Vanadium 7,7,8,8-Tetracyano-p-quinodimethane (V[TCNQ]₂)-Based Magnets

Abstract

A new family of molecule-based magnets of general formula V[TCNQR(2)](2).zCH(2)Cl(2) has been synthesized and characterized (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane; R = H, Br, Me, Et, i-Pr, OMe, OEt, and OPh). In addition, solid solutions of V[TCNQ](x)()[TCNQ(OEt)(2)](2)(-)(x)().zCH(2)Cl(2) composition have been prepared. Except R = Br, magnetic ordering was observed for all materials, with T(c) values between 7.5 K (R = Me) and 106 K (R = OEt), with R = H at 52 K. The substitution of electron-donating OMe and OEt groups for H in TCNQ increased T(c), whereas the substitution of less electron-donating alkyl groups (with respect to alkoxy groups) decreased T(c). The results of MO calculations indicate that neither the spin nor charge densities of the disubstituted TCNQs are sufficiently different to explain the wide range of critical temperatures. Although the structures of the amorphous materials are not known, it is proposed that the oxygen atom of the [TCNQR(2)](*)(-) acceptor (R = OMe and OEt) and the V(II) interact to form a seven-membered ring. This interaction could stabilize the structure and enhance the magnetic coupling, leading to an increased T(c). The magnetic properties of V[TCNQ](x)()[TCNQ(OEt)(2)](2)(-)(x)().zCH(2)Cl(2) deviated from the expected linear relationship with respect to x, exhibiting magnetic behavior more characteristic of a step function in a plot of T(c) versus x.

A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

“…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). [8] The reaction of V(PhMe) 2 with tetracyanobenzene (TCNB) also forms a magnet (T c = 200 K) of composition V…”

Room‐Temperature Organic‐Based Magnet (Tc≈50 °C) Containing Tetracyanobenzene and Hexacarbonylvanadate(−I)

“…To date, V[a,a'-dicyanoperfluorostilbene] 2 (T c = 205 K), [14] V-[TCNP] 2 (TCNP = tetracyanopyrazine; T c = 200 K), [15] and V[TCNQ] 2 (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane; T c = 56 K), as well as several 2,5-disubstituted TCNQs [16] are the few reported examples of magnets which are compositionally related to V[TCNE] x . While these structures are unknown, based upon the composition, they are assumed to be similar to V[TCNE] x , Figure 1.…”

“…[23] Nonetheless, absorptions in these regions were not observed for the reaction of [V(CO) 6 ] and TCNE, [3b, 8, 10] TCNQ, [16] TCNP, [15] , and others [14] as CO is facilely lost. [18] Heating the V CO ·solv.…”

“…To confirm the presence of CO and its facile loss, high-resolution mass spectra [25b] as a function of heating were obtained for these samples, and a significant amount CO was detected when the samples were heated to 33 8C. [14] TCNP, [15] TCNQ [16] ) magnets. Hence, V PhMe ·CH 2 Cl 2 is proposed to have a structure similar to V[TCNP] 2 ·z solv.…”

Isolation of p-tricyanovinylphenyldicyanomethide ion via a [2+2] cycloaddition of 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules

“…Typically, this easily reducible compounds form radical ion TCNQ À in its reactions with metal complexes, leading to mono-, di-, tri-or tetranuclear nitrile-bonded r compounds, to p compounds with side-on coordination, or to corresponding ion pair compounds without direct coordination. Due to its powerful electron-accepting properties, TCNQ forms intermolecular charge-transfer (CT) complexes with various organic and inorganic electron donors, some of them exhibiting high electric conductivity or interesting magnetic behavior [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. These properties make TCNQ still an attractive subject of contemporary advanced material research.…”