Structure–property correlations in a family of decamethylmetallocenium charge-transfer salt magnets using dialkyl dicyanofumarates as the one-electron acceptors: Ferromagnetism versus metamagnetism

The synthesis of molecule-based magnets derived from decamethylchromocene, CrCp2∗, and dialkyl dicyanofumarates, DRDCF, R = n-propyl (nPr) and isopropyl (iPr) yields two new members of a family of charge transfer (CT) salts, these being metamagnetic solids isomorphous with and reminiscent of the known diethyl (R = Et) homolog. The antiferromagnetic properties of these compounds contrast sharply with the previously reported ferromagnetic dimethyl (R = Me) compound. An examination of the four crystal structures provides an explanation for the observed behavior: although the pseudo-one-dimensional mixed stack structure is retained in all of the solids, a new relationship between the stacks is observed for the higher homologs that is different from that found for the DMeDCF salt. In the corresponding decamethylmanganocene, MnCp2∗, family, CT salts with DnPrDCF and DiPrDCF are both metamagnets that appear to enter a spin glass state well below their TN’s, exhibiting hysteresis with large very coercivity at 1.8 K, again similar to behavior previously seen for the corresponding diethyl compound and different from the dimethyl compound. These and other results reported herein indicate that meaningful structure–property correlations are possible in this class of compounds.

Graphical abstractCharge-transfer salts from the reactions of decamethylmanganocene or decamethylchromocene and di-n-propyl dicyanofumarate or di-isopropyl dicyanofumarate have been prepared and characterized. Taken together with previously published compounds, a homologous series has thus been assembled that exhibits a change from ferromagnetism to metamagnetism correlated to a change in crystal structure.Figure optionsDownload full-size imageDownload as PowerPoint slide