.46 (3)°, Z = 4, V= 2801.2 Å3 T = −108 °C, R(F02) = 0.053, Rw(F02) = 0.056] and possesses segregated …·D+·+D+D+… and …AAA…-1-D chains of 5 = ½ cations and S = ½ anions. The anions are canted 28.75° with respect to the c axis and exhibit uniform spacings of 3.224 Å between the planes of the anions. The shortest interchain FeIII…FeIIIdistance is 7.287 Å, whereas the shortest intrachain Fe…Fe distance is 8.701 Å. The second 1:1 polymorph crystallizes in the triclinic P1 space group [a = 7.532 (7) Å, b = 14.776 (6) Å, c = 14.981 (6) Å, α = 115.90 (4)°,β = 95.76 (6)°, γ = 101.74 (5)β, Z = 2, and V = 1442 Å3 at room temperature] and is isomorphous with [Co(C5Me3)2]+{C3[C(CN)2]3}·[a = 7.421 (5) Å, b = 14.763 (7) Å, c = 14.969 (6) Å, α = 115.90 (3)°, β = 96.02 (4)°, γ = 101.22 (4)°, V= 1413 (3) Å3, R(F02) = 0.065, Rw(Fo2) = 0.063 at -40 °C], which possesses …D·+D·+D·+… and …A ·− A·− A·− … segregated chains of S = ½ cations and S = ½ anions. Both the cations and anions form chains parallel to a. The anions exhibit uniform spacing of 3.20 Å between planes of the anions. The 1:2 [Fe(C6Me3H3)2]2+{{C3[C(CN)2]3}}22- phase crystallizes in the triclinic P1 space group [a = 9.156 (2) Å, b = 9.171 (2) Å, c = 1 1.523 (3) Å, a = 77.92 (2)°, β = 80.20 (2)° γ = 81.31 (2)°, V= 925.7 (8) Å3, Z = 1, R(F02) = 0.077, RW(F02) = 0.092 at -91 °C]. This complex exhibits segregated chains of S = 0 dications and S = 0 dimer dianions, but also has unusual …D2+A22−D2+A22−… mixed-stack linear chains in which the anion planes are nearly perpendicular to the C6ligand rings. This motif results in intermolecular contact distances between the cyano nitrogen atoms of the |C3[C(CN)2]3)22−dimer pair and the ring carbons of the [Fe(C6Me3H3)2]2+cation that are less than the sum of the van der Waals radii. The planar 5 = ½ anion has average ring C—C, ring—C(CN)2, C—CN, and C=N distances of 1.385, 1.383, 1.437, and 1.126 Å, respectively, and ring-C-CN and NC-C-CN angles of 120.6 and 118.9°, respectively. The corrected molar magnetic susceptibilities of the 1:1 monoclinic and triclinic phases obey the Curie-Weiss expression, x = C/(T-θ), with θ = -3.4 K and μeff= 2.98 μBand θ = -3.4 K and θeff= 3.10 μB, respectively. Above 78 K, each of the [Fe(CsMe5)2]·+polymorphs exhibit classical singlet 57Fe Mössbauer spectra typical of the low-spin Fe(III) cation. For the monoclinic phase, the 0.36 K spectrum indicates a magnetic hyperfine splitting, Hn, of 455 kG. For the triclinic polymorph Hnis 431 kG at 4.68. The Mössbauer spectra are consistent with slow paramagnetic relaxation extending to unusually high temperatures as opposed to an onset of 3-D magnetic ordering. The magnetization data for the monoclinic phase indicate that the anion chain is diamagnetic, i.e., it exhibits strong antiferromagnetic coupling. Below 40 K in a field of 30 G, the susceptibility for this phase exhibits a broad maximum at ~4 K consistent with a Bonner-Fisher type of 1-D antiferromagnetic exchange interaction, which is attributed to 1-D antiferromagnetic coupling along the cation chains. However, applied fields greater than 100 G result in decoupling of the weak intrachain-cation antiferromagnetic magnetic interaction, inducing an essentially complete transformation to a higher moment state. For [Fe(C6Me3H3)2]2+(C3[C-(CN)2]3)22−, magnetic susceptibility and EPR studies indicate the presence of a thermally populated triplet state 0.11 eV (890 cm−1, 1280 K, 2.56 kcal/mol) above the ground state that is associated with the dimer dianions.

Original languageEnglish (US)
Pages (from-to)4063-4072
Number of pages10
JournalInorganic Chemistry
Volume29
Issue number20
DOIs
StatePublished - Jan 1 1990

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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