Article pubs.acs.org/IC
Hexacyanobutadienide-Based Frustrated and Weak Ferrimagnets: M(HCBD)2·zCH2Cl2 (M = V, Fe) Jingjun Hao,†,§ Royce A. Davidson,§ Marzieh Kavand,‡ Kipp J. van Schooten,‡ Christoph Boehme,†,‡ and Joel S. Miller*,†,§ †
Material Research Science and Engineering Center, University of Utah, Salt Lake City, Utah 84112, United States Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, United States § Department of Chemistry, University of Utah, 315 S. 1400 E. RM 2124, Salt Lake City, Utah 84112-0850, United States ‡
ABSTRACT: Hexacyanobutadiene (HCBD) and M(CO)x (M = V, x = 6; Fe, x = 5) react in CH2Cl2 to form new organic-based magnets of M[HCBD]2· z(CH2Cl2) composition. Analysis of the IR spectrum [M = V: ν(CN) 2193 and 2116 cm−1 (fwhh ∼400 cm−1); Fe: 2196 and 2145 (fwhh ∼150 cm−1)] suggests that HCBD is reduced to the radical anion, [HCBD]•−, and the broadness suggests multiple and variable nitriles sites are coordinated to the V(II), leading to a complex mixture of magnetic couplings and behaviors that deviate from paramagnetic behavior below ∼150 K, and a frustrated magnet with Tc ≈ 9 K is observed for V[HCBD]2, the first cyanocarbon-based frustrated magnet. Fe[HCBD]2 behaves as a weak ferromagnet (canted antiferromagnet) with some spin glass behavior with a 10 K Tc.
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INTRODUCTION Organic-based magnets with enhanced and controllable properties with technological interest are a focus of worldwide studies.1 Ferro- and ferrimagnets based on cyanocarbon radical anions as well as ferrimagnets based on nitroxides2,3 have been reported. Among the cyanocarbons, materials possessing the [TCNE]•− radical anion (TCNE = tetracyanoethylene) have in many instances shown to stabilize the magnetically ordered state. These include ionic [FeIII(C5Me5)2]•+[TCNE]•− that has a magnetic ordering temperature, Tc, at 4.8 K,4,5 [MnIIITPP][μTCNE] (H2TPP = meso-tetraphenylporphryin) (Tc = 18 K),6 Mn I I (μ 4 -TCNE)I(OH 2 ) (T c = 171 K), 7 Mn I I (μ 4 TCNE)3/2(I3)1/2 (Tc = 171 K),8 and V[TCNE]x (x ≈ 2) (Tc = 400 K).9,10 In addition to TCNE, substituted ethylene-based magnets, e.g., tricyanoethylenecarboxylate (Tc = 275 K),11 2,3,5,6tetrafluorophenyltricyanoethylene (Tc = 315 K),12 pentafluorophenyltricyanoethylene (Tc = 307 K),13 and dicyanoperfluorostilbene (Tc = 205 K)14 have been described. Hexacyanobutadiene, HCBD, is a related linear percyanocarbon,15 with reversible one- and two-electron reduction potentials of 0.60 and 0.02 V (vs SCE in MeCN),16 respectively; thus, it is substantially easier to reduce HCBD than TCNE (0.23 and −0.74 V,16 respectively), and like TCNE, [HCBD]n (n = 0, 1−, 2−) are stable species.17 While [FeIII(C5Me5)2][TCNE]4,5 magnetically orders, [FeIII(C5Me5)2][HCBD] is paramagnetic at ambient pressure,18 but under pressure becomes a weak ferromagnet.19 Herein, we report the reactions of V(CO)6 and Fe(CO)5 with HCBD to form organic-based magnets of M(HCDB)2 (M = V, Fe) composition. © XXXX American Chemical Society
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EXPERIMENTAL SECTION
General Considerations. All manipulations were performed under an inert nitrogen atmosphere (
