A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

Abstract

Since the discovery of the first organic-based magnet, [Fe(C 5 Me 5 ) 2 ][TCNE] (TCNE = tetracyanoethylene), [1] efforts worldwide have focused on the discovery and characterization of new magnetic materials with enhanced and controllable magnetic properties.[2]The organic-based magnet of V[TCNE] x ·zCH 2 Cl 2 (x ≈ 2; z ≈ 0.5) composition with an ordering temperature T c of about 400 K can be synthesized via the reaction of V(C 6 H 6 ) 2 [3a] or V(CO) [5]With the goal of finding new organic-based magnets the reaction of V(CO) 6 with numerous polynitrile electron acceptors led to the discovery of several new V-based magnets with T c below room temperature. These include a,a′-dicyanoperfluorostilbene, (T c = 205 K), [6] tetracyanopyrazine (T c = 200 K), [7] and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ; T c = 52 K). (CO) 6 ] 1/2 ·zS (4>x > 3.5; S = CH 2 Cl 2 , PhCF 3 ) composition that orders above room temperature at 50°C (323 K). [9] A mild electronic acceptor methyl tricyanoethylenecarboxylate (MeTCEC; Scheme 1) has recently been used to synthesize isostructural decamethylmetallocene electron-transfer salt magnets of [MCp* 2 ][MeTCEC] (M = Cr, Mn, Fe) composition from which only Mn salt orders ferromagnetically below 7 K.[10] This is a little attenuated with respect to that observed for [MCp* 2 ][TCNE] (T c = 8.8 K).[11] Nonetheless, we targeted V[MeTCEC] 2 as a new organic-based magnet to identify the advantages and disadvantages of the reduced symmetry of the electron acceptor as well as the role of the ester carbonyl oxygen (C = O) in formation of additional superexchange pathways. Herein, we report a new organicbased magnet prepared from the reaction of V(CO) 6 and MeTCEC with T c close to room temperature. MeTCEC underwent a reversible one-electron reduction at -0.05 V (vs. saturated calomel electrode (SCE) in MeCN), [12] that is ca. 0.3 V harder to reduce than TCNE, but easier to reduce than tetracyanopyrazine (-0.31 V), [13] and a reaction with V(CO) 6 was expected. Reaction of MeTCEC with V(CO) 6 in CH 2 Cl 2 rapidly occurred and the system turned dark blue with CO evolution, and a dark precipitate formed suggesting the formation of an organometallic polymer similar to V

Characterization of Tetracyanopyridine (TCNPy)‐Based Magnets: V[TCNPy]2⋅z (CH2Cl2) (Tc=111 K) and V[TCNPy]3⋅z (CH2Cl2) (Tc=90 K)

“…The composition of the initial precipitate after allowing the reaction to proceed for two hours, was determined to be V[TCNPy] 2 ⋅ z (CH 2 Cl 2 ) from the observed elemental composition as well as the thermogravimetric analysis. This is expected and is commonly observed, that is, A=TCNE, α,α′‐dicyanoperfluorostilbene, TCNP, TCNQ, tricyanoethylene‐carboxylate, 2,3,5,6‐tetrafluorophenyltricyanoethylene, etc.…”

“…Reaction of TCNPy with V(CO) 6 in CH 2 Cl 2 rapidlyo ccurs and turns black with CO evolution, and adark insoluble precipitate forms,i ndicating formation of an extendedn etwork structured materials imilar to V[TCNE] x ,T CNB, and TCNP.T he compositiono ft he initial precipitate after allowing the reaction to proceedf or two hours, wasd etermined to be V[TCNPy] 2 ·z (CH 2 Cl 2 )f rom the observed elemental composition as well as the thermogravimetrica nalysis. This is expected and is commonly observed, that is, A = TCNE, [8-10] a,a'-dicyanoperfluorostilbene, [11] TCNP, [12] TCNQ, [13] tricyanoethylene-carboxylate, [14] 2,3,5,6-tetrafluorophenyltricyanoethylene, [15] etc.…”

“…New organic‐based magnets synthesized through the reaction of V(CO) 6 with neutral polynitrile acceptors have led to several new magnets of V(polynitrile) 2 composition. These include α,α′‐dicyanoperfluorostilbene, ( T c =205 K), 2,3,5,6‐tetracyanopyrazine (TCNP) ( T c =200 K), 7,7,8,8‐tetracyano‐ p ‐quinodimethane (TCNQ) ( T c =52 K), tricyanoethylenecarboxylate ( T c =275 K), and 2,3,5,6‐tetrafluorophenyltricyano‐ethylene ( T c =315 K) . In contrast, the reaction of 1,2,4,5‐tetracyanobenzene (TCNB) with V(CO) 6 forms the complex V II [TCNB] − 1.5 [TCNB] 0 x −1.5 [V −I (CO) 6 ] 1/2 ⋅ z S (4> x >3.5; S=CH 2 Cl 2 , PhCF 3 ) that orders above room temperature at 50 °C (323 K) …”

Magnetic surfactants as molecular based-magnets with spin glass-like properties

“…demonstrating proper spin glass behavior with ethyl tricyanoethylene carboxylate (MeTCEC) [12]. This paper reports the use muon spin relaxation (μSR) spectroscopy [13] to reveal the spin freezing process and spin glass-like behavior of a new magnetic surfactant with a lanthanide counterion [14], 1-decyl-3-methylimidazolium tetrachloroholminate ([C10mim][HoCl4], Figure 1).…”

MnII(TCNE)3/2(I3)1/2–A 3D Network‐Structured Organic‐Based Magnet and Comparison to a 2D Analog

“…[1] Most intriguing are several room temperature magnets, but their understanding and exploitation has been thwarted by their amorphous nature. [2][3][4][5] The best studied is V [TCNE] x [tetracyanoethylene (TCNE); x $ 2]-a ferrimagnetic semiconductor that magnetically orders above room temperature (T c $ 400 K). [2,6,7] Its valence and conduction bands are spinpolarized [8] suggestive of multifunctional and ''spintronic'' applications.…”