121192-67-4Relevant articles and documents
Ferromagnetic behavior in linear charge-transfer complexes. Structural and magnetic characterization of octamethylferrocene salts: [Fe(C5Me4H)2]?+[A] ?- (A = TCNE, TCNQ)
Miller, Joel S.,Glatzhofer, Daniel T.,O'Hare, Dermot M.,Reiff, William M.,Chakraborty, Animesh,Epstein, Arthur J.
, p. 2930 - 2939 (2008/10/08)
The reaction of FeII(η5-C5Me4H)2 with cyano acceptors A {A = TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyano-p-quinodimethane), n-C4(CN)6 (n-hexacyanobutadiene), C6(CN)6 [tris(dicyanomethylene)cyclopropane], DDQ (2,3-dichloro-5,6-dicyanobenzoquinone), TCNQF4 (perfluoro-7,7,8,8-tetracyano-p-quinodimethane)} results in formation of 1:1 charge-transfer salts of [FeIII(C5Me4H)2] ?+[A]?- composition. The TCNE and TCNQ complexes have been structurally characterized. The [FeIII-(C5Me4H)2] ?+[TCNE]?- salt belongs to the centrosymmetric Cmca space group [a = 14.990 (3) A?, b = 11.580 (7) A?, c = 12.503 (4) A?, Z = 4, T = 23°C, V = 2170 (3) A?3, Ru = 0.037, Rw = 0.040]. The anion exists as isolated planar [TCNE]?- radicals. The C-C, C-CN, and C≡N bonds are 1.385 (6), 1.426 (4), and 1.135 (5) A?, respectively, and the NC-C-CN, NC-C-C, and N≡C-C angles are 118.7 (4), 120.6 (4), and 179.6 (4)°, respectively. The [FeIII(C5Me4H)2] ?+[TCNQ]?- salt belongs to the centrosymmetric P1 space group [a = 8.636 (1) A?, b = 9.574 (3) A?, c = 10.025 (4) A?, α = 63.77 (3)°, β = 70.22 (2)°, γ = 162.79 (2)°, Z = 1, T = 23°C, V = 651.6 (3), Ru = 0.052, Rw = 0.054]. The anion exists as isolated planar [TCNQ]?- radicals. The HC-CH, HC-C, C-C(CN)2, C-CN, and C≡N bonds are 1.358, 1.419, 1.405, 1.417, and 1.148 A?, respectively, and the HC-C(H)-C, HC-C-CH, NC-C-CN, NC-C-C, and N≡C-C angles average 121.6, 116.7, 115.6, 122.1, and 178.9°, respectively. The solid-state structure for both salts consists of linear chains of ?D?+A?-D?+A ?-D?+?. The cation for both salts has a staggered conformation with the Fe asymmetrically bonded to the C5 ring; i.e., the average Fe-CH and Fe-CMe separations are 2.057 and 2.099 A?, respectively. The Fe-C5 ring centroid distance is 1.694 A? for the [TCNE]?- salt and is 1.710 A? for the [TCNQ]?- salt. The high-temperature magnetic susceptibility for polycrystalline samples of these complexes can be fit by the Curie-Weiss law, χ = C(T - θ)-1, with θ = +0.5 ± 2.2 K, and μeff ranges from 2.71 to 3.97 μB, suggesting that the polycrystalline samples measured had varying degrees of orientation. The 7.0 K EPR spectrum of the radical cation exhibits an axially symmetric powder pattern with g∥ = 4.11 and g⊥ = 1.42, and the EPR parameters are essentially identical with those reported for ferrocenium and decamethylferrocenium. No EPR spectrum is observed at 78 K. Akin to the [Fe(C5Me5)2]?+ salts, these salts have 57Fe Mo?ssbauer spectra consistent with complete charge transfer; however, unlike the case for the former complexes, quadrupole splittings of 0.30 and 0.22 mm/s are observed at 4.8 and 298 K, respectively. The absence of strong interionic magnetic coupling for the [Fe(C5Me4H)2]?+ salts contrasts with the behavior of the [Fe(C5Me5)2]?+ salts.
