Dialkyldicyanofumarate Diesters:  Tunable Building Blocks for Molecule-Based Ferromagnets

Abstract

Dicyanofumarate diesters have been discovered to be viable and versatile alternatives to tetracyanoethylene as building blocks for the synthesis of molecule-based magnets. The reaction of decamethylmanganocene, Mn(Cp*)2, and dimethyldicyanofumarate, DMeDCF, in methylene chloride at −50 °C gives a one-to-one charge-transfer salt ferromagnet, [Mn(Cp*)2][DMeDCF], that possesses one of the highest Curie temperatures, 10.6 ± 0.1 K, ever observed in this class of compounds. At 1.8 K, this compound exhibits hysteresis with H coer ∼ 7 kG. Measurement of ac susceptibility suggests some glassiness in the ferromagnetic state, similar to that seen for the tetracyanoethylene analogue, [Mn(Cp*)2][TCNE]. Diethyldicyanofumarate, DEtDCF, reacts with decamethylmanganocene to give the homologous salt, [Mn(Cp*)2][DEtDCF]. In contrast to the dimethyl ester, the magnetic properties of this compound are those of a glassy, hysteretic metamagnet that exhibits coercivity of around 10 kG at 1.8 K.

Design and Synthesis of a Library of Molecule-Based Magnets: The Charge-Transfer Salt Approach

“…Also, elemental analyses of dried samples of both the chromium and manganese analogues of this CT salt show that essentially no solvent is present (12). The desolvated crystals are not su$ciently crystalline for singlecrystal structural analysis, although powder di!raction indicates a degree of periodicity.…”

“…Reaction of the dimethyl dicyanofumarate, DMeDCF, with Mn(Cp*) in dichloromethane at !503C followed by slow addition of ether causes microcrystals of [Mn(Cp*) ][DMeDCF] to be deposited. Like the TCNE analog, these are quite air and solvent sensitive and must be isolated and dried thoroughly at low temperature (12).…”

“…As expected, we have found that reaction of diethyl dicyanofumarate, DEtDCF, and decamethylmanganocene at !503C in dichloromethane gives rise to another charge-transfer salt magnet (12). Because the only di!erence between DMeDCF and DEtDCF is two methylene units, while the core system is essentially unchanged, we would predict that, if the stacking is maintained, the intrastack coupling (as re#ected by ) should be una!ected.…”

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

“…Dialkyl dicyanofumarates E - 1 , similar to tetracyanoethylene (TCNE), are well-known as one-electron acceptors. They react with metallocenes 99 , such as manganocenes [ 73 – 74 ] and chromocenes [ 75 ], to form one-to-one charge-transfer salts 100 ( Scheme 31 ), which are molecular magnets. Their physical properties depend on the size of the alkyl groups of the ester function [ 73 ].…”

“…They react with metallocenes 99 , such as manganocenes [ 73 – 74 ] and chromocenes [ 75 ], to form one-to-one charge-transfer salts 100 ( Scheme 31 ), which are molecular magnets. Their physical properties depend on the size of the alkyl groups of the ester function [ 73 ]. Some chromocene complexes with E - 1a , b were studied by means of X-ray crystallography [ 74 , 76 ].…”