Structures of the Solvated Organic-Based Ferromagnet Decamethylferrocenium Tetracyanoethenide, [FeCp*₂]^·+[TCNE]^·−·<i>y</i>RCN (R = Me, Et, <i>n</i>-Pr)

The ferromagnet [FeCp*2][TCNE] (Tc = 4.80 K) has two structural phase transitions at 249 and 282 K that has thwarted the determination of its structure by single crystal X-ray diffraction; however, its structure at 100 K is reported [P21/c, a = 9.710(1) Å, b = 14.214(2) Å, c = 18.753(2) Å, β = 113.207(2)°, V = 2378.7(5) Å3, Z = 4, T = 100 K]. Because of the facile loss of solvent, the ferromagnetic solvates, [FeCp*2][TCNE]·yS {S = MeCN [y = 1, P, a = 9.556(2) Å, b = 9.781(2) Å, c = 16.152(2) Å, α = 74.860(2)°, β = 84.333(3)°, γ = 65.030(4)°, V = 1321.0(4) Å3, Z = 2, T = 100 K], EtCN [y = 1/2, Pnma, a = 14.750(5) Å, b = 10.577(5) Å, c = 33.972(10) Å, V = 5301(3) Å3, Z = 8, T = 100 K], n-PrCN [y = 1/2, C2/m, a = 35.902(6) Å, b = 10.488(2) Å, c = 14.302(2) Å, β = 101.396(3)°, V = 5279(1) Å3, Z = 8, T = 173 K]} have also been difficult to crystallographically characterize, but have been determined from single crystal X-ray diffraction data. These structures consist of parallel chains of alternating [FeCp*2]·+ and [TCNE]·− ions, with an intrachain Fe···Fe distance of 10.54 ± 0.09 Å. The solvates additionally possess chains of solvent that separate the alternating chains of [FeCp*2]·+ and [TCNE]·− ions. The MeCN solvate forms layers of chains that separate two rows of chains, while the EtCN and n-PrCN solvates form chains surrounded by six chains, and have fewer nonmagnetic coupling pathways that result in higher ordering temperature with respect to the MeCN solvate.