TTF based charge transfer salts of [Cr(NCS)4(phen)]−: bulk magnetic order and crystal structures of the TTF, TMTTF (tetramethyltetrathiafulvalene) and TMTSF (tetramethyltetraselenafulvalene) derivatives

Abstract

A series of new charge transfer salts of electron donors based on tetrathiafulvalene, TTF, with the anion [Cr(NCS)₄(phen)]⁻ (phen = 1,10-phenanthroline) have been prepared. Single crystal X-ray diffraction provided structures for salts with donors TTF, TMTTF, tetramethyltetrathiafulvalene, and TMTSF, tetramethyltetraselenafulvalene. The salts were found to be [TTF][Cr(NCS)₄(phen)] at 293 K, [TMTTF][Cr(NCS)₄(phen)]·CH₂Cl₂ at 250 K and [TMTSF]₃[Cr(NCS)₄(phen)]₂·0.5CH₂Cl₂ at 293 K. For the TMTSF compound the solvent is disordered at 293 K so the structure was also solved at 120 K when the solvent becomes ordered. All of the salts have multiple S⋯S or S⋯Se close contacts between the anions and cations. The TTF salt is a bulk ferrimagnet with T_c = 9 K and is an insulator whereas the TMTTF salt is an antiferromagnetic (T_N = 3.0 K) insulator. Both have close atomic interactions of the phen–donor π-stacking type, but the TMTTF salt also contains close anion–anion contacts and dimerised cations whereas the TTF salt consists of stacks of alternating cations and anions. The TMTSF salt is a paramagnetic semiconductor and does not display π stacking but has close inter-donor Se⋯Se contacts and isolated anions which afford the magnetic and transport properties.