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

Abstract

The ferromagnet [FeCp*(2)][TCNE] (T(c) = 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 [P2(1)/c, a = 9.710(1) A, b = 14.214(2) A, c = 18.753(2) A, beta = 113.207(2) degrees, V = 2378.7(5) A(3), Z = 4, T = 100 K]. Because of the facile loss of solvent, the ferromagnetic solvates, [FeCp*(2)][TCNE] x yS {S = MeCN [y = 1, P, a = 9.556(2) A, b = 9.781(2) A, c = 16.152(2) A, alpha = 74.860(2) degrees, beta = 84.333(3) degrees, gamma = 65.030(4) degrees, V = 1321.0(4) A3, Z = 2, T = 100 K], EtCN [y = 1/2, Pnma, a = 14.750(5) A, b = 10.577(5) A, c = 33.972(10) A, V = 5301(3) A3, Z = 8, T = 100 K], n-PrCN [y = 1/2, C2/m, a = 35.902(6) A, b = 10.488(2) A, c = 14.302(2) A, beta = 101.396(3) degrees, V = 5279(1) A(3), 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 A. 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.

Zero-dimensional organic-based magnets possessing decamethylmetallocene

“…30 and then mounted for study. 31 In this manner, the structure of [Fe(C 5 Me 5 ) 2 ][TCNE] was determined at 100 K via a single crystal analysis, and the results are in accord with that determined via the Rietveld analysis. 30 Each phase possesses parallel chains of alternating [Fe(C 5 Me 5 ) 2 ]c + cations and [TCNE]c À anions, with intrachain Fe/Fe separations of 10.63, 10.58, 10.52, and 10.…”

“…While the physical and magnetic properties of [Fe(C 5 Me 5 ) 2 ]-[TCNE] have been well established, 15 its structural properties, as well as those of the solvates, have been elusive, but very recently determined. 30,31 At room temperature the structure of [Fe(C 5 -Me 5 ) 2 ][TCNE] is disordered. 5,30 Cooling to decrease the structural disorder failed, as it undergoes two phase transitions at 249 and 282 K (Fig.…”

“…45 A at 295, 250, 100, and 12 K, respectively. 30,31 Hence, a 1.7% contraction occurs upon cooling from room temperature to 12 K. Adjacent chains are both in-and out-of-registry. At 295 K, both the cation and anion are very disordered (Fig.…”

“…These relaxation rate maxima are associated with the development of short-range order above T c s and the static susceptibility of a ferromagnetic 1-D Ising linear chain in accord of the analysis of the critical constants is observed. 27 In 31 The chains of S are depicted in green. [TCNE] with a T c of 2.1 K has also been reported; however, its structure has yet to be elucidated.…”

Pressure induced transition from spin glass-like behavior to a metamagnet exhibiting weak ferromagnetism observed for decamethylferrocenium hexacyanobutadienide, [FeCp*2]˙+[HCBD]˙−

“…3,15 The structures of 1 and 2 are similar to the TCNE and TCNQ analogues, differing primarily in their interchain cyano-Fe nearest neighbor distances, due to the differing structures of the organic radicals. 1 has the closest Fe⋯Fe, Fe⋯N, and N⋯N interchain distances of 8.719, 5.153, and 3.311 Å, 9 respectively, most closely resembling [FeCp* 2 ]˙+[TCNE]˙−, at 8.205, 15 5.145, 16 and 3.488 Å, 16 respectively. Only the ferromagnetic TCNQ analog has comparably small distances at 8.609, 5.020, and 4.337 Å, respectively.…”